In the past, contaminated pork was the most common source of infection, but today, in the United States at least, most cases are caused by eating feral meat, such as bear or wild boar. Man is particularly susceptible to trichinosis infection. Soon after ingestion, the larvae penetrate the intestinal wall, where copulation and multiplication occur. The next generation of larvae then enter the blood stream, are distributed throughout the body, and finally enter and grow in skeletal muscle. The muscles of the diaphragm, eyes, tongue, chest, shoulders, and calves are often affected.
Laryngeal involvement is uncommon.
In tissue, the larvae elicit an eosinophilic and lymphocytic inflammatory response. The severity of the clinical manifestations depends upon the location and the density of the larvae. The first symptoms occur within two days of ingestion. During the initial stage of infection, diarrhea, nausea, and malaise are common. Some cases are complicated by urticaria, splinter hemorrhages, and angioedema.