cestod

Cestoda, commonly called tapeworms, are a class of endoparasitic flatworms within the phylum Platyhelminthes. They are elongated, ribbon-like worms composed of a scolex for attachment and a succession of proglottids that form a continuous body called the strobila. The scolex bears attachment organs, such as suckers and, in some species, rostellar hooks. Cestodes lack a true digestive system; nutrients are absorbed directly through the tegument from the host’s intestinal contents.

Most cestodes are intestinal parasites of vertebrates, including humans. They are hermaphroditic, with each proglottid containing male and female reproductive organs. As proglottids mature, they become gravid and eventually detach to pass eggs into the environment. In many species, development involves one or more intermediate hosts, in which larval stages form in tissues before being transmitted to a definitive host that harbors the adult worm in the intestine.

A typical life cycle begins with eggs or gravid proglottids released in the feces of the definitive host. An intermediate host ingests these eggs or larvae, and within its tissues larval forms such as cysticerci or hydatid cysts develop. The cycle is completed when the definitive host acquires the parasite by eating tissue containing infective larvae, or, in some species, by ingesting eggs that subsequently establish in the intestine.

Human infections are caused by several species, most notably Taenia saginata (beef tapeworm), Taenia solium (pork tapeworm), and Diphyllobothrium latum (fish tapeworm). Echinococcus species cause hydatid disease. Diagnosis typically involves stool examination for eggs or proglottids, supported by imaging or serology for cystic disease. Treatments include praziquantel or albendazole; larger cystic lesions may require surgical or percutaneous intervention.