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Trichinellosis (Trichinella spiralis)
Etiology
Human trichinellosis (also called trichinosis ) is caused by consumption of meat containing encysted larvae of Trichinella spiralis, a tissue-dwelling nematode with a worldwide distribution. After ingestion of raw or inadequately cooked meat from pigs (or other commercial meat sources such as horses) containing viable Trichinella larvae, the organisms are released from the cyst by acid-pepsin digestion of the cyst walls in the stomach and then pass into the small intestine. The larvae invade the small intestine columnar epithelium at the villi base and develop into adult worms. The adult female worm produces about 500 larvae over 2 wk and is then expelled in the feces. The larvae enter the bloodstream and seed striated muscle by burrowing into individual muscle fibers. Over a period of 3 wk, they coil as they increase about 10 times in length and become capable of infecting a new host if ingested. The larvae eventually become encysted and can remain viable for years. Sylvatic Trichinella spp. ( T. brivoti, T. nativa, T. pseudospiralis, and T. murrelli ) present in traditional native foods such as walrus meat, and game meat may also cause disease similar to that caused by T. spiralis .
Epidemiology
Despite public health efforts to control trichinellosis by eliminating the practice of feeding garbage to domestic swine, epidemics and isolated cases of Trichinella spp. infection continue to be a health problem in many areas of the world. It is most common in Asia, Latin America, and Central Europe. Swine fed with garbage may become infected when given uncooked trichinous scraps, usually pig meat, or when the carcasses of infected wild animals such as rats are eaten. Prevalence rates of T. spiralis in domestic swine range from 0.001% in the United States to ≥25% in China. The resurgence of this disease can be attributed to translocations of animal populations, human travel, and export of food as well as ingestion of sylvatic Trichinella through game meat. In the United States from 1997 to 2001, wild game meat (especially bear or walrus meat) was the most common source of infection. Most outbreaks occur from the consumption of T. spiralis –infected pork (or horse meat in areas of the world where horse is eaten) obtained from a single source.
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