Trichinosis

The life cycle of Trichinella spiralis includes several different stages. The adult worm lives in the intestinal lining of such carnivorous animals as swine, bears, walrus, and rodents. After mating, the male worm dies, while the female worm goes on to develop the offspring.

The embryonic stage, a stage often occurring after birth in many nematode species, occurs within the uterus of the female T. spiralis, so that the offspring which are ultimately discharged from the female are in the larval second stage of life. These larvae (about 1500 from each female worm) travel through the circulatory system, to the heart, then through the blood vessels leading to striated muscle (the muscle of the skeletal system and the heart). Any larvae not arriving in striated muscle will die.

Those larvae that reach striated muscle will grow to a length of about one millimeter, coil, and enclose themselves within a protective wall called a cyst. These cysts continue to live for up to 10 years in this form.