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AFRICAN PROGRAMME FOR ONCHOCERCIASIS CONTROL(APOC)

ORIGINAL: FRENCH

OVERVIEW OF THE STATUS OF VECTOR ELIMINATIONPROJECTS IN THE APOC PROGRAMME

Prepared for APOC

by

Prof. S. Traor6

Tem porary Advisor/WHO/APOC

APRIL 2OO2

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PLAN

EXECUTTVE SUMMARY ........... .................. I

1. TNTRODUCTTON .................... 1

2. NOTES ON ONCHOCERCIASIS lN AFRICA: VECTORS-DISEASE-CONTROL. 1

3. FOCI SELECTION CRITERIA 4

4. PANORAMA OF SITUATION IN FOCI 4

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4.1.1. Presentation of focus ..4.1.2. Nature of works..........4.1 .3. Results obtained .........4.1.4. CDTI status in the Tukuyu focus .........4.1.5. Budget for vector elimination activities4.1 .6. Discussions - Remarks ................4.1.7 . Conclusions-Suggestions ..............2. BIOKO FOCUS....4.2.1. Nature of works....4.2.2. Outcomes obtained....4.2.3. CDTI status in the focus.........4.2.4. Budget for vector elimination activities4.2.5 . Discussions - Remarks ................4.2.6. Conclusions - Suggestions...............

4.3. ITWARA FOCUS4.3.1. Presentation of focus4.3.2. Nature of Works4.3.3. Results obtained4.3.4. CDTI status in the Focus4.3.5. Budget for vector elimination activities4.3.6. Discussions-Remarks ...........4.3 .7 . Conclusions-Suggestions

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..304.4. FOCUS OF MPAMBA-NKUSI ................... 32

4.4.i. Presentation of focus4.4.2. Nature of works4.4.3. Results obtained4.4.4. CDTI status in the Focus4.4.5. Budget for vector elimination Activities4.4.6. Discussions-Remarks ...........4.4.7 . Conclusions-Suggestions

s. oVERALL CONCLUSTON ....376. AKNOWLEDGEMENT 38

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7. BIBLIOGRAPHICAL REFERENCES8. ANNEXES...

EXECUTIVE SUMMARY

I. INTRODUCTTON

In most of tropical Africa, human onchocerciasis or river blindness, a dermalfilariosis, caused by the parasite, onchocerca volvttlus, is still a serious public hlalth problem.The parasite is transmitted to humans by the black fly, Simulium damnosum s.l . The AfricanProgramme for Onchocerciasis Control (APOC) was established to control the diseasethrough control of the parasite populations, in African countries, outside tn" oferatlonal areaof another onchocerciasis control organization, the Onchocerciasis Control pro-framme (OCp)in West Africa.

APOC's Strategy is Community Directed Treatment with Ivermectin (CDTI).However, in some isolated foci at Tukuyu in Tanzania, Bioko in Equatorial Guinea, Itwaraand Mpamba-Nkusi in Uganda, APOC has also initiated vector elimination activities duringthe past least three years. Following recommendations of a mid-term external review ofAPOC's Programme, principally, the action plan for phase tI and a phasing out period, theManagement of APOC has decided to convene a meeting to critically ,""rri"* the vectorelimination activities at all foci. As part of preparations foi the meetinr, *" frovide here asynopsis of progress made at each of the vector elimination considered focus.

2. TUKUYU FOCUS

The Tukuyu Focus located between the Tanzanian and the Malawian borders covers an areaof about 3000km2- It is watered by three river basins: Kiwira, Mbaka, and Lufilyo. TheSongwe river, a main river bordering Malawi lies outside the focus. From WHO estimates in1995, about 650, 000 people in the focus have onchocerciasis; but the exact figures ofendemicity are yet to be known through a survey. Ivermectin distribution started at the focusin 1994 and the CDTI, with a therapeutic coverage of 66o/o, is going on satisfactorily.

A syrthesis report of Maegga (1997) indicated that between I976 and 1997 several randomtransversal entomo-parasitological surveys were conducted in the Tukuy,, focus. However,Since october 1998, the surveys have become regular with technical and financial supportfrom the APoc programme. The results obtained

".. ". follow:

- Breeding periodicity of Simulium : Studies conducted during the 19g0s and 1990s(involving Walsh & Maegga) agree with earlier ones, conducted in the 1970s andearly 1980s (by Lebene and Guillet) that ; there are larval stages of Simulium stagesof Siruulium darnnosum s./ in the three major river systems in the Tukuyu focus.Studies carried out by a national team during late 1998 and early 2002 revealed that;out of 85 breeding sites visited, simulidae were present at 46;34 of which hadS'damnosum s.l. observations made rn 2OO2 also indicated that 22 of 49 iverbreeding sites visited had aquatic developmental stages of Simulium while 9 out of2l tributaries were also positive.

- C1'totaxonomic identification has confirmed that the Simulium clamrtosrzrz species inthe three main river systems within the Tukuyu focus is S.damnosum kiwira type(l 419 I 1479 Simulidae).

- Oncliocerciasis transmission in the area has been indicated to occur during tlie dryseason based on occulrellce on high populations of bitting females during the period.However, this observation must be treated cautiously b."uur" it is not certain flycatchers have followed the standard protocol exactly.

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Sensitivity of S.damnosum s.l at the Tukuyu focus to 20o/o temephos was put forwardby Guillet (1981) and later confirmed by Bano (1999-2000). The LC95 has beendetermined to be 0.66 mg/l and 0.384mg/l for low and high mortality ratesrespectively. Tests in rivers indicate that lor a discharge of 4.3m3 /s and a dose of 0. Img/l, the effective carry for ( 100% of d6chrochement) of temephos was 7,060km. Bthad a maximum efficacy cary of one km. Analysis of amual distribution ofsimuliidae populations and density enabled Pederson and Maegga to conclude tfiaLthc dry season (June-November) would be the ideal period for larviciding, asaccessibility to breeding sites at that period would also be easier. The first groundlarviciding took place between December 2001 and February 2002. The three mainbasins of the focus were subjected to a weekly larviciding using temephos at the doseof l.33mg/l for 6 weeks. After the first week, no breeding site on the main riversvisited proved positive.Geographically, the natural barriers surrounding the focus (Lake Nyasa , mountains),initially, created the impression that the focus was isolated. Then in 1981, followinga series of surveys including that of the Lumbira and Songwe rivers, Guilletconcluded that the focus was not as isolated as previously considered. However,based on cytotaxonomical, entomological and epidemiological studies, the Tukuyufocus was declared isolated. Nonetheless, the data obtained in 1996 showed that S.

damnosum s./. thrives downstream of river Songwe, the natural border betweenTanzania and Malawi .

Moreover, in the south west of the focus, a few kilometers from Lumbira, is the largeand perennial river Kilando which could also harbour S. damnosum s. l. With the Kilondo andSongwe rivers located outside Tukuyu focus, it is not likely that the focus is isolated.

Based on the different results, it could be deduced that

tlre present distribution of S danmosum rn the Tukuyu focus notably during low waterlevel period is yet to be established.Some authors assert that the Tukuyu focus is isolated . Others, based on the proximityof the river Songwe and its tributaries and the presence of S. damnsum s.l in some ofthem are cautious. It is therefore important to conduct an entomological re-assessmentin the Songwe basin in Tanzania and Malawi. In addition, to accept or reject thehlpothesis of potential reinvasion of the treated area by S.datnnosunl from outside thefocus, it would be necessary to undertake a vector identification in areas concerned.

3. THE BIOKO FOCUS

The Bioko Island, a massive volcanic land covering 2017 krnz, is situated in the Gulf ofGuinea off the coast of Cameroon and Gabon. Its watershed is made up of small rivers withlow discharges which take their sources from mountains. The epidemiology of onchocerciasisis tlre forest type with an average prevalence rate of about 75Yo. For CDTI, the targetpopulatior-r is estimated at 60,000 pcople and the therapeutic coverage was 42"/o in the year2001.

Studies on the onchocerciasis vector on the Bioko island starled in 1989. A TDR feasibilitystudy on vector elimination in this focus rvas carried out in 1996. In 1999, various additionalstudies u'ere conducted through APOC funding. Thc results obtained led to the following :

'l'[re southem part of the island, about 40% of total landarea is inaccessible. However,nrany surveys have been carried out in the accessible zone. The results indicate thattlre .S. darutosutt't complex is represented in the Bioko Island only by the Bioko fonn

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of s' yahen'se' The rivers are many, short (7km long on average) and protected by aIuxurious vegetation, rendering the numerous riveri inacc".si6d. in ,rr" dry season,the discharges- of the rivers generally fall below.lm3/s and they are clean and cool(turbiditv < 5JTU) ; (l9oc<temperature<26otc).water. il ;il;aginar stage of:-l,ffi :3iHH' r"|J['::l "u""' s oo'n

"l'i *1.]*h ne, some ui, io' *"." cap rured at

- The authors were unanimous on the fact that the Bioko focus is isolated. In fact, it isan island where weather conditions in irai,[ *iro n-,ou"-"nt, -nrJ.i""n

consideredto negate re-invasion of the foc1s, Additioni'lly, cytotaxonomical, morphological andcytogenetical obviousnesses lead !o ihe .."ogriiion of the ruo ,rrui ii e s. yohense inBioko is different flrom tlie standard ,vp.. irr.." is therefor" u i*riaered genetic

Uf:,r::;flr"IT. ," the known ,imuriio"e ,p."i", and th; found on the

- It has been observed that apart !9m the dry season (January to April), the simuliidaepopulation densities ut" 'oi significant. o, tt.

""rtrary, IvtBR u"t^r""n r305 and 11475 has been recorded in April- May and u.i*.", zg 7o'andr-o isffi February. Thismeans that even in the dry season, tie simulriiae. popuration density can be high.- In 1996 the dissection of 56

.females helped to record up to 14.6% of infectiousfemales' In 1999, the dissection of 878 f.;;i.s revealed 44o/o infecred and g%infectious females' Despite the fact trrat, ttre aip has not u" "riuirirt "d

for the year2002' the MTP obtained in April ura ruru/"itt. uu.iou. ""11";;;';;ints were high(MTp minimum:130 in BaLcha; maximum-: qll at Musora y. iirru. arso beenindicated that apart from collection points ro.rt.a at high-altitudes (0<pMT<7 2), atlthe others MTP are located between 319 at Sampaka and 1275 at Musola. variousstudies of agree and indicate that transmission i. ,i-!-rrin"unt on the Bioko Island.

- Results recorded in 1989 and 1998 show that after 9 years of ivermectin treatment,prevalence has drasticallv changed fro- r,yp"."ni"*,"iv oq.ayr;)-;"liypoendemicity(38'6%)' such a shift should be reflected uv.i.riir- infestation.'Thus, flom r993 to2002' the number of infecting larvae ror ttioo pu.", o.op"d from 400 to 74 and MTpfrom 1600 to l5' However, ti" inf..tution.ut. L"".o"a during 2001 does not seem toff ]fr::,ro

bv the use orlvermectin: MTp betwe.n:19 in Sampaka and 1275 at

- The first ground larviciding compaign rook place in Bioko during 2001 dry season.During the period of the exlrcise, only 30 rivers had enough ;".t^"i n"*irg to enabretreatment' Hence' out of 248 proposed treatment points serected, only 92 wereretained' The selected insecticide ro. g.ourJ^-iarvicioing was temephos at theoperational discharge dose of 0.4 litres/miz.. rt " tieatment, which lasted five weeks

X1il,:Tl:1":X,r:in;J:" rrom Febru;.r;2d^ 2oot p.o,., ir," numerous data

. IH;:irr,".f H;::"cricide

was between I and 3 km for discharges ranging from

I'he Iife span of 1he preimaginal stage of sinrulium rvas rather rong (,rore than two weeks)because water tetnperatures were rrurily low ( from IE,Cio 24"c).The recolonisation ofbreeding sites after each treatment was in"..fo.. very slow.

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Adult population density feel sharply after the commencement of the treatment. Fly

catching was nil at some points after only four weeks of treatment, although rivers were

not totally treated.

- At the structured operational dosage, the number of chironomides was reduced

however, repopulation was relatively fast. On the other hand, fish and shrimp

populations were not undurely affected ( no mortality, normal behaviour ) by the

larviciding.- At the end of the first exercise which took place in the north of the island, expert

consideration indicated that due to inaccessibility of some rivers, ground larviciding

alone cannot eliminate the vector from the Bioko focus. This objective could however,

be achieved in a one single season through combined ground and aerial larviciding.

However, as authorities stated, the use of helicopter for the exercise should be

indicated by proper answers to some questions. Such as : what is the impact of twelve

years of ivermeitin distribution on the simulium capacity to transmit the disease?

What is the cost of the aerial operation advocated ? How many people will be

protected through this oPeration?

Reference to the target objective, which is to eliminate the vector, various results obtained

in Bioko, indicate the following :

The geographical location, weather conditions and cytotaxonomical, morphological and

cyogenetic criteria confirm that the Bioko Island is isolated.

Based on the distribution of the rivers and prospected breeding sites, it is evident that each

suryey, would reveal at least a new breeding site (discovered in a river already itemized or

not). Moreover, the presence of the adult vector in high altitude is a reinvasion risk factor for

a tieated zone. This situation impedes the total coverage of breeding sites by through

larvicidings as a must for the vector elimination'

4. Itwara Focus

At about 25 km north of Forte Portal, lies the Itwara focus surrounding a forest reserve

that bears the same name. Hydrological conditions are generally conducive all year round for

the development of the pr6-imaginai stages of S. neavei. The breeding sites are mainly located

on rivers Sogohi, Siisa and Aswa. Onchocerciasis is highly endemic in that densely populated

zofie.

The Itwara focus community and its sub-foci (Siisa, Aswa) are isolated from the other

onchocerciasis foci. The nearest focus being about 100km away and mostly infested by S

neavei whose flyrng range does not exceed 10 km (Garms, 1997.)

In the 1970s, the use of DDT, emulsifiable concentrate at 25o/o of active ingredient

disrupted the transmission of onchocerciasis in the ltwara focus (Garms et al., 1994)' Due to

tack of funds and insecurity, the control was interrupted from l9'15 to 1977 '

However, in 1990, a new funding jointly provided by the German Cooperation Agency

(GTZ)a.d the Ugandan Ministry of Health made it possible for data collection to continue. In

this connectiol, all tlie rivers iit"ty to harbour S. neat'ei s.s were surveyed and the adult

population of S. treavei studied through fly catchings, dissections and determination of

infestation rates. The larviciding of temephos carried out from August 1995, proved to be

effective rvith promising results afte. only three larviciding cycles. In fact, between I 994 and

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1995, the simulidae density dropped from 481 to 0 at the Kijura bridge and from 365 to 2 atBusasa. Considering the results obtained, larviciding were extended to the major breedingsites for S. ncavei in the focus.

The entomological data collected betwecn l99l and1994 prior to the treatment withtemepl.ros indicate that38.9o/o of crabs captured in the river Sogohi (Itrvara focus) carried thepr6irnaginal stages of S. neavei.

Results of various surveys tally and show that treatment of breeding sites withtemeplros drastically reduced the S. neavei preimaginal population irrespective of the focus orits sub-focus (Siisa, and Aswa). Even when treatments were discontinuld, Iow densities wererecorded. Post-treatment controls in the Itwara locus revealed tliat since 1997, infested crabsare nearly absent. The same is true, since year 2000, in the Siisa sub-focus. Between Januaryand August 2001, surveys conducted by the national team have made it possible to catch 4656crabs in the Itwara focus, with the breakdown as follows: 948 in Itrvara, 630 in the Siisa sub-focus and 3078 in Aswa sub-focus. No pr6imaginal stage was discovered on the crabs fromltwara. Only a larvae was detected on one crab (i.e. 0.2% of population) from Siisa. Thehighest percentage (0.4%) of crabs showing positive were noticedin Aswa.

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From the beginning of treatments in 1995, the S. neavei population density hasdropped, reaching the zero mark in 1996 at Kijura and Sogohi. As the treatment went on, thetendency has intensified because no biting female was captured in 2002 in the entire focus(Itwara, Siisa, Aswa). Results recorded in 2001 confirmed the absence of biting females in thezone. It is worthy to note that prior to the treatment with larvicides, the simuliidae populationdensity was 19,000 bites per person and per year.

With the current situation, vector elimination activities in the Itrvara focus and its sub-foci (Siisa, Aswa) can be called a success. It is likely that children born since the beginning ofoperations would no longer be carriers of the micro-filaria. However, ivermectin distributionshould continue due to the longevity of the adult O. volwtlus worns carried by old patients.

5. The Mpamba -Nkusi Focus

The concemed vector elimination area, covering a landarea of 100 km2 lies in theNorthern part of the Kibaale District. The district is made up of 3 prefectures but it is only inBuyaga prefecture that onchocerciasis is endermic. The population at risk is about at 70 000with a prevalence rate between 58oh and 80%. Therapeutic coverage was 74%o in 2001 in theKibale District- Perennial rivers with breeding sites for S. neat,ei all tlie year round constitutethe hydrography of the focus.

During surveys for larvae carried out in lgg9, 28 (41%) crabs out of 688 were carriersof S. neavei Pre-imaginal stages. The same data for the years 2000 and 2001 were respectivelys061623 (81%) and 3931642 (s3.4%)

Characteristics of female vectors recorded at Sioni were as follows: 33.g% pares; 14.7%infected, 2.7oh infectious; MPT frorn l3 to 50 Lil1000 pares. At Rurembo, 26.5o/o parcs20.4% infected, 0.6% infectious, 21Lill000 pares and PMT value of 28 were obtained. AtNyabugando, transmissiotr rates rvere: 27,8n1, lcntclles parcs, 18.3% inf'ectetl pares,6lLi/1000pares and a PMT valuc of 86.2%.

A pilot treatment exercise was carried out on Mpamba river in November 2000. Thisreduced the infestation rate of crabs living in the river fronr about 66,70/o to 92.5o/o.

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The same was true for crabs confined in experimental cages and placed at river bedswhere reduction rate ranged between 98.5% and 100%. S.damnosunt and other simulidaebreeding sites were all negative after larviciding. The non-targetted fauna (trichopterre,bloodsuckers, water scarabs) were not affected. buring the experirnent, the discharge ofMpan-rba river was 1126m3/s, with water temperature reading 19.z"C and insecticide carryestimated at 5knt. The experimental treatment carried out in 2001 on Mushandikwa andRwabutuji rivers also showed a drastic reduction in crab infestation (100% mortalityrate over2km ).

To conclude, the following must be noted ;

' Sampling conducted indicates that the sirnulium flies in the Mpanrba- Nkusi focusare 'S. neavei and S danrnosum, Nkusi type. Even though considered non-anthropophile, the latter species' characteristics and its vectorltatus must be well-defined.

' The biology of S neavei, success chalked by the experimental larviciding, extent ofthe focus, ecological and geographical isolation oi the focus and the all-weatheraccessibility to rivers are factors indicating that the vector elimination exercise inMpamba-Nkusi focus can be carried out with good chances for success. Theproblem of insecurity which, at any moment could slow down or even impede theconduct of anti vectoral activities is yet to be solved.

' Despite the efficiency of larviciding and probable elimination of the vector fiomthe Mpamba-Nkusi focus, Ivermectin distribution should continue considering theIongevity of the adult O volvulus worrns present in previously infected persons.

GENERAL CONCLUSION

The presentations on vector elimination in different foci of Tanzania, EquatorialGuinea and Uganda provided the opportunity for assessing the progress made in each project.It is very clear that the projects were implemented on the basii oifactors such as focus size,its isolation and the availability of baseline data. However, project feasibility was not givenenough consideration and some factors (actual limits of the focus, accessibility to breedingsites, reinvasion risks) were sometimes underestimated. With the S nea,ei vector, the factorsenumerated above do not always pose problems due to the bio-ecology of the vector.However, with S damnosuttt s. /., the limiting factors keep on increasin!: many supports,difficult accessibility to all breeding sites, generally high simulidae populaiion Oensitiei, trigtrflying capacity- Total coverage of breeding sites is a sine qua non condition for the vectorelimination. Moreover, it was understood that in the selected foci vector elimination wouldbe complete, definitive and fast. This objective remains achievable in the Itwara andMpamba-Nkusi foci.

On the contrary, what actually comes lrom tlie field compels us to admit that thevector elimination in the Tukuyu and Bioko loci could have been a very ambitious objective.We should be mindful of one of the recommendations of JAF6 that if the meeting decides tostop the vector elimination activities in the focus, recornmendations should be made to thecountries concemed to enable them to continue fighting the vector in a national or bilateral(cooperation) context. Irt the casc where activities should be pursued, some convenie,tarrangements should be taken at the APOC level to execute, supervise and evaluate thelarviciding acti vities.

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I1. INTRODUCTION

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onchocerciasis is a human disease caused by a nematode filanar won,, onchocerca vorvurus,transmttted to man bv the Black Flv Simutium. rrr. ai.""." which i. -;;;i;;; by skin lesions,vrsual imperment and blindness is stitt a major public rr"rlir', prorrrem in most part of tropicar Africa.As at lee6, rhis endemic disease ufr."t"a ii,; ffi;;;.;i::", of whom ls;in.n (8s%) lrved incounrries outside the onchocerciasis a?"I:11:g.r,irr.'icjcp) area r, w.ri'aiica. The Africanil:f,i[H,i:!'3ffii,",',TJ:;:",'""#::rtU:^:]":r"in].".L;" designed ,"

"""o"r this criricar

The overall objective of onchocerciasis control is, usuaily, being abre and in a sustainablemanner' control the endemic disease, though the finaiof""ir" set-by apoC i. ti.irimination of thedtsease' as a serious.public health ptou-t-"*, and an obstacre,o .o-",o-""onomic deveropment in Africa.The strategy adopted is the commrnity-pi..",.d Di.il;;;rtt,r..,n""tin (GDTI).However' since the launching of APoc, vector elimination projects have underpinned theGDTI in some counrries. These ;;"1";, whicir u." uppro*a uv tn"'c";;;" of SponsoringAgencies (csA) and ratified bv the 1",.,t-e.1g rorum i;ili-:* ongoing in uganda (in the foci ofItwara and Mpambu*t,r, r"r-ri" iruci of Tukuyuj,'il;,i'Eqratoriar dil";?;;;i of Bioko). Theconhol strategy applied in all these foci has u""n

"ont or oipoputrtions of the diground larviciding aimed at elimination of the vector, and consequentry the disease.

isease vector by

The APoc programme undertook th-ese vector elimination- activities on the basis of elementssuch as the size and &tent "f ir;i;;., of foci, uu.. autu'l*ilable, and the

"o.t or operationalcampaigrs' Besides' it could be said that this type of """o"i r,u, ."u".ur ;;r;i;" aspects: rapidtntemlption of transmission, no consequences for-the .ru,-n*"nt, and in principle, and the definite[#: ;T:H] ;ff "jl.i[l: ;ffi,: ;h'*i:,

lil il";il',lo,n, *u.,r,l inl'.i i.ination or the

The acceptance and financing br.:h:toc programme of the various vector eriminationilffi:::H:.'ffi|!$X,'.T,'flff:+ffie8. ro date, ai r;,;;;." years have erapsed, and it is worrrrex temar- revi ew), *r,r.r,, i n on.

" i i,, .".ffi ffi :xT,il: jl',oh'.' jL[: Sj

"g ;ffiEl:organize a meeting charged to att"t.ni* irr. p-g.r.*. ffi; for vector elimination for the 2.d:iffi;l,,Ht d;I:ffi.* TBI:* was to carl on ul1-he,expe;;; i;#;r, parricipating

aftention wourd be accorded rorhe,dirlfFffiT?Brff:,3i.$ H ff"xii:H' *ttransmission of onchocerciasis' The raFi-"rr" to determine that no n.* .,re"tor etimination projectwould be undertaken during phase 2, una arlns th. *;;;;;;;ioir:" of Apoc. It also confirmed that:iil:ffffTi1ilL.|.:.,'LJ ""tiJilv.""J.*.d,t th. b"si;;i,i; orphase 2, in orderio decide on the

In line with the recommendations -made

after the mid-term Externar Review of the ApocProgramme' as well as on the basis of tt "

ptun ."r

a",,", r";';;;." 2 and the graduar withdrawar ofAPoc' management decided to hold ii"r."a. eliminatron."uil* meeting in apoc countries in May2002'rt is' therefore' wtth respect '"

iir" p-r"eparations for the saia meeting, that this surnmary tries tonote the progress made, since the start-up lf activitres in each of the roci.

|J-"f..SoNoNCHocERCrASrsrNAFRrcA:vECroRs_DrsEAsE_

The disastrous consequences of ocular signs of the onchocerciasis disease are we, known.However' until recently the suffe.ir;;; by skln r;"^ ;;;" onchocerciasis, and the anenda,rtntolerablc rtcht.g had been u,,att ti,,"u*I. ti ,, u.r.n"a i"a"r",i", onchodermite represents a heary

2

burden and that its manifestations bring about serious psychological not only on

but also on their families and communities. In addttion, the itching is the most painful effectpatients,

of the oaflection

nchodermite. In some communities, however, 80% of the popula suffers from this

complexesIn Africa, the onchocerctasis vectors that are known are Srmihum

(S.dntnttosutrr complex, S. neavei group, and the S' albivirgtrlalurr group)' In

Central and East Africa, the following could be noted:

peculiar case of

The vectors of the s. damnosurtt complex have tendency of confining t :lves to areas that

are sulrounded bY either non-anthropophilous black fly populations, in ecosystems that

don't sutt them. The sPecies, therefore become "stationary". As they y reproduce in

big watercourses, their breeding srtes are relatrvely accessrble for I ding. Punctual

operations of vector control could , therefore, be carned out in these fo with a good cost-

effective ratio.ln several foci, the vector found is the S. neavei, the species that require presence of fresh

water crabs, which the Pre-imago stages use as suPPort. Because this, the S. neavei

population does not generallY attain the high densities that characterize S. damnosunt. lnhas problems in

addition, the bibliograPhic data indicate that this grouP of

reconstituting its populations when they are greatly reduced.

Until 1987, onchocerciasis control in West Africa was solely based on

continues to be the mainstaY of control, but with the advent of ivermectin, therecontrol. The latter

a new tool that has

radically changed the confrol strategies. The latter are mostly determined on one hand, by the

geographical location of Pathologies, and on the other, bY the existence, fficacy and cost of

intervention too,1s, which are as follows:

Ivermectin, which is a microfilaricide, administered orally to man;

Vector control: thanks to insectrcide spraying, thrs method enables the sequence

to be broken, bY destroYing the vector at the most vulnerable stage, i the larva stage. The

frequency of treatment dePends on the duration of development of the -imago stages, and

especially the time that separates the hatching of larvae from their stage

ln the OCP area, the control of the disease was essentially based on vector ,1. In APOC zone,

this strategy often Proves to be technically impossible or less profitable' It is this reason that the

However, in some

isolated foci, it has been decided to undertake vector elimrnation.

In west Africa, there are no cases of onchocerciasis vector ellmination, for t

drttrtosunt complex move over long distances' On the contrary' in East Afri

treatment of larvae breeding sites has enabled the elimination of vectors in si

Kenya(McMahonetal,1958),intheDemocraticRepublicofCongo(Walsh,lprentice, lgi4).This success indrcates that a vector elimrnation operahon coul

iocus that has srmilar characteristics as these six foci'

main method used bY APOC is the community-based distnbution of i

focus, may, neverthe:less have palpable effects on the S. neat'ei vectors, rf

several months or if they are carried out intermittently over 6 to S-month

hre black flies of r/rc S.

pa. the use of ground

[r. small foci, found in1990). and in Uganda

H be undertaken in anY

are continued over

In these S. neat'ei

f.

Expenence has shown that smaller-scale operations, which don't co cover the entrre

foct, eliminatron is the solution to the onchocerciasis problem. The latter is so vantageous that:

Rrsks of reststance and environmental degradation are low;

Costs of insecticides are reduced, since control is tntermtttent'

'l'hc lact of regularlY using rnsecticides is a potentlal risk factor to the tic environment In

vrew of this risk. a lot of attentton needs to be paid to the survetllance I of the aquatlc

environment, and to the choice of larvtc ide. This choice is hnked to the (cost-effective ratlo,

toxrcity lbr non-target fauna, formulation characteristics), to the wa (hydrologrcal pattern,

3characteristics of breeding site), and to the black fly population present (level of sensitivity to therecommended product)' whichever insecticide u."d,'th;-;;;;;ntrations must be imperatively have aj3,1':ri:1,1;:::T[:1'.tJi:l nv ta*'l popuration, tt.o,giir," insecticide, and a'legrigibre and/or

with respect to ground treatment, various works have shown very good performances ofTemephos' with an active matter of 20%o emulsifiable "o*"*u,.. tt i, in o.gr.,ophosphorousbiodegradable compound, with no toxic effects o, .nr*.*t;; il.- r,.'irrpr", il*non_,u.ret fauna:llliifi1':,i1lii',1",?;rTi,:Hff:;;fli*,*1,#,i.'r," ittu, tt*ii,,lini,,* a,,(Bt) courd

It is to be noted that an error of appreciation in the_quantity of insecticide to be sprayed may havemultrple repercussions on a vector "ont

or programme. tn the eveni ;i;;;ffi;iJ.",l*,r. insecticrdcconsumption has senous financial and./or ecological ";;q;;;;"s., if the chemical ,."a i. expensrveor relatively toxic' on the conhary, ou"tdo," may, on the one hand,.favour the appearance of resistantblack fly populations, and on ttre oitrer t uno,

"uu." "" i;;;;'ii ui,ing rates, andience an increase infd''ffi:?,r$il:#:;:il**[:it".,*;ffi;,i'"*"* *,,i u" p,i'i" prace ar the

The impacts of the insecticide treatment on the vector populations and parasite transmission areappraised through entomological evaluation. The latter .t .t.-p.io. ,o .or*r op..*on., through acomplete inventory of larvae breeding sites, and the couectior lrurr. a#;,#,;:.tity of speciesof the complex' the rate of bites ani transmi..io, pot"ni*i.. nr.i.g lh. "p;;"; enromorogicalsurveillance makes it possible to detect a sizeable lo"ri p."Jroion of brack flies, due to treatmentlapses or to resistance' and to detect u, "^og.rous

input of vectors. Treatment may, then, be reducedor stopped in the regions where there are .,o blu"k ni".. nv .nuCing.the "..if;;;;;'or rr," efficacy oftreatment at the pre-imago (prospecting of rive^).,"rJ,.n1g;:;;;:. (capture, identification, dissectionof females)' entomologicat euatuation

"-onui*n. tn" mairs-taf of'th. .ont or operations.Data collected during the entomological evaluation allows folthe establishment of entomologicarindices of transmission' which are the Annual Biting nui., (ir*), and the Annual TransmissionPotential (ATP)' They quantlry urac[ ny'uggr...ion- and pr*rir. t rn.rirrron .J[."ti.r.ty for asub';ect placed at a given point, becaur" ,t li ..pr...rruir,I. oi ,rr. most dangeroui situation thatprevatls in the region. rnl een ,ra arp *. looJ "o-p;r;;u" indicators Jr ,rr" entomorogicarsituation' They usually constitute the basis of evalultion .i;il;;;;"r conrror resurrs.

4

3. FOCI SELECTION CRITERIA

Vector elrminatron can only be undertaken rn a focus that has a number of critena

'fhe focus must be isolated (not at the mercy of re-invasion by exogenous black flies).

The vector must be identified in order to adapt control to the species.

The vector eliminatron activity must be easy to manage, and must guarantee a quick

investment turnover for an increase in productivity, and a reductlon, rn the long term, in the

need for CDTI.

4. PANORAMA OF SITUATION IN FOCI

4.I. TUKUYU FOCUS

The bibliographic data on onchocerciasis in the Tukuyu focus are relatively abundant:

FISHER (1932),newrrNc (i940), Anonymous (1976, 1911), LE BERRE (1979), WALSH et al

(1981), pioBnsoN and MAEGGA (1985), wALSH et al (1985), PEDERSON and LOLSTROP

irgaOi, MAEGGA (111Z),MAEGGA and CUPP (1993, 1994), WALSH and MAEGGA (1996). The

uuthois especially dwelt on the entomological, epidemiological, cytotaxonomic components, and

vector control, using insecticides. These different works help to characterize this focus.

4.1.1. Presentation of focus

The focus of Tukuyu (fig 1), located at the frontier between Tanzanta and Malawi, spans an

area of about 3,000 sq km. The Iegion under review is found between 905 - 9045 of west longitude

urrJ f f ozo - lq6zq of West latitude. It extends from Lake Nyasa (south) to the Volcanic Mountains in

the north and has to do with two distncts (Runge, Kyela), two administrative regions (Mbeya region,

I.nga region). The focus, thus demarcated, was declared isolated, since it is surrounded by natural

ba..lers, namely Lake Nyasa and the surrounding mountains (Livingstone, Rungwe, Umalila, Undah,

Mporoto).

The clmate in the region is characterizedby a dry season (June-October), and a rainy season

(November - Muy). However] rarnfall is all year round, with the peak in March, April and May (fig' 2,

i, 4;. Rarnfall figures in some areas are regularly around 2,000 mm per annum (fig. 5).

The weather is relatively cold at the summit of the mountains (average 60C). On the other

hand, in the plains, the weather rs hot and humid all year round. This situation ts due to the mountains,

which annuls the influence of seasonal winds'

The focus of Tukuyu is watered by three river basins, whose matn watercourses are the

Kiwira, the Mbaka and the Lufilyo. They take their source at a hrgh altitude (2,400 - 2, 800 m) on

Mount Rungwe. Then they descend to the plains, flowing over the slopes of the mountain, creating of

rapids and lavourable coniitrons (especially rn the dry season) for the installatron of pre-imago stages

of g. dr*.rorr* ,.1. On therr way, the Ktrvira and the Lufilyo receive some tnbutanes (Luswist'

U*1tiri, Rr*akah) from othcr mountains (Mporoto, Undali, Kipengere, Ltvtngstone)' Songrve'

located in the rvest, and outside the focus, rs a watercourse on the frontrer u'tth Malawr' Vegetation

varres from savanna to dense forest and degraded forest. The latter covers the largest part of the

Tukuyu focus, wrth Savanna and dense forests coverlng the slopes of the mountatns'

The populatron of t5e zone undcr study rs broken tnto the dtstrtcts of Kyela and Rung$'e,

rvhrch t,a,r. in. hrghest human populatron frgure in the focus (about 69 rnhabitants/sq km). -lhe

malonty of rnhabitants arc engaged in intcnsive agriculture, whrch is undertaken on fertrle volcantc

sorl. The forest has, partly, been cleared lor agro-industrial plantations (tea, coffee, cocoa, banat]a.

q

5

rice' cane sugar), and for market garden produce and fruit (tomatoes, mangoes, pears, oranges).Fishing is undertaken along the watercourse and on Lake Nyasa ty .o*" of the inhabitants.

The identification works of PDERSON and MAEGGA (1985) and of MAEGGA and cupp(1993, 1994) indicate that the black flies thatare responsible for rransmrssion in the focus of rukuyubelong to the S' damnosum complex. [t is, specifically, the S. damnosum, Krwrra type. The other blackflies found in the area are the S. nyasalandicum and S. bovis.

Thc highest onchocerciasis prevalence rate (62.8%) was recorded at Kilugu, a village locatedat an altitude of 760 m on the Lufilyo- The human settlements upstream or downstream of Kuluguhave much lower prevalence rates (20 to 5l%). In the entire zone, skin lesions are severe, andconstitute the real onchocerciasis problem. with respect to prevalence, the area has been covered bythe ol ivermectin distribution programme, since July 1994.

4.1.2. Nature of works

Several ad hoc surveys were carried out in during lg76-lgg7the Tukuyu focus prior to the start-upof APoC activities. The summary of them indicates i-hat they a*"it o., the following:- The determination and distribution of levels of endemicity;- The location Simulium breeding sites;- The identification of vectors;- The dynamics of pre-imago populations;- The dynamics of adult populations;- The behaviour of adurt popurations (namely, the rate of aggressiveness)- The vector characteristics of females of the s. damnos,irir (rate of pu*.ition, infestation ofblack flies, transmission of onchocerciasis) ;- The determination of the duration of larvae life;- The feasibility of vector elimination activities.

The protocol approved by APOC in 1996 also made provision for the follou,ing:

- The location of main breeding sites, namely those found at a high altitude;- The collection of larvae of the s. dantnosunts./. in the camoy on an positive breeding site;- The capture and dissection of blu"k fli" coming frornfre-selection points (Lufilyo crater onthe Lufilyo river, Lwanga Masoko on lower t<iiryiri, Tapio Bndge on the lower Lufilyo, andKambasegela on the Mbaka);- The collection of rainfall and hydrological data;- Training of personnel.

Finally, for the elimination of the oncho vector in the Tukuyu focus, the spraying of remephos, asan anti-black fly larvicide, was recommended. Before any'operation, a survey will have to beconducted to:

- Determine the actual rmpact of Temephos;- Measure the sensibility of the larvae of the S. darttrtosttttts./. to Temephos,- Train local personnel on the management of nver krals and sensibrlitv tests.

4.1.3. Results obtained

The presentatton of outcomes takes account of the data collection period, either before or after thebegrnnrng of APoc activities in the focus. This drstrnctron should enable:

- The apprarsal of elcments that allowed APoc to engage in vector elrminatron actlvltles lnTukuyu;- Stocktakrng of the progress made in vector elrmrnahon in the focus.

6

4.1.3.1. Data collected prior to APOC

a) Prospecting brecding sites

ln the 1970s and 80s, the pre-imago stages of the S. datnnosurrt s. /. were harvest in the dry andwet seasons on the Kiwtra, Mbaka and Lufilyo rivers (Le Berre, 1970; Guillet, 1981; Walsh et al,1981,198s).

The works of Pederson and Maegga (1985), then Walsh and Maegga (1996) confirm that thelarvae breeding sites of the S. damnosum s.l. exist in the Tukuyu focus. In the dry and rainy season,the three main nvers (Kiwira, Mbaka, Lufilyo) and some tributaries shelter pre-imago stages of the S.

damnosuttt s./. The production of black flies is, nevertheless, the most important in low water periods,and on breeding srtes at mid-altitudes (600-700m). Dispersion is important in the rainy season. On thecontrary, rn the dry season, the productive breeding sites are located on the middle courses of majorrivers. In addition to the latter, the Songwe River and its tnbutary (the Mwati), shelter some pre-imagostages of the S. damnosum s./. during the dry season. The same goes for the Lumbira River, whoselower course is an important source of black flies (,S. dqmnosum s./., especially), due to the highnumber of breeding sites.

The cytotaxonomic identification (Maegga, 1992; Maegga and CUPP, 1993, 1994) indicateDthat the S. damnosum species, which lays its eggs in the main three rivers of the Tukuyu focus is the S.

dantnosunt, the Kiwira type. In actual fact, out of the 970 identified larvae, 910 (about 94%) were ofthe S. danulosum, Kiwira fype. Besides, 509 larvae from the hatching of eggs laid by 70 gorgedfemales on captors, were all identified as being of the Kiwira type. This vector is different from theother types of the S. damnosum found in the neighbouring foci.

b) Captures-dissection-transmission.

Between 1979 and 1981, adult captures for determining the activiry cycle of the S. danmosunts./., and for specrfying the vector characteristrcs, were camed out on 9 sites, spread over the Tukuyufocus. [n each of these points, two consecutive days of capture took place every two weeks, i.e. 4 daysper month. The capture was spread over the whole day. Drssection of these flies and the search for O.volwilus helps to determine that onchocerciasis transmission was mainly a dry season transmission(low-water penod), due to the high density of biting females, and to their best contact with humanpopulations. This was particularly high near villages of high prevalence.

The rarnfall figure-temperature-biting rate correlation was confirmed in a study conducted in1987 and 1988 on four of the nine previous sites. It indicates that the ABRs were low, and did not gobeyond 20,000, except on the middle course of the Lufilyo. The highest black fly densities in the dryseason were obtained at between 500 and 800 m altitude. The rates of parlurition were low (22oh), andATP was generally lower than 1,000. On the conhary, the rate of infective parous females was high(38.3%).

Pederson and Maegga (1985), after examining a population of 19,500 of the S. damnosuttr,Kiwira type, confirmed that the annual biting rate fluctuated between 2,000 and 23,800.

The drssectron of 13,200 females (68% of capture) enabled 7.6oh of infected ones, 1.5o/" ofrnfectrve ones, and an ATP fluctuating betrveen 0 and 1120 to be recorded. The latter rate wasobserved in an area, where the average prevalence of carriers of microfilaria rvas 54.6%. At the end ofthis study, the authors confirmed that transmission was a dry season phenomenon.

c) Larvicidc treatment

Based on experlences from the Kenyan and Ugandan foci, Walsh, in 1990 indicated that it wastechnrcally possrble, usrng rnsecticide treatment, to ehmrnate the vectors (5. danmosurn s./. and S.

tteavci), from the onchocerctasis foci of Tanzania. The cost of such operations rvould, to a large extent,de pend on the nature of thc terrarn and on the srze of the larvae breeding sites ol each focus.

7

Given the very good performances of the Temephos, with an active matter of 2Oo/oemulsifiable concentrate, it was recommended for ground treatment in the Tukuw focus. Thisinsecticidc was successfully used rn several foci (e-spccially Sogohi ; ug;^;;;, but was neverexperimentcd in Tukuyu. I{owever, Guillet (1981) indicated tnut tn. sensibiliy oiin" larvae in thislocus was normal. In addition, the duration of pre-imago laboratory dcvelopment (egg - adult) was190'5-210c,(threeweeks),withtwoweeksbeingforthJdurationoflarvaerir". ontiecontrary,the:i:i::|^

field tcsts for determtning the duration separating egg laying from adult hatching were norposltrve.

The operational.efficacy of remephos in the Tukuyu focus was estimated, taking into accountthe experience acquired with ocP (walsh, 1985; wash et al, lggl; Kurtak, lgg0), and the resultsobtarned in westem Uganda (Garms et al, 1986). Thus, under the hydrological conditions of rukuyu, itwas establtshed that the doses to be sprayed would be 0.33 I and 0.4 l/m3 lespecti""ti;. output higherand lower than l0 m3/s.

With respect to the period of treatment, the analysis of annual distribution of black flydensities enabled Pederson and Maegga (1985) to decide thai the dry season (il"; t; N"vember) wasthe period when access to the breeding sites is easiest. Besides, the flow rate of watercourses isregularly low and gradual, 1

llvae breeding sites are confined to some places of the watercourse. Forthese reasons, it was decided that insecticide teatments would take place in the dry season. Eachbreeding site would be treated every two weeks, and in principle, 8 treatment cycles spread over 16weeks, should be enough for eliminating the vector. As for the spraying points, u d"tuil"o prospectingof the main rivers and their tributaries enabled a selection of 26 oithem.

d) Prevalence

The first report on onchocerciasis in Tanzania had to do with the Tukuyu focus (Fishe r, 1932).Hawkig (1940) confirms the presence of onchocerciasis in the focus. The dishibution of this diseasewas, therefore, established gradually (woodruff, 1965; wHo 1966; wegesa, 1970)- In 1995, wHoestimated the number of people affected to be 650,000, but the exact extent of the endemic diseaseremained to be determined through investigations.

Granback (1973) determined that 64% of the 260 people that were examined in the village ofLufilyo were carriers of the o. volvulus microfilaria. pedlrson and Kolstrop (1gg6) examined 2,34gpeople aged between I and above. This sample, coming from 2l villages, ."r"ul"i that the highestprevalence rate of 62-8% was recorded at760 m altitudeln the village of-fKilrg,.. rheianer is locatedon the middle course of the Lufilyo. In the other 20 villages, prevalence fluctuated between 20T and5l%' Dermatological affections constitute_the.-most ".li"ui problem, ro. "* tow parasitic loadscause lesions in some patients. And yet Mwaiko et al (1990) estimated that about 120,000 peoplewere affected by onchocerciasis in the focus.

Ivermectin distribution started in 1994, and until 1ggg,20,000,25,000,40,000 and 42,000persons had benefited from treatment.

d) Isolation of the Tukuyu focus

The geographical siting of the focus, surrounded by natural barriers (Lake Nyasa, mountains),naturally led to the idea that the focus was isolated. This peculiar situation, if verified, would makevector elimination feasible.

In 1981' following a series of prospecting, includrng that of rivers Lumbila and Song*,e,Gurllet concluded that the focus was not as rsolated as thc g"eographical environment made it look.Consequently, vector eliminatron became hypothetical

cytotaxonomic studies (Maegga, 1992; Maegga and cupp, lgg3 and 1gg4) waived thedoubtsofGuillet(1981)astotheisolatronoftheTukufJfocus. Ineffect,apartfrom thes.clrnrtosrttt,

8

Kiwira Ope, no other cytotype could immigrate into the focus. In other words, from the cytotaxonomicpoint of view, this was an isolated focus, which only contains the S. darnnosum, Kiwira type species.The extent of isolation is, however, very high, otherwise only one type would not be so predominant inthe area. It is therefore, on the basis of these works, the entomological studies (Pederson and Maegga,1985) and epidemiological studies (Pederson and Kolstrop, 1986) that the Tuduyu focus was declaredrsolated. Vector elimination of the said focus could be undertaken with success (Walsh and Maegga,l 996)

4.1.3.2. Data collected after the start-up of APOC activities

a) Prospecting breeding sites

This was mostly done by the national team.

Between October and December 1998, the productivity of breeding sites of the main rivers(Kiwira, Mbaka, Lufilyo) was regularly monitored. This study aimed at determining the upper limit(altitude) of the distribution of pre-imago stages (fig.6).Thus,31 breeding sites were geo-referencedand prospected for harvesting pre-imago stages in the regions of Mbeya (Rungwe, Kyela, Illeye,Mbarali), Iringa (Ludewa) and Rukwa (Sumbawanga, Mbeya). Out of l8 positive breeding sites, only9 shelter the S. damnosum s.l. In the districts of Rungwe and Kyela, only a breeding site was found ttbe positive, out ofthe l7 prospected.

ln September-October of 1999, the S. danmosum s.l. was found in the entire breeding sites(13) on the main rivers (10 breeding sites), and on some tributaries (3 breeding sites). There was,however, some disparity between the plethoric imago population and the scarcity of pre-imagopopulation in the breeding sites.

In 1999,24 breeding sites were prospected and 14 were found to shelter larvae and./ornymphs of the S. dantnosuttt s./. All the positive breeding sites were geo-referenced, and larvae weresampled in the Camoy. This activiry continued in February 2000 when two breeding sites were foundto be positive, out of the I I prospected.

Befween July and September 2000, the prospecting undertaken by Barro, apart from the pre-established limits (Walsh and Maegga,1996), made it possible to visit 28 breeding sites, 13 of whichwere positive on the main watercourses (Kiwira, Mbaka, Lufilyo). [n addition, out of the 2l breedingsites prospected on the tributaries, 9 sheltered pre-imago stages of the S. damnosuru s.l. From thealtitude point of view, the distribution of the S. damnosttm s.1., was between 472 m and 1,000 mapproximately. This distribution was variable, depending on the nver basins.

b) Captures-Dissection-Transmission

These activities were carried out by the national team. The analysis of capture and dissectionsheets indicate that the captors did not generally apply the usual standards for capturing black flies(Barro, 2001). The following results are therefore to be considered with caution.

Between October and December 1998, a day of capture per month, was undertaken at Tapioand Kambasegela, as against two days at Lufilyo-crater and Lwangwa-Masako. These capture pointstally with the vanous levels of prevalence in the area that is under treatment with ivermectin. Thus,225 females were captured and dissected. These dissections enabled the recording of 99 parousfemales (44%),19 infected (19%) and 7 infective females (7%).

Between January and December 1999, tables I ,2,3 and 4 indrcate that 144 days of captureenablcd a harvest of 1,362 females at Lufilyo-Crater (499 females), Lwangwa-Masako (635), Tapio-Brrdge (149) and Kambasegela (79). The dissection of 1357 females revealed 390 parous females(28.7"h),40 infected (10.2%) and 3 infective ones (0.16%). The ATP was 83, for MTP was 23 in June,60 in August and zero for the other ten months. The average black fly density was 9 bites/man/day, but

r

t

9

ffil[:;X:il::r'TiliJg1ffi'.:ll"Hi":il:t, it was 3, r3 and 6 ar Kambasegera, Lunryo-crater,

The entomological evaluation undertaken between January and December 2000 (tables 5, 6,7and 8) indicate than in 144 days, 6240 femrales were "ro*i ,l iwangwa-Masako 1tt t sy, Tapio-Bridge(1893)' Kambasegela (300), and Lufilyo-c.ate. (2To;. out of ttresJr.,,ur"r, iii;;".. dissected, ofwhrclr 176r were parous (30.5%), t++ inructed (8%,), ;;'is inr."trr" rlv,l.'i"rr. rnn fluctuatedbetween 8 and 3930,465 and:srd,:o rnJ'r695, ano uetween 9s and :oos at iwar,*'.,)u_rrar.rko, Tapio_Bridge' Kamasegela and Lyfilyo-crater respectively. For tr,.."1u*" capture points, the MTp was nil forsix months of the year: January, e"U*u.y, irfarch, April, May and November,

In 2001' 9923 females were captured in the Tukuyu focus (fig.7). The average density was 4gbites/man/day' Besides, females *... **. abundant o, ,n" irnry, toc uir".i*",i,aay), then on theKiwira (38 bires/man/day),and finaily ", i1. Mbaka (la bites/man/day). For these sar

ff,yj,1l[ffifi.:.ff:i"]:o ana ssso,'b.,*"",,:s-""0 +oiruna u"t*""n ii;;j#s0i:.,i.""".Hi;:

c) Larvicide treatment

The sensibility tests' river hials and the first ground treatment of the focus were entirely carriedout by the ocP team under Mr' Barro. ti i. *o.tti*t,;;;; the nationar team took part in rheseoperations' An APoc employee also participated in tt i, n.rig.oirnd treatment operation.

The sensibility tests that were carried out in octob er rgggindicate that the rarvae were subjectedto a series of concenrrations: 0.00975 ^mg/I, 0

93: mg/i, 0.1'sz-^gt,o.:rzsn, o.t)i"^it,I.25 mg/r and2'5 mg/t- At a temperature of 2o-22o.d,i"*,rq_;t", ois0"7",;o;l'^ra"ioon ii"?'" ...o.a.a, withconcentrations of 0' 156 mgll, 0.3125 mg/i and 0.ai6 mgA;;i;;;;" respectivety. These results indicare

::ili,T::;T:'Jy,:i'::rryrn:to r..;h;; is excereit. r, "ir*,, tne br gs

"r,n"'i"; mortariry (onry

Two river trials of the Temephos were conducted in 1999 on the Mbaka and the Lufilyo. Forthrs latter watercourse' the section "no..n

was about rs m iorrg. This stretch was treated at a dose of0'411m3 i'e' a concenhation oro.:: mg)r. Due-to th" p;;;i;; of inaccessibiriry, no evaruation wascarried out before and after treatment f,"yond the Lufily;*r.ruri .onnr*".]' i. fo. the resurts;',iiX'.T:::"Ti5i'*?,:1fl::H*::-r,**Jei,,.ei1e.".pno, r,,'!ir."i, ro. a norv or4 3must be noted thai the cieai ""r* "i,r,:,ryir-#:ijfljir',f",:*1"""J:XHi ;"yi?rT H ,[temperature ( l8- l90c) conhibuted to lessen the effect or ,t. i"*"phos. The ratter first of a, settres onthe particles in susnension (need ro. u tigr, turbidiry."i.l, *rri"rr^are then injected by the larvae.

"':ffi:;::iJ:I:ffiff'r'""J"Tr'*,: 'rti'u"..o*., ;iffiil d.to. ro, toxiciry Jr organophosphorous

Between Julv and September 2000, two sensibiliry tests were conducted on the Kiwira andLufilyo rivers' witlh a clgi of 0.384 mg/l ro. u t,igr, 'rr"i"riry .ut., trr" .L...rti. inai"ut. a good;H'3*'J'J:.1n.'.T;rii:::f:,x1** t,T*rl;;," or,00% i. "u."*"a,, o ozi ig)L

The river tests of the Bt H14 Tecknar on river Mabaka show that at the normal dose of 0.7 2 mgrlbv m3/s and a flow of 2'5 m3/s, ;;iv^;i.;i. of detactrmeri'"r"ri". tu.rr" ui;.;H iom the point ofspraying were recorded' The -aximal effective "i*,ru "r*ij.our"*.a i. uiori'r'un. Besides, onl;?'i!l?l,ilii"",,;itr,1 i::i*::#tX1,;X,;?;jil,H,/,, ,;. i"",i,,,, ;,,o,0 ,u*u. is only

The first ground treatment campaign meant to eliminate.the S. damnosum s.l. of the Tukuyutbcus through Tenrephos :p.u-yi1q, took plie ffom Decemi.. ioor," February 2002. .rhe

three basrnsof the focus (Krwrra, Mbfa, irriivoy *"1" .uu-itt"J ;;;;il;;"rtmenr with Temephos for six weeks,at a dose of l'33 mg/l' Each rvee-k, trre inrecticide was.p*vii'rr 53pornt, and a torar of ggl riters of

10

Temephos was used for the entire campaign (fig. 8,9). The results indicate that prior to treatment, 35breeding sites prospected sheltered all the pre-imago stages of the S. damnoru* ..^1. After the first weekof treatment, no breeding site visited on the main rivers was found to be positive (fig. 10, I I , l2). On thecontrary, two positive breedrng sites were found on the tnbutaries (on the fusyrtJnu and a tributary ofthe Mbaka (Mb300). The total absence of nymphs indrcates, however, the excellent efficacy of theTemephos.

d) Isolation of the focus

The data acquired after the works of Walsh and Maegga (1996) rndicate that the Songwe River,a natural frontier between Tanzania and Malawi in the downstream section, shelters the S. damno.r-..l. (NOTF, 2000). Besides, hibutaries of this watercourse take their source from the territory of the focus,mainly along the Mwalisi. The latter is the main tributary of the Kirwira River. It flows into the sectionthat shelters the S. damnosum s.l. (Barro, 2001). [n addrtion, a number of tributaries of the Songwemay, from this river, constitute the contamination corridor of the Mwalisi River. Finally, the Sonlweand Kiwira rivers are close to each other, near the border post at Lake Nyasa.

It is also worth noting that in the South Eastern part of the focus, some Km from Lumbira, is theKilondi River. It is big, perennial and may also shelter the S. damnosum s.l. Since this river and theSongwe River are located outside the Tukuyu focus, could the latter be isolated?

4.1.4. CDTI status in the Tukuyu focus

The CDTI project in the Tukuyu focus within I year. The data collected between May 2000 andApril2001 may be summed up as follows:

The population of the Tukuyu focus is broken down into 46 villages, 38 of which are in theRungwe drstnct, and 8 in that of Kyela. These districts are located in the meso and hyper-endemic onchocercal areas.In November 2000,261 boxes of mectizan, representing 130,500 3 mg tablets were supplied tothe NOTFs.For activity implementation, 82,635 US dollars (of which 47 dollars rvas transferred to theNOTF) was put in place by APOC. This funding was used to procure material and to coverexpenses relating to fieldwork.87 to 100% of the training objectives for technical personnel involved in the CDTI wereattained.The inhabitants around the Tukuyu focus are estimated to be 84,310 persons, 65,211of whomwere treated with 123,000 ivermectin tablets. The rate of coverage is 660/o. Non-eligiblepersons (children below 5 years, expectant women, patients), and absentees represent ll%o and9.7To respectively.

This means that the coverage rate of 66%o is excellent, since the number of people who refusetreatment represent only 0.3%.

ln conclusion, it could be said that CDTI is going on satisfactorily in the Tukuyu focus. Thearrangements made (namely undertaking treatment in the dry season, providing financing, and acquiringivermectin in time) should contribute to improving the therapeutic coverage rate of the next CDTIcampaigns.

I

4.1.5. Budget for vector elimination activities

For the start-up and continuation of eltmtnatron actrvitres, APOC provrded regular financralassrstance on tlte basts of letters of agreement (contracts). 'fhc table belotv sums up the budgetcomponent of the project.

11

Pcriod covered Cash translcrred toficld

Amount spentUS$

Purchaseequlpment

o Total cost

Oct 9B-S 99 2s,01 I I 1,880 88,3 ss r 00,235Oct. 99-Scpt 00 50,711 32,5 l8 92 455 124 913Oct. 00-Scpt 0l 43,199 29,216 8 000 31.216Oct. 0 1-Se pt 02 48,983 NA 11,940 t1 940Total 167,910 73,614 206,750 280,364

4. I.6. Discussions - Rcmarks

Grven the various results presented above, it appears that prior to the start-up of the activities ofAPOC, several pieces of technical information were available, due to regular .u*.y, carried out in theTukuyu focus. This data helped to select the focus for vector elimination activities. However, beforestarting control, APOC assistance helped to cristalise some points. These included mainly: choice ofcapture points, determination of the duration of larvae life on the field, determination of vectorcharacteristics on the entire focus, the sampling and distribution of all blacl ny ,p""i". found in thefocus, the determination of insecticide spraying points, the effective .9arrying "upr"i! of the Temephos

and the sensibilify of larvae to the chemical on the main rivers and tributariei, ,na nnutty the faining ofpersonnel on all aspects (technical, practical) of entomological evaluation. These results are analyzed inthe paragraphs on the distnbution of the S. danutosunr s./. in the focus, isolated f.o*irre focus, vectorcontrol and entomological evaluation.

a) Distribution of S. da nosum

Vector eltmination is the result of total efficacy of larviciding of all ve ctor breedrng sites, u,hichhad been rccorded ovcr a sufficiently long period. But the spraying points meant to cover the entirebreedrng sttes rvent from 26 (Walsh and Maegga, 1996) to 5i (eu.ro, 2002), Thus, follo*,rngprospectron, it appears that the main tributaries of the Kirvira and the Mbaka are almost all colonized b!the S domrtosrun s l ln addition, the small streams, u'hich enter the rvatercourses (main rivers andtrrbutaries), rvhose stretches shelter the S. damnosum s.1., are also colonized by their.*bou"hr..r. Theresults of the prospecttng carried out in 1998, 1999,2000 and 2001 indicated that tire distribution of theS- darrtrtosturr s./. in the Tukuyu focus is more important and more extensrve than the limits mentioned inthe Walsh and Maegga report (1996). The onchocercrasis vector is found both upstream anddorvnstrcam of thc said limits. Besides, given the great number of secondary tributaries, it is probablethat some florv dunng a part of the year (even all year round), hence the plssibility of breeding sitessheltering the S. damnosum s.l. (Barro, Z0O2).

Thts means the curent distribution of the S. damnosum in the Tukul,u focus, is perhaps notdefinrtely establtshed. Horvever, it rs of utmost impo(ance to identify the S. damnosum s.l. found on thevarious watcrcourscs. In effect, Maegga (2001) notes that for the pu.t th.". y.r.r, tl* larvae harvestedhave not undcrgone an1' cytotaxonomic tdentrficatron. And yet, somc breedrng sites (for instanceMrvaltst on t1-re Mbaka) shelter several pre-imago stages, rvhereas the number of bies/man/day remainslorv' 'lhrs contradictory status poses a problem of the idcntity olspecies, u,hrch are so anthropophrlous.Bcsrdcs' the rdentrficatiort u'rll have to do with the tnbutancs (namely Rrvers Mrvatr and Mtumbrvrz),Rtver Songrve tn Tanzania and in Malawr. For the latle r, Maegga (200 1) proposes that a .;oint mrssion of'l-atlzatltatl and Malarvt cntomologtsts should prospcct thc Clirprta and Misuka mountarns rn the northemllrovince ollt4alarvr, u'hrch is adjaccnt to thc Bundah antl Urnalila mountarns olthr- Tanzanran drstrrct ofIIt1c.

lr) Isola(iort oIlhc [ocus

'l hc llrst condtttott rcqutred for unde(aktu{ r'cctor elrmrnatron rn a locus rs that it must bctstllalcd ln thc casc ol thc 1-ukuyu focus, thc'cssentral gcographrcal critc.a (presc.ncc of naturallrrrrrcrs). rtld cYttttaxt)llol1llo ttlcttttficatron oltlre vcctor ancl its unrqtrenc-ss to Llte focus (S,. dotttrto-\ttttr,

t2

Kiwira type), made some authors (Walsh and Maegga,1996; Le Berre, 1970) conclude that the saidfocus was isolated. On the contrary, other works (Guille! 1981; NOTFs, 2000i Barro, 2000 and 2002)reported the presence of the S. damnosum s.l. in the middle course of the Songwe River, which is anatural frontier between Tanzania and Malawi. Besides, the numerous small tributaries of the Songwe,during the period of flow, could be sources of replenishing of the S. damnosunt s.l. Of course att tlesewatercourses are found outside the Tukuyu focus, but the flying ability of the S. Damnosurn s. /. is suchthat it can get to any breeding site of the focus. It must be noted that some watercourses are so close tothe focus that simple dispersion would be sufficient. These last results call for another entomologicalevaluation of the Songwe basin, located on the western side of the focus in Tanzania, but also in Maiawi.The same might go for the Kilondo River, located in the southem part of the focus. This river is big,perennial and could shelter the S. damnosuru s.l. Meanwhile, there are doubts as to whether the Tukufrifocus could be called an isolated focus.

c) Vector control

The sensibility tests conducted in 1999 and 2000 by the OCP team (Barro) underpins theobservations made in previous works (Guillet, 1981; Walsh et al, 1981; Garms et al, 19g6), and confirmthe very good performances of Temephos with an active matter of 20Yo emulsifiable concentrate. Notonly did the river tests help to solve the problem of carrying capacity of the Temephos, but it alsoshowed the superiority of its performances, as compared to those of the Bt H14 Tecknar. Thus, the firstvector elimination campaign proved to be efficacious, for after only a week of treatment, no positivebreeding site was found on the main rivers. Additionally, the total absence of nymphs also shows theefficacy of Temephos on the breeding sites around the tributaries. This chemical remains the selectedinsecticide for contolling the S. damnosum s./. in the Tukuyu focus. For each series of spraying, there isstill a problem relating to heatment cycles, accessibility to spraying points, and the determinafion ofinsecticide quantities to spray (especially in the absence of a spate gauge). Treatments was weekly, thistime lapse between two treatment sessions sufficiently covers the duration of larvae life, which in viewof the water temperature (180C-190C), is at least two weeks.

d) Entomological evaluation

The entomological evaluation is the tool for appraising the results of insecticide treatment on thevector population and parasite transmission. The data collected, though has information that may differfrom a document to another, may be characterized by some traits as foilows:

the capfures have great variation in the number of females harvest from one year toanother. Thus, for the same capture point, the same month (practically the sameconditions), and the same number of days of capture, the MBR recorded in 2000 atTapio-Bridge is 3 to 607 times higher than that observed in 1999 at the same capturepoint. The same goes for Kambasegela, Lufilyo crater and Lwangwa-Masako.It is generally agreed that, apart from the periods of re-invasion, when the black flydensity lowers, the physiological age increases, and vice versa. The results obtained atTukuyu do not tally with this rule. The dissected black fly population seems, in allperiods, to be made up of young females. It must be noted that this part of thepopulation is usually captured in the first hours of the morning (7.00 a.m.-9.00 a.m), orin the last hours of the aftemoon (1600-1800).No infective female was caphrred in 1999 at Kambasegela, Lufilyo-Crater and Tapio.Ard yet 527 parous females were dissected, of which 55 were infected. Even atLrvangwa-Masako, only 3 infective females were recorded.Certainly, the MTP is nil for some months of 2000, but each of the ATP obtained at thediff'erent capture points is high (minimum ATP:I12 at Lwangrva-Masako, maximumATP:282 at Tapro Bndge), with a tolerable hmit (threshold) of 100 Lilman/year in thesavanna zone of West Africa.

,

l34. 1.7. Conclusions-Suggcstions

Thc "vector elimination projcct" rn Tukuyu now has weak point, whrch must be undcrscored irrordcrto make control activities nlorc effective. Iior thc attainmcnt of the sct o[1ccti'c, rvc rvould lrkc toItst sornc clenrcnts on which rt would be nccessary to dwcll.

- vector elrmination requires total efficacy of larvicidrng, rvhich rs undcrlakcn on alI brcedingsrtes' Grven the topography of the terrain in the Tukuyu focus, it rs of ob.oirt" nccessity tocontinue with prospecting, especially in periods of low water whcn thc carrying capacity ofTemcphos is considerably reduced.- The need lor larvae controls to evaluate the efficacy of larviciding, thc probablc increase in thenumbcr of watercourses to be treated, and the topography of thc t"-.ruin'..q*.e, rrit6 respect toservlce qualtty, thc recrurtment of temporary stalf durrng each control .rn.,pu,g,,.,-.- The water levcl gauges in the focus now are generally locatcd at the extrem" Jnas (upstream anddownstream) of the watercourses. Due to this, their exploitation is difficuit in the middlecourses, which prove to be the areas with the highest black fly densities. Besides, there is nowater level gauges on the tributaries. This situation needs to b.

"o.r."i.Jfiro[ing gauges,updating of tarage graphs), in order to make for good projection of doses and quantity oflarvicides to be sprayed.- In order to monitor the evolution of the settlement of lotical organisms, apart fiom black flies,under the effect of black fly larviciding, it i._n...rruryIo hurr" Lf"..n"L iiya.*Uiotogi"ul data.It is therefore of utmost necessity to collect the maximum of data on-.n,o.nofauna andichtyofauna- Some authors affrrm that the Tukuyu focus is isolated. others, horvever, given the proximity ofthe Songwe River, its tnbutaries and the presence of the s danunosu,n, l. In .o.n. *u,..courses,have reservations on this. It is therefore necessary to und..tuk*n

",rtomological re-evaluationof the basin of the Songwe in Tanzania and Malawi. In addition, and i, or"d.. to confirm orinfirm the assumption of a re-invasion of the treated zone by the exogenous s. darrtrtosrr, rn thcfocus, it is necessary to identify the vectors, with precisron.- The results of rnsecticide treatment on the vector population, and the transmissron of the parasiteare appraised, thanks to the entomological evaluation. But the current data on captures shorvsome serious drsparities. It is imperative that vrgorous action is laken (sensitization,supervision) in order to make these data more reliable. in actual fact, the capture and dissectronresults ralse somc issues:* were captures carried out according to the standards (7 a.m. - Ig00), or oply at ceftain ti.resof the day (namely rn the moming, given the physiological age)?* Is the search for stages of o.r'olvulus in paroui females suficiently done u,rth precision?- The tmplcmentation of the "vector elimrnation" project at Tukuyu ,uppo.... *rl.rt means andlogistics' The latter, '"r'htch are made availabie io the proJect by Apoc, are not partiallyallocated to the said proJect. A solution rvrll need to be iound, so that urL irr. logrstics madeavailable by APOC will be actually devoted to the implementatlon of the pro_;ect.

In view of the various points above' whtch sum up the various difllcultics that canre up duri,g thepracttcal tntplcmentatlon on the field, the eradrcation of the S. tlantnosunr s.l. b;, ground treatmcnt i. theTukuyu focus, rtsks to be an oblective that is too ambitious. on the other hand. tlie therapeutic co'eragerate (66o/") and that of pcrsons (0.3%) rvho refuse treatment rvith ivermectin, indrcate that CDTI is gorngon satisfactonly ut the Tukuyu focus- Thc nreasures taken (namely,, undcrtakrng i..-rtrr._nt rn the dryseasoll' fir'rdr.g financtng, artd proc.ring lvemectin rn trme) should .ont ,bit. to rrnpro'rng thethcrapeutrc covel-agc rate oleach of the next ()DTI campargns.

t4

4.2. BIOKO FOCUS

Thc island of Biokr rs a mass o[earth of volcanic origin of 2,017 sq knr (72 km long and 35 kmwidc). 11 is locatcd in the GulI of Gutnca, on thc coast of Cameroon and Gabon, betrvcen lalitrdes 3n4gjN and 3012'N and Iongitudcs l2t'7'E and 12040'8. Thc rsland rs charactcrizedby a very rugged relief,made u1l of mountains, some surnmits ol'which are partrcularly high (Basilc p"ut, :Ot lm; Caldcra daLuba. 2661 m; Biao peak: 2009 m).

Thc clrmate of equatorial type, with two scasons: a dry season (November to March) and a rainyseason (April to Octobcr). Thc annual average temperature is 250C. Rarnfall vanes 6om l930,r,r i. thcNorth to 10.990 mm rn thc South (lig. l3).

The island of Bioko belongs to the kopical forest belt. About 90% of the territory is covered byforests. They are particularly dense and entirely cover the rivers, which are very difficult to access. [nthe upsheam and downstream parts of the only main road, only paths link cocoa farms, which provideaccess to the rivers.

The hydrographic network (fig l4) is made up of small low-output rivers, which descend fromthe mountains. Some watercourses don't have buffer zones (estuaries, iagoon)); They flow directly inthe sea, hence the influence of the seawater on their aquatic fauna. Due to ihe slope, the rivers flow fast(0.3 to 1 m/s) and the current is turbulent. They are particularly numerous (241),tut short. The averagelength is about 7 km (maximum: l5 km). Each watercourse shelters several breeding sites.

The epidemiology of onchocerciasis recalls that of West African tropical forests (Mas et al,1995)- The average prevalence is about 75% (85% in persons aged over l5). For CDTI, the targeipopulation is estimated to be 60,000 persons.

The Broko island rs the only rsland knorvn, to date, to be endemic rvith onchocerciasis. Thevector rs a member of the S. damnosum complex, identrfied under the name S. vahense, Bioko type.The geographical location of the island shelters it from re-invasion. This rsoLtro,, q0 km from thcCameroonian coasts, led to thc thought of vector elimrnation, coupled rvith ryermectin drstribution,whrch started in 1990.

4.2.1. Nature of rvorks

The studies on the onchocerctasis vector on the Broko rsland started in i989. Then a TDR studyon the feasrbility of vector elrmination rn this focus rvas conducted in 1996. Finally, in 1999, variouscomplcmentary studies u,ere carried out under the pro..;ect, financed by APOC, arid entitled ..Vectorehmination of thc Broko Island".

Thc objectrves arc specific to cach studv, and arc presented as folloil,s

a) TDII study on feasibrlrty

detenline tirc productrvrty ol larvae brecdrng sltcs tn the dry season;trace the plans ol insecticrde treatmelil;cstabhslt thc rdentrty of vcctors, tn rclattorr ri,rth that olblack I-lrcs ol- the nc-arcst zoncs. rvrth avrcw to appraisrng tl.re extent ol- rsitlatron ol thcsc vectors:cvaluate thc ltossrbrlrtv of rc-invasroti liont llrc coasts.collcct all trsclirl tnlirt'rtrltlrtltt to tlre rrnPlenrcrrtalron o1'tlte "r,cctor clrnrrrietr,rn" prt4ccts.

lr) Elirninating the vcctor fronr thc llioko island

(rarn thc national tr-arn orr thc collcctron olbasc cntouroloqrcal data,collcct cntornolclqrcal basc tllt:r,

L

l5

- cstablish base data relating to the impact of treatment on the environment (obtain base data onthe aquatic fauna, evaluate the impact of Temephos on the rnvcrtebrates and ichtyofauna andrivers of thc island);

- study the scnsrbihty of larvac population of thc S. damnosum s.l. to TcprepS.s;- study thc dynantics oIrrvers and their tributarics;

,- utrderlakc a first ground treaturcnt campaign, and cvaluate its impact on thc transmrssion ofonclrocct cIasls.

4.2.2. O utcomes ob tai ncd

Thc vector elirr-rination project rs the result of several years (at lcast l0 r,cars) of prclrminarystudrcs, torl'ard dcten.ninrng thc feasrbilrty of such an opcration at Broko. rir" ,rui,ors results arcprescnted below' in items entttled: isolation of the island, prospccting, larvrciding and entomologicaievaluation.

a) Prospecting of breeding sites

The works carried out in April and May 1996 by wilson, indicate that 224 rivers wereprospected, i.e.9l%:o of the entire watercourses of the island. At this period, 20 of the.iu"., prospectedwere inaccessible, 17 of which sheltered the larvae of the S. vahense, Bioko rype. on the contrary, I30(58%) of the rivers showed a flow, and 45 of them (210%) w-re- positiv" uiln. pre-imago stages ofSimulidae, 23 (10%) of which are of the S-. damnosum s.1. The 2i7 prospecting i..rions carried outenabled a breakdown of the rivers irto t*o.ut.go.i"r, those that shelter the S. doirnosu,t s.l.,and thosewhose flow was sufficient for the settlement of pre-imago stages of S. dattrtrostutt s.[.lt must also benoted that 2l rivers could not be prospected, 12 of which were capable of sheltering s.darrtrtosurtt s.l.breeding sites. With respect to c1'totaxonomic belongrng, the 474 specimens examined indicated thatthey had exclusively to do with thc S. yahense. Since its chromosomc characteristics do not correspondto tlrose olthe standard yahense, it has been baptized the S l,altense, Bioko type.

'l-he numerous prospecttng activities undertaken rn January-February 1999 (Barro) confirm thatthe rivers are numerous, short (7 k* long in the average), u,ith fails and rapids. Their flou, rates weregenerally lorv (lou'er than 1m3/s), hence the insignificant invasion by the'5.1antrtost,rt s.l. Even theartificral supports were not densely colonized in the third rveek. [n additron, most of the lan,ae u,ere attntemredtate stages. No pre-imago stage was harvested beyond an altifude of 600 metres or iu *,atersrvhose tenrperature was lou,er than22o5C.

ln March-April 1999, Meyer carried out a senes of prospecting of nvers of the Broko Island. IIeconcludes that most of the u'atercourses are protected by a luxuriant vegetatron. hence the difficulty inprospecting. The South, u'hich accounts forabout40% of the territory, is rnaccessrble on thc ground. Inthe..dry season, the florv rate of watercourses is generally betrveen 0.2and I mrls. Cool u.ater(190C<'0<260C) and clear rvater (turbidity generally lou,er than 5iTU), florvs on the rocky ground at anaverage spced ol0.5m/s (0.3m/s<speed<lnr/s). The pre-rmago stagcs were rare, due to thc fluctuatron-stn rvater level, following rntermrttent rarns. Prospectrng on thc- Musola and the Eba (tlbutary) rndicatc-that betrvecn 500 m and 800 m, there was no S. datnnosrutt s.l

Chckeetal.carriedoutneu'prospectlngrnAprrl lgggonllrrvcrsolthc-rsland.-l-hc-objectrvcu'as to dcternrtue the maxtnral altitude at whrch thc S. darnnosum s.l could colonrze thr- breedlng srtes.Prc-ttllago stagcs werc han'ested on the 'l-rburor.res rrvcrs (North). MLrsola, Boolo, A,u. Coo andIlaloa;I' -llic tnals conducted at 345 m,554 nr and 808 m could only cnablc'thc collectron 9f S.tlatrll.tostlt.t.t Strnultdac. It rs to br- Itotcd that it u'as thc llrsr lunc a ptlsrtrvc lrrr'cr.lrrg srtc r'as clrsco'erc-tl,rn llrr'll.rlo.r]rl

In I)ecenrbcr 1999, prosltcctrng was on somc \\'atercoursc-s rn thc rcgron 0l'Maluba -l-hc rcsultslrrcsentcd by MCCall (1999) rndtcate that24 srtcs, tncludrng 8 at altrLudc i:-so-t.l00nr) u,ere ,rsrtecl.'l'hc

$. cLlrrllosurl s.l. (prc-rnrago slagcs) was encouutered ur fivc rrvers (Nale. ISaloapr, [.ou, Broco anda tlvcr rr.'tllloul a tlarlre ), u'hrclr clo noI apPcar on Ihc lrs( dr.au,n up by \\,rls.n ( 199(,) N. ,.srtr'c

I6breeding site was found beyond an altitude of 600 metres, nor in the waters with temperaturcs bclow220bc' on the contrary, in the Moca region, two biting females were captured at 750 and 1,250 m. Atthe time of the investigation, the florv.ui. *u, 1.05,0.a4 and 1.05 m3/s on thc Apu, Biala and Malahorcspcctivcly.

As part of thc studrcs on tltc distributron of prc-imago brcedrng sitcs on thc isla,d of Bioko, 54rrvcrs wcrc visrtcd at thc bcgrnning of thc ratny season (June-July). M-as et rl. (2000;;onclude that outof thcsc watercourscs, watcr tcmpcraturc r"r, i5'c. [n additron, out of 52 accessible'rivers, g shelteredprc-rmago stagcs o[ thc .S- damnosurn s.l. It ts to be noted that during ttr" san-,c fe.ioJ, , lot of adult Sdamnosum s'l wcre captured during the prospection. The prospection carricd out i.. January-Febrrary2001 by Meycr et al', just before the beginningof larvicid,ng *u. to determrne access points to thcrivers, rivers to be treatcd, larvrciding po,nt, unJdor". to be ap"pliea at each breedrng srte. 39 sites *,eretherclore lrrospectcd alnollg whrch 8 wcre havrng s.damnosun ut p..-i-rgo stages. water tcmperaturesfluctuated between 1809 and 250c. Flow rates w-ere between 0.1 to 5m3/s] rn.In.."iilla. *u. sprayedat 40 points, and out of the l0 breeding sites controlled after treatment, 3 were found to be positive.

ln February 2001, Meyer and wilson undertook prospecting of the southern part of the BiokoIsland, between fuaba and Luba. out of 40rivers, they noted fou. mui, basins qraav, rioaba, osa, ole).Each of these rivers is a series of falls and rapids. At the time of prospecting, tt "

cj." River was almostdry, but the other three had good flow. The flow rates were zo jo*ft ,"a"slil;i; on the Moba andole respectively. These flow rates are such that the BT seems to point to the need for treatment ofbreeding sites, except that these treatments, preferably aerial, would take time due to the nature of therelief.

Pre-imago stages were harvested in abundance, sometimes, on these \\,atercourses; they usedleaves and stems that stand out of the water as supports. As for the small tnbutaries, they were coveredwith vegetation, but due to the topography of the terrain, there are openings that should make aerialtreatment possible.

b) Capturcs-dissection-transmission

Right from 1992, the captures made on the Sampaca and Timbabe ri'ers helped to establishannual fluctuattons of the MBR (fig. 15, 16). From January to April, black fly densities were generallylorv (MBR<100)- On the contrary, from May tkough oecemuer, the MBR fluctuate between 300 and4,000, and between 1,000 and 8,000 at Trmbabe und Surnpu.a respectivcly. The maximum capture rsrecorded in October.

In 1996, the dissection of 56 females enablcd wrlson to observe 14 parous ones (25%),2 ofu'hich were carrlers of infecting larvae. For comparison purposes, 369 females tliat had been conscrvedin alcohol since 1993 rvere softened, coloured and disseltea. rn. results indrcated 42 inf'ected fen-raies(11.4%) and 8 infective ones (2.2%)

Betrveen January and Apnl 1999, 3146 fe malcs u,ere harvested in 29 da1,s of capture car.ed outby the national team at Sampaka, Barley conr, Musola and Balada Luna oba. imongit. szs fe.r-ralcsdissectcd, the physiological agc fluctuated betrveen 14.8% and li.3o/o. The inlcstation ratcs u,erclrartrcularly hi gh (rn fected females: 44o/o; irfecti'e fcmal es: gzo).

In March 2000, Mas and l-trados rccorded 74Lrl1000 parous females and a M'l'p equal to 1-5'l'l.lesL- rcsults helpcd to extrapolatc thc data olGcenen (1993), and to obta,r a,raxrnrum ol-400 I_i/1000l)rlrous and a MTP of 1,600. Frnally, rn 1997, Mc call antl N,las obscrved 1,440 I-rl1000 parous {-e.ralesrn the- tirssectiou results.

('allturcs, lilllou'cd by drsscctrttns, \\/crc ca|r'rctl ()u1 b)'tlrc rratronal tealn rn Aprrl-May 2000 clnthe San-rpaka (Sampaka), Apu (Barley Corn), I\4usola (lrlusola; and Ilunra (llalacha of l{raba) rivcr-s.l-ablc 9 rndtcatcs that tn 3l days, 5l3ti fcnralcs \\'erc captured, 2,g90 dissc-clcd, ol- u,hich 1,215 $,creParous (4201,),85 inlccted (6.9o1,), and 25 rnl'cctrvc (2,2u) 'l-hc avcragc black 11y, clc,srty lor thc pcrrod\\as about l6(r bitcsinlan/day (rrtrrturturrt-40, rnaxrnrrrnr-38-l). lrence the rrsually hr96 I\41]lt

a

o

t7(minimum=1305; maximum:l1,475). Taking into account a distributron by point of capture, thephysiological age fluctuated bctween 33.5'/, and 53o/o. With respcct to infestation rates, they werebctrvccn l.6oh and ll.syo, and betwect't 0.5%o and 5o/o for the iniccted and inlcctive parous fcmalesrcsllcctivcly. Transmisston was lowcst in May at Balacha (MTP:ll), and hrg6est in April at Musola(MTP=270).

'lhe rcsults of thc captures carrrcd out in February 2001by thc uationaI tcam (table l0), duringlarvictdtng, is as follows: 9 capture points, 17 days of capture (l to 3 days per point;, 3,293femalescapturcd, of which 1304 dissected. Thc parous fcmale percentages go from n.G% b 640/o, and thernfestation ratesare from5.3% to25o/o (infected females), from0 to 9% (infectivc females). Apart fronrMoca at river Chuba (6 females, MBR = 300), the black fly densities rvere relarively high (minimumMBI{=2970; maximum=[0,380). The trials carried out at thc upstrear]r part oltlie rvatercourses helpedto capture 632 females, of whrch 149,279, 198 and 6 were captured at altrtude 550 m, 600m, 7g0 m and1,250 respectively. In addition to the February results, those of the captures-dissection of the othermonths of the year 2001 are indispensable for appraising the impact of the first ffeatment campaign ononchocerciasis transmission. These elements should be available at the project Coordinator,s, for oi ZgiiNovember 2001, Dr. Mas wrote to the Director of APOC: "J.M. Mba, entomology technician, is sendingresults of the Simulium catches and dissections, on a periodic basis, to Dr. Wilson',.

c) Preparations towards the first ground larviciding campaign

At the end of prospecting conducted on all the watercourses of the Bioko Island, Wilson (1996)concluded that 1,020 km of stretches, belongingto 5}rivers, were to be subjected to larviciding.

The "vector elimination at Bioko" started in January 1999. From this date to the end of July2000, the vanous activities are summed up as follows:

In January 1999, a team of external scienttsts staycd at Bioko. Advantagc u,as taken of their sta1,to tratn four entomologist-technrcians on fieldwork (capture and dissection of black flies). Besides thri.two scientists of the Spanish Cooperation underwent trainrng at OCP, to enable them ensure effecti'esupervision of the collection of entomological data.

Two insectrcide tests rvere conducted in January-February 1999, and the results shorved thatlarvae of the S- damnosum of Broko u,ere very sensitive to Temephos. hr effect. Barro (1999) notes thatrvith 100% of nrortality at 0.3125 mg/l, the results of the insecticide tests conductea on the lan,aeharvested rn the Musola and Apu Rivers were excellent. These sensrbrlity studies indicate that at flo*,rates of 0.14 m'/s, 1.05 m3/s and 1.6 mr/s, corresponded to the effective carry capacities of 650 m, 25 knrand 38 km respectively.

In March-April 1999, rvorks on the tmpact of insecticide trcatment on the environment werecarried out in the Broko focus by scientists from thc Museum of Natural History rn London, and fromthe Water Resources Instrtute of Accra. These studres wcre aimed at collecting base data for an impactevaluatton on larvicidrng of the non-target fauna (nantely rnvertebrates and fish)

Meyer (2000) notcs that most of the rtvers may be treatecl from thc bndqes that span the marnroad. Thc latter is located at an altltudc of between 100 an<j 400 m, and l-4 kr, fiom the sea.'l'hc ri'erzone, wlre rc the pre-tmago stages of the S. danutosunr arc most numerous, rvould thus, be covcred bytreatt]rents conductcd from the bndges. Ifc also rccor.nnrcnds that aerial prospectlug be undertake' rn thcsoutl.rcm part olthc island in 200 1, tu order to collect ir.rlbrrnatron on thc acccs.rbil,ty of rivers, and tht-productrvrty of thcrr bree ding sitcs.

At the crld ol'2000, and alier scvcral sclcctron tests. srx persons \\,cre trarned rn [lcld*,ork.lrarvcst and idcntilicatron of larvae , nymphs and adults of the S dotrtnosurtt.s.l., har,,,est of larvac of the .Stlurttrtosttttt s./. rn thc Carnoy for thc cytotaxononrrc studrcs, capture and drssectron o[ black t-lres,deterrr-rtnatiou ol larvae stages of O. r,olvulus, conscrvatlon oI parasrtcs for DNA analysis, rarsrng oIlllack llrcs lror.rl tlic nymlth stagc, reacltng of rvalcr lcve'l gaugcs, usc of thc (jlrS. s,r-ayrng of inscctrci6c.IIou'evcr. Mcycr (2000) sard thc first lgound lrcalnrcnI ri,ould bc prcccdcii bv sci,cral r,,,ccks ol r.c-

r8

trarnlng of tcchnicians on pre-treatrnent prospecting, experimental treatment, insecticide tcsts, andhydro-biological activrties.

Dcsprtc thc trunrerous dclays in srgnatures on docunrents, and thc late application oIordcrs anddclrvcry, rnost ol thc matcrial and equtpment (except a 4 x 4), havc gradLrally bccn procurccl apdrnstallcd at Malabo.

Since the first ground trcatmcnt was scheduled for 2001, Meycr indicatcd that all the accessrblerrve rs below an altrtudc of 500 m be trcated every 2 km, and twice a rveek. All the authors (Wilson,1996; Bano, 1999; Mas et aI,2000; Meyer,2000;Cheke,2000) are unanrmous on the fact that the idealpcriod for treatments is from January to April, for the hydrology, rarnfall lcvels and black fly densrtiesarc llallrcularly lavourablc for a good trcatment exercise. The rnscctrcrde recomnrendcd is;l'e,rep5osrvtth atr acttve matter of 20u/o emulsrfiablc concentrate, due to its qualrtres (biodegradable, withoui anytoxrc effect on mammals and fishes, moderate impact on non-target fauna, and good efficacious carryin!capacity). The dose will be 0.3 Vm3 of flow rate, hence about 1,200 I will be .,i..."ry for the

""*puigi(Meyer, 2000). The latter proposes that to lessen costs, insecticide should be negotiaied and taken fromOCP stock, which would include the quantity required in its next order. It must be noted that in theevent of very low flow rates, (lower that 0.5 m'/s;, it is necessary to increase the dosage, and thisrequires a greater quantity of insecticide. To address this imperative, a stock of 2,000 I oi Temephoswould be a good precautionary measure. Since the Bacillus thuringiensis Hl4 is being proposed ai thestand-by insecticide, in the event of resistance of the larvae to Temophos, Meyer (21000) deems thesccurity stock to be 300 l. Treatment is scheduled to be carried out on the ground, but the inaccessibilityof some breeding sites could entail the use of a helicopter.

From the point of view of expected outcomes, Philippon (2000) notes that the first groundtreatmettt operation should, at least, shorv the feasibiliry of a control in the northem part of the island,and at bcst, rts tsolation from the southern part. The timing of re-colonization by adults and larvae *,rllhave to bc carefully monitored. [n addrtion, the analysrs of molecular biolopX, should alloq, for thedetcrnltnatton of the origin of nerv black fly populations. On the other hand, this ground treatmentshould not provide a lot of tnlormation on a possible aerral treatment. As a matter of fact, it is notobvious that tnaccessible breedrng sites on the ground could be treated by helicopter, due to the canopy.It seems, therefore, a bit premature to rush into aenal treatment. It is only after anall,zing the results ofground the treatment that a dectsion could be made.

d) Conduct and results of first ground trcatmcnt operation

Phrlrppon (2000) states tliat at the end ol 2000, base data that are nceded for control rvasavatlable, Iocal experttse was rn place, an action plan was drawn up, and the tasks rnvolved in thrs rvorkrvere entrusted to rndrviduals, u,ho wcre expenenced in this kind of operatrons.

The first ground treatment operation took place at Bioko dunng the dry season (January-March)2001 Thrs u'as preceded by the collection of pre-treatn-rent data on cytotaxononr)/, the sensitrvity of thevector to inscctictdes, the drstnbution of s1lccrcs (nan-rely at altitudc), and the rmpact of larvrcidrng ontton-target lauua. At the trme of the rvorks only 30 watercourses were florvrng sufficiently to nrerrttreattncnt. As seven (7) of thc rvatercourses have cor.r.r1.llex basins (severaI small rnaccessrble tributaries),out olthe 248 proposcd sprayrng points, only 92 rr,erc sclcctc-d. The florv rates oltfic lvers rverc lou,r-rthan lnrr/s, and thc water rvas clear (turbiclrty<5JTLl) and cool (190<240C)

'llic ltersonncl in charqe of thc spraying nurrbcred 10, broken into tu,o tcanrs. cach of u,hrch had

a tcaltt leader,3 techntcrans and a drrvcr. llor easc olnrovcr.r.rr-ut, oltl-re staff, AI)OC purchascd thrce neu,Iot'ot.t llrlLrr dttublc-cabrn velttcles tu,o tntcks and chirns lirr Iorvrng ve lrrclcs, In adtirtittri, thc- Spar.rrsh( tlollcratttlti ol'licc pu1 a Landover at thc drsposal olthc teanr. Iu addrlr<ln to thc sltrayrng, lhrs ltcrsonncluas ttrtcgratcd trtto othcr acttvtttcs: capturc and drsscctton of black 11rcs. hydrobrologl,rvorks, scnsrbrlrtytcsts and llrospccttng olrivers. Meyer (2000) uotes that thcsc rvorks shttuld contlbulc to starltng up theclml)algn, ri,hrcli u,ould cornbtr.tc ground treatlnent ri,rth acnal sltraying.

G

t9The insecticide for the ground treatment is Temephos, and the operational dose was 0.4litcrs/m3/s of flow' instcad of 0.3 ll=mr/s as originally planned. Thrs shght inc.case rs due to the prevailingcondttions during trcatmcnt: water tcmperature (100C-240C), u"ry lo* flow rates 1ior"". than lmr/s;,last current (0.3 at lnr/s) and last drspersion of insecticide. Thc latlcr rvas sprayed, thanks to spraycrs (5In all) Bcflhoud cosrnos 18 type. This sprayer was selected for scvcral reasons: it is casy to use, rtswcight urakes carrying over long distances possible, it allows lor rapid u,-,0

-.,n-,pi" applrcation ofrnsccticide , the quantrty of chcmtcal to bc sprayed could be measurcd with precrsion, a,rd contact rviththc insecticrde does not corrode the apparatus.

To conduct the entire treatment, a stock made up of 2,000 I of Temephos, 500 I otBt and 40 I ofRhodaminc werc dispatched to Bioko. I{owever, to address the problcm oi a"lry u., .to"t delrvery, anaddrtional I 50 I of Tcmcphos was sent by air, as matter of urgency.

Treatment started on l2 February 200l,and spanned five weeks, at the rate of one treatment perweek' The first two treatment cycles took 4 days to cover all the breeding sites. onlf .iu".s *hose flowrates were equal to or lower than 0.01m3/s were not included in the tritm""t.-ft,ur, 92 points weretreated each week, with approximately 21 liters of Temephos. of course reatment was planned for lZcycles, but it stopped after the fifth application, for technical reasons (mainly inu""".ribility of breedingsites).

one of the objectives of the first campaign was to collect a maximum of information, following thespraying with Temephos, in order to appraise its e fficacy in the operational conditions of Bioko. Fromthe several data collected, our conclusions are as follows:

a) The insecticide carrying capacity was I to 3 km, for flow rates going from 0.05mi/s to0'2m3/s- As Meyer indicated (2001), in the event of aerial t"rt,i-,.nt] rhi. lo* carryingcapacily rvill cause an increase in the nun-rber of flrght hours, and hence an increase rnbudget.

b)

c)

d)

The cycle of pre-imago development was partrcularly long (more than 2 rveeks), for thetemperature of water was usually low (190C-240C). The re-colonization of supports aftereach treatment was, therefore, very slow.No pre-imago stage was harvested beyond an altrtude of 500 m. on the contrary, adultsrvere captured at an altrtude of behl,een 500ni and 1,250 m.Adult population densities fell quickly after the starting treatment. Captures were nri atsome polnts, after only 4 weeks, though no nver rvas entirely treated. it should be noted thataccessibrlity to the watercourses rs very drfficult, and se'eral tribulanes cannot be reached.

At the end of the first campaign, which rvas conducted in the northern part of the island, Meyer(200 l) and cheke (200 1), note that due to the inaccessrbrlrty of some watercourses, ground treatmentalone rlray never succeed in ehminating the vector from the Broko locus. On the "other

hand, thisobjective may be arrived at, in only one season, thanks to an action of ground keatment coupled u.ithaerlal sprayrng' This positton rvas butlressed, follorvrng the aerial prospecting carried out rn the southernpart of the island, and rvhtch revealed that most of thc rrvers (some of rvhich shclter the S. damnosunrs'l') werc partrally or totally rnacccssrble on the ground. I'hus, Meycr 2001) and Cheke (2001) are olthe'tew

that ae.al operatlons are feasrble for the follorving reasolls:

r. The stock ol'l'erlephos at Bioko rs sulllcrent for covcrinq a ground and aenal treatr.ncnt.ir' An extenston ol' the coutract betu,ccn OCP and thc coilpanl, in chargc ol ac-.altrcatlnent rn Wcst Africa should be lcasrblc:

llt' 'l-hc flrght hour, csttttratcd at S1,030, thc ctrst of thc aenal opcralror-I. u.ould rise to $300--1(X),(10().

l\' 'l'hc prtltcctcti lltlllulatron ts esttmatccl al 7-i.0(l() ltcople, rc. Altolrt j US dollars/ltcrsrtn.

IrrotI tlie loregorng, and consrdenng thc ccssatron of OC-P actrvities at the e nd of 2002, Mcycrand Cllckc (200 l) are olthc vrerv tltat rlthc aerral cantparqn rs r.rgt cu11rcd out i6 2002. Alro(, q,rll ntrssthal tolden rtltltortunrty.

20

c) Problems and diflicultics cncountcred at Bioko

Various scierrtrsts havc reported a nurnber olobstacles to the snrootlr runni69 of activitics of the"vcctor clrtrinatiorl prolect at Broko". We arc mentionrng herc those that still lced to be adclrcsscd(Mcye r, 2001):

l'hc movemcnt olteams is often difticult, due to polrce and nrrlrtary check points. The securityagcnts don't seem to have undergone any good sensitization.working relations are particularly difficult with the NOTF Coordinator, hence the numerousproblems that might hamper the chances of success of the control etfort;'lasks are drstributed in the natronal team in such a way that thc absence o[ an employcc(cspccrally thc No'l'F coordinator) may rmpede the smooth running olthe outfit;Tlte nattonal team may be effecttve, but it needs discipline and supervision of its actryrLies.These two aspects are, most of the time, lacking.

Q Prevalence

Mas et al (1995), following an epidemiological survey conducted on the entire island, mentionthat average prevalence was75%o (85% in persons of over l5 years). The population at risk was thenestimated to be 62,000 people. Epidemiology is the forest type, characterized by 0.8% of blindness, 3l%of nodule carriers, 29%o of carriers of dermatological lesions, and lympho-adenopathics estimated at42%. Most of the villages are found in the northern part of the island, at 2-3 km of the sea.Onchocerciasis prevalence is high in all the areas. It is 16.50/, at Basapu, located at km only fromMalabo. As for the highest prevalence (87.1%), it rvas recorded at Ureca, in the southern part of theisland.

An epidemiological survey, conducted rn 1989 (Mas et al.) u,ith a populatron of 1759 inhabrtantslionr l2 r'tllages, enabled a prevalence of 14.6% (hyper-endemic) to be recorded. in 1998, after 9 yearsof ivenrrectrn distribution to the inhabrtants of thc same villages, the rate of prevaience was only 38.2o/"(hypo-endemrc), for a populatron of 1,167 inhabitants. The same gocs for the percentages that arecarrrers of nodules and dermatological lesions, rvhich fell by 2.8oh and 7.97o respectively.

g) lsolation of the island

The vector control activrtres can only be undertaken in an isolated focus (\\ralsh, 1990). That ofBioko lias a uuntber of cntena for geographicaI isolation.

thc closest sources of re-invasion are the nerghbourhoods of Mount Cameroon, locatedin the northeast, and parl of the Cameroonran coast rn the East. The distances from thcsepaces are 40 l<m and 80-130 ktn respecttvely. The Atlantic Ocean is in the West andSouth, where thc Principe Island (240 km), Sao Tome and Anabon are found. The latterlras nevcr slicltered the S. dcunnosruu s.l. (Mas, unpublished), and the black flies havenot been examined on the other lrvo rslands (Santos gracio, 1990).The meteorological condittons severely rmpede the movemcnt of black flies from thecontinent torvard thc island. Actually, almost all year round, domtnant rvrnds, comingliom the South or South Wcst, blorv across thc rsland torvard the continent. Even rn thednest period of the dry season, hardly does the intcr-troprcal convcrgence zonc (ITCZ)gct to thc island (Teran, 1962). Havrng black fltes comc from the north or east rs

rntprobablc, bccausc this wrli bc tn the ol)posrte drrectron of thc domrnant q,inds.'fhe cytotaxonomrc (Boakye, 1993), cyto-{r,enctrcs (wrlson and Post. 1994). andtttotlllttlltlqtcal cttlcrra (\\/rlsrtn, 199(r) rrttlrcatc tliat thc [rlack t'11 Po11Lll1111ttu o1-lJrrtko rs

esserrtrally ruadc u1t <11'thc S. yahense, []roko typc And yc1 ar.ry ltossrLrlc re-utvasroltcould <rrrly cornc lionr thc Catlcrootttan coasts, rvhcrc the .S. Squutnosurtr and Sdunrnosurn s1. spccies arc found. 'fhts nrc-ans that the Bioko population rs genctrcallyrsolated.

2l

h) Irnpact o[ trcattnent on thc environntent

Brooks and Jackson carried out a survey on the Broko rsland rn March-Apnl 1999, to dctcrmincthc drstrrbutton of odonatcs. The results indicatc that the l7 srtes visitcd arc located at altitudcs ofl'500n.' 600 m and bclorv 500 rn. Irerv gdonatcs (47) atthe larvae stage were harvested. Thrs sarnplc(bcfore treatt,ent: 22; aftcr trcatment: 25) does not help assess the effeclof tr,. r..,.,"pr-,os on this group.on the contrary, 260 adults representing 24 species, includrng 6 new ones, were harvested. Distributionis 6 specics encountered solely above 500 m, l7 below 500 m and l3 in both sites. [t n1ust ue noted thatout of the 2l I dragonflies recorded on the island, only 7 rvere found during tt-," ,u..,"y.

A study of the impact of larviciding wrth Temephos agarnst the S. damnosum s.l. on fishes andshrimps of Bioko, was conducted in the ay 19.u.on itttur.t"-np.il). Abban (1999) notes that fishesencountered during the survey included t2 families,2l geneva and 25 species. out of this there wereonly 9 freshwater fishes whose populations would be ixposed to larviciding effects The small-sizespecies made up the majority of fishes. The shrimps *e.e pa.trcularly numeroi. i,,ji',t" rivers. Theirbehaviour and reactions were normal. The same goes for the doies of 0.5, o.zJ--rna 0.125 mg/I.However, a fish, exposed to doses of I and 2 igll showed disorderly nro*,.*..,,r, and ended upbecoming stationary in some minutes (2-5). Howeu.., th" transfer of individuar, in u ,iutionary phase inwater without insecticide revived them in less than one hour. As for the experiments conducted withhigh doses, they show that all the fishes exposed to doses of 30 and l5 mg/l died rn less than one hour.At doses of 7'5 mg/l and 3.75 mgll' the trme of survival was 12-24 hours and -o." tt"., 24 hours,respectively.

The distribution of the macro-fauna was studied on 10 rivers of the Bioko island (Amatrq,e andArnegbe, 1999)' The aquatrc fauna rvas regular and generally more abundant belo*, an altitude of 500 m.Tlie effect of Temephos on the lattcr, rvas monrtored on the Ruma, Musola and Apu nvers located in theeast' west and northrvest respectrvely of the focus. out of the three sites, the us. of Temephos led to areduction in the number of chtronomtdes, but re-colonizatron rs relatively faster. The orthoclamidaervere the most affected by the rvat'e of insecticrde, whilc the Tanrpodinae were less affected.

i)Training

At the end of the various mtssions, rt appcars that the local staff benefited from theoreticaltralnlng (background on onchocercrasrs), and rr..e rnitrated, on several occasrons, on the usc of thetechntques applred in the area of vector control: larvae prospectlng, capturc and dissection of females,estimation of the florv ratc of a rtver (u'ith or u'ithout u grug"), calculation of insectrcide doses, using theflorv rate, ground larvrciding of black flies, a,d p."/porit..Itment .ro*rtoring.

4.2.3. CDTI status in the focus

'fhc populatron olthe Ilioko Island rs estrn.rated at 90,000 inhabitants rn 6g communrtres. CD-I-Ihas to do r'vrth 6[ conl-rlunitics located rn hyper and meso-endenrrc areas. Thc targe-t population is about60'000, half of *'hrch ltves ,r the tou'n oi Mrlrbo- Ilelbrc irstrtutrng the Apoc programmc, all thecomtt'tut.ttttcs \\/cre recctvirlg l\/L-nttL-ctrrl, bas-cd on the vertrcal uppror"h. But gi'cn thc comnrrtnrent ollhe gove mnlent, arld lltc good clrsPosrtron ol the populatron, the boll upp.oach u,as adoptcd in 2000lrarrting ol thc tcchnrcal stal-l'rrtvolvcd tn rvernrectrn drstrrbr.rtron rvas i,irrated. Sc.srtizatr.n wasconducted u'rth tht- poltrtlatttttr to crplarrr 1[rrs ncu,n'roclc ol-clrug cLstnbutro..

'l hc- results <ll'thc sectttltl yeltt o1'treatlnenI rndrcate that out ol 1g.2]-1 l)L-rsons, 7.-5fi2 u,eretr-cated, r c a thcrallcLlllc c()\('r.lgc |atc ol- 42'/,,. l'hc populatron trcated rs bctrl,ce, thc <lrst.cts ofIr4alabo (2928 pcrso.s), Ilar,ct'(2270 pcrso,s), Luba (1575), and lLaba (g0l pe..o,rj. For rhesc samcdrstrrcts' Lhe geograplttcal co'crase rs 100'2,. 8loh, loo'ri,and 93% r.-spcctiveiv. nt,sc,rrccrs,r rs l.righ,lirr (hc- t.habttattts ar.c all'atrl .l-tlrc srde ci-licts .r'r'cr,reclr,, "t;:;':;i;,ir.'.l"l,r,zri1r().

sh.uldctttitrrltttte Io lncrca\c Iltc vanoLrs cover-agc rAtts_

22

4.2.4. Budge( for vcctor elimination activitics

To allow lor thc start-up and continuatron of vector eliminatron activities, tlie APOC progranlrcprovrdcd rcgular financial assrstance on the basis of lettcrs of agrce nrcnt (Contracts). Thc table belou,sulus up thc budget componcnt ofthe project.

Pcriod covcrcd Cash transferredTo lield in $US

Amountexpenscsin $US

o Purchaseequipmcnt

o Total cost

March 99-Fcb 00 21,984 16,618 168,490 1 85,1 08March 00-Feb.0l 54,77 6 25,436 124,660 150,096March 01-Feb 02 55,390 NA 136,400 136,400

Total 132,150 42,054 429,550 471,604

4.2.5. Discussions - Remarks

a) Distribution of S. dantnosuru s.l.

The southern part of the Bioko Island, about 40% of the total area, is inaccessible. On the

contrary, several prospecting activities have been carried out on the accessible part. Thesc prospecting

actrvities were carried out the rvhole year, but they were mainly concentrated in the dry season (mainlyin January to April), the idcal period for treating larvae breedrng sites (Wilson, 1996; Barro,1999;Meyer, 1999; Meyeretal; 2001).Dcspitethegreatnumberof rvorks,theresultsof alltheauthorsagreeon several points:

The S. darnnosunt complex is represented on the Bioko island exclusively by the S. yahense,

Bioko type;Rivers are numerous and short (averagrng 7 Km long);

Watercourses, protected by luxuriant vegetation, are hardly accessible;

ln the dry season, the flow rate of rlvers are generally belou, 1m3/s. Water ts clear

(turb idity<5 JTU) and cool ( 1 goCctemperature( 260 C);

The pre-rmago breedrng srtes below an aititude of 500 m, arc generally posittve, u'hen the

temperature of the u,ater is higher than 2205C. No pre-imago stages have been harvested

beyond 500 m. On the other hand, adults have been captured at altitudes of behveen 550 and

1,250 m.

It is agreed that vector ehmination rn a glven lbcus is only possrble rf all tlie breeding sites are

sub.;ect to larvicidrng. Horvever, the results of the various prospecting carrted out at Bioko indrcate

clearly that the rivers arc very nulnerous and protected by dense vegetatton. This means that a nur.tlber

of breedrng srtes remarn unknoun, due to the inaccessibility of u,atercourses. This situation also poses

thc problem of choice of spraying points. It must ensure a-100% coverage olall thc breeding sites. Ofcourse, the authors agree that ntajonty of the posrtivc breedtng sitcs are localed belou'an altitude of 500

m. However, the prcscnce of adults betwcen 550 and 1,250 m nsks undernttning the chances of success

(possiblc re-invasron), slucc thc arca located beyond an altrtude ol 500 n.r is excluded from larvrcrdlng.Besides, followrng thc prospectrng undcrtaken tn the southern par1 of thc Island, Meyer (2001) notes that

apa11 fror.n the Musola Ilrvcr, atrd tts tnbutary,, the [:ba. I1o rt\/er ri'as acccsstltlc beyoncl an altittrcL- tll-500l1 lrycl lre lrlu,-50() 1t. scvcral \\.rtcrc()urscs u'crc prtttrally'or ctlrtrpl.-tel1'ttracct-ssrblc, 'l'liis Ittc.lll\ til.ltn() r-l\/cr coulcl bc trcate cl ()lt lts e tttlre coLlrsc-

a

23

b) lsolation of thc Bioko focus

Thc authors are unanimous in agreeing that the Bioko focus is isolated. In actual [act, it is anisland wltcrc meteorological conditions (especially wind movement; Tcran, 1962; Nasti, 1942) hamperthc rc-invasion of the locus. Besides, cytotaxonomic (Boalrye, I993), mo.pt-,otogical (wilson, 1996)and cyto-genctic (wilson and Post, 1994) evidence make one recognize that thei. yahense found atBioko is drlferent from the standard type. There is therefore, a genetic isolation, as comparcd to thenearcst black fly species, and those found on the cameroonian coasr.s.

c) Vcctor control

Rrver tcsts revcalcd that the selected rnsecticide for the treatments in fleld conditions at Broko,was Temephos with active mattcr of 20Yo emulsifiable concentrate. The experienced gained during thepreliminary works' indicate that the vector elimination project at Bioko would in"."a'se its chances ofsuccess, if control operations started in the dry -season,

and spread over 34 months. At the usualoperational doses, the spraying of insecticide is followed by a reduction in the number of chironomidae,but the re-colonization is relatively fast. on the other hand, fish and shrimp populations are not affected(no mortality; normal behaviour) by the insecticide treatment. This means that a teatment campaignagainst pre-imago stages of the S. damnosum s.l. through Temephos spraying in the watercourses of theIsland of Bioko should not have irreversible negative consequences on the non-target fauna. (Abban,1999), notes that there is a very large gap bet'weln the operat'ional doses and the toxic doses for fishesand shrimps' However, since the first campaign came off in 2001, it is necessat;;; to undertake apost-treatment collection, in order to assess the impact of five treatment cycles on th" aquatic fauna andthe environment. Besides' since some positive breeding sites of the Grande Ruma and Musola Ri'ersare inaccessible on the ground, their treatment could bl subject to aerial treatment. Given the ocpexperience, Meyer (2001) and cheke (2001) recommend the helicopter as the best means for giving theindispensable support to the total coverage of all the breeding sites. This option seems tuttressed by thefact that in the south of the rsland, ,"u".il rvatercourses shelter the S. damnosurn s.l. which were totallyor partially inaccessible. As Seketili (2001) indicates, the fact remains that the use of the hclicoptersupposes, first of all, responding to a number of questions:

- has ivcrmectrn been distributed over the past l2 years?- what is the cost of aerial an operation? 300400,000 US dollars, as recommended by Meyer(200 1)? It must be noted that parkrng rights, and transfer costs of the aircraft are not taken intoaccount in the amounts mentioned above. The same goes for the cost of entomologicalevaluation, and the cost of tickets, per diem, insurance, etc.. of external persons (experts andscientists), who will be involved in the operations,

- How many persons will be protected by this operation? For information purposes, the targetpopulation of the island is about 60,000, half of who live in Malabo. There is need to re call thatthe JAF6 had recommended that the decision to carry out aerial treatments would only be after aclose analysis of the results of the first ground treatment.

d) EntornologicaI evaluation

The PAT and ATP are good indicators of the entomological situation. for they quantify the blackfly aggression and thc transuission of thc o vo,lt,ttlus respectiviy. on the island olBioko, and lrom thecaptures made in 1992, wilson (1996) notcs, that apafl fronr the dry season (frorn January to April), theblack fly densities are high. Thc period from Septembcr to No'embcr remai,s that when the black flrcsare most abundant. Howcver, Anonymous (2000) and cheke (2001) record MBRs betrvcen l--105 and11,475 rn April-May, and bctwccn 2910 and 10,380 rn February. This nreans that even rn the dryscasoll' thc black fly dellsrtrcs niay ltc hrqh Grvcn thrrt thc, black fly spccres rpvolvcd rs the S.tlanlttosutrl s.l;, tt rs probablc that the rauly scasorl rs u,hcn aggresslvencss rvrll be nraxrmal.

Irrorn 1996, it has been cstablrshcd that thc lemales of the S damnosurn s.l. capturcd on thcrsland olBroko had hrgh inlestation rates (wilson, 1996). In effect, the pcrcentagc of infecti'c fernalc-s(tlrtse susceptrblc- to trars.rrI thc parasrtc at trre ,cxt bric) rvas r4.6,%. orr1, tri ,*rnt". of crrssectcdli'nralcs (56) at thc tintc, \\'as an rnrpedrnrcnt to an cnhanced rrrtcrprctatrol of the rcsults. -l.hc lattcr arc.

24

neverthclcss, confirnred in 1999 by the dissection of 878 females, which reveal44o/o of infected femalesand 8% of infective females (Anonymous, 1999). Of course the ATP could not be established for 2000,but thc MTPs obtained in Apnl and May at the various pornts of capture arc by far higher (MTpnrininrum = 130 at Balacha; maximum :473 at Musola) at the tolerablc threshold of 100 Lrlman/ycar ipthc savanna zonc o[West Afnca. The works of Cheke (2001) corroborate the previous rcsults, becauseapart from thc points of capture located at altrtude (0<MTP<72), all thc other MTPs arc highcr than 100(nrininrum : 3 l9 at Sarnpaka; maximum :- 1215 at Musola). The various works ol authors agrec o1 this,and tudtcate that the transmtssion rate is hrgh on thc Bioko island. Thc infcstation rates recorded rccallthosc rccorded on the small rivers of forest areas ln West Africa, whcre the vcctor is also the S. yahcnse.

Irrom our reference to the results recorded in 1989 and 1998 (Mas et al), it clcarly appears thataltcr 9 years oltrcatnrcnt with rvcrmectrn, prevalence had gone fronr hyper-cndcr:ric (74.6rh) to hypo-endetltc (38.6%). Such a change usually tells on the levcl of black fly infestatron. This assumptron iscorroboratcd by the results of some authors. Thus, from Geenen (1993) to Mas and Tirados (2000), thenumber of infecting larvae for 1,000 parous goes down from 400 to 74, and the MTP from 1600 to 15.On the other hand, this is not the case, if we refer to the infestation rates recorded by Cheke (2001).

The absence of pre-imago stages should mean the exclusion of breeding sites located beyond analtitude of 500 m, from all treatment campaigns. But the adults wee captured between 550m and 1,250m. The egg-laying points of these altitude females remain to be determined for setting the limits of thearea to undergo larviciding. In effect, these females may come back to lay eggs in the breeding siteslocated below the 500 m altitude, as prospecting may not have been precise (abundance of breedingsites, difficult access to rivers, due to vegetation) for detecting the positive breeding sites located beyondthe altitude of 500 m.

4.2.6. Conclusions - Suggestions

Apart from the feasibility study conducted in 1996, scveral surveys u,ere carried out on theBioko island betrveen 1996 and 200 1. The ob.;ecttve u,as to collect rndrspensablc data for conductrngtreatmcnt campaigns and their evaluation. The first campaign of ground treatment took place inFebruary-March 200[, and the various outcomes, in relatton to the set objecttve for vector elimination,enable the following points to be established:

The geographical situation, meteorological condrtions and the cyto-taxonontic, morphologic andcy'to-genetic criteria confirm that the island of Broko is an isolated focus.Gtven the drstnbution of rivers and the prospected breeding sites, rt appears that to eachprospecting corresponds at least a new breedrng site (discovered on a river that is already ltstedor not). Besides, the presence of adults at altrtude, places the treated zone under thc menace ofre-invasion. This situation poses the problem of totaI coverage of breedrng sites by insectrcidetreatment, rvhich is an rndispensable conditron for vector ehmination. It therefore, seenlspreferable to plan thc treatment of all the rtvers thathave sufficient florv to favour the settlementof pre-rmago stages of the S. dantrtosurtr .s.1. ht vieu, of thrs, punctual investigations should beundertaken to make up for the lapscs or the lack of tnformatron on the mapping of the breedingsi1es, thc spraying points and the accessibilrty of breeding srtes.

The geographical configuratron (naniel;, r,egctatton cover), is such that, apart frour a feu,exceptions, larvicidrng rvrll have to be carrtcd out by ground spral,ing. Portablc sprayrngmachines (Berhoud type) rvould be the most efl-tcactous, lor they spray out thc tncasurcdquantities of rnsecticrde. 't'hc ideal pcrtod lbr larvrcrding u,ould be the beginnrng of the dryscason, rvhereas thc florv rs strll sufllctcnt lor a good canJlng capacrty of the insectrcide. Thc"llrccdu.rg srle by brccdrng srtc" treatnrent cotrlr'1. tlius. lrc avordcd, ancl thrs u'ill lrnng ultout a

nrLrItrpIrcalron o[- spray,rng pornts.'l'hc black t-ly density on thc Broko Islancl rs usualiy,abrrndant, arid transntrssron rs excltrsivel),etrsurcd by' the S. ),alrcrtsc, Bioko type. 'l'hc vector cl.raraclcristrcs (inlcstatron ratcs, ltarastttckrads) rccorded arc hrgh and recall those obsen,ed rn the forcst arcas of Afrrca, u,hcrc tl.re .S.

l l.tltutsa ts also thc rrraur vcctr)r-

25

The base data and those of impact studies on the envrronmenl of the Bioko lsrand, in rclationwith the treatment rvrth Temephos, will be indrspensrul" ar.ing thc c'aluation of thc controlactivirrcs. Thc coilcction works must therefor; #;;;;;;JJ. "itnur, ro,- , t

"ti". Lo*t"ag" orthe non-targct entonric fauna, Yam"ogo lzoot) notcs th;t,; would bc desrrablc to.avequalrtativc samplrng of the vegetation il"uu"r, rmmerged dead wood), and the under-gra'cr.Bcsides, the high predom.rnance (75%) of the plm",au" o,i thc Lada river, necessrratcstnvestigations on thts famrly and iis living cnvironment. on thc other hand, the optron or-organism indlcators (namcly odonates), for monrtonng it"-inrouct of treatment on the non_target fauna' needs to bc reviewed' The same goes ror tne .er."tion or p"..nriui'*'ur"."ou....,;[:i#J,T:ril:,b,| ['Ji".l,[""nstitute

."r,g" zones rh"-r,;; *ouri shertcr, noi'onry non-'l-he local staff' called tn to u,dedake implcnrertatlon and monrto'ng or vector errmrnatro.acLrvities' was identified and selected. Staff m"*b"rs hro orriirr, trarnrng during the variousinvestigations that were carried out on the island of Bioko Regular evaluation (technicalknowledge' professional conscience), followed uy ..-trulning,

'if n."...ury, is desirable for thisstaff in order ensures continuity andefficiency oicontrot u"tiurti... For exampre, the resurts ofApril and May 2000 indicate that the computation of infestation rates (oZ of infected parous

*["*:i,f.:,lTf::." parous remales) uni indi... "r;;;;;.;on (MBR, ABR) are st,r norIt is clear from the varjous investigations mentioned in the reports that the activities of the Iocalteam stop' sometimes immediately it is alone in organizing nfrJ*".t. It rvould be desirable thatpersonnel be sensitized so that the relational issuel i"""rr"g liiiurarut. and/or institutions donot hamper the smooth running of control activitres.To ensure monitoring of roulne activities of the natronal team,. it u,ould be proper that thecoordinator of the project solicit a progress report, on a regular basrs, and be more present on the

26

4.3. IT\\/AITA FOCUS

Uganda rs onc oIthe first countnes, whcre onchocerctasis vcctor control \\Ias successful.'l'htrs,

tlic S. r!a1uro.rur,1 s.l. rvas elrmrnated frorn the Victona Nile focus, and thc S. naavei temporary kicked

oLrt of the I3udongo locus (Prcnticc, 1974)-

In the 70s, thc use of DDT wrth active matter of 25o/o of emulsifiable concentrate, helpcd to

rntemrpttransmissionofonchocercrasisinthefocusof Itwara(Garmsetal., 1994). Duetotheabsence

of furrdrpg, and thc insecurrty, control effo(s stopped from 1975 to 1911. But in 1990, trov fundrrrg

proyrdcd by the Geman Coopcratron (GTZ), and the Mrnrstry of Hcalth of Uganda, enable data

collection to continue (Garms et al., 1992). It is under this that all the rivers susceptible to shelter the S.

neavei.s..s. were prospected and the adult population monitored, thanks to the captures, dissections and

determination of infestation rates (Garms et al. 1994). The spraying of Temephos, which as carried out

from August 1995, were found to be efficacious, and the results promising, after only 3 treatment cycles.

In effect, between 1994 and 1995, the black fly densities went down from 481 to 0 on the Kijura bridge,

and from 365 to 2 at Busasa. Given these results, keatment was extended to the main breeding sites ofthe focus that shelter the S. neavei. The elimination of the vector from the [trvara focus became an

attainable objective. To safeguard its gains, and to contribute to the elimination of the disease, the

Technical Consultative Committee (TCC) approved the surveillance and continuation of larviciding ofthe breeding sites of the focus of Itwara, and all the foci of Siisa and Aswa. 'l'his choice is part of the

objectives of APOC, which in some particular cases, is onchocerciasis control, through vector

elimination. Fromlgg6,thefocusofltwarawasselected,becausepre-treatmentdatawasavailable,andqualified staff and control activities were already ongoing'

4.3.1. Prcscntation of focus

The Itrvara focus is located around the forest reserve beanng the same nanle, at about 25 Km in

tlre norlh of Fort portal (fig. l7). The reserve covers about 20 sq Km, 22'h of u'hich are made up of tree

vegetatron (I{orvard, 1991). It is bordered by large plantattons of tea, subsistence crops and ranches

along the rivers (Sogohi, Kahamba. Muzizi, Mpanga). This is to sa)' that the onginal forest has been

exteisrvely cieared for the sake of plantations. The rvatercourses arc, neverlheless protected by dcnse

forest gallcrtes.

The iandscape is characterized by rvooded valleys and mountains u'tth altrtude s varying betu'e en

1,250 and 1,460 m. Tempcratures are. therefore, moderate'

The clrmate of the area rs characterized by a humtd heat, and all-ycar-round rains. Maxilnun-r

rainfali figurcs (1,000-1,400) are obserucd from September to Novcmber. The dn'season stretches fron-r

Deccmbcr to Fcbruary, but it rs ncver totally dry'

liydrologrcal coldrtrons arc gcnerally favourable, all year round, for the devclopmcnt of pre-

,r1ago stilges of thc S. ttauvci- 'l-he larvae brecding sttcs are found essentralil'on the Sogohr and its

tlbutales (Wanrsc, Nyakrbuguta, Kar.raba, Kafunda), tl.re Srrsa arrd tts trtbutanes (Kyasa, Mohabura)

and fir-rally thc Asu'a Rtvcr.

T6c area rs dcnsely,populatcd, and onchoccrcrasrs rs hrghly ctrdetrltc hcre . hl 1997' S0% olthe

45 ,ersrl.s u.h. lrved in tlie rrcrghbourhood of the lbrcst rcscn/e \\'erc ttrlcst.-.l br'thc- () t'o^'itlir.s

(( i.lt llt. I ()()7)

'l-hc black 11y specres to chntrnate {iclnr thc lircus rs tlie S. rtcal'cI s.s., the nlaitr otrchclcclclasls

,ector (Barnlcl,and Prcr1trcc, 1958; I)rcr.ttrcc, 1974; Ganns et al., 1992). It flying capacity r^s abotrt 6-10

K.t'l'Sclrft'spa,<tf tl.rclarvars3--4u,t-cks,dut:tothcri'atertelrlpcraturc,q'ltrcl.rbetu'er-t.t lSoCarld l9"C-

4.3.2. Nature of Works

'l'hc works carrred out lrontcsscntrally on:

4.3.3. Results obtained

27

1970 to 1997 (cspccrally in 1994) in the lrwara focus, du,crr

- Dynaulcs of pre-imago and imago populatlons;- Detcnninatron of the duration of pre -imago developmcnt;- Vcctoridentification;- Drstribution of breeding sites with thc S. tteavei in and around thc focus;- Vector characteristics of the S. neavei;- niver tests of the Temephos (determination of doses and carrying capacity).- 'lrarning

of pcrsonnel.

As part of the works carried out, with the support of APoc,.the naLional team, in charge of thevector eliminatton activities, undertook intense activities of surveilrance and supervision, in order toensure that vector collection is properly done. The activities are summed up as follows:

- Regular prospecting of the main control points in the main ltwara focus, and in the sub-foci of Aswa and Siisa; ' :

- The capture of black flies at pre_selected points;- The teatment of rivers at intervals of 4 weeks, in the sub-foci of Siisa and Asrva.

a) Prospccting brceding sites

Tlte entomological data collected betu'een'199i and 1994, prior to instrtuting treatment u,rtl.r

ffi.J'|,];.Ijf:i:'r:Tj :2:* or the crabs captured on the Sogohi river (rt'r;ara i"i,.l carried pre-

Though treatment rvas discontinued on the rivers on the rvestern side of the Itrvara focus, Ganns(1991)' lt must be noted that the latter were not re-invaded. Since the last crabs were found to bepositrve at Nyakibuguta in August 1995, the nver was treated in December 1995. Nevertheless, the 479crabs han'ested at Nyakibuguta rn 1996-1997 u,ere all negative. Besrdcs, none of the l6g3 crabs fromItrn'ara' St tsa and Aswa carried pre-imago stages of thc s. ieavei . The last crab shelten.,g only one la^,aof the s. ttcat'eidates back to Novembei 1996, and rvas harvested on.r,er Sogohr..

The prospecting canred out in May, June and october 1991 inthe Itrvara focus made it possibleto catch 871 crabs, nore of u'hich carried pre-imago stages (Lakwo et al. l99g). The same goes for thc.50 crabs han,ested at Sogohi in February 199g.

'l'he Strsa and Muhabura rlvers were also prospected rn May, June and october 1997. out ol614 crabs examrned, only 2 carrred larvae of the S. neat,L,i.

Irronr l\{arch to Junc i997, thc sub-fbcus of Asu,a u,as trcated wrth 17.5 i of Temephos. Lak*,oet al' (1998) cstablrsh that the post-trcatment control conducted r, May, Junc-. August and octoberettablc thc sanrplrng or5g5 crabs, l 5 (2.6%)of u,rrroh,u.r..royurg pr(--rmago staqr-s of the S. ncayei.

Irl I\{arch 1997, (Garnrs). aboul 900 crabs [..r, the Itu,ara focus u,ere eramrncd, a.d all r'crt-ll('11'ltl'c (11() llllL'ctl()ll Il! tlle S Ilcltvct). 'l lrc slrrnc *crrl lor -19.1 cnrbs har.rc.ictl , the- sub-lircrrs .1-Strsa ()rt tlle ctlrttr.ary, rn tlrc sub-lircus ol-Asrva, t6e craLrs *,erc r.fcstccl.

I, c)ctober 1991 ,354 crab.s wcrc harvested by 1he natronal team rn the sub-focus of Srisa (179)and Aswa ( 17-5). and 2 (r'y,,) and 4 (2"/u) respr-ctrvt'11,, canrc-d larwac or-thc S. rtctrt.ci

28

From September 1998 to September 1999,7 rivers were prospected in the Itrvara focus by thcnational tcam. Thc 872 crabs captured wcre all negatrve. During the samc pcriod, only 0.3% oI thcll84 I cr-abs harvestcd in the sub-focus of Sirsa carricd pre-rmago stages o[thc S. rtcatci . On t5c othcrharrd, in the sub-focus of Aswa,6.1% of the 1616 crabs examtncd were carricrs of the S. rteut,ei.

In 2000, thc 6 prospccting sessions carrted out tn the focus of Itrvara by the national teapr helpcdtolrarvcst539crabs; all wcredcvordofpre-imagostagesof theS. neavci. Duringthesame period, 1479crabs harvcstcd at Srisa were equally all negativc. On the othcr hand, l16 (3.2%) of the 3674 crabssamplcd at Aswa were infested with the S. neavei. The infestation rates varied from l .2,/o to l9o/o. Itmust be noted that beforc larviciding, 80.4% of the 92 crabs caught on the Musabira River were positive,whcreas;ust after 4 treatnrent rounds, nonc of the 470 crabs examined carried pre-imago stages of the S.ttauvci.

Between January an August 2001, the prospecting of the national team made it possible toharvest 4656 crabs in the Itwara focus (948), 630 in the sub-focus of Siisa, and 3078 in that of Aswa.No pre-imago stage was found on the crabs of Itwara, and only one larva of the S. neavei was taken froma crab (0.2% of the population) from Siisa. The highest rate (0.4Yo) of positive crabs was observed atAswa.

lr) Captures-Dissection-Transmission

The adult capture sessions were less than larvae prospecting. Nevertheless, the following couldbe notcd:

In 1994, prior to starting larviciding, the dissection of 2889 parous females revealed622 infected females (24%) and I 20 infective ones (4%).Larviciding carried out from June to August 1995 brought about a drop in the blackfly density (rable 11). It rvent from 4882 rn 1994 ro 3904 in 1995, and to 6 in 1996,atthe capturc point of Busasa. The same data gave 6403,2546 and 0 at Kr3ura and2390,64 and 0 at Sogohi.ln March l99l , it rvas establtshed that the drshibution of rvermectin only intemrptedtransmission partially. In effect, out of 153 parous females examined in 1991,21.89% rvere infectedand2.6o/o rvere rnfectrve. Ln1992,1993 and 1994, the samedata were 684ll3l%15.6%,3990126.8%13.5o/o and 3011171.9%13.7% respectrvely.The number of infecting lanae by 1000 parous females rvas 124 in 1991, 276 in1992,169 rn 1993 and 176 rn 1994. The data collected at Kicheche shou,that after6 years of distribution of ivermectin, transmission rvas still intense. In effect, out of115 parous females, 48 (42%) rvere infected, 11 (9.5%) rvere infectivc, and thenumber of Lrl1,000 parous ones rvas 470.

The captures made in the Susa focus tn May, June and October 1997, rvere allncgative. Besides, as olFebruary 1998, no adult ofthe S. neevei had been capturedfor tu,o ycars in thc Itwara focus. The same goes for the sub-focus of Aswa, g'here

the captures u,ere nil from September 1998 to September 1999, at the capture pointscallcd Arrdrcu' and Tourist.

Lastly, the cntrre 2000 u,as marked by the capture of negativc catches of the S. rreaver, at thedrflerent capturc pornts of thc ltu,ara focus, and thc sub focr of Srisa and Asu,a. On the other hand, 140

S. dutnnttstur s./. u,crc capturcd rn the focus ollts,ara (39 females) and 111 fen-ralcs in thc sub-focus ofAsn,a.'l'hcdrsscctionofthescfemalcsdrdnotreveal an1,rnfectronduetotlte O.volwrlus.

c) Larvicirlirrg

'l'hc llrsl cxpennlclrts rverc carndd out by (iarms rn August 1994 on the Sogohi rrver, lbrasscssurg thc eflicacy olthc Tcmephos, and the Bt ll14 rn the cor.rtrol of thc S. neavci (fig l8). l'hcresult shorvcci that at a dosc ol'0.1 mg/I, Tcmephos docs not elrrnrnate a[[ thc larvae of thc S. ncavci ovcr.Ionq clrstanccs. On thc othcr hand, conccntratrous ol 0I and () -1 nre/l gavc better rcsults, u,lrrlc havrng

29

no ncgative effects on crabs- The cxperimcnts with the Bt did not give any good rcsults, due to the lowcarry capacity of this insecticide.

In the ltwara focus, the last trcatment with Temephos dates back to Fcbruary 1997. [t rvascarricd out on thc Sogohi River. But trcatment on thc other nvcrs of thc locus rvere suspcnded .ruc6carlicr. Thus, thc last treatment on thc Nyakibuguta datcs back to Decembcr 1995.

I"orthe cntrrclarvicidrngcarrrcdoutintheltwarafocus,anditssub-foci of Siisaa.dAsrva, 160lrtcrs ofTemephos wcrc used from lgg4 to lgg]. Srnce this date, punctual treatments have beenundcrtaken rn the sub-foci(Aswa, especially). Thus in 2000,58.75 liters of Temephos were used in thesub-focus of Aswa- The latter was also treated between Septembcr 1998 and December 1999. Thernonthly spraylng rvas carried out at Andrerv's pt, Guaging pt, Tounst pt and I'oprs,s pt. It nrust benotcd that for logistics rcasons (lack of insectrcrde), treatment rn the sub-focus of Asrva only started i,1991.

d) Isolation of Focus

The Itwara focus is not totally isolated from the two sub-foci, located around the Siisa and Aswarivers (Garms, 1997). On the other hand, the entire set (focus and sub-foci) is at least 100 Km from thenearcst breeding site (Kashogi-Kitomi focus). Besides, the latter shelter mainly the S. neavei, rvhoseflying capacity is reduced (6-10 Km, maximum)

c) Impact of treatment on environment

It has been proved that Temephos, at operational doses, is without toxic effect on mammals andfishes. However, its impact on on-target fauna is moderate.

At the end of observation camed out in Uganda, Garms (1997) establshes that crabs of the fociand sub-foct ol Itu'ara, Siisa and Asrva, \\,ere not affected by the operational doses of Temephos.Ilorvever, spectal studtes on the impact of trcatment on the environmcnt u,ere not conducted in thcvector elrrnrnation zonc.

0 Training

Staff trarning was camed out during the several u,orks carried out bet$,een l91O and 1991(Garms, l99l). In 1998, the necded staff for the running of APOC activitres u,as available, qualrfied andcxpcnenced.

4.3.4. CDTI status in Focus

The ltrvara focus is locatcd in the drstrict of Kabarolc. [n thc lattc-r, covered by phase 2 of tireCDl'l in Uganda, thc total population olthe endenric zone rs 82,597.'Ihrs popularron is drstributed over147 cor.nnlunitres, 120 of whrch are in a hyper-endcmlc zone, and2'l in a meso-endemic zone. ln 2000,t[.rc rate oltherapeutrc coverage was'l2o/o (58,121l80,i91), and rn 2001, rt was 73,h (60,235/gZ,5g7). Ofcourse the target population of the drstrict is known, but rt rs also rndispcnsablc to determine that of tliclbcus. T'his precisron u'ould enable a monrtoring o1 lhe evolution of tlie therapeutic covcraqe rn t5elbcr-rs, and to assess thc tn.rpact oltvernrcctrn thcre on onchoccrcrasls transnlrsslon.

11.3.5. Iludgct for vcctor clirnination activitics

-l'tl cnablc vcctor clttlltnatton actrvrtrcs [o conllltuc, thc AI,OC I,rograntnte cnsurcd a rcgular

tlllarloral asslstallcc on thc basrs ollcttcrs ol'agleenrcnt (('ontracts). Thc tablc tle kr$,sutits up the ltr-rdgctcotrlponcnt of thc prolcct.

30

CoveredPeriod

Cash transfcrrcd tofield US$

Amount spent irr

US$Purchase

equipntcnto 'l'otal cost

Ircb.99-Aug00 16,151 15,917 12,029 21 946Scpt 00-Aug0l 10,951 NA 12,298 12,298

Total 27,108 15,917 24,327 40,244

4.3.6. Discussions-Remarks

'l'he results of thc various prospecting works agree and rndrcate that rvhatever the focus (Ilrvara)or sub-focus (Srrsa and Aswa), the treatment of the breedrng sites with Temephos brings about a drasticreduction tn the numbers of the pre-imago populations of the S. neavei. Even when treatment isdiscontinued, a drop in densities is recorded. The post-treatment controls indicate, however, an almosttotal absence of positive crabs, since 1997, in the Itwara focus. The same goes for the sub-focus of Siisasince 2000. This means that the entire breeding sites of ltwara and Siisa are under larviciding. On theother hand, the presence of positive crabs in the rivers of the sub-focus of Aswa, reveals the piesence ofnon-treated breeding sites. The latler must be listed and included for treatment, for only total coverageof all the positive breeding sites would make it possible to envisage vector elimination.

This objectrve is achievable, because it is enhanced by the fact that the area to be cleared (Itwarafocus, Siisa and Aswa sub-foci) is isolated from the other onchocerciasis foci. tn effect, the nearest fociare found at 100 Km and shelter essentially the S. neaver, whose flying capacily does not exceed 10 Km(Garms, 1997). Besides, the authors are unanimous that Temephos, given its qualities (efficacy, goodcarrying capacity, moderate effects on non-target fauna), is the selected larvicrde for ground treatment olthe breedrng sites of the Itwara focus and its sub-foci.

-lhe first factor that conditions the existence of the rmago population is the pr-imago population.Srnce the latter is very sensitive to larviciding (Anonymous, 1985), this bnngs about a reduction (evendisappearance) of the adult population. The results obtarned at Ihvara, Siisa and Asrva are in Ine s.it5thrs rule. [n effect, since treatment started in 1995, black fly densities (5. neavei) dropped to zero in1996 at Kr.;ura and Sogohi. As treatment took place, the trend heightened, since no biting female u,ascaptured rn 2000 on the entire focus (Itrvara, Siisa, Asrva). The results rccorded in 2001 confirm theabsence of bitrng females in the area. It must be noted here that prior to lan,iciding, the black fly densityreached I 9,000 bites/manL/year.

From the viewpoint of kansmission, the drssectron of females captured before larvrcidrngreveals hrgh infcstation rates in the S. neat,ei (% rnfested females :24o/';7o infective females :4%)Besides, after 6 years of tvermectin distribution, transmission u'as always intense at Kicheche (%" oftnfected females = 4Z%; % of infective females:9.5%r.470 Lill,000 parous ones). These data confimrthc liyper-cndemic nature of the Itwara focus, and of rts sub-tbci (Srisa and Asu,a). They alsoconoborate the observations of other authors, u4ro assert that ivemrectrn does not totally rntelrupttransnllssron.

4.3.7. (lo nclusions-Suggcstions

'l'he rcsulLs above rndrcate that the treatment of thc- ltw'ara locus and tlie sob-foci ol Snsa andAsu'a hcll'r ttt cltnttnatt- thc vcctor in lhis regron of LJqanda It rs thcrcftrr-t- inrltcratrvt- [o crtrrtrnr.re sroundtlc.ltltleItt. csltccralll, ru tlic sub-litcus o[- Asrrl, rvlirclt re ulalus actrvc (ltunctLral ltitsrtrvc breedrns. sltc5).Irt cl'lcct 11s pr()xiruty ts such that black l'ircs can easrll,reacl.r the ltu,ara and Srisa brccdrng srtes.'l'hclatlcr rvrll liavc to contu.ruc to bc survcyed u,rtli prccisrou, during thc penods considered to be of hrghtrlack 11y 1tr<ldttctrvtly, rn ordcr to confir-nt that black flrcs are ct-lcctrvcly and de finrtely abscnt lionr thesard locr

a

31

of course bibliographical data indicate that the s. neavei .has difficulty in reconstituting itspopulations when they have bcen greatly reduced. But the fact still rcmains that a,y interruption intrea(nlent contributes to a rapid rcconstrtution o[ thc black fly population. It must bc noted t'at thclatlurcs of trcatnrcnt may also lead to the same rcsults (incrcase on black fly dcnsities)- Rcgularsupcrvision by ficld tcams (captors espcctally) should enablc fluctuatron i1 dcnsity that reflccts t.ccfificacy of larvicrdrng to bc rccorded. Any treatment lailure could, thcn, bc quickly detectcd andaddrcsscd, since it would be related-to a spccific cause.

The vector to be eliminated in the Itwara focus, and its sub-focr (Siisa and Aswa) is the s.tteavci ' This specics is however, wlnerable, for under the pressure of insecticide treatment, thepopulation decreascs very fast. I{owever, a sudden re-infestation is improbable because the s rtcayaillopulattons rcconstltute ve ry slowly (long pre-imago deve lopmcr.rt; phorctrc aspects), and thcdclorestation does not favour the drsplacement of black flies. In addition, srnce the focus is isolated,vector elimination has multiple chances of success in the area. However, the problem of insecurity needsto be addressed, since in certain periods, this impedes or even stops activities.

ln view of the current situation, vector elimination activities in the Itwara focus and its sub-foci(Siisa, Aswa) should be successful- It is probable that the children population does not practically haveany microfilaria carriers. However, the distribution of ivermectin must continue, to take intoconsideration the longevity of adult worns of the o. volvulus,which might be ";;il; older parients.

32

4.4. FOCUS OF MT'AMBA-NKTISI

In l)ccembcr 1996, thc project Mpamba-Nkusr \\ras approved as part of thc "Vector eliminatio,projcct in thc ltwara focus". On the rccommcndatton of the Technical Consultative Committee of thcAPOC programme, the said prolcct was re-defined and separatcd fronr thc ltu,ara focus in 199g. TheProjecL was then approved as a fcasibiliry study olthe vector elrnrinatron pro1cct o[thc Mpamba-Nliusrfocus.

4.4.1. l'rcscntatiou of focus

Thc area concerned by the vector elimination is located in the northern part of the Kibbledrstrict. The focus was discovered in 1991 by Adele and Walsh, who, given the proximity of the town ofKibble, called it "Kibble focus". The size of the focus is not known, but it is estimated to Ue tOO sq Km.the average altitude in the area is between 900 and 1,500 m. A good roads network allows foieasyaccessibility of the various points of the focus.

The district of Kibaale has 3 prefectures: Bugangaizi, Buyanga and Buyaga. Only the latter isonchocerciasis endemic; the population at risk is estimated at 70,000. The Buyaga prefecture is dividedinto sub-prefectures. Among these, onchocerciasis is found in Kagadi and Kyanaisoke, which arewatered by the river Mpamba, at Muhooro on the Nkusi and Ntengo rivers, and at Mabaale on theMutungulu River.

The rainy season is from August to November, and the dry one from December to March. Forthe rest of the year, the whether is sometimes dry or rainy. In a year of very sood rainfall figures, thehighest can go up to 1,200 mm.

The hydrography of the focus is made up of perennialnvers. Thcy run belou, the forest galleries.but remain accessible. They shelter the S. neat ei breedrng sites, u,hich are productive all year round. Thevector, at the larva stage, lives in phoretic associatron rvrth crabs of the potamonautic. Thc zone ischaracterized by high vegetation. (elephant grass), and forest gallenes along u,atercourses. Some forestsare practically rmpenetrable.

The area of the focus, previously sparsely populated, has seen the arnval of several migrants.The latter come from the densely populated areas oIthc regron to the West Nrle (districts of Ara, N,[oyaand Nebbi), and the valleys of Kigezi-Highlands to the southeast (drstricts of Kabale and Rukungin) ofUganda. These two areas, the origin of the mrgrants, shclter onchocercal tbci (namely the focr of\\/adelai, West-Niles and the forest focus of Brvindi), u'hrch have hrgh prevalence rates (56 to 80%:Nelson, 1958; Mc Crae,1962).

Thc area meant for vector eltmtnattot.t ts tsolated. nr pnncrple, becausc the nearest focus rs 40Knr arvay, a distance whtch rs beyond the flying capaclty of thc S. ncot,ei. Besrdes. ivermectrn has beendrstnbuted in the focus srnce 1992 by Sight Savers Intcrnatronal (SSI).

4.4.2. Nature of u'orks

No follorved-up sunrcy rvas conductcd rn the Ir{panrba-Nkusr {ircus b,--lorc APOC activrtrcs.IIou cvcr, sottte soul)(lrnus takcrt ort tlic vccttrr (rticntrlr'. strgrports ol- pr e -rrneqo s1at]cs). alttl thcllrcralcttcc til-tltc drscasc (l{aprd Iilttdcnlttlogrcal Asscssrncnt l{l-A. skrn snrp tcsts) u,cre car-r'rcd oLrt lll1hc 1 990s.

1'he oblectivcs of these ,'r,orks \\/erc cor)rl)atrblc u,r1li thosc ol thc l-casrbrlrty stucl;, appr6r,cd try,r\l'(X'to bc ttnplcn.rentcd rr.r thc Mpanrba-NkLrsr lircus 'l'her,.rrc strrr.rr.ncd up as fbll6g,s.

I

,

33

Determine the identity of the vector;Deternrine the lrmits of the reproduction sites of the s. neat,ei;Speci[y thc dynamics of the pre-imago a,d rmago popuratrons of trrc \rector;Dcterminc thc natural vector charactcrrstics: rnlcstation ratcs, MTp, ABR, trans'.rissio.indices.collcct basc hydrologrc data; they are rndrspcnsable to thc conduct of treatment;Dctcrmrnc thc spraying points, and the frequcncy of treatment of brceding sites,Evaluatc the scnsibilrty of larvae to Temephos (dose, cfficacious carrylng capacity).

4.4.3. Results obtained

a) I'rospecting of breeding sites

From september to December Lggg, 45 breeding sites were prospected on the main rivers(Mpamba, Nyabwegyereka, Rwabutuju, Ntengo, Murungri, Mutunguru and Nkusi). This prospectingenabledtheharvestof 688crabs,of which 284_(41%) clniedpre-imagostagesof the s. neavei. Thecrabs were highly infested on the Mpamba and Rwabutuju riveis, whereas thI load *u. uu".ug. on theNyabwegyereka. on the Mutunguru, however, the crab population was very weak, and no s. rzeayer washarvested on this watercourse.

From January to November 2000, all the rivers of the focus were again prospected to determinethe area of distnbution of the s. neavei breed_ing sites. The captures and examination of crabs were donein accordance with the techniques of Mc Mahon (1958) and Raybould (1969). The results show that outof 623 crabs captured,506 (8 I%) were positive, and the average number of larvae of the S. neavei,percrab, was 10' Taking into account a monthly distnbution, the lJwest load (5 tu*u"l".ruj rvas recorded inJune, and the highest(16larvae/crab) in March. The most infested crabs were found inihe Mpamba andNyabugando rivers. The identification of han,ested samples rndrcates that the S. rtearei rvas loundeveryrvhere, except on the Nkusr river, rvhere this species was replaced by the s. rlortrttosul,, Nkusr type .

The preliminary works are in thetr second year, and activities were esserltrally based onprospecting of breeding sites, and the choice of sprayrng points in the dry season. 1rr., u.t*een Januaryand August 2001,642 crabs, of rvhich 343 (53.4%) weie infested, were harvested in the rivers of thefocus. Thc most infested crabs were from the Mpamba Rrver.

b) Captures-Dissection-Transmission

In 1999,399 females rvere captured between September and December at Sroni, a 'rllaqelocated in the valley of the Mpamba Rrver. The 167 parous iemales dissected revealed 35 (21%) infcctedand 7 (4o/o) i nfective females.

FromJanuarytoNovember2000,adultcaptureswerealsocarledoutatSioni. Outofthe 1743females captured, a number of 524 parous oncs were recorded, 126 (24%) infected, 243 (0.6%)infedrve

ones, and 40 Lrll000 parous ones. As for the captures at Rurembo in October and Noyember 2000, they,hclped to harvest 129 females, rncluding 27 pirous ones, 10 (37%) infected ones. 2 (1.4%) rnfectrr,eones and 111 Lrl1000 parous oncs. Irinally, frorn May to No'en-,ber 2000 l4g4 fenrales \\rere captured atNyabudango' The dissectron of these I-emales revcaled 363 parous ones,99 (21 .3%) rnfected ones, l9(52%) rnfective one s and 47 l_i/ 1,000 parous ones.

In 2001, captures \\rere also can-red out at tlirec capture polnts ol'the lbcus. Thc 'cctorcharactcrtstrcs rccordcd a1 Sronr wcrc 3J 9uln ol ltarous fernalr-s. l4.Jo,1t <.tf lltfL-ctc(l oltcs. l loi, rr1rrrlecltVc ()lles. a I\4 I'l'of l--l and 50 l-rl1,()()0 Par.oLrs one.:. z\t llurcnrrrtl, 26.5,1,t.1-par.us lcrrales ucreobscrvt'd, 20A% olinfectcd ones,0.6'2, ol-rnf'ectrvc onc-s,21 t-rl1,000 parous o,-,", lr,J a M l.l) cqual to28 rvas lrotcd' Frrlalll', at Nyabugando, thc rcsults of transurrssron \\,erc 2J .gol, of parclus l-cmale-s, I g .19,"of rrrtectcdparousones,3.5Trolrnfcctrvcones,6l I.i/l000parousones,andaMTpcqr,ral to g(t.2(,/o.

34

c) Larviciding

An cxpcrimcntal treatmcnt scssion rvas conductcd on thc Mpanrba Rivcr in Novcmber 2000.'[-hrs trcatrncnt was preccded by prc-treatment data collection on the crabs, breedurg sites of t5e Slunttosttrtr s./, tl-rc water of the rtver (pl{, tcmperaturc, conductivrty) and thc' flow rate ol thewatcrcourse. '['hc rcsults of insecticide treatment indrcatc a reductron in inlestation of crabs of thc river,gorng fronr 66.loh 1o92.5%'. The samc goes lor the crabs enclosed ln expenmcntal cages placed in thcrivcrbed, where thc reduction ratc fluctuates between 98.5% and 100%. As for the supports that shelterlhe S damnosutn s.l. or other Simulidae, they wcre all 100% negative, through the insecticide rvave.IJowever, the non-target fauna (trichoptera, leeches, water bcetles) rvas not affected. During theexperimcnt, the flow rate of the Mpamba river tvas 1,126 mr/s, the rvater tcmperature rvas 19.20C, andthc carryrng capaclty of the rnsecticide estimated at 5 Knr.

The objectivc of the experiment conducted in July 2001 was to dctermrne the effective carryingcapacily of Temephos in the dry season. The Mushandikwa and Rwabutuji rivers rvere selected for thetests. Cages, containing 4 to 7 crabs bearing pre-imago stages of the S. neavei, were placed in the rivers.The latter were treated with 300 ml (Mushandikwa) and 500 m, Rwabutuji) of Temephos. The post-treatment controls, conducted 48 hours after spraying, revealed that the effective carrying capacity(100% of mortality of larvae) of the Temephos was about 2 Km, for flow rates that could not bemeasured, since they were too low.

d) Onchocerciasis prevalence

Onchocerciasis is endemic in the Mpamba-Nkust focus. Nelson (1958) and Mc Crae (1962) putlhe prevalence between 56%o and 80%. In the valley of the Mpamba River, an epidemiological surveyconducted at Nabrvereba revealed 92o/' of oncho patients tn the community (Ayele and Walsh, 1991).Prurrt is recognized as being one of the most severe clinical manifestations of onchocerciasis.

In 1995, the REA survey brought to the lorc tliat tire prevaience of nodules varied bctrveen 467oand 53%. Except that in the region of Kagadr, the r.r.rost affected villages rvere Nl,abs,ereba (53%) andSonr (60%), whereas in the Kyanaisoke reglon, 46.10A and 30% of carners of nodules were counted atKanyabeebe and Mpamba respectively.

c) Isolation of Focus

The Mpamba-Nkusi focus has simrlar aspects (geographrcal, ecologrcal) u rth the sub-focus ofSusa rn the Babarole distnct. The preliminary data tndtcate that the sard focus rs ecologically andgeographrcally isolated. In effect, the S rreavel specles rs practrcally thc sole vector of the focus, for the

S. darnnosunr s.l. found are essentrally ornrthophilae (colbourne and Crosskey, 1965). Besides, the focusolBugorna in the norlh rs extrnct (Walsh et al. 1996). L.r thc r-ast, the N4utunguiu Rrver only shelters a

small quantity of crabs, hencc the absence of the S. neaver. Frnall1,, the ecological conditions are suchthat no re-invasron can comc lrom the east or sor,rth, excellt the \\'cst, rvhere prospectlng should enablethe Iinrits of thc focus to be dctermined.

0 Training

The intplententatlon ol a control progrulnrc, as plrnne-d rn the N{pamba-Nkusr focus,necessitatcs qualrficd stafl'(high-levc[, technrcran and captors) -l

hr- trarnrnq ollocal staff on all tccluiicaland pracLrcal asltccts olcntonrologrcal evaluatton ts o1- tltrlrost rtccesstt\,. Llertarnlr'. an enlomologrst and

lirur calttttrs arc already operational, but thrs ts tustrl-llctcnt to c()\'L'r thc eutirc- focr.rs. Pcrsonnel ol theI1urrr..r fttcus (corul)e1eut antl crpcrrenced)coul.l gtve lccltrtte.tl sLrpltttrl to thal r-rl'N'lparnba Nkr.rsr

4.4.,{. (IDTI status in I.'ocus

l'lrc Mltantba Nkusr lbcus rs krcatcd rrt tltc Krli.r.rle rir:trrct I'he total pclpulation ol-thc endcn'rrc,/()nc ls I 12,3E4 l)crror\s, u'hrcli rs clrslnbr.rtcJ ovct I 5-1 c,rtttnrttnrtrcs. <il' rvhrch 136 are rn an onclttr

l

35

hyper-cndemic zone, and l8 in a meso-endemic area. Mass treatment with ivermectin started in 1992,

YILjh" SSI campaigns. From 1994,ll1,154 persons were treated with ivermectin. I must be noted thaiCDTI rvas adoptcd in 1999, and the first distribution rvas complcted in August of the sanre year, i.e. oncnronth bcforc the start-up of the "vector ehmrnation" pro.;cct. In 2000, the thcrapeutlc coveragc rate was65% (63,841/98,8 I 6). 'fhis ratc is I4o/o (83299t11 2884) rn 200 I .

'l-he 4'r' pltasc of CDTI in Uganda covers thc Mpamba Nkusi focus, and rt rs the secondconsccutlvc ycar that treaLnrcnt is bcrng financcd by APOC. Of course, the target population of thcdtstrtct is known, but it is equally indispensable to determine that of the focus. tnis precision wouldmake it possible to monitor the progress of therapeutic coveragc in the focus, and to assess the impact ofrvermectin on oncho transmission.

4.4.5. Budget for vcctor elimination Activitics

To enable vector elimination activities to begin and continue, the APOC programme providedregular financial assistance, on the basis of letters of agreement (Contracts). The tabi-e below'sums ufthe financial component of the project.

Covered period Cash transferredto field (in US$)

Amount spent (inUS$)

Purchase oflpment

Total cost

iv1ay.99-Dec 00 46,051 30,664 60,240 90,904Jan.0l-Dec 01 15,3387 NA 17,560 r 7,560

Total t67,910 30,664 77,800 108,464

4.4.6. Discussions-Remarks

- The various prospecting activities undertaken in the Mpamba-Nk-usi focus agree on thc identityof the vector causing onchocerciasis, namely the S. neat,ei. This specles, given the u,orks conducted in2000, is present all year round in the breeding srtes of the focus. Its pre-imago population is the leastabundant on the crabs between May and August. Of course the S. dotnnor,rr,, the Nkusi $pe, is foundrn the breeding sites of the Nkusr River, but the species rs not anthropophrlous (Colbourne and Crosskey.1965). The abundance and distnbution of the pre-imago stages of the S. ,ruor"i help to direct larvciding,preferably torvard the Mpamba and Rwabutqu nvers, whrch shelter the most infested crabs.

The resuits of captures and dissectron carried out between September I999 and November 2000show that in the Mpamba-Nkusi, the S. neavei is a good vector of onchocerciasis. [n effect, the numberof tnfective lemales per 1000 parous females vanes from 42 (Sionr) to 74 (Rurembo), ivhile the tolerableltne tn the OCP arca is one infective female per 1000 parous ones. The same goes for the number ofinfectrng larvae per 1000 parous ones, which fluctuate betrveen 40 and 111, whereas the acceptable limrtts 10 Lil1000 parous ones. The vector characteristics (MTP; Nb L71000 parous) recorded in 2001, areequtvalent (even hrgher) than those observed in 2000 Thrs means that the nsk is real for humanpopulattons hving in contact wrth the S. neat,ei in the Mpamba-Nkusi focus. OI course, the phorcticassoctatton u'tth crabs lrmits the reproductron of black flres (number of brtcs/man/day, generally lorverthan 30). 'Ihe fact strll remarns that these low densrtres are capable of causing rntense transmrssion.Transnlisston remains high, despite the distributron of ivermectin. It must be sard that this phenomenon.observcd equally at Krcheche (drstrict of Kabarolc), rvas reported by scveral authors. The latter arcutlanittrous lrt asserltng that ivernrectin does not intemrltt transntissron. but partiallr,.

I lle exllcrtnlcrttal Lreatnrcut, rvhrch u'as clrncd ()u[ ()n tltc MItantlra Irvkusr ILrver in 2000.llrought abtlttt a drastrc reductton in the rnlestatron ((r(r.7'7o-100%) of crabs- It *,as the same lbr 200 1.rvhcr.r tltc trcaLnle nt of thc Mushankikrva and Rrvabutu-; i rrve rs causetl 100'% of ntortalrty of larvae o'er ?Knl- 'l-his rcsult con'oborates the obscrvation made in othcr lbci (ltu,ara, Srrsa, Asa), and indicatc-s thatIltc'fcrlrcllhtls ts the sclccted lan'rcidc for ground lrealurcnt of brcc-clrpg srtcs u,r1h .S trca,ei. Its ci]lcac'

36

and activc carrying capacity help to clean up the breeding sites after some treatment cycles. Whatremains to bc addresscd is the problem of dosage, in relation to the flow rate, and the numbcr o[spraying points.

4.4.7. Co nclusio ns-Suggcstio ns

'lhe expcrtcnce gatned by OCP in the arca ol rccordrng ol entonrologrcal results, helped t6istnstttutton to finalize cxcellent data collection forms. lt is therefore prefcrable to use thesefornts, for thcy bctter report captures, identification, dissection and black fly infestation. Theseforms enable each person to verify and interpret results.TIlc rdcntrfication of samplcs that arc harvested indicatc that t5e black flies found r' thcMpamba Nkusr focus arc of Lhe S. neat,ei and S. damnosunt, Nkusi typc. The lattcr, thoughclassified as non-anthropophilous, needs to be better characterized, and its vector status welldefined.The training of local staff, which will guarantee the continuity and efficacy of control activities,is of utmost necessity. Staff will have to be ffained on all technical and practical aspects oftreatment with insecticides). The personnel of the ltwara focus, which is competent andexperienced, could technically assist the Mpamba Nkusi staff.The biology of the S. neavei, the success of the experimental larviciding, the extent of the focus,the geographical and ecological isolation of the focus, and the accessibiliry of the rivers in allseasons, are some elements that indicate that the elimination of the vector in the Mpamba-Nkusifocus could be undertaken with success. The problem that remains to be solvld is that ofinsecunty, rvhich, at any time, may impede the conduct of vector control activities.

Dcspite the efficacy of larviciding, and the probable elimination of the vector from the MpambaNkust focus, the distribution of ivermectin rvill have to continue, to take into considcration the longevityof adult rvorm olthe O. volwrltts that are found in former patients.

!

37

5. OVERALL CONCLUSION'l'his surlts up the points pcrlalnrng to the training of local staff of pro.;ccts, supenisio. of activities, a,dllrc allarnnrcnt of tlrc fi,al oblcctrve of thc various vcctor clrminarron pr.oJccts:

'l-hc cxpcricnce acqutrcd by ocl' rndicatcs that the implcmentation oI a co'trol programme, asplanned in thc Tukuyu, Bioko, Iwara and .Mpamba-Nku' ro"i, calls for qualified pcrson.el.Enhancing training of this personnel rs indisiensrut" 1"rp""i"iiv ", Bioko). Given the actualtraining needs in all the countries, measures need to be iakln, noi onty in the countries inarnelythe objective sclection of candidates), but also in A?oc 6o.guni,ng training).

1'hc clficacy oI vector e ltmtnation operatio,s rs lrnked to thJ contrnurty rrr 'e

ctor control actrons.fhc lattcr is evaluatcd, thanks to eniomological surveillance. ttrc ocp expcrience indrcates thatthc supervision of activrties remains the key to success, for it ensures quality in data collection.It is' therefore, desirable that measures are taken-to ensure ,uf.*,.ion of activities (essentiallyentomological surveillance) conducted under the various "".ro. elimination projects. Thecoord-inators of projects and ApOC must play prominent roles.

The longevily (10-15 years) of adult o. volvulus worrns is such that the distribution ofivermectin will have to continue in all foci for at least ro v""." Even in foci where eliminationactivities are successful, distribution of ivermectin must continue, are to the presence of formerpatients (camers of nodules).The reports on the elimination of the vector in the different foci in Tanzania, Equatorial Guineaand Uganda' were an opportunity to assess

.the state of p.ogr".. of each project. It clearlyappears that the projects were undertaken on the basis of .l;n.;t., such as the size of the focus,its isolation, base data available, and the cost, as compared to cD'fI. The only thing is that thepractical feasibility of projects was not sufficiently taken into account, and some factors (actuallirnrt of focus, accessibility of brceding site,.risk of re-in,asronj *,..", at times, underestimated.of course' rvhen the vector is s- nea,ei,the factors mcntioned utor,. u." more or less attcnuated,l ust by the nrere fact of thc bro-ecology of the vector. on the other hand, *,ith the s. dorrtrtost,us'l'' the hmrting factors becotnc nr*".or.. abundant .uppo.i.,-difficult accessibility to allbreeding sites, black fly densities, which are ge neraily r,ig'r-,, t igrr flying capacity. And 1,et a_100% coverage of breedtng sites is an imperati'e conditr; for vector elimination. Besides, 11was agreed that in the selected foci, the eltminatron of the vector u,ould be complete, definrteand fast' This objective remains achievable for the foci of Itwara and Mpamba Nkusi. on thecontrary, the reality on the field makes it mandatory to recognize that

'ector elimination atTuk-uyu and Broko rtsks liaving an ob.;ectivc that rs too ambitioris. It ls u,orth recalling here oneof the recommendattons of the JAF6: if thc meetrng decides that 'ector elimination acti'rtresnlust cease tn the focus, recommendations will need to be made to thc country concemed, so asto enable it conttnue

'ector control in a national or bilateral context (cooperation). on the otherhand, in tlie e'cnt r*.'here acti'ities u'ill have to be continued, f.u"t,.ut measures must be takenby APOC for tmplcmentatton, supervrsion and e'aluatron of treatment actl'rtres.

6

38

AKNOWLEDGBMBNT

Wc arc pleascd to thank hcrc all lhosc who ln any manncr enablcd thc preyraratron thc currcutsyrthcsis on thc onchoccrciasis vectors climination activittcs in somc locr of Central Africa (Broko inIlquatorial Guinea) and thc East (ltwara and Mpamba-Nkusr rn Uganda, Tukr-ryu in Tanzalia).

We would hke to thank particularly :

Doctor A. SEKETELI, Director of the AIOC Progranrmc, for his trust on me bygiving mc the analysis and update of the data of all krnds which arc pertincnt to decideon the possibilities and conditions of vectors elimination. IJis experience andknorvlcdge of the various loct rverc vcry useful to us rn thc prcparatlon of tSrsdocumcnt.

Doctor M. NOMA who, with his remarkable knowledge of the foci and his availabilitygave remarkable and efficient help.

Our work was carried out thanks to the assistance of many peoples (administrative andfinance officers, secretaries, drivers) whose competence,, dlmamism and faithfulnessare appreciated.

39

c

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42

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I

43

ANNNEXES:TABLES AND FIGURES

44

Table 1 : Captures and dissections at Lufilyo crater (TUKUYU - year lggg)

Table 2 : Captures & dissections at Lwangwa masako (TUKUYU - Year l ggg)

I

a

0

0

BMBR 0 oo ZJ 840 '166s '1507

00 0 0 0

It{oulhs

Jan Feb March April May June July Aug Sept Oct Nov DecTotal

Nb of days4 4 4 4 4 4 4 4 4 4 4 4 4B

Captured 175 46 IJ74 J 19 B4 22 I 7 12 35 499

Dissected 174 74 45 13 3 19 84 22 I 7 12 35 497

Parous 53 13 14 5 1 5 21 B 2 2 3 18 145

lnfected 16 3 3 0 1 0 0 1 0 0 0 0 24

lnfectious 0 0 0 0 0 0 0 0 0 0 0 0 0

Nb de Ll 0 0 0 0 0 0 0 0 0 0 0 0 0

MBR 1 305 555 345 98 23 143 630 165 6B 53 90 263

MTP 0 0 0 0 0 0 0 0 0 0 0 0 0

Morihs

TotalJan Feb March April May June July Aug Sept Oct Nov Dec

Nb of days4 4 4 4 4 4 4 4 4 4 A+ 4 4B

Captured 1 0 0 1 3 112 222 201 62 7 26 0 635

Dissected 1 0 0 1 J 110 222 201 62 7 26 0 633

Parous 0 0 0 1 1 19 63 B4 5 2 6 0 1Bl

lnfected 0 0 0 0 0 2 EJ 4 2 0 0 0 13

lnfectious

Nb de L1

0 0 0 I 0 I 0 0 0 0 J

0 0 0 0 a-) 0 o 0 0 0 0 11

0

0

46s

0

.JJ 195 0

0 B30 0

,

i rurF 23 60

0

Nb de Ll

45

Table 3 : captures & dissections at rapio bridge (TUKUyu _ year 1999)

Table 4 captures & dissections at Kambaseqera (TUKUyU - year lggg)

0

A4ontlts

Jan Feb March April May June July Aug Sept Oct Nov DecTotal

Nb of days2 2 2 2 2 2 2 2 2 2 2 2 24

Captured 1B 43 11 1 0 6 1 19 I 4 35 2 149Dissected 1B 42 11 1 0 6 1 19 o 4 35 2 148Parous 6 15 6 0 0 2 0 6 1 2 2 0 40lnfected 0 1 0 0 0 0 0 0 0 0 0 0 1lnfectious 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0

270 645 165 15 0 90 15 285 135 60 525 30MTP 0 0 0 0 0 0 0 0 0 0 0 0 0

l,[onthsJan Feb March April May June July Aug Sept Oct Nov Dec

Total2 2 2 2 2 2 2 2 2 2 2 24Nb of days

tured 2 0 J 0 3 6 14 .)J 0 25 22 79

Dissected1 2 0 0 J 6 13 J 0 25 22 7B

Parous 0 0 0 0 0 0 7 0 0 5 11 24Jnfected 0 0 0 0 0 0 0 1 0 0 0 2

0 0 0 0 0 0 0 0 0 0 0 0 0

lnfectious

Nb de L1 0 0 0 0 0 0 0 0 0 0 0 0 0MBR 15 30 0 45 0 45 90 210 45 0 375 330

0MTP 0 0 0 0 0 0 0 0 0 0 0

,

1

1

1

Mottths

TotalJan Feb March April May June July Aug Sept Oct Nov Dec

Nb of days4 4 4 4 4 4 4 4 4 4 4 4 4B

Captured 24 72 220 281 228 409 328 228 202 182 13 43 2230

Dissected 24 72 220 277 227 407 326 228 200 180 13 43 2217

Parous I 15 56 95 61 126 113 140 50 16 2 1B 701

lnfected 1 1 4 18 14 15 I 20 6 4 0 7 99

lnfectious 0 0 0 0 0 1 1 6 0 0 0 1 INb de L1 0 0 0 0 0 1 5 13 0 0 0 2 21

MBR 180 540 1 665 2108 17 10 3068 1 809 1710 1515 1 36s 98 323

PMT 0 0 0 0 0 B 28 9B 0 0 0 15 149

Table 5

Table 6

46

Captures & dissections AT Lufilyo crater (TUKUYU - year 2000)

Captures & dissections AT Lwanga-Masako (TUKUYU - year2000)

I

0

ltIonths

TotalJan Feb March April May June July Aug Sept Oct Nov Dec

Nb of days4 4 4 4 4 4 4 4 4 4 A+ 4 4B

Captured 1 1 3 36 198 470 405 524 79 90 7 1 1815

Dissected 1 1 J 36 193 456 402 440 79 90 7 1 1 709

Parous 1 0 2 C) 51 165 139 151 4 5 il 0 524

lnfected 0 0 0 0 1 5 (J 2 0 0 0 0 16

lnfectious 0 0 0 0 0 1 2 1 0 0 0 0 4

Nb de L1 0 0 0 0 0 4 6 4 0 0 0 0 14

MBR

MTP

B

0

B

0

ZJ

0

270

0

3s25

31

3038

45

3930

36

tro2

0

675 53

0

B

0 112

1 485

Montlts

Jan Feb March April May June July Aug Sept Oct Nov DecTotal

Nb of days2 ) 2 2 2 2 2 2 2 2 2 2 24

Captured 129 161 81 31 43 258 607 B1 144 220 95 43 1 893.Dissected 129 160 B1 30 42 ,troLJU 311 BO 143 159 95 43 1 531Parous 49 53 19 12 10 71 115 51 47 21 6 a 463lnfected 0 .)

1 0 3 6 8 1 1 1 0 0 24lnfectious 0 0 0 0 0 1 0 1 1 0 0 40 0 0 0 0 a 0 6 4 10 0 0 23

Nb de LI

1 93s 3415 1230 465 645 3870 91 05 1215 2160 3300 1425 645MTP 0 0 0 0 0 45 0 15 60 207 0 0 327

47

Table 7 captures & dissections at rapio bridge (TUKUyu - year 2000)

Table B captures and dissections at Kambasegera (TUKUyU - year 2o0o)

299

1

I330

0 0

Itfonths

Jan Feb March April May June July Aug Sept Oct Nov DecTotal

Nb of days2 2 2 2 2 2 2 2 2 2 2 2 24

4 32 36 I 2 14 ooaa) 113 20 )) J 17 300C.^tured

urssected A 32 36 B 2 14 28 113 20 )) 3 17f arous 0 5 5 0 1 7 o JJ 4 Cl 1 7 77lnfected 0 0 0 0 0 0 0 0 2 0 2 5

US 0 0 0 0 0 0 0 0 1 0 n 0Nb de Ll 0 0 0 0 0 0 0 0 o 0 0 0MBR 30 480 540 135 30 210 420 1 695 300 45 255MTP 0 0 0 0 0 0 0 0 0135 135

1

1

Balacha de Riaba Barleycorn Musola Sampaka

April May April May April May April May

Nb of days

.)

.) 5 2 5 4 4 J 5

Captured 419 839 765 17 17 345 182 331 540

Dissected 3'16 464 334 517 345 182 264 468

Parous 115 184 141 199 147 61 140 228

lnfected 5 5 13 4 18 7 15 1B

lnfectious 2 1 2 2 8 3 2 5

Nb de Ll I 1 5 5 36 27 5 3B

MBR 41 90 5034 11475 10302 2586 1 365 3310 3240

MTP 119 11 172 99,6 270 203 63 263

Table 9

Table 10

River Eba on road to Moka

Moka at river Chubaf"tat

48

Captures and dissections at Bioko (april-may 2000)

Captures and dissections at Bioko (february 2001)

a

1

17

6 lr

1 304

Nb ofdays

Captured DissectedParous Parous

infectedParouswith L3

NbLi MBR MTP

Sampaka 1 222 106 49 .E 5 5655 319

1 155 B9 23,6 19 9,5 t)

Barleycorn 1 213 65 32,3 19 19 q 61 35 349

1 196 93 409 5,3 0 0

Musola Village I 282 BO 48,7 179 7,7 35 9490 12751 340 96 61,4 a.) 1,7 1

1 327 92 46,7 25,6 0 0

Balacha da Riaba I 118 69 33,3 8,7 0 0 351 0

1 116 B6 39,5 11,8 0 0

Riaba 1 359 65 26,1 0 0 0 1 0380

72

1 JJJ BO 36,2 10,3 6,9 1

Granja da MusolaRiver Musola

1 209 80 30 O,J 0 0 41 85 655

1 70 B6 64 14,6 7,3 26

Granja da Musola River Eba 1 149 60 43,3 11,5 0 0 4470 0

1 123 BO 32,5 19,2 0 0 2970 191E IZ 44,4 12,5 6,2 1

0 0 0 02689843293

601

300

49

Tablel l captures of simuries before and during vector contro! campaign

BUSASAKIJURA

SOGOHI

1 994 1995 1996974 743 0632 514 0786 266 0)o) 250 0606 315 0652 277 0193 159 0325 11 0748 1 0431 9 0283 1 0481 0 0

6403 2546 0

SIISA1994 1995 1996

148 428 1187 387 16740 316 0337 111 16360 149 2571 751 q

121 391 6217 303 2104 10 1

72 4 044 2 026 J 0

2927 2855 49

Months 1 994 1 995 1 996Janu 312 827 0Febru 262 333 0March 484 720 3

ril 672 919 2M 624 450 0June 500 430 1Jul 260 187

449 18 0Se r 373 4 0October 337 12November 344 3december 365 1

Total 4982 3904 6

Months 1994 1 995 1 996Janua 96 19 0

99 7 0March 428 6 0

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June 311 24 0Jul 123 c 0

312 1 0S mber 151 0 0October 14 0 0November 23 1 0december B9 0 0Total 2390 64 0

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50

Tukuyu Onchocerciasis focus: Altitude range, dry season, S. damnosumlarval habitats

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Fiq.3: S. damnosum monthly biting rates (MBR) at four catching points inrelation to monthly rainfall in Tukuyu focus, October 1999 to September2000

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