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Trichinosis

Trichinosis (trik-ih-NO-sis), sometimes called trichinellosis, is a type of roundworm infection. Roundworms are parasites that use a host body to stay alive and reproduce. Trichinosis occurs primarily among meat-eating animals (carnivores), especially bears, foxes and walruses. Trichinosis infection is acquired by eating larvae in raw or undercooked meat.

When humans eat undercooked meat containing trichinella larvae, the larvae mature into adult worms in the intestine over several weeks. The adults then produce larvae that migrate through various tissues, including muscle. Trichinosis is most widespread in rural areas throughout the world.

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

Symptoms Causes Risk factors Complications Prevention

Abdominal symptoms can occur within two to seven days of infection. Other symptoms usually start one to eight weeks later. Severity of symptoms usually depends on the number of larvae consumed 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 recognizable symptoms. Symptoms can develop with moderate or heavy infestation, sometimes progressing as the parasite migrates through your body.

Initial signs and symptoms

You swallow trichinella larvae encased in a cyst. Your digestive juices dissolve the cyst, releasing the parasite into your body. The larvae then penetrate the intestine, where they mature into adult worms and mate. At this stage, you may experience:

  • Diarrhea
  • Abdominal cramps

Later signs and symptoms

About a week after infection, the adult female worms produce larvae that penetrate the intestinal wall, enter your bloodstream, and eventually burrow into muscle or other tissue. This tissue invasion can cause:

  • High fever
  • Muscle pain and tenderness
  • Swelling of the eyelids or face
  • Weakness
  • Headache
  • Sensitivity to light
  • Pink eye (conjunctivitis)

When to see a doctor

If you have a mild case of trichinosis with no symptoms, you may never need medical attention. If you notice gastrointestinal problems or muscle pain and swelling about a week after eating pork or wild-animal meat, talk to your doctor.

There is no effective treatment to eliminate trichinella once larvae invade tissue. At that point, treatment is for symptoms only until the parasites die on their own.

People get trichinosis when they eat undercooked meat — such as pork, bear, walrus or horse — that is infected with the immature form (larvae) of the trichinella roundworm. In nature, animals are infected when they feed on other infected animals. Pigs and horses can become infected with trichinosis when they feed on garbage containing infected meat scraps. Other cases have been linked to eating beef that was mixed with infected pork or ground in a grinder previously used for contaminated pork.

Due to increased regulation of pork feed and products in the United States, pigs have become a less common source of infection. Wild animals, including bear, continue to be sources of infection.

Risk factors for trichinosis include:

  • Improper food preparation. Trichinosis infects humans when they eat undercooked infected meat, such as pork, bear or walrus, or other meat contaminated by grinders or other equipment.
  • Rural areas. Trichinosis is more common in rural areas. In the United States, higher rates of infection are found in hog-raising regions.
  • Consumption of wild or noncommercial meats. Public health measures have greatly decreased the incidence of trichinosis in commercial meats, but noncommercial, farm-raised animals have higher rates of infection — particularly those with access to wild-animal carcasses. Wild animals, such as bears and walruses, are still a common source of infection.

Except in severe cases, complications related to trichinosis are rare. In cases of heavy infestation, larvae can migrate to vital organs, causing potentially dangerous complications, including:

  • Myocarditis — an inflammation of the myocardium, the thick muscular layer of your heart wall
  • Encephalitis — an inflammation of your brain
  • Meningitis — an inflammation of the membranes (meninges) and cerebrospinal fluid surrounding your brain and spinal cord
  • Bronchopneumonia — an inflammation of your lungs and bronchial tubes
  • Nephritis — an inflammation of your kidneys
  • Sinusitis — an inflammation of the mucous membranes in your sinuses
  • Pneumonia — an inflammation of your lungs

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

  • Avoid undercooked pork, walrus, horse, bear or other wild-animal meat. Be sure whole meat is cooked to an internal temperature of 145 F (63 C) throughout, and don't cut or eat the meat for at least three minutes after you've removed it from the heat source. Ground pork must be cooked to at least 160 F (71 C) and can be eaten immediately after you remove it from the heat source. Using a meat thermometer is the best way to ensure the meat is thoroughly cooked.
  • Have wild-animal meat frozen or irradiated. Trichinosis can occur in any meat-eating mammal. Irradiation will kill parasites in wild-animal meat, and deep-freezing for three weeks kills trichinella in some meats. However, trichinella in bear meat does not die by freezing, even over a long period. Neither irradiation nor freezing is necessary if you ensure that the meat is thoroughly cooked.
  • Know that other processing methods don't kill parasites. Other methods of meat processing or preserving, such as smoking and pickling, don't kill trichinella parasites in infected meat.
  • Clean meat grinders thoroughly. If you grind your own meat, make sure the grinder is cleaned after each use.
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