cestode

Cestodes are parasitic flatworms in the phylum Platyhelminthes, commonly known as tapeworms. They are endoparasites of vertebrates and inhabit the small intestine of their definitive hosts. Cestodes lack a mouth and digestive tract, absorbing nutrients across a syncytial tegument. Their body plan consists of a scolex for attachment, followed by a strobila made of numerous proglottids that contain the reproductive organs.

Life cycles typically involve an intermediate host. Gravid proglottids release eggs in feces; upon ingestion by an intermediate host, the eggs hatch into larvae that form cysticerci or hydatid cysts in tissues. When a definitive host eats the intermediate host, the larvae develop into adults in the intestines, completing the cycle. Humans can become accidental definitive or intermediate hosts depending on the species.

Several genera are of medical importance. Taenia saginata (beef tapeworm) and Taenia solium (pork tapeworm) infect humans through undercooked meat; Dipylidium caninum is common in dogs and cats; Echinococcus granulosus and E. multilocularis cause hydatid disease and alveolar echinococcosis, usually via contact with definitive hosts. Clinical presentation ranges from mild digestive symptoms to tissue cysts, notably neurocysticercosis with T. solium eggs.

Diagnosis relies on stool examination for eggs and proglottids, supported by imaging or serology when tissue infection is suspected. Treatment typically uses praziquantel or albendazole; hydatid disease may require surgical management. Prevention focuses on proper cooking of meat, good hygiene, and controlling animal hosts to reduce transmission.