Trichinosis (trih-kih-NO-sis) is a parasitic infection that comes from eating raw or undercooked meat. It is caused by species of the roundworm Trichinella (trih-kih-NEH-luh).
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What Is Trichinosis?
Also called trichinellosis (trih-kih-neh-LO-sis), trichinosis can occur when people eat meat that is infected with the larvae * of Trichinella roundworms (also called nematodes, NEE-muh-todes); Trichinella spiralis (spy-RAL-is) is the most common species that causes trichinosis. People can become infected only by eating infected meat; the disease is not spread through human contact. The parasite also can spread when animals eat the infected flesh of other animals. Most often, meat infected with the parasite comes from pigs or wild game, such as bear, horse, wolf, and fox.
Trichinella larvae form cysts (SISTS, shell-like sacs that contain the larvae in a resting stage) in meat. When an animal eats this meat, the animal's stomach acid dissolves the cysts, and the worms are released into the body. They travel to the small intestine * , where they grow into adult worms and mate. After about a week, the mature female worm releases larvae, which travel through the bloodstream to the muscles. There they form the hard cysts that began the cycle. The cysts remain in the muscles, and people become infected when they eat these cysts in animal meat.
How Common Is Trichinosis?
According to the U.S. Centers for Disease Control and Prevention (CDC), there were 16 cases in 2000, down from an average of 38 cases per year from 1991 to 1996. The decline came about because people are now more aware of the dangers of eating raw or undercooked meat; better storage and freezing methods of meat are being used; and laws prohibiting the feeding of raw meat to pigs have been passed. Most trichinosis cases now are associated with eating wild game.
* larvae (LAR-vee) are the immature forms of an insect or worm that hatch from an egg.
* small intestine is the part of the intestine—the system of muscular tubes that food passes through during digestion—that directly receives the food when it passes through the stomach.
How Do People Know They Have Trichinosis?
The length of the period between eating the infected meat and the first symptoms of illness depends on the number of parasites in the meat and how much a person has eaten. It can range from 1 to 45 days, but symptoms
How Do Doctors Diagnose and Treat Trichinosis?
A blood test or muscle biopsy * can be done to determine whether a person has trichinosis. The blood test can detect antibodies * working to destroy the parasite, and the biopsy shows the presence of cysts in the muscles. Asking if a person has recently eaten game or traveled outside of the United States may provide information useful in making the diagnosis.
The infection can be treated with various medications to kill the worms in the intestine, but the medication does not get rid of the larvae that have produced cysts in the muscles. These larvae remain in a dormant (inactive) state in the muscle tissue. If the infection is mild, symptoms usually go away after a few months. Muscle aches and weakness may last longer. Some people require only bed rest; others need to be hospitalized and receive oxygen and intravenous (in-tra-VEE-nus) fluids (fluids injected directly into a vein). Severe complications of trichinosis include inflammation of the heart muscle, heart failure, lung problems, delirium * , and coma * . The disease can be fatal if it is not treated.
How Can Trichinosis Be Prevented?
The best way to prevent infection is to eat only thoroughly cooked meat. Curing, drying, salting, and microwaving meat may not kill Trichinella larvae. When cooking meat, the juices must be clear (not bloody) and the meat must reach an internal temperature of 170 degrees Fahrenheit. Freezing meat at subzero temperatures for several weeks also should kill any larvae in cysts. Raw meat can contaminate work surfaces, so it must not touch surfaces used to prepare food, and grinders and other utensils used with raw meat must be cleaned thoroughly and not used to prepare cooked meat.
* biopsy (BI-op-see) is a test in which a small sample of skin or other body tissue Is removed and examined for signs of disease.
* antibodies (AN-tih-bah-deez) are protein molecules produced by the body's immune system to help fight specific infections caused by microorganisms, such as bacteria and viruses.
* delirium (dih-LEER-e-um) is a condition in which a person is confused, is unable to think clearly, and has a reduced level of consciousness.
* coma (KO-ma) is an unconscious state in which a person cannot be awakened and cannot move, see, speak, or hear.
Gittleman, Ann Louise. Guess What Came to Dinner? Parasites and Your Health. New York: Avery Penguin Putnam, 2001.
National Institute of Allergy and Infectious Diseases (NIAID), Building
31, Room 7A-50, 31 Center Drive MSC 2520, Bethesda, MD
20892. The NIAID, part of the National Institutes of Health, posts
information about trichinosis and other roundworm infections at its
U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton
Road, Atlanta, GA 30333. The CDC is the U.S. government authority for
information about infectious and other diseases. It has a fact sheet
about trichinosis at its website.