Trichinosis is a disease caused by eating meat that has not been thoroughly cooked and contains cysts (larvae, or immature worms) of Trichinella spiralis. Trichinella spiralis can be found in pork, bear, walrus, fox, rat, horse, and lion meat.
Wild animals, especially carnivores (meat eaters) or omnivores (animals that eat both meat and plants), should be considered possible sources of roundworm disease. Domestic meat animals raised specifically for eating under United States Department of Agriculture (government) guidelines and inspection can be considered safe. For this reason, cases of trichinosis are rare in the United States though it is a common infection worldwide.
When a person eats meat from an infected animal, Trichinella cysts break open in the intestine and grow into adult roundworms. The roundworms produce other worms that move through the gut wall and into the bloodstream. The worms invade muscle tissues, including the heart and diaphragm (the breathing muscle under the lungs). They can also infect the lungs and brain. The cysts remain alive for years.