Trichinosis - Life Cycle

Life Cycle

The typical life cycle for T. spiralis involves humans, pigs, and rodents. Pigs become infected when they eat infectious cysts in raw meat, often pork or rats (sylvatic cycle). Humans become infected when they eat raw or undercooked infected pork (domestic cycle). After humans ingest the cysts from infected undercooked meat, pepsin and hydrochloric acid help free the larvae in the cysts in the stomach. The larvae then migrate to the small intestine, where they molt four times before becoming adults.

Thirty to 34 hours after the cysts were originally ingested, the adults mate, and within five days produce larvae. The worms can only reproduce for a limited time because the immune system will eventually expel them from the small intestine. The larvae then use their piercing mouthpart, called the "stylet", to pass through the intestinal mucosa and enter the lymphatic vessels, and then enter the bloodstream.

The larvae travel by capillaries to various organs, such as the retina, myocardium, or lymph nodes; however, only larvae that migrate to skeletal muscle cells survive and encyst. The larval host cell becomes a nurse cell in which the larvae will be encapsulated. The development of a capillary network around the nurse cell completes encystation of the larvae.