Trichinosis

NWDC is in the process of updating this fact sheet. 

Other names: Trichinellosis

Cause

Trichinosis is a disease of mammals, birds, and reptiles caused by nematode (roundworm) parasites in the group Trichinella. These parasites live inside muscle cells.

Significance

Humans can contract trichinosis by eating undercooked meat from many species of wild and domestic animals, especially those who eat pork, horse, crocodile, bear, walrus, seals, and other wild game. People who contract trichinosis can face mild (vomiting, fatigue, fever) to severe (difficulty breathing, loss of coordination) symptoms that may last for a month or more. Trichinosis can be fatal. There has been a significant decrease in the number of human cases of trichinosis in the United States due to improvements made in the pork industry and increased public awareness of the dangers of eating raw or undercooked meat, but cases still occur frequently in Europe and Russia. While the prevalence of trichinosis in domestic swine in the US is <1%, the prevalence in black bears in the northeast varies between 1-5%.

Species Affected

Most mammals are susceptible to trichinosis, but it is primarily a disease of carnivores. In North America, Trichinella has been detected in black bears, coyotes, cougars, gray wolves, skunks, bobcats, raccoons, wolverines, fishers, lynxes, walruses, red foxes, grizzly bears, polar bears, and more. This parasite has also been found in rodents, beavers, opossums, whales, crocodiles, and carnivorous birds. Trichinella is a significant parasite of domestic and feral swine. Humans can also become infected.

Distribution

Trichinosis has a worldwide distribution. Different species of Trichinella are associated with different geographic regions and different host species. Several Trichinella species are known to occur in North America.

Transmission

Trichinosis is transmitted when carnivores and omnivores ingest meat of infected animals that have Trichinella larvae encysted within their muscle cells. Once ingested, the larvae imbed themselves within the intestinal lining of the new host and develop into adults. The adult worms mate and the females release live larvae. The larvae migrate to muscle tissue and enter individual muscle cells where they grow, destroy the cells, and encase themselves within cysts. Some larvae end up in the intestines and are released in the feces. These larvae can then infect new hosts. Infective larvae encysted in muscle can survive freezing and for several weeks in decomposing carcasses. 

Clinical Signs

Trichinella is not known to cause clinical signs of illness in wildlife. However, the parasite may be associated with abnormal behavior and decreased reproductive success.

Diagnosis

Trichinella larvae may be found by microscopic examination of muscle tissue. The tongue, diaphragm, the muscles used for chewing, and the muscles between the ribs usually contain the most larvae. Antibody tests are also available for diagnosis. 

Treatment

Treatment of trichinosis is generally not attempted in animals.

Management

It is probably not realistic to attempt to control trichinosis in wildlife. This disease can be more easily controlled in domestic animals by preventing them from feeding on uncooked meat and wildlife carcasses. Trichinosis was once much more common in domestic pigs, but control efforts have nearly eliminated the parasite in these animals in North America. In order to prevent contracting trichinosis among other diseases, people should always cook meat thoroughly (a meat thermometer should read at least 165° F).

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