Trichinella species are nematodes infecting the striated muscle of warm-blooded animals, and infection occurs by consumption of raw or insufficiently cooked infected meat. Most human infections are associated with undercooked pork, although horsemeat and wild carnivorous game, such as bear and walrus meat, may also be sources of infection.1 The disease occurs worldwide in both high- and low-income regions, with outbreaks reported in the United States, Mexico, Southeast Asia, and Europe. Because of the mode of transmission, disease is relatively uncommon in predominantly Moslem and Hindu countries where pork is rarely eaten. Most cases are linked to common source outbreaks from contaminated meat. Pork or pork products account for 75% to 80% of infections. In the United States, trichinosis is most commonly diagnosed in far northern Native Americans, such as the Inuits, who acquire infection with Trichinella nativa from walrus meat or meat from other sea mammals. In this group, intestinal symptoms are the predominant clinical manifestations.

While the worldwide prevalence of trichinosis appeared to decline in the 1970s and 1980s, from 1990 on there has been a resurgence of this disease in both developed and developing countries.2 This increase has been attributed both to the mass marketing of meat products, increasing the population at risk from single source outbreaks, and to the growing proportion of outbreaks attributed to sylvatic (wild animal–associated) Trichinella species, either through consumption of wild game or spillover to domestic animals. The disease is naturally perpetuated by cannibalistic rats consumed by higher carnivores, and the practice of feeding pigs garbage containing infected meat maintains the infection in pigs.

Also of note is the economic impact of trichinosis, which is significant due to the cost of meat inspections designed to control the disease. In 1998 to 1999, the European Union spent approximately $570 million yearly to inspect nearly 200 million pigs slaughtered annually, and the United States spends approximately$1 billion annually for regulatory activities to control infection in pigs and pork products.

When undercooked meat infected with Trichinella cysts is eaten, larvae excyst in the duodenum, invade the mucosa of the small intestine, and develop into tiny adults in 5 to 7 days (eFig. 332.1). Adult nematodes mate in the intestine and fertilized eggs hatch in utero, so larvae are discharged into the gut throughout the 1 to 4 months of the adult female’s life. By the second week, larvae are migrating throughout the body, and by the third week, encystment in striated muscle occurs. Here, the larvae may remain viable for years, but they usually die within 6 to 9 months and slowly calcify.

###### eFigure 332.1.

Trichinella spiralis life cycle.

Mucosal petechiae and gastrointestinal bleeding are possible during the intestinal stage of the disease. The primary lesions are in striated muscle, where there is fiber hypertrophy, edema, and degeneration with ...

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