What is trichinosis?

Causes and Symptoms

Trichinosis is a zoonosis (disease acquired from animals) caused by nematodes (roundworms)
belonging to the Trichinella genus, most commonly T. spiralis. Trichinella are parasites of carnivores that show little host specificity, infecting pigs, bears, horses, and humans among other mammals. Undercooked, contaminated pork and bear meat are the most significant sources of human infection. While food processing requirements in developed parts of the world have resulted in decreases in trichinosis, other areas, particularly Latin America (Argentina, Mexico, Chile) and Thailand, continue to experience outbreaks of this disease.

The worms are ingested as larvae that are encysted in the muscle of the infected animal. Once ingested, the larvae hatch from the cysts and mature as adults in the upper intestine. There, the worms mate. Gravid female worms penetrate the intestinal mucosa and deposit larvae that migrate in the bloodstream, eventually becoming encapsulated in the muscle of the infected individual.

Ingesting large numbers of larvae results in gastrointestinal symptoms such as nausea, vomiting, diarrhea or dysentery, fever, and sweating that begin seventy-two hours after infection and may last two weeks. As the larvae migrate, edema (swelling) may be observed around the eyes, side of the nose, temples, and hands. Encysted larvae often result in muscle inflammation and pain, and respiratory symptoms such as cough and hoarseness may be observed late in the infection.

Diagnosis is difficult because of the number of body systems affected and the variety of symptoms. Changes in blood, including an increase in the number of eosinophils (eosinophilia), can be monitored. Because the nematodes are highly antigenic, the human immune response is strong, and antibodies in the blood indicate infection. Sensitive tests involving fluorescently labeled antibodies and enzyme-linked immunosorbent assay (ELISA) can be used to detect circulating antigens in blood serum. Definitive diagnosis is made by examining muscle biopsies for the presence of encysted larvae.

Treatment and Therapy

Trichinosis is usually treated using antihelminthic compounds. Early in the infection, mebendazole (Vermox) may be used. Treatment with these compounds is often accompanied by the administration of corticosteroids to prevent hypersensitivity reactions. The effectiveness of treatment depends on a variety of factors, including the stage of infection, the nature of the infected individual’s immune response, the species of nematode, and the initial number of larvae ingested.

Control of the disease is primarily through control of feeding and processing of meat food products, especially pork. In Europe, feeding garbage to pigs has been banned, and in the United States, any garbage-fed pigs and hogs must be pretreated. Inspectors examine animals at slaughter, and in the United States freezing, heating, or freeze-drying of meat products is required during processing. Educating the public to cook pork thoroughly to a temperature of 71 degrees Celsius (161 degrees Fahrenheit) is an important focus of control and prevention efforts.

Bibliography

Centers for Disease Control and Prevention. "Parasites—Trichinellosis (also known as Trichinosis)." Centers for Disease Control and Prevention, August 8, 2012.

Doyle, Michael P., Larry R. Beuchat, and Thomas J. Montville, eds. Food Microbiology: Fundamentals and Frontiers. 3d ed. Washington, D.C.: ASM Press, 2007.

Forbes, Betty A., Daniel F. Sahm, and Alice S. Weissfeld. Bailey and Scott’s Diagnostic Microbiology. 12th ed. St. Louis, Mo.: Mosby/Elsevier, 2007.

Jay, James M., Martin J. Loessner, and David A. Golden. Modern Food Microbiology. 7th ed. New York: Springer, 2005.

Moorhead, A., et al. “Trichinellosis in the United States, 1991–1996: Declining but Not Gone.” American Journal of Tropical Medicine and Hygiene 60 (1999): 66–69.

Ray, Bibek and Arun Bhunia. Fundamental Food Microbiology. 4th ed. Boca Raton, Fla.: Taylor & Francis, 2008.

Vyas, Jatin M. "Trichinosis." MedlinePlus, November 11, 2012.