cestodiasis, infestation with cestodes, a group of flattened and tapelike hermaphroditic worms that are intestinal parasites in humans and other animals, producing larvae that may invade body tissues.
For humans there are two kinds of tapeworm infestations: (1) intestinal cestodiasis, in which the mature worm lives in the lumen of the intestine, producing eggs that are evacuated in the feces and develop further in other animal hosts, and (2) visceral and somatic cestodiasis, in which the larvae form lesions in body organs. Various species of tapeworms cause intestinal cestodiasis in humans. The more common ones include the following: Taenia saginata, or beef tapeworm, about 4.5 to 6 metres (15 to 20 feet) long; T. solium, or pork tapeworm, about 2 to 3 metres long; and Diphyllobothrium latum, or fish tapeworm, about 9 metres long—the largest parasite that can infect humans—acquired by eating undercooked beef, pork, or fish that harbour larval forms of the worms.
Hymenolepis nana, or dwarf tapeworm, only a few centimetres long, releases eggs that require no intermediate hosts. It is possibly the most common cestode found in humans, affecting chiefly children. Symptoms of intestinal cestodiasis include abdominal pain that may be relieved by eating and that may be associated with distention, flatulence, and nausea. Often, however, there are no symptoms, and first notice of infestation may occur only when segments of the worms are passed in the stools. Treatment may involve surgery or the use of antiparasitic drugs.
Visceral and somatic cestodiasis include the following infections: (1) Echinococcosis, or hydatic disease, is caused by the larval stage of Echinoccocus granulosus or E. multilocularis. In humans the first organism produces cystic, slowly expanding lesions principally involving the liver and lungs; the second organism produces an alveolar (pitted) type of lesion that progresses rapidly, may occasionally form lesions in the brain and bones, and is invariably fatal. The symptoms of echinococcosis are generally those of a slowly growing tumour and vary depending on the body structure involved. The adult worm lives mainly in dogs, and human infestation is contracted by the ingestion of eggs present in dog excreta. Surgical removal of the lesions is the only cure. (2) Sparganosis is caused by the Spirometra mansoni larva, which may be acquired by drinking water that contains water fleas harbouring the first larval stage. The larvae may grow to a length of 30 cm (12 inches) in the abdominal wall or in the region of the eye socket; surgical removal of the larva is the current treatment.