Tapeworm Infection
Tapeworm infection is an intestinal disease caused by one of several species of tapeworms, including Taenia saginata (beef tapeworm), Taenia solium (pork tapeworm), and Diphyllobothrium latum (fish tapeworm).
 See the figure A Beef Tapeworm.
Tapeworms are large, flat worms that live in the intestine and can grow 15 to 30 feet in length. Egg-bearing sections of the worm (proglottids) are passed in the stool. If untreated human waste is released into the environment, the eggs may be ingested by intermediate hosts, such as pigs, cattle, or (in the case of fish tapeworms) small crustaceans, which are in turn ingested by fish. The eggs hatch in the intermediate host, then the larvae invade the intestinal wall and are carried through the bloodstream to skeletal muscle and other tissues, where they form cysts. People acquire the parasite by eating the cysts in raw or undercooked meat or fish. The cysts hatch and develop into adult worms, which latch onto the person's intestinal wall. The worms then grow in length.
People may also act as an intermediate host for the pork tapeworm, Taenia solium. Pork tapeworm eggs reach the stomach when a person swallows them in food or water contaminated with human feces or from contact with the unclean hands of a person infected with adult worms. The eggs may also reach the stomach when proglottids are regurgitated from the intestine. Once the larvae are released, they penetrate the intestinal wall and travel to muscles, internal organs, the brain (see Section 6, Chapter 89), or tissue under the skin, where they form cysts (cysticerci). This form of the disease is called cysticercosis.
Symptoms and Diagnosis
Although tapeworms in the intestine usually cause no symptoms, some people experience upper abdominal discomfort, diarrhea, and loss of appetite. Occasionally, a person with tapeworms may feel a piece of the worm move out through the anus. Rarely, tapeworms acquired from fish cause anemia.
Cysts in the brain and meninges (the tissues covering the brain) in people with cysticercosis may cause inflammation, resulting in headache, confusion, other neurologic symptoms, and commonly, seizures.
A doctor diagnoses intestinal tapeworm infection by finding worm segments or eggs in a stool sample. Cysticercosis is more difficult to diagnose; however, cysts in the brain can be seen with computed tomography (CT) or magnetic resonance imaging (MRI) scanning. Blood tests for antibodies to the pork tapeworm also are helpful.
Prevention and Treatment
The first line of defense against tapeworms is careful evaluation of meat and fish by trained inspectors. Cysts are visible in infected meat. Thorough cooking (such that all meat reaches more than 135° F) and prolonged freezing will kill cysts. For this reason, freshwater fish should not be served as sushi, and should only be eaten after it has been cooked, frozen, or cured. Smoking and drying do not kill cysts.
A person with tapeworms is treated with a single oral dose of praziquantel. Cysticercosis is usually not treated unless it involves the brain, in which case antiparasitic drugs (such as albendazole or praziquantel) may be given along with corticosteroids, which help reduce inflammation.
| 
