Tapeworms (cestodes) are flat, hermaphroditic worms that can live as parasites in the human gastrointestinal tract. Some of these organisms are primarily human pathogens, while others have animals as their natural hosts but can also cause human infection.
Taeniasis, Diphyllobothriasis, Hymenolepiasis, and Dipylidiasis will be reviewed here. Ingestion of the eggs of Taenia solium causes cysticercosis, a tapeworm infection that is discussed separately. (See "Epidemiology, transmission and prevention of cysticercosis" and "Clinical manifestations and diagnosis of cysticercosis" and "Treatment of cysticercosis".)
Adult tapeworms consist of a head, neck, and segmented body. The head (also known as a scolex) is equipped with suckers, hooks, or grooves (depending upon the species); the worm uses these to attach itself to the intestine of the host.
Each segment (known as a proglottid) has a complete set of reproductive organs. Depending on the species, the adult worm may have hundreds or thousands of proglottids. In some species (such as Taenia), the distal segments can separate from the rest of the body and the proglottids (or the eggs they contain) are passed in the stool. In other species (such as Hymenolepis), proglottids degenerate within the host so only eggs are found in the stool.
Tapeworms are covered with a tegument through which they absorb nutrients and secrete waste. Different species of tapeworms can be differentiated by morphologic characteristics of the scolex, proglottids, and eggs .