Transmission is through ingestion of uncooked or undercooked meat that contains T. spiralis cysts. Such cysts are found primarily in swine and less commonly in dogs, cats, bears, foxes, wolves, and marine animals. These cysts result from the animals’ ingestion of similarly contaminated flesh. In swine, infection results from eating table scraps or garbage consisting of raw food.

After gastric juices free the worm from the cyst capsule, the worm reaches sexual maturity within a few days. The female roundworm burrows into the intestinal mucosa and reproduces. Larvae are then transported through the lymphatic system and bloodstream and become embedded as cysts in striated muscle. The muscles most commonly invaded are the extraocular muscles of the eye; the tongue; the deltoid, pectoral, and intercostal muscles; the diaphragm; and the gastrocnemius muscle. Human-to-human transmission doesn’t take place.

Although common worldwide, trichinosis is seldom seen in the United States because of regulations regarding animal feed and meat processing.

Trichinosis can cause such complications as encephalitis, myocarditis, pneumonia, and respiratory failure. Death is rare but may occur 2 to 8 weeks after infection.

The patient’s history may reveal ingestion of uncooked or undercooked meat, especially pork. When symptoms do occur, they vary with the stage and degree of infection: