Cestodes (tapeworm) Introduction

Дата канвертавання27.04.2016
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Cestodes (tapeworm)

* Introduction:

The cestodes, or tapeworms, differ in a number of ways from other flatworms. Their bodies are long and flat, made up of many segments called proglottids. Each proglottid is a reproductive unit. Adults lack cilia and their surface is a tegument, but in cestodes the tegument is covered with tiny projections, microvilli, which increase its surface area and there by its ability to absorb nutrients from a host. Digestive tracts are absent completely. At the tapeworm's anterior end is a specialized segment called a scolex.

Most the cestodes are require at least two hosts, with the host of the adult tapeworm a vertebrate. Intermediate hosts are often invertebrates. A number of tapeworm species inhabit humans.


 Taeniasis is a tapeworm (cestode) infection acquired by the ingestion of raw or undercooked meat of infected animals.  Although many species exist, two species, Taenia saginata and Taenia solium, cause pathology in humans.  T. saginata is associated with the ingestion of the worm's larval form found in infected beef while T. solium is associated with that of infected pork.

1- T. saginata

1- scolex: is equipped with four suckers without rostellum and hooks.
2- The neck: it’s the narrowest part of the body and budding zone containing germinative tissue.

3- Immature proglottides: located in the anterior part of the body and inner organs are developing.

4- The mature proglottid contains the uterus (unbranched), ovary (2 lobes), genital pore, testes, and vitelline gland.

5- The gravid proglottid is typically longer than wide; 15 to 30 uterine branches are usually present on each side of the uterus.

2- Taenia solium


1- The scolex: measures from 1 to 2 mm in diameter and is equipped with four suckers. It contains fleshy rostellum and double crown (row) of well-defined hooks.

2- The neck: it’s the narrowest part of the body and budding zone containing germinative tissue.

3- Immature proglottides: located in the anterior part of the body and inner organs are developing.

4-Mature proglottides are square in shape and located in the mid part of the body and testes, a centrally straight uterus and 3 lobes of ovary.

5-Pregnant (gravid) proglottides are longitudinal rectangle, located in the posterior part of the body and contain a branched uterus filled with eggs. The number of main branches on each side of the uterus stem is 7-13

The eggs of T. saginata & Taenia solium are somewhat roundish. The egg consists of a hexacanth embryo including the standard three pairs hooklets . the embryo is surrounded by a yellow-brown embryophore, upon which resides distinct radial striations.

* Life cycle

The adult worm lives in the intestine of humans. These humans shed the proglottids containing the eggs in their faeces. The eggs are ingested by bovines (T. saginata) or swine (T. solium) where a cysticercus is developed in the muscle. Humans acquire the infection by ingestion of raw beef/pork containing the cysticercus bovis in cattle and cysticerus cellulose in pigs . For T. saginata humans are the final host. This is also true for T. solium but in T. solium humans can also be the intermediate host. This is the stage in which health problems occur for T. solium.


*Clinical signs and pathogenesis

People infected with adult taenia often are asymptomatic.  Infected people may become aware of infection by noticing proglottid segments of the tapeworm  in their feces. Symptoms of infection, if any, are general: nausea, abdominal symptoms such as hunger pains, diarrhea and/or constipation. Increased eosinophils may be a sign of infection.

A more severe form of taeniasis, cystercercosis, can occur upon ingestion of T. solium eggs found in the feces of infected humans.  These eggs hatch in the small intestine and migrate to various tissues of the body and form cysts.  T. saginata rarely causes cystercercosis.

The pathology associated with cystercercosis depends on which organs are infected and the number of cysticerci.  Those that form in voluntary muscle tend to be asymptomatic, but may cause myositis, with accompanying fever and eosinophilia.  On the other hand, a few cysticerci, if located in a particularly "sensitive" area of the body,  For instance, a cysticercus in the eye might lead to blindness, a cysticercus in the spinal cord could lead to paralysis, or a cysticercus in the brain (neurocysticercosis) could lead to traumatic neurological damage.


Taenia eggs and proglottids can be identified though microscopic identification. Microscopic examination of eggs does not distinguish between the two species. Species can be distinguished, however, by examining proglottids. Also, immunological tests can detect the presence of cysticerci and improved imaging techniques such as X-ray can be very useful in detecting cysticerci in various organs.


* Management and Therapy:

The best way to prevent taeniasis is to make sure meat is cooked thoroughly.   Freezing to kills the larvae as well.  As with most cestodes, treatment involves the use of Praziquantel.  Niclosamide is also effective.

For T. solium, extra care and hygiene (such as frequent hand washing) must be used to keep from ingesting eggs and developing cysticerci in the brain.  Surgery, praziquantel, and albendazole can be used to treat cysticerci.





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