These small (2-3 mm long) nematodes infect a variety of mammals in all parts of the world. They are unusual in that each individual host first serves as the definitive host, where the adult parasites develop and mate, and then becomes an intermediate host as larvae accumulate in its tissues. Trichinosis can produce a range of symptoms depending on the number of parasites that initiate the infection, but in serious cases infected muscle tissue can harbor tens of thousands of infective larvae (each almost 1 mm long) per gram, and death can result.