Trichinosis is infection caused by the roundworm Trichinella spiralis. Symptoms include diarrhea, abdominal cramps, muscle pain, and fever.
Trichinella larvae live in the muscle tissue of animals, typically pigs, wild bears, walruses, horses, and many carnivores. People develop trichinosis if they eat uncooked or poorly cooked meat from an animal that carries the parasite. In most people, infections result from eating pork, particularly in regions where pigs are fed uncooked meat scraps and garbage, or eating meat from wild boar, bear, or walrus. Trichinosis is now rare in the United States.
When a person eats meat containing live Trichinella cysts, the cyst wall is digested, releasing larvae that quickly mature to adulthood and mate in the intestine. After the male worms mate, they die and thus play no further role in infection. The females burrow into the intestinal wall and, by the seventh day, begin to produce larvae.
Production of larvae continues for about 4 to 6 weeks. Then, the female worm dies or is excreted from the body. The larvae are carried through the body through the lymphatic vessels and bloodstream. The larvae penetrate muscles, causing inflammation. In 1 to 2 months, they form cysts that can live for years in the body.
Certain muscles, such as those in the tongue, around the eyes, and between the ribs, are most often infected. Larvae that reach the heart muscle are often killed by the intense inflammatory reaction they provoke.
Symptoms vary, depending on the stage of infection, number of invading larvae, tissues invaded, and general physical condition of the person. Many people have no symptoms. Symptoms occur in two stages.
If many larvae are present, the heart, brain, and lungs may become inflamed. Heart failure, abnormal heart rhythms, seizures, and severe breathing problems may result. Death can occur but is rare.
Without treatment, most symptoms disappear by the third month of infection, although vague muscle pain and fatigue can persist longer.
Unlike most other worm infections, trichinosis cannot be diagnosed by microscopic examination of the stool. Blood tests for antibodies to Trichinella spiralis are fairly reliable, but they are not positive until 2 to 3 weeks after symptoms start. If the results are negative, a doctor usually bases an initial diagnosis of trichinosis on symptoms and the presence of elevated levels of eosinophils (a type of white blood cell) in a blood sample. The antibody test is repeated several weeks later to confirm the diagnosis. A biopsy of muscle tissue (in which a sample of tissue is removed and examined under a microscope), done after the second week of infection, may reveal larvae or cysts but is seldom necessary.
Prevention and Treatment
Trichinosis is prevented by thoroughly cooking meats, especially pork and pork products, to a temperature of 160° F (71° C). Alternatively, larvae can usually be killed by freezing meat at 5° F (-15° C) for 3 weeks or at -20° F (-29° C) for 6 days. However, larvae of worms that infect arctic mammals can survive these temperatures. Smoking or salting does not reliably kill the larvae. Also, pigs should not be fed uncooked meat products.
Mebendazole or albendazole, taken by mouth, eliminates the worms from the intestine but has little effect on the cysts in muscle. Bed rest and analgesics help relieve muscle pain. Corticosteroids (such as prednisone) may be prescribed to reduce inflammation in severe infection. Most people with trichinosis recover fully.
Last full review/revision March 2007 by Richard D. Pearson, MD