Trichinosis

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).

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.

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

often surface in 10 to 14 days. Symptoms can be mild and even go unnoticed, but they usually start with fever, diarrhea (dye-uh-REE-uh), belly pain, nausea (NAW-zee-uh), vomiting, and extreme tiredness. Other symptoms may follow, such as headache, cough, chills, muscle and joint pain, eye swelling, and constipation. If the infection is severe, a person may have trouble with coordination as well as heart and breathing problems.

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.