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Trichinella spiralis life cycle.

1. Animals that are fed (eg, pigs) or eat (eg, bears, foxes, boars) other animals acquire trichinosis by ingesting meat containing cysts (encysted larvae) of Trichinella sp. Humans may be accidentally infected when they eat raw, undercooked, or underprocessed meat from infected animals. 2. After exposure to gastric acid and pepsin, the larvae are released from the cysts in the small intestine and penetrate the mucosa. 3. There, they develop into adult worms. 4. After 1 wk, the females release larvae that migrate to the striated muscles where they encyst. The cycle continues only if encysted larvae are ingested by another carnivore.

Image from the Centers for Disease Control and Prevention Image Library.