Tapeworm infection of the intestine occurs when people eat raw, contaminated pork, beef, or freshwater fish.
Several species of tapeworms, such as Taenia saginata (beef tapeworm), Taenia solium (pork tapeworm), and Diphyllobothrium latum (fish tapeworm), can cause infection in people.
The pork and beef 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 into larvae in the intermediate host. 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 certain types of freshwater fish. The cysts hatch and develop into adult worms, which latch onto the intestinal wall. The worms then grow in length and begin producing eggs.
For the pork tapeworm only, people who ingest the eggs can become an intermediate host (people cannot be intermediate hosts for other tapeworms). They may swallow the pork tapeworm eggs in food or water contaminated with human feces, or they may transfer the eggs to their mouth after contact with an infected person or with contaminated clothing and furniture. Or eggs may reach the stomach if proglottids are regurgitated from the intestine. As in animal intermediate hosts, the eggs develop into larvae. The larvae penetrate the intestinal wall and travel to the brain (see see Parasitic Brain Infections), muscles, other organs, or tissue under the skin, where they form cysts (cysticerci). In people, 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, people with a tapeworm can feel a piece of the worm move out through the anus or see part of the ribbon-like tapeworm in stool. The fish tapeworm can cause anemia because it absorbs vitamin B12, which is necessary for red blood cells to mature.
Cysts in the brain and the tissues covering the brain (meninges) in people with cysticercosis can result in headaches, seizures, confusion, or other neurologic symptoms. Rarely, cysts develop in the eyes, sometimes causing blindness, or in the spinal cord, sometimes causing muscle weakness or paralysis.
A doctor diagnoses intestinal tapeworm infection by finding worm segments or eggs in a stool sample. In people with cysticercosis, cysts in the brain or other tissues can be seen using computed tomography (CT) or magnetic resonance imaging (MRI). Blood tests for antibodies to the pork tapeworm may also be helpful.
Prevention and Treatment
The first line of defense against tapeworms is thoroughly cooking meat and freshwater fish to a temperature of more than 135° F (57° C). Prolonged freezing can also kill cysts. Thus, freshwater fish should not be served as sushi and should be eaten only after it has been cooked, properly frozen, or cured in brine. Smoking and drying do not kill cysts. Another line of defense is careful evaluation of meat and fish by trained inspectors. Cysts are visible in infected meat. Adequate treatment of human waste interrupts the life cycle and thus helps prevent cysticercosis.
A person with an intestinal tapeworm is treated with a single oral dose of praziquantel. Cysticercosis is usually not treated unless it involves the brain. If the infected person has symptoms, corticosteroids such as prednisone are given to reduce inflammation.
Depending on various factors, such as symptoms and the number and location of cysts in the brain, antiparasitic drugs (such as albendazole or praziquantel) and corticosteroids may be given. These drugs are not used to treat cysts in the eye or spinal cord because they can trigger severe inflammation that can damage nearby tissues.
Last full review/revision March 2007 by Richard D. Pearson, MD