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Any of the species of flatworms of the class Cestoda, phylum Platyhelminthes, which are intestinal parasites of humans and other animals. A typical tapeworm consists of a scolex, with hooks and suckers for attachment, and a series of a few to several thousand segments, or proglottids. New proglottids develop at the scolex, so that a worm is actually a linear colony of immature, mature, and gravid proglottids; adult worms range from less than an inch to 50 ft or more, depending on the species. The terminal proglottids, which contain fertilized eggs, break off and pass from the host in the feces. The eggs develop into small, hooked embryos, which, when ingested by the proper intermediate host (usually another vertebrate such as a pig), develop into encysted larvae (cysticerci) in the muscle tissue. Humans acquire tapeworm infestation by eating undercooked meat that contains the cysticerci.
SEE: Diphyllobothrium latum for illus; SEE: Taenia
Species of medical importance are Diphyllobothrium latum, Echinococcus granulosus, Hymenolepis nana, Taenia saginata, and T. solium.
SEE: cysticercosis; SEE: cysticercus; SEE: hydatid; SEE: taeniasis

Symptoms are often absent, but abdominal discomfort, bloating, or changes in bowel habits may be present. If tapeworms are very numerous, they may cause intestinal obstruction (but this is rare). Some species of tapeworms may cause severe disease: Echinococcus can cause life-threatening cysts in the liver or pericardium; Taenia solium can encyst in the brain and cause seizures or strokelike symptoms.

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