Cestodes
Tape-like endoparasites
Cestodes, or tapeworms, owe their name to the flat, tape-like shape of their bodies. They parasitise the small intestine of the final host. Nutrients are absorbed through the surface of the body.
The body of the tapeworm consists of a head portion (scolex), which is designed as an attachment organ; a non-segmented neck region; and a constantly regenerating series of segments (proglottids). The entire chain of segments (strobila) can be up to several meters long, although some tapeworm species are only a few millimeters in length. Each proglottid is an independently functioning unit.
Cestodes are hermaphrodites
Almost all tapeworm species are hermaphrodites, each proglottid having its own complete set of male and female reproductive organs. In its mature state, full of eggs, the entire proglottid separates from the worm. The neck region constantly generates new segments to replace the mature proglottids that have been shed. Both in their fully grown (adult) form and in their larval (cystic) form, tapeworms pose a threat to the health not only of companion animals but also of humans.
Cestodes life cycle and infestation
Their life cycle involves one or more intermediate hosts. If the intermediate host is a mammal - and this may include man as an accidental host - the hooked larva penetrates the gut wall and is distributed throughout the body via the blood and the Iymph system. In certain organs (sites of predilection) of the intermediate host it develops into an infective cyst. This cyst, which already contains a rudimentary scolex, may then for example be ingested with the raw flesh of the intermediate host by the final host (dog, cat). In the intestinal tract of the final host the scolex becomes exposed and attaches itself to the intestinal mucosa, where the tapeworm develops into the adult form.