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micrograph  of Trichinella spiralis cysts in muscle tissue

Trichinella spiralis cysts embedded in a muscle tissue specimen.
Credit: CDC


Trichinosis is a parasitic roundworm disease. Human cases of trichinosis have been associated with eating raw or undercooked meat, especially homemade sausage that contains pork or horse meat, as well as eating walrus or bear meat. Fewer people get trichinosis today because of legislation prohibiting the feeding of raw-meat garbage to hogs, commercial and home freezing of pork, and the public awareness of the danger of eating raw or undercooked pork products. Although trichinosis is very uncommon in the United States, it is found occasionally in rural areas.


Trichinosis is caused by the larvae (immature form) of a highly versatile parasitic roundworm, Trichinella spiralis. This parasite can infect virtually every meat-eating mammal. The parasite is especially common in rats and in swine that feed on raw-meat garbage.

Unlike some of the other parasitic roundworm diseases, trichinosis is not an intestinal infection in the usual sense. Symptoms are caused by the movement of the larvae from the intestines throughout the body, and also by their encystment (becoming enclosed in a capsule) in muscle tissue.

Typically, the life cycle of the parasite follows these steps:

  • A person or an animal eats contaminated meat containing parasite larvae.
  • Digestive juices from the stomach dissolve the capsule-like cyst and release the larvae.
  • The larvae then enter the intestine where they mature into worms and mate.
  • Female worms pass larvae into the bloodstream where they make their way through the capillaries (tiny blood vessels) into the muscle fibers.
  • The larvae encyst in the muscle fibers, where they can live for a long time.


If you are infected with the worms, you might not have or notice any symptoms. Symptoms of larvae in your intestines include

  • Diarrhea
  • Abdominal cramps
  • Tiredness

A week after you are infected, larvae enter your muscle tissue and can cause these symptoms:

  • Muscle aches and pains
  • High fever
  • Swelling in your eyes and face
  • Eye infection (conjunctivitis, or pink eye)
  • Rashes

Being infected by a large number of parasites can cause serious problems affecting your heart, breathing, and coordination.

Except in severe cases, symptoms usually go away within a few months. Mild pain and fatigue, however, may last for many months.

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Your healthcare provider may suspect that you have trichinosis based on your symptoms. If you have eaten raw or undercooked meat, be sure to tell your healthcare provider. You can be diagnosed in the following ways:

  • A blood test that shows an increase in the number of a type of white blood cells called eosinophils
  • Examination of muscle tissue (biopsy) under a microscope to look for larvae​


There are several safe and effective prescription drugs available to treat the symptoms of trichinosis. Treatment should begin as soon as possible. Your healthcare provider can decide on the most appropriate treatment based upon symptoms, exposure to raw or undercooked meat, and laboratory test results.


You can kill the parasites by fully cooking (allowing all parts of the meat to reach at least 170ºF) or freezing meat. You should keep in mind, however, that smoking, pickling, and other methods of processing or preserving meats do not kill these parasites.


Researchers supported by NIAID are conducting basic and clinical research on the prevention, control, and treatment of a variety of parasitic diseases, including some caused by parasitic roundworms.​

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Last Updated September 21, 2015