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Parasitology ResearchFounded as Zeitschrift fürParasitenkunde ISSN 0932-0113Volume 109Number 1 Parasitol Res (2011) 109:1-8DOI 10.1007/s00436-011-2252-4

Diurnally subperiodic filariasis in India—prospects of elimination: precept toaction?

A. N. Shriram, K. Krishnamoorthy,B. P. Saha, Avijit Roy, V. Kumaraswami,W. A. Shah, P. Jambulingam &P. Vijayachari

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REVIEW

Diurnally subperiodic filariasis in India—prospectsof elimination: precept to action?

A. N. Shriram & K. Krishnamoorthy & B. P. Saha &

Avijit Roy & V. Kumaraswami & W. A. Shah &

P. Jambulingam & P. Vijayachari

Received: 6 November 2010 /Accepted: 12 January 2011 /Published online: 1 February 2011# Springer-Verlag 2011

Abstract The elimination of lymphatic filariasis in theAndaman and Nicobar Islands provides unique opportuni-ties and challenges at the same time. Since these islands areremote, are sparsely populated, and have poor transportnetworks, mass drug administration programs are likely tobe difficult to implement. Diurnally subperiodic Wuchereriabancrofti vectored by Downsiomyia nivea was consideredfor the scope of vector control options. Considering thebioecology of this mosquito, vector control includingpersonal protection measures may not be feasible. How-ever, since these islands are covered by separate adminis-trative machinery which also plays an important role in

regulating the food supply, the use of diethylcarbamazine(DEC)-fortified salt as a tool for the interruption oftransmission is appealing. DEC-fortified salt has beensuccessfully pilot tested in India and elsewhere, operation-ally used by China for eliminating lymphatic filariasis.Administration of DEC-fortified salt though simple, rapid,safe, and cost-effective, challenges are to be tackled fortranslating this precept into action by evolving operation-ally feasible strategy. Although the use of DEC-fortifiedsalt is conceptually simple, it requires commitment of allsections of the society, an elaborate distribution mechanismthat ensures the use of DEC-fortified salt only in the

A. N. Shriram (*)Division of Vector Borne Diseases,Regional Medical Research Centre(Indian Council of Medical Research),Post Bag No. 13, Port Blair 744101 Andaman and NicobarIslands, Indiae-mail: shriraman@icmr.org.in

K. KrishnamoorthyDivision of Health Economics and Disease Burden,Vector Control Research Centre(Indian Council of Medical Research), Medical Complex,Indira Nagar, Puducherry 605014, India

B. P. SahaDivision of Malaria, Filaria and Vector Borne Diseases(National Vector Borne Diseases Control Programme),Directorate of Health Services, Andaman andNicobar Administration,Port Blair 744101 Andaman and Nicobar Islands, Indiae-mail: bpsahanvbdcp@gmail.com

A. RoyDivision of Health, Directorate of Health Services,Andaman and Nicobar Administration,Port Blair 744101 Andaman and Nicobar Islands, Indiae-mail: dravijit@gmail.com

V. KumaraswamiDivision of Immunology and Internal Medicine, TuberculosisResearch Centre (Indian Council of Medical Research),Mayor V Ramanathan Road, Chetpet,Chennai 600031, Indiae-mail: kumaraswami@gmail.com

W. A. ShahG B Pant Hospital, Directorate of Health Services,Andaman and Nicobar Administration,Port Blair 744101 Andaman and Nicobar Islands, Indiae-mail: wajid15@rediffmail.com

P. JambulingamDivision of Vector Biology and Control,Vector Control Research Centre(Indian Council of Medical Research), Medical Complex,Indira Nagar, Puducherry 605014, Indiae-mail: pcsaja@gmail.com

P. VijayachariDivision of Microbiology and Molecular Medical Microbiology,Regional Medical Research Centre(Indian Council of Medical Research),Post Bag No. 13, Port Blair 744101 Andaman and NicobarIslands, Indiae-mail: vijayacharip@yahoo.com

Parasitol Res (2011) 109:1–8DOI 10.1007/s00436-011-2252-4

e-mail: kkrish_3@yahoo.com

Author's personal copy

endemic communities, and a vigorous monitoring mecha-nism. Here, we examine the inbuilt administrative mecha-nisms to serve the tribal people, health infrastructure, andpublic distribution system and discuss the prospects ofputting in place an operationally feasible strategy for itselimination.

Advances in the epidemiology of diurnally subperiodiclymphatic filariasis in India

Lymphatic filariasis (LF) is an important public healthproblem in India contributing about 40% of the globalburden (Ramaiah et al. 2000a, b). The prevalence of LF inAndaman and Nicobar districts in Andaman and NicobarIslands in India was identified as early as 1942 (Wilcock1942) when Nicobar group of islands showed an infectionrate of 5.8% with Wuchereria bancrofti. Subsequentsurvey conducted in 1958 (Basu 1958) showed the preva-lence of this infection in both Andaman and Nicobar groupsof islands. Diurnally subperiodic form of Wuchereriabancrofti (DspWB), transmitted by Ochlerotatus niveus, isendemic only in a small pocket of seven islands, viz.Nancowry group of islands of the Nicobar district inIndia (Kalra 1974). The first report on the prevalence ofDspWB, transmitted by O. niveus (now known as Down-siomyia nivea; Reinert et al. 2004), came from Nicobargroup of islands in 1974 (Kalra 1974). Subsequent studieson its prevalence, distribution, and assessment of ende-micity status (Russel et al. 1975; Tewari et al. 1995;Shriram et al. 2002), vector incrimination (Tewari et al.1995), clinical epidemiology (Shriram et al. 2002), host-feeding activity (Shriram et al. 2005), transmissiondynamics (Shriram et al. 2008), and vector populationdynamics and bioecology (Shriram and Krishnamoorthy2010) of this infection have shown its prevalence in all theseven islands of Nancowry group of islands of the Nicobardistrict and confirmed its continued existence withperennial transmission.

Lymphatic filariasis elimination strategy

During the past decade, research advancements have led usto better understanding of parasitic diseases enablingdevelopment of appropriate strategies for their control,monitoring, and certifying eradication or elimination pro-grams (WHO 2000). In tune with the Global Programme toEliminate LF (GPELF), a program has been initiated torealize the National Health Policy of India (Ministry ofHealth and Family Welfare, GOI 2002) to eliminate LF by2015. The key strategy is to distribute single-dose DECwith albendazole (alb) to all individuals annually for at least

4–5 years. Currently, the elimination program is underwayin 243 districts out of 593 endemic districts spanning 20states and Union Territories. In the Andaman and Nicobarislands, the program to eliminate LF was launched in 2004by the Directorate of Health Services, Andaman andNicobar Administration, implying that DspWB would alsobe eliminated.

Research findings and challenges to the currentelimination strategy

Despite the fact that single-dose DEC treatment was foundeffective for reduction of microfilaremia and parasite load,but it is not always sufficient to eliminate all the micro-filariae, especially when mean microfilariae density washigh (>40; Chandra and Paramanik 2008). Researchfindings suggest that logistical and operational aspects(Ramaiah et al. 2000a, b) and parasite dynamics in humansin relation to the number of annual treatments (Das et al. 2001)have significant implications on the program to eliminate LF.Poor treatment compliance rates (Ramaiah et al. 2000a, b)and persistence of microfilaremia after 4–5 rounds of massdrug administration (MDA) necessitate rethinking on theadequacy of four to six annual rounds of treatment, which isbelieved to be sufficient for eliminating LF. Interventionefforts need to be strengthened by prolonging the MDA orsupplementing intervention measures (Stolk et al. 2006;Ramaiah et al. 2007), apart from improving compliance toover 80% which is central to move toward elimination of LF(El-Setouhy et al. 2007). Post-MDA-I survey results in oneof the endemic islands for DspWB filariasis in the Nancowrygroup of islands showed microfilaremia prevalence rangingbetween 3.2% and 23.1% in different villages with a meanparasite intensity of 37.31 (range 1–492)/60 mm3 among themicrofilaremics.Mf prevalence and geometric mean intensity(GMI) of mff densities did not differ significantly betweenpre-MDA and post-MDA (Anonymous 2006). Despite fourrounds of MDA, it is probable that DspWB LF could stillpersist as an important public health problem among theNicobarese. In view of its risk of spreading from the loneendemic focus to other areas that are currently nonendemicfor this infection, but receptive with competent vector, it isessential to hasten the process of elimination of thisinfection. This can be achieved with additional controlpressure, as an adjunct to the current strategy of mass annualsingle-dose treatment.

What next and where do we go from here?

Annual single-dose two-drug regimen (albendazole pluseither DEC or ivermectin) or 6 months to a year of DEC-

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medicated salt (Ottesen 2000) has been recommended forelimination of LF. The first reported use of DEC-medicatedsalt was in Brazil in 1967, by Hawking, who first identifiedantifilarial properties of DEC in the 1940s (Hawking andMarques 1967; Gelband 1994). Since then, it has been usedintermittently in India, Africa, and Asia. The efficacy ofDEC-medicated salt was first assessed in close communities(Gelband 1994; Kanda et al. 1967; Davis and Bailey 1969).Subsequently, small- and medium-scale trials using 0.1%to 0.26% fortified salt were undertaken in India andother countries. The results of these trials in India andelsewhere showed that microfilaria density dropped bymore than 90% and that microfilariae disappeared fromthe blood in 31% to 98% of the infected population(Raghavan et al. 1968; Sen et al. 1974; Krishna Rao et al.1976; Katiyar et al. 1977; Narasimham et al. 1979;Krishna Rao et al. 1980; Narasimham et al. 1989). Ramaiahet al. (2009) concluded from a study on the impact of DEC-fortified salt that residual infection was found to persist aftercessation of intervention. However, 0.60–0.70% microfilar-emia (mf) prevalence is a safe level with no recrudescence ofinfection, and rigorous interventions measures are requiredto eliminate the residual infection.

Promising results have been obtained from DEC-medicated salt medium-scale trials, covering population inthe range between 1,000 and 7,000 (Fan et al. 1975a, b, c, d;Wang 1979; Fan 1990; Shenoy et al. 1998; Adinarayanan etal. 2007), and one large-scale trial covering a whole endemicprovince with a large-scale trial covering a whole endemicprovince with a population of over two million in Chinawhere the problem was as serious as it is in India(Anonymous 1976). The mf prevalence declined by 96% to98% and microfilaria density by 87% to 99%. In anotherstudy, it was reported that the rates of medication, cure,microfilaria reduction, and infection in vector were 100%with no refusals or excuses (Fan 1990). The major successachieved by the use of DEC-fortified salt in China and partsof India in reducing the mf prevalence (WHO 1992)indicates its potential role in LF elimination. Thus, it impliesthat DEC-medicated salt provides an operationally viablealternate/adjunct option to MDA and has the potential toovercome the challenges to the current elimination strategy;it could in principle hasten the process of interrupting/eliminating transmission in areas having persistent foci in acost-effective manner, than tablet-based programs (Hawkingand Marques 1967; Meyrowitsch and Simonsen 1998;Freeman et al. 2001; Michael et al. 1996; Houston 2000).

Implications of endosymbiont Wolbachia

Wolbachia is an intracellular bacterium, belonging to theorder Rickettsiales, which was discovered in the seventies

(McLaren et al. 1975; Vincent et al. 1975; Kozek 1977).This bacterium has been detected in a number of filarialspecies examined so far, including the major human filarialparasites W. bancrofti, Brugia malayi, and Onchocercavolvulus (Kozek and Figueroa 1977; Taylor et al. 2000a, b;Warren 1997; Sironi et al. 1995; Taylor and Hoerauf 1999).Wolbachia maintains a mutual symbiotic association withthe filarial nematode. Several studies indicate that Wolbachiahave been implicated in a variety of roles, includingdevelopment, fecundity, the pathogenesis of the filarialinfections, and survival of the filarial nematodes. Filariasisis characterized by recurrent episodes of inflammatorypathogenesis, and Wolbachia appears to precipitate thisinflammation (Bandi et al. 1998, 1999; Taylor and Hoerauf1999; Taylor et al. 2000a, b). The lipopolysaccharide (LPS)of Wolbachia appears to mediate elicitation of Toll-likereceptor-4 signaling which in turn directs the production andregulation of Th1 and Th2 cytokines associated withdifferential disease manifestations observed in onchocercia-sis (André et al. 2002). Recently, polymorphisms in Toll-likereceptor-2 have been associated with asymptomatic bancrof-tian filariasis in Thailand (Junpee et al. 2010). With these inperspective, chemotherapeutic strategy targeting the endo-symbiont Wolbachia with tetracycline class of compoundshas been envisaged for the treatment of filariasis (Taylor andHoerauf 1999; Taylor et al. 2000a, b). The liposomizedtetracycline was found to be significantly more effectivewhen compared to the free form of the drug. In contrast tothe 90/120-day oral administration of the drug, the treatmentschedule using the liposomized form of the drug wasreduced to 12 alternate days with better efficacy of thetreatment (Bajpai et al. 2005). Preliminary studies undertak-en in India, to assess the symbiosis of Wolbachia in W.bancrofti microfilariae (mff), have indicated its presencefrom wider geographical locations (Hoti et al. 2003; Gayenet al. 2010). Besides, Wolbachia has been detected only inW. bancrofti mff from Kimuta Island, Papua New Guinea,and Sri Lanka (Taylor and Hoerauf 1999; Bazzocchi et al.2000). Wolbachia strain wMelPop suggested to be useful inthe global effort to eliminate lymphatic filariasis andpossibly for the control of other mosquito-borne parasiteswhere immune preactivation inhibits parasite development(Kambris et al. 2009). One potential augmentative interven-tion to MDA is the elimination of vectors via repeatedinundative releases of male mosquitoes made cytoplasmical-ly incompatible via an infection with Wolbachia bacteria(Brelsfoard et al. 2008, 2009).To the best of our knowledge,there are no data on the prevalence of association ofWolbachia endosymbionts with the DspWB. Therefore, itwould be valuable to generate information on its associationfrom the endemic pocket (Nancowry group comprising sevenislands), of the Andaman and Nicobar archipelago, so as toassess the usefulness of chemotherapy with antibiotics.

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Utility of DEC-fortified salt strategy on themainland, India

Despite the theoretical advantage of DEC-medicated salt, ithas not been given the impetus by the LF community inIndia as a public health intervention. Paradoxically, twomajor public health successes have not also received thepublic attention they deserve and they have directrelevance to the use of DEC-fortified salt (WHO 2003;Liu et al. 1992). First, China, the country with the largestnumber of cases and largest population at risk, haseliminated transmission of the disease owing to, at leastpartly, the use of DEC-fortified salt. Second, the saltindustry has been mobilized world over to increase thehousehold use of iodized salt from low levels worldwideto more than 70% globally within the last 15 years,impacting on cretinism and iodine deficiency disordersand thereby improving IQ of millions of people (Delangeet al. 2001; Andersson et al. 2005; Pretell et al. 2004).These two milestones highlight the importance of consid-ering the contribution that DEC-fortified salt and iodinecould perhaps make to the effort to eliminate/control LF inIndia. The public distribution system in India is wellorganized, and the likelihood of distribution of DEC-fortified salt through this system needs to be explored.From the programmatic perspective, pilot studies in urbanKaraikal (Subramaniyam and Venkatesvarlou 1996), dis-tribution was primarily through organized efforts by thelocal health department in collaboration with salt providers,viz. merchants and vendors, and with the administrativesupport. While in another instance in Kanyakumaridistrict, Tamil Nadu, the state government implementedthe distribution through public distribution system.Alternatively, the option of introducing DEC-medicatedsalt into open market needs to be considered. In orderto accomplish this, first, a permissive regulatory effort isessential so that DEC-fortified salt is available as a foodproduct and not as a medicine. Second, forging strongpartnerships with salt producers is required so thatnormal marketing channels can be used to introduceand sell DEC-medicated salt. Third, component of socialmarketing is central to build up the consumer demandfor DEC-fortified salt. In order to support both iodiza-tion and LF elimination program, either more restrictiveregulatory control is essential, which would includeenforced consumer packaging, else Government of India(GOI) needs to develop active partnerships with saltproducers to increase supplies of salt and consumerdemand for DEC-medicated salt. Increasing the chancesof LF elimination program can be viewed in terms ofsettings where iodization salt program has achieved ahigh coverage and where iodization is needed to offerus opportunities, and in such settings, integrating andfortifying with DEC into existing iodization programs

perhaps offer a simple and rapid approach for eliminat-ing LF from India. Nevertheless, scaling up a distribu-tion mechanism for DEC-fortified salt is a challengingtask.

Perspective of vector control strategyand operationalizing DEC-fortified salt in Andamanand Nicobar Islands

From the perspective of vector control program, which mayreduce or eliminate transmission in endemic tracts as asupplementary measure (Bockarie et al. 2009), none of theantilarval nor adulticidal measures would be feasibleincluding cost-prohibitive personal protection measureowing to their exophily (outdoor resting) and diurnal (daytime) feeding behavior of the vector mosquito. Further-more, the larvae are not amenable to larvicidal controlbecause of the predominant breeding source, the tree holeswhich are innumerable and inaccessible (Shriram et al.2002, 2005, 2008; Shriram and Krishnamoorthy 2010).Personal protection measures (use of repellent creams orinsecticide-impregnated materials) are cost-prohibitive forthe tribal community who are at the risk of infection.Typical ecogeographical location of the island situationwith closed communities and the tribal chieftains wieldingenormous control over the community augurs well forputting in place a rational strategy for tackling this problem.In such epidemiological settings, the potential alternativemethod of eliminating this infection may possibly be theuse of DEC-medicated salt where the inflow of non-medicated salt can be controlled. Therefore, the situationin the Andaman and Nicobar archipelago is ideal todemonstrate the administration of DEC-fortified salt foreliminating the lone foci of diurnally subperiodic filariasisfrom India. So, we believe that administration of DEC-fortified salt can be used as a potential alternative forelimination of this form of filariasis in a program mode.

Overall public health benefits

The National Vector Borne Disease Control Programme(NVBDCP), under the Directorate General of HealthServices, Ministry of Health and Family Welfare, is thenodal agency for drawing up strategies and implementingpreventive measures for the control of vector-bornediseases. In view of achieving the National Health Policy,which aims at elimination of LF by 2015, NVBDCP withits regional centers in several parts of the country in alliancewith research institutes of the Indian Council of MedicalResearch has launched annual mass single-dose DEC andmorbidity management program in 243 known endemic

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districts in India. Furthermore, in seven districts, DEC isbeing administered along with albendazole, thus in overallcovering a total of over 500 million people. Besides, theyhave developed manuals for its program managers inprogram implementation with well-defined methodologiesfor MDAs and lymphedema management—all major stepssignifying the progress of the network. The conceptualbasis for the elimination of DspWB in the Andaman andNicobar Islands is illustrated in Fig. 1. The challenge forthe next years as the program rolls out into its fifth yearsince its launch in these islands relates to financing, toachieving a regional approach and ownership (given thesignificant differences in epidemiology), and in increasingadvocacy.

The cliché “window of opportunity” is very relevant tothe elimination of the lone foci of the DspWB LF from thecountry. The power of DEC and albendazole will provideadditional synergistic health effects. The infrastructureavailable with the Directorate of Health Services providesan opportunity for albendazole distribution which could bealigned with other interventions such as deworming. Aperfect case in point is the Union Territory Health Mission(UTHM), an implementation under the National Rural

Health Mission (NRHM) by the Government of India,mandated to improve the quality of health services in theseislands so that every person living in far flung islands hasaccess to proper and equitable quality treatment to setpublic health standards. The Andaman and Nicobaradministration, in particular the Deputy Commissioner(DC) of Nicobar district and Assistant Commissioner(AC) of Nancowry Tehsil, having administrative jurisdic-tion over the pockets of islands endemic for DspWB, needsto be sensitized on the LF elimination strategy. Nicobardistrict is designated as Integrated Tribal District, with DCas the ex officio Chairman of Integrated Tribal Develop-ment Agency (ITDA). The various poverty alleviationprogram sponsored by Ministry of Rural Development isbeing implemented through District Rural DevelopmentAgency (DRDA), headed by DC. The Tribal Councils inthe Nicobar district provide a fulcrum, around whichvarious developmental schemes for the welfare of the tribalpeople revolve. Tribal Councils are the traditionally electedbody looking after the welfare of the local people. Everyvillage in the tribal area has a village council headed byTribal Captains. Every island/group of islands has in place aTribal Council, constituted by the first Captains of Village

RNTCP- Revised National Tuberculosis Programme

NVBDCP-National Vector borne Disease Control Programme

EPI-Expanded Programme on Immunization

DRDA-District Rural Development Agency

IDSP-Integrated Disease Surveillance Programme

UNICEF-United Nations Children Education Fund

ITDA-Integrated Tribal Development agency

UTHM- Union Territory HealthMission, an implementation under National Rural Health Mission (NRHM)

Fig. 1 Conceptual frameworkfor elimination of DspWB LFin a total health package. EPIExpanded Program onImmunization, IDSP IntegratedDisease SurveillanceProgramme intersectoralcollaboration/communityparticipation

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Councils falling in their jurisdiction. These first Captainsselect Chief and Vice-Chief Captains of the Tribal Council.Currently, in Nicobar district, there are seven Tribalcouncils, viz. Car Nicobar, Katchal, Nancowry, Kamorta,Teressa, Chowra, and Pilobhabi, respectively. They are thelink between the Andaman and Nicobar administration andthe tribal people of the island. All these elements need to befactored and have to be involved in assisting in theelimination of this form of LF, which provides us thenecessary entry points to communities and leadership inbest practice. Albendazole is also effective against hook-worm (Ottesen et al. 1999) and hence has a significantimpact on anemia; any improvement in anemia status willcontribute to alleviation of problems of pregnancy-relatedmalaria and will improve birth weight—low birth weight,being a major cause of neonatal infant malaria-relatedmortality (Brabin et al. 1999). Hence, the impact of DEC-fortified salt for lymphatic filariasis transmission is only apart of the overall health benefits provided by deworming,head lice and scabies control, improved nutritional status,and reduced problems of anemia, all are benefits that couldpercolate from various schemes under the ambit of activitiesof the local Directorate of Health Services. Improvement ofanemia status may be a measurable indicator of the successof LF control when combined along with DEC-fortified saltadministration as an entry point; the community healthbenefits would be expanded and ensure adherence andcommunity compliance of health programs.

Concluding remarks

Programs to eliminate a given communicable diseaseshould be time-bound, and extension tends to result inoperational lethargy, necessitating improving programperformance so as to achieve the goal in time. Studiesindicate that unless compliance over 80% is ensuredparticularly in high infection areas, recommended durationof 5–6 rounds of MDA would not be sufficient to achieveelimination of LF. Additional intervention pressure there-fore becomes inevitable. Either mass DEC-fortified salt orvector control can be considered as two potential optionsthat could be supplemented for strengthening the effect ofthe ongoing MDA and to hasten the process of eliminationof Culex-transmitted W. bancrofti infection. Neither vectorcontrol nor personal protection measures are feasible due tounique vector behavior and cost-prohibitive personalprotection measures. Typical ecogeographical location ofthe island situation with closed communities and the tribalchieftains wielding enormous control over the community,reasonably well-organized public health infrastructure, andpublic distribution system in these islands augurs well forputting in place a rational strategy for tackling this problem

through mass DEC-fortified salt. However, for large-scaleuse in different operational/geographical settings, it isnecessary to develop appropriate delivery mechanismscoupled with strong social mobilization component. There-fore, a salt situation analysis needs to be undertaken whichwould enable in understanding the patterns of salt distribu-tion in the tribal community in the islands endemic for thisform of filariasis. Thus, the situation in the Andaman andNicobar archipelago presents an ideal scenario to demonstratethe administration of DEC-fortified salt for eliminating thelone foci of diurnally subperiodic filariasis from India.

The challenges of improving health status and elimina-tion of DspWB, vulnerable to effective intervention, willremain, but targeted and well-managed DEC-fortified saltprogram provides significant opportunities beyond thefocus of the elimination of this infection. Such a programwill involve partnerships at all levels, improve healthsystems management, and enhance interest from the localadministration, providing a significant platform for aneffective alliance between the research institutes, TribalCouncil/Village Council and the Directorate of HealthServices through the nodal agency, NVBDCP. The focusof such an alliance should not only be on scientificinformation but also on the operational aspects. From suchan alliance, the following issues need to be addressed:

1. evolving a plan for DEC-fortified salt supply andputting in place a delivery mechanism;

2. cost and cost-effectiveness of the DEC-fortified saltprogram in the elimination of diurnally subperiodicfilariasis—can a limited quantity of DEC-fortified saltbe supplied free of cost?;

3. assessing the levels of acceptance of DEC-fortified saltby the tribal community—can it be enhanced if thesupply is made free of cost along with administration ofalbendazole?;

4. assessing its operational feasibility and communitycompliance; and

5. how to carry out background including xenomonitoringfor the risk of resurgence and final evaluation for thecertification of elimination.

The conclusions put forth by Fan (1990), who has donepioneering work on the control of LF in China, are relevantin the present day context. He emphatically says thatadministration of DEC-fortified salt is simple, rapid, safe,cost-effective, and realistic method for filariasis control and/orelimination. Can we translate this precept into action?

Acknowledgments The authors are thankful to the Indian Councilof Medical Research (ICMR), New Delhi for extending financialsupport for studies undertaken on transmission dynamics of diurnallysubperiodic filariasis in the Andaman and Nicobar Islands videscheme no. 5/8-7(137) M98-ECD-II.

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