Chapter 291 Trichinosis (Trichinella spiralis)
Etiology
Human trichinosis (trichinellosis) 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 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 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.
Epidemiology
Despite veterinary public health efforts to control and eradicate the parasite, reemergence of the disease has been observed in many areas of the world in the past 10-20 yr. Trichinosis 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 USA 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 (T. brivoti, T. nativa, T. pseudospiralis, and T. murrelli) through game meat. In the USA from 1997 to 2001, wild game meat (especially bear 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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