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- Trichinosis occurs with ingestion of undercooked meat contaminated with infective larvae of Trichinella spp.
- 7 species of roundworms from the genus Trichinella cause human disease: T. spiralis (most common), T. nativa, T. nelsoni, T. britovi, T. pseudospiralis, T. murelli, T. papuae.
- Species differ in infectivity for humans, host reservoirs, pathogenicity and resistance to freezing.
- Epidemiology: worldwide.
- From 1986-2009, there were 65,818 reported cases across 41 countries.
- Life cycle:
- Undercooked meat containing encysted larvae is eaten.
- Larvae are released from the cysts with exposure to gastric acid and pepsin.
- Larvae invade the small bowel mucosa, where they mature into adults.
- Adult females release larvae that migrate to striated muscle where they encyst and may remain infective for years.
- Adult worms are 1.5 x 0.05mm (male) and 3.5 x 0.06mm (females).
- Carnivorous animals keep the life cycle going by feeding on infected rodents or meat from other animals.
- Common hosts: pigs (most common source for human infection worldwide, but most U.S. swine fed grains and therefore uninfected), bears (most common source in U.S.), foxes, birds, horses, hyenas, lions, and panthers.