Trichinellosis

Other Names: Trichinosis

Cause

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

Significance

Humans can contract trichinellosis by eating undercooked meat from many species of wild and domestic animals. People who eat pork, horse, crocodile, bear, walrus, and other wild game are at a greater risk. There has been a significant decrease in the number of human cases of trichinellosis in the United States due to improvements made in the pork industry as well as increased public awareness of the dangers of eating raw and undercooked meat, but cases still occur frequently in Europe and Russia.

Species Affected

Most mammals are susceptible to trichinellosis, 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 an important parasite of domestic and feral swine. Humans can also become infected.

Distribution

Trichinellosis 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

Trichinellosis is transmitted when carnivores and omnivores ingest meat of infected animals that have Trichinella larvae encysted within 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 can also survive 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, the 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 trichinellosis is usually not attempted in animals.

Management/Prevention

It is probably not realistic to attempt to control trichinellosis in wildlife because its life cycle depends on natural predation and scavenging activities. This disease can be more easily controlled in domestic animals by preventing them from feeding on uncooked meat and wildlife carcasses. Trichinellosis 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 trichinellosis among other diseases, people should always cook meat thoroughly (a meat thermometer should read at least 135° F).