Trichinella sp. life cycle. Trichinella sp. life cycle. (A) Main sources of Trichinella sp. infections for humans (including pigs, horses, wild boars, dogs, walruses, foxes, and bears). (B) Trichinella sp. cycle in the host body. In the enteral phase, muscle tissues are digested in the stomach, and larvae are released (1); larvae penetrate the intestinal mucosa of the small intestine and reach the adult stage within 48 h p.i., and male and female mate (2); female worm releases newborn larvae in the lymphatic vessels (from the fifth day p.i. onwards; the length of newborn production, from 1 week to several weeks, is under the influence of host immunity) (3). In the parenteral phase, the newborn larvae reach the striated muscle and actively penetrate in the muscle cell (4); the larva grow to the infective stage in the nurse cell (the former muscle cell) (5); and, after a period of time (weeks, months, or years), a calcification process occurs (6). (Modified from www.iss.it/site/Trichinella/index.asp with permission of the publisher.)‏ Bruno Gottstein et al. Clin. Microbiol. Rev. 2009; doi:10.1128/CMR.00026-08