Answer to Case of the Week 59
Answer, Part I: Trichinella spp. Although Trichinella spiralis is the most common species to infect humans in the United States, it is generally not possible to speciate based on morphologic features. The exception is Trichinella pseudospiralis whose larvae are not encapsulated compared to T. spiralis, T. nativa, T. nelsoni, T. britovi, and T. murrelli which do have encapsulated larvae. These species are the predominant to infect humans.
Answer, Part II: What is the most common source of infection worldwide? Domestic pigs. What about in the United States? Wild game
According to a publication by the Centers for Disease Control and Prevention (Roy et al.”Trichinellosis Surveillance — United States, 1997–2001.” Centers for Disease Control and Prevention), trichinellosis has been steadily decreasing in the United States due to tightened regulations on pig farming and pork processing. They state:
Although trichinellosis was associated historically with eating Trichinella-infected pork from domesticated sources, wild game meat was the most common source of infection during 1997–2001. During this 5-year period, 72 cases were reported to CDC. Of these, 31 (43%) cases were associated with eating wild game: 29 with bear meat, one with cougar meat, and one with wild boar meat. In comparison, only 12 (17%) cases were associated with eating commercial pork products, including four cases traced to a foreign source. Nine (13%) cases were associated with eating noncommercial pork from home-raised or direct-from-farm swine where U.S. commercial pork production industry standards and regulations do not apply.



