Trichinosis

Alternative names:

trichinellosis; trichiniasis

Definition:

A roundworm (Trichinella spiralis) infestation, usually transmitted by eating raw or undercooked pork or bear meat.

Causes, incidence, and risk factors:

Trichinosis is a parasitic disease that results from eating undercooked meat, most frequently pork, which contains cysts of Trichinella spiralis. It is not an uncommon infection worldwide but is seldom seen in the United States because of regulations regarding the feeding of domestic animals and meat processing inspections.

The muscle of infected animals contain cysts that, when ingested, hatch within the human intestinal tract to produce an adult roundworm. The adult then produces numerous larvae that migrate through the gut wall and bloodstream to muscle tissue, where they form cysts. The cyst form is part of the parasite's life cycle in which the tissue is eaten and the parasite is passed on to the next animal. Humans are an end host for the parasite because T. spiralis encysted in human muscle will never be eaten.

Early symptoms of infestation with T. spiralis are usually gastrointestinal -- cramping and diarrhea can occur. The larvae migrate to muscle, where they cause an inflammatory reaction that produces muscle pain (myalgia). Pain is most notable on movement and in muscles that are constantly in motion (the breathing muscles such as the diaphragm and rib muscles) can be very painful. During migration of the larvae through tissue, the infected person often develops swelling in the face and around the eyes. Larvae can invade the muscle of the heart and cause erratic heart rhythm (arrhythmias) or damage to the heart muscle.

Domestic meat animals (hogs) raised specifically for consumer consumption under USDA guidelines and inspection can be considered safe. Wild animals, especially carnivores or omnivores should be considered as a reservoir for roundworm infestation.