Friday, April 25, 2008

Tapeworm

A tapeworm is a ribbonlike colony of parasitic flatworms, of the class Cestoda, that infest humans and other vertebrate animals. Species that most commonly infest humans are the beef tapeworm, Taenia saginata, the pork tapeworm, T. sollium and the fish tapeworm, Dibothriocephalus latus.

The tapeworm head (scolex) has hooks or suckers used to attack the parasite to the host’s intestinal lining. The “body” is composed of segments (proglottids) which are separate, sexually functional individuals that can synchronize their muscular activity to keep the colony mobile.

An addult pork tapeworm lives in the intestines of humans, folding itself in accordion style to fit its long body into small spaces. A pork tapeworm, which grows up to 10 m (33 ft) long, can live in the small intestine, which is 6 m (20 ft) long. Humans get tapeworms by eating poorly cooked pork that is infested with tapeworm eggs.

Younger proglottids have testes; are the worm get older, the testes shrivel up and are replaced by ovaries and a uterus. Proglottids having male sex organs release sperm that travel to the older proglottids and fertilize the eggs.

Proglottids that contain developing embryos break away and are excreted with feces. Larvae develop and, if the waste matter is eaten by an animal, become dormant and encrysted in the animals muscle tissue. Humans eating poorly cooked animal meat can then ingest the encrysted larvae. Adult tapeworm infestations can be eliminated with chemotherapy. Humans, however, can also serve as intermediary hosts, the larvae forming cyst up to 25 cm (10 in) in diameter in the brain, lungs, liver, or other organs. Such infection can only be treated surgically, if at all.
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