Medical Edge Newspaper Column

What's Cooking with Trichinosis?

April 30, 2007
Dear Mayo Clinic:
Is there a test to determine if one has trichinosis? How do you get it, and what are the effects? What can be done to cure it? -- Wheeling, Ill.

Answer:
Trichinosis is an infection caused by Trichinella -- a type of parasitic roundworm found in uncooked or undercooked meat from pigs, horses, and certain wild animals such as boars and bears. In nature, carnivores get trichinosis when they feed on other infected animals. Domesticated pigs and horses acquire it when they eat garbage that contains infected meat scraps. Given increased regulation of animal feed and products, however, pigs and horses are now infrequent sources of trichinosis. The most common cause in the United States is now considered to be bear meat.

Humans are affected when they eat meat containing viable Trichinella, which enter the body as larvae encased in cysts. The stomach's digestive juices dissolve the cysts, and the larvae then penetrate the wall of the small intestine, where they mature into adult worms, mate, and release newborn larvae. The larvae migrate via the circulation system to muscle tissue, where they become encysted.

Symptoms of trichinosis depend on the number of larvae ingested. Small quantities produce few if any symptoms. A larger amount may initially cause abdominal pain, diarrhea and nausea, followed by swelling around the eyes, muscle pains and weakness. Severe infections can also cause fever, headache and difficulty breathing. After a few weeks, the symptoms usually subside. Long-term effects are uncommon, as the larvae eventually die.

A blood test is the main laboratory measure for diagnosing trichinosis. The test detects specific antibodies, which the body produces in response to the infection. An elevated count of eosinophils -- a type of white blood cell -- may also be an indicator of trichinosis or other parasitic infections, because these cells are deployed to fight them.

If the Trichinella infection is discovered early, in the intestinal phase, the anti-parasitic medications albendazole (Albenza) or mebendazole (Vermox) can be effective in eliminating the worms and larvae. If the infection is discovered after the muscle-invasion stage, these drugs are no longer effective. The infection must then run its course, though symptomatic relief -- pain relievers for muscle aches and corticosteroids to control inflammation -- is available.

Infection can be avoided by consuming meat that has been adequately cooked (to an internal temperature of 150 degrees F), irradiated or frozen (to 5 degrees F for three weeks); all of these processes kill Trichinella larvae. One should also be aware that smoking or pickling the meat will not kill them. Fortunately, trichinosis is rare in the United States, with fewer than 100 cases reported annually.

-- William F. Marshall, M.D., Infectious Diseases, Mayo Clinic, Rochester, Minn.