1

Parasitology Cestodes Lecture: 1

Dr. Usama Ali 21 -11-2017

Helminthes (Page number1-11)

Cestodes (Tapeworms)

Helminthes2-Phylums

Nematodes

(Roundworms)

Platyhelminthes

(Flatworm)3-Classes

TurbellariaFree living organisms

Trematoda (flukes

Cestodea(tapeworms)

General Characteristics:

Cestodes in Greek mean girdle or ribbon.

They are parasitic in all or nearly all stages of their life cycle.

Majority are long, segmented and tape-like are called tapeworms.

The worm flattened dorsoventrally, creamy to white in color.

Size varies from a few mm to several meters.

Adult live attached to the mucosa of the small intestine of man and animals.

Larval stages are parasitic in the tissues or body cavities of vertebrate or invertebrate

hosts.

Parasites of man include both adult &larva.

Head or scolex is provided with suckers and sometimes with hooks that serve as

organs of attachment.

2

The adult consist of:

1. Scolex or head organ of attachment.

2. Neck region of growth &proliferation.

3. Proglottids or segments (immature, mature& gravid one which contain eggs).

Neck + proglottids Strobila

Scolex knob-like & provided with 4-cupped suckers symmetrically arranged, 2-

ventrolaterally &2-dorsolaterally. In Diphyllobothrium scolex is spatulate & is

provided with a long median ventral & a similar dorsal sucking groove or bothrium.

As long as the scolex remains attached, a new strobila will be formed from it.

Sexes are not separate.

Body cavity is absent.

Alimentary canal is entirely absent.

Excretory and nervous systems are present.

Reproductive system is present and complete in each segment.

3

NO. of proglottids varies from 3-4 in the Echinococcus to 1000 or more in beef

tapeworm Taenia saginata & 3000-4000 in fish tapeworm Diphyllobothrium latum.

According to maturity of reproductive organs, three types of segments of the strobila

can be recognized:

1. Immature: male and female organs are not differentiated.

2. Mature: male and female organs have become differentiated (male organs

appear first).

3. Gravid: uteri are filled with eggs (other organs are atrophied or have

disappeared).

Covered with tegument containing microvilli (microtrichs).

The worm lacking a digestive system & absorb nutrients through this tegument.

The adults reside in the gastrointestinal tract, but the larvae can be found in almost any

organ.

Human tapeworm infections can be divided into two major clinical groups:

1. In one group, humans are the definitive hosts, with the adult tapeworms living in

the gastrointestinal tract (Taenia, Diphyllobothrium, Hymenolepis, and

Dipylidium).

4

2. In the other, humans are intermediate hosts, with larval-stage parasites present in

the tissues; diseases in this category include echinococcosis, sparganosis, and

coenurosis.

Each mature segment contain:

1. Excretory system: consists of paired ventrolateral and dorsolateral longitudinal

canals, at frequent intervals are numerous tubules that originate from flame cells

in the tissues.

2. Genital organs: full growth & function in the mature proglottids. In most species,

there is one complete set of ♂& ♀organs. According to egg ovi-position cestodes

can be divided to two orders:

Cestodes

2-Orders

Cyclophyllidea Pseudophyllidea

I. Order Cyclophyllidea Characteristics:

Large or small worms consisting of chains of segments.

Scolex is quadrate with four cup-like round suckers.

An apical rostellum with hooklets may be present.

Vitelline glands concentrated in a single mass.

Common genital pore is marginal (on lateral side of segment).

No uterine opening for the exit of eggs from the gravid uterus.

Eggs only escape from the rupture or disintegration of ripe segments.

Eggs are not operculated and can develop only in the intermediate host, fully

embryonated.

Oncosphere is never a ciliated embryo.

5

Larval development proceeds in one intermediate host.

Adult Worms in the Intestine:

Taenia saginata

Taenia solium

Hymenolepis nana

Hymenolepis diminuta

Dipylidium caninum

Larval Stages in Man:

Hydatid cyst of Echinococcus granulosus and Echinococcus

multilocularis

Cysticercus cellulosa of Taenia solium

Coenurus cerebralis of Multiceps multiceps

Coenurus glomeratus of Multiceps glomeratus

II. Order Pseudophyllidea Characteristics:

Large worms consisting of a long chain of segments.

Scolex “head” has two slit-like sucking grooves called bothria instead of suckers.

Vitelline glands are widely scattered in the parenchyma and is composed of many

acini.

Genital pores are on the ventral surface of the segment and are not marginal.

Uterus opens to the exterior through which eggs come out.

Eggs are operculated and can develop only in water; immature when oviposited

(unembryonated) and oncosphere gives rise to ciliated embryo.

Larval development proceeds in two intermediate hosts:

First larval stage is called procercoid.

Second larval stage is called plerocercoid.

Adult worms in Intestine

Diphyllobothrium latum: Fish Tapeworm.

Larval stages: Plerocercoid in Man

Sparganum mansoni

Sparganum proliferum

6

7

Taenia saginata

Beef tapeworm / Hookless tapeworm

Taeniasis saginata or beef tapeworm infection

The name taenia is derived from the Greek word meaning tape or band

Epidemiology:

These cestodes have a worldwide distribution, but incidence is higher in developing

countries.

Human infection follows consumption of raw and undercooked beef.

Cysticerci can be seen as shiny white spots in infected beef on visual inspection.

Former popular practice of prescribing beef juice or raw beef for debilitated persons

responsible for many infections.

The infection is not found in vegetarians and those who do not eat beef.

Epidemic factors:

1. Egg or gravid proglottid contamination of grass and soil.

2. Method of raising domestic animals.

3. Unhygienic dinning habit of eating raw or undercooked meat.

Morphology:

The adult worm lives in the middle third of small intestine.

T. saginata can be up to 4 to 6 meters long or sometimes up to 24 meters and 12 mm

broad.

It has a pear-shaped head (scolex) with four suckers and a single apical depression but

no hooks.

It has a long flat body with 1000-2000 segments (proglottids), of them 1/3-1/2 are

nearly gravid.

Only a single specimen occurs in an infection, but there may be more.

Proglottid: the more distal increase in breadth and width reach to 12 mm.

Mature proglottid contains a full set of function ♂ and ♀ reproductive organs.

8

Taenia SPP. Mature Segment

Gravid proglottid more elongated, narrow as a result of the development of the large

number of branched lateral arms of the uterus (15-20).

The terminal proglottids become separated from the strobila and migrate out of the

bowel or are evacuated in the stool with only partial loss of eggs.

The egg is 31 x 43 micrometers, roundish and yellow-brown. It has a thin transparent

outer embryonic envelop and a thick brown shell composed of many slender rods

cemented together. It contains hexacanth embryo, which has 3-pairs of delicate lancet-

shaped hooklets. It is liberated by rupture of ripe proglottids & does not float in

saturated salt solutions. Eggs are resistant and remain viable for 8 weeks. It infective

only to cattle

9

Taenia spp. Egg.

Life cycle:

A tapeworm larval cyst (Cysticercus bovis) is ingested with poorly cooked infected

meat.

The larva escapes the cyst and passes to the small intestine (middle third of

intestine) where it attaches to the mucosa by the scolex suckers.

The proglottids develop as the worm matures in 3 to 4 months. The adult may

live in the small intestine as long as 25 years and pass gravid proglottids with the

feces.

Eggs extruded from the proglottid contaminate and persist on vegetation for

several days and are consumed by cattle in which they hatch and form cysticerci.

Man is the only natural definitive host of T. saginata and the infection results

from eating raw beef.

10

Humans are the only definitive hosts for Taenia saginata. The adult tapeworms (length:

usually 5 m or less, but up to 25 m) reside in the small intestine, where they attach by their

scolex. They produce proglottids (each worm has 1,000 to 2,000 proglottids), which mature,

become gravid, detach from the tapeworm, and migrate to the anus or are passed in the stool

(approximately 6 per day). The eggs contained in the gravid proglottids (80,000 to 100,000

eggs per proglottid) are released after the proglottid becomes free and are passed with the

feces. The eggs can survive for months to years in the environment. Cattle and other

herbivores become infected by ingesting vegetation contaminated with eggs (or proglottids).

In the animal's intestine, the eggs release the oncosphere, which evaginates, invades the

intestinal wall and migrates to the striated muscles, where its develop into a cysticercus. The

cysticercus can survive for several years in the animal. Humans become infected by ingesting

raw or undercooked infected meat. In the human intestine, the cysticercus develops over 2

months into an adult tapeworm, which can survive for more than 30 years.

11

Cattle acquire the infection by grazing on moist polluted grass with the feces or

raw sewage containing the egg.

The egg may remain viable in soil for 6 months.

After a year or more the cysticercus bovis become calcified.

Human infection result from ingestion of uncooked or undercooked meat.

Pathogenesis & Symptoms

Light infections remain asymptomatic, but heavier infections may produce

abdominal discomfort, epigastric pain, vomiting and diarrhea.

Deprivation of nutrition or loss of appetite.

Allergic reactions.

Weakness.

Weight loss.

Mild irritation at site of attachment.

Appendicitis.

12

Obstructions of the intestine (mass of worms), also in bile and pancreatic

ducts and appendix because proglottids are actively motile.

Diagnosis:

Microscopic Examination of faeces shows the eggs.

Species identification cannot be made from the eggs.

Diagnostic stage:

Egg (indistinguishable from egg of T. solium & Echinococcus) or gravid

proglottid in stool or from the perianal area.

Note:

Gravid proglottids deposit eggs in the perianal area as they crawl from the rectum, so the

diagnosis may be made by use of a cellophane tape technique or perianal swabs (like

enterobiasis).

Treatment:

Praziquantel or niclosamide is the drug of choice, 5-10mg/kg single dose.

Expulsion of scolex must be assured to assume a satisfactory treatment.

Areca nut + pumpkin seed+ purge.

Criteria for cure:

Recovery of the scolex.

Negative stool examination 3 months after treatment.

Control:

Sanitation.

Adequate cooking or freezing of caw meat or beef are effective precautions, since

cysticerci do not survive temperatures below -10° C and above 50°C.

Meat inspection.