Trichinosis
Trichinosis is infection caused by the roundworm Trichinella spiralis.
Trichinella larvae live in the muscle tissue of animals, typically pigs, wild bears, horses, and many carnivores. People develop trichinosis if they eat uncooked or poorly cooked meat from an animal that carries the parasite. Most human infections result from pork, particularly in regions where pigs are fed uncooked meat scraps and garbage. 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. The male worms play no further role in illness. 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, after which the female worm dies. The tiny larvae are carried through the body by the lymphatic vessels and bloodstream. The larvae penetrate muscles, causing inflammation. By the end of the third month, they form cysts.
Certain muscles, such as those in the tongue and around the eyes, and between the ribs, are most often infected. Larvae that reach the heart muscle are usually killed by the intense inflammatory reaction they provoke.
Symptoms
The symptoms of trichinosis vary, depending on the number of invading larvae, the tissues invaded, and the general physical condition of the person. Many people have no symptoms at all. Sometimes, diarrhea, abdominal cramps, and a slight fever begin 1 to 2 days after eating contaminated meat. However, symptoms from the larval invasion usually do not start for 7 to 15 days.
The main symptoms of trichinosis are muscle pain, weakness, fever, muscle soreness, and swelling of the upper eyelids. The soreness is often most pronounced in the muscles used to breathe, speak, chew, and swallow. A non-itchy skin rash may occur, and some people develop diarrhea. Some people develop redness in the whites of the eyes, pain in the eyes, and sensitivity to bright light. 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.
Diagnosis
Unlike most other worm infections, trichinosis cannot be diagnosed by microscopic examination of the stool. Blood tests for antibodies to Trichinella are fairly reliable but only when performed 2 to 3 weeks after the start of the disease. A doctor bases an initial diagnosis of trichinosis on the symptoms and the presence of elevated levels of eosinophils (a type of white blood cell) in a blood sample. A biopsy of muscle tissue (in which a sample of tissue is removed and examined under a microscope), performed after the fourth week of infection, may reveal larvae or cysts, but it is seldom necessary.
Prevention and Treatment
Trichinosis is prevented by thoroughly cooking (to a temperature of more than 140° F) meats, especially pork and pork products. Alternatively, larvae can usually be killed by freezing meat at 5° F for 3 weeks or at -4° F for 1 day. Larvae of worms that infect arctic mammals are able to survive these temperatures.
Oral doses of mebendazole or albendazole are effective against the parasite. Bed rest and analgesics help relieve muscle pain. Corticosteroids (such as prednisone) may be prescribed to reduce inflammation of the heart or brain. Most people with trichinosis recover fully.
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