Tapeworm infection of the intestine occurs mainly when people eat raw or undercooked contaminated pork, beef, or freshwater fish or, for the dwarf tapeworm, contaminated food or water.
Adult tapeworms, which live in people's intestine, usually cause no symptoms, but they may cause abdominal discomfort, diarrhea, and weight loss.
The pork tapeworm can also form cysts in the brain and elsewhere in the body (called cysticercosis).
Cysts in the brain can cause various symptoms, such as headaches, seizures, confusion, and sometimes severe, life-threatening disease.
Doctors diagnose the infection by finding worm segments or eggs in a stool sample or, for cysts elsewhere in the body, by doing imaging or blood tests.
Thoroughly cooking pork, beef, and freshwater fish can help prevent the infection.
Antiparasitic drugs such as praziquantel may be used to treat infection in the intestine, and albendazole and/or praziquantel plus corticosteroids may be used to relieve symptoms caused by cysts in the brain.
Several species of tapeworms can cause infection in people. They include
Adult tapeworms of other species—Echinococcus granulosus and Echinococcus multilocularis (dog tapeworms)—live in the intestine of dogs or other canines. These tapeworms sometimes infect people, causing cysts in the liver or other organs.
The pork, beef, and fish tapeworms are large, flat worms that live in the intestine of people and can grow 15 to 30 feet in length. (People are considered the definitive host because tapeworms mate in them.) Egg-bearing sections of the worm (proglottids) are passed in the stool (feces).
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 freshwater 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 wall of the intestine. The worms then grow in length and begin producing eggs.
Life Cycle of the Pork Tapeworm
Dwarf tapeworms are small, only up to 2 inches (40 millimeters) long. People become infected with dwarf tapeworms by consuming tapeworm eggs, rather than cysts, as occurs in pork and beef tapeworm infection. The eggs may be consumed in food or water contaminated by human stool or may be transferred to the mouth after contact with infected people. Sometimes people accidentally consume infected insects, such as fleas and beetles, in grains.
The eggs develop into adults that live in the intestine. The adult tapeworms lay eggs that are passed in stool. The eggs may be consumed by another person or by the same person, resulting in infection with a new generation of adult tapeworms.
For the pork tapeworm only, people who ingest the eggs can become an intermediate host (people cannot be intermediate hosts for the beef and fish tapeworms). People may become an intermediate host when one of the following occurs:
They swallow the pork tapeworm eggs in food or water contaminated with human stool.
They transfer the eggs to their mouth after contact with an infected person or with contaminated clothing and furniture.
People with an adult worm in their intestine may reinfect themselves when they swallow eggs from their stool (for example, in contaminated food or water) or possibly when egg-bearing segments of the worm (proglottids) move from their intestine into the stomach and release eggs.
As in animal intermediate hosts, the eggs develop into spheres containing larvae (oncospheres) when they reach the intestine. The spheres penetrate the intestinal wall and travel to the brain, muscles, other organs, or tissue under the skin, where they form cysts. In people, this form of the disease is called cysticercosis.
Although tapeworms in the intestine usually cause no symptoms, some people experience upper abdominal discomfort, diarrhea, and other symptoms. 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 dwarf tapeworm is more likely than other tapeworms to cause abdominal symptoms such as nausea, vomiting, diarrhea, abdominal discomfort, loss of appetite, and weight loss.
The fish tapeworm can cause anemia because it absorbs vitamin B12, which is necessary for red blood cells to mature.
Cysticercosis symptoms are caused by cysts that form in the brain and other organs (such as the spinal cord, liver, lungs, and eyes). These cysts can cause severe, sometimes life-threatening symptoms years after the initial infection, when the cysts start to deteriorate. Cysts in the brain and the tissues covering the brain (meninges) 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. (Antibodies are proteins produced by the immune system to help defend the body against attack, including that by parasites.)
The first line of defense against tapeworms is
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
Cysts are visible in infected meat.
Adequate treatment of human waste interrupts the life cycle and thus helps prevent cysticercosis and dwarf tapeworm infection.
Dwarf tapeworm infection can also be prevented by avoiding the following:
For example, when traveling in countries where food is likely to be contaminated, people should wash, peel, and/or cook all raw vegetables and fruits with safe water before eating.
A person with an intestinal tapeworm is treated with a single oral dose of praziquantel. For dwarf tapeworm infection, nitazoxanide may be used instead.
Cysticercosis treatment depends on various factors, such as symptoms and the number and location of cysts in the brain.
Cysticercosis is usually not treated unless it involves the brain. Then, antiparasitic drugs (such as albendazole or praziquantel) and corticosteroids (such as prednisone) may be given. Corticosteroids are also given to people with symptoms to reduce inflammation. Antiparasitic drugs are not used to treat cysts in the eye or spinal cord because they can trigger severe inflammation that can damage nearby tissues.
Occasionally, surgery is necessary—for example, when cysts are blocking the flow of fluid that surrounds the brain and spinal cord (cerebrospinal fluid) or when cysts are causing problems in the spinal cord or eye.
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