Overview

Trichinosis (trik-ih-NO-sis), sometimes called trichinellosis (trik-ih-nuh-LOW-sis), is a type of roundworm infection. These roundworm parasites (trichinella) use a host body to live and reproduce. These parasites infect animals such as bears, cougars, walruses, foxes, wild boars and domestic pigs. You get the infection by eating the immature form of the roundworm (larvae) in raw or undercooked meat.

When humans eat raw or undercooked meat containing trichinella larvae, the larvae grow into adult worms in the small intestine. This takes several weeks. The adult worms produce larvae that travel through the bloodstream to different parts of the body. They then bury themselves in muscle tissue. Trichinosis is most widespread in rural areas throughout the world.

Trichinosis can be treated with medication, though it's not always needed. It's also easy to prevent.

Symptoms

Signs and symptoms of trichinosis infection and how severe the infection is can vary. This depends on the number of larvae eaten in the infected meat.

Possibly no signs or symptoms

Mild cases of trichinosis — those with only a small number of parasites in your body — may cause no signs or symptoms. Symptoms can develop with moderate or heavy infestation ⸺ a large number of parasites in your body. These symptoms sometimes get worse as the roundworm (trichinella) larvae travel through your body.

Initial signs and symptoms

You swallow roundworm (trichinella) larvae in tiny sacks (cysts) containing the parasite. Your digestive juices dissolve the cysts, releasing the larvae into your body. The larvae then enter the wall of your small intestine, where they grow into adult worms and mate. Digestive symptoms can begin 1 to 2 days after infection. At this stage, you may experience:

  • Diarrhea
  • Stomach (abdominal) pain
  • Severe tiredness and weakness (fatigue)
  • Nausea and vomiting

Later signs and symptoms

About a week after infection, the adult female worms produce larvae. The larvae go through the wall of your intestine and enter your bloodstream, They travel around the body and bury themselves in muscle tissue. Here, each larva coils up and forms a cyst around itself. The larvae can live for months to years inside the muscle tissue.

Symptoms caused by muscle tissue invasion usually start 2 to 8 weeks after infection and include:

  • High fever and chills
  • Muscle pain and tenderness
  • Aching joints
  • Swelling of the eyelids or face
  • Weakness
  • Headache
  • Sensitivity to light
  • Pink eye (conjunctivitis)
  • Itchy, irritated skin

With a large number of parasites, muscle pain and weakness can be severe. This can limit moving, breathing and speaking.

Symptoms last for several months. But symptoms generally lessen when the larvae form cysts. Even after the infection is gone, fatigue, mild pain, weakness and diarrhea may last for months or years.

When to see a doctor

If you have a mild case of trichinosis with no symptoms, you might not need medical care. If you have digestive problems or muscle pain and swelling about a week after eating pork or wild-animal meat, talk to your health care provider.

Causes

People get trichinosis when they eat raw or undercooked meat that is infected with the larvae of the trichinella roundworm parasite. You can't pass the parasite on to another person.

Animals are infected when they feed on other infected animals. Infected meat anywhere in the world can come from wild animals such as bear, cougar, wolf, wild boar, walrus or seal. Domestic pigs and horses can become infected with trichinosis when they feed on garbage containing infected meat scraps.

In the United States, pigs have become a less common source of infection due to increased control of pork feed and products. Wild-animal meat is the source of most cases of trichinosis in the U.S.

You can't get trichinosis from beef, as cows don't eat meat. But some cases of trichinosis in people have been linked to eating beef that was mixed with infected pork.

You can also get trichinosis when beef or other meat is ground in a grinder previously used to grind infected meat.

Risk factors

Risk factors for trichinosis include:

  • Improper food preparation. Trichinosis infects humans when they eat raw or undercooked infected meat, including pork and wild-animal meat. It can also include other meat contaminated by grinders or other equipment.
  • Rural areas. Trichinosis is more common in rural areas around the world. Higher infection rates are found in hog-raising regions.
  • Eating wild or noncommercial meats. Public health measures have greatly lowered the number of trichinosis infections from commercial meats. But noncommercial farm-raised animals — particularly those with access to wild-animal carcasses — have higher rates of infection. Wild animals are still common infection sources.

Complications

Except in severe cases, complications related to trichinosis are rare. In cases with a large number of roundworm (trichinella) larvae, larvae can move through the body to muscle tissue in and around organs. This can cause potentially dangerous, even fatal, complications, such as pain and swelling (inflammation) of the:

  • Muscle layer of the heart wall (myocarditis)
  • Brain (encephalitis)
  • Protective tissue layer surrounding the brain and spinal cord (meningitis)
  • Lungs (pneumonitis)

Prevention

The best defense against trichinosis is proper food preparation. Follow these tips to avoid trichinosis:

  • Avoid raw or undercooked meat. Be sure to thoroughly cook cuts of meat until brown. Cook pork and meat from wild animals to an internal temperature of 160 F (71 C) at the center. Use a meat thermometer to make sure the meat is thoroughly cooked.

    Don't cut or eat meat for at least three minutes after you've removed it from the heat.

  • Freeze pork. Freezing pork that is less than 6 inches thick at 5 F (-15 C) for three weeks will kill the roundworm parasites. But roundworm parasites in wild-animal meat won't die by freezing, even over a long period.
  • Know that other processing methods don't kill parasites. Other methods of meat processing or preserving, such as smoking, curing and pickling, don't kill roundworm parasites in infected meat. Also, microwave cooking isn't recommended as a way to kill roundworm parasites. This is because using a microwave doesn't provide even cooking to ensure all parasites are killed.
  • Clean meat grinders thoroughly. If you grind your own meat, make sure the grinder is thoroughly cleaned after each use.
  • Hand washing. Wash your hands thoroughly with soap and water for 20 seconds after handling raw meat. This can prevent spreading infection to other food.

May 25, 2022
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