| Description |
Trichinella spiralis is a nematode that is found throughout the world. Infection in humans occurs by eating raw or undercooked pork (and, less frequently, horse, bear, wild boar, and cougar meat) containing encysted larvae. After being released from the muscle fibers of the ingested meat, the larvae migrate tothe stomach, where acid pepsin digestion dissolves their capsules within a few hours. They then pass into the small intestine, where they invade the intestinal mucosa at the bases of the villi. They subsequently mature rapidly intobo th male and female adult worms. The worms copulate, after which the males die and are eliminated in the feces. The female worms remain buried in the mucosa where, 57 days after mating, they each deposit 10005000 larvae in the mucosa over a period of 26 weeks, following which the females die and are expelled in the feces. The motile larvae subsequently penetrate the intestinal wall and pass intothe lymphatic vessels and lymph nodes, from which they are carried to the thoracic duct, where they enter the blood stream, pass through the right side of the heart and the lungs into the arterial circulation, and are distributed to skeletal muscle and to various organs throughout the body. They burrow into individual muscle fibers, gradually increase 10 times in length, coil, and become encysted. The heaviest infiltrations of muscles, which begin 23 weeks after infection, are in the diaphragm, intercostal, masseter, biceps, gastrocnemius, and extraocular muscles. The process is completed within 3 months, following which the encysted larvae eventually calcify. No further development occurs unless the infected muscle is eaten by another mammal. |
