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Trichinosis is a type of roundworm infection. Roundworms are parasites that use your body as a host to stay alive and reproduce. Trichinosis occurs primarily among meat-eating animals (carnivores), especially bears, foxes and walruses. The infection is acquired by eating viable larvae in animal flesh. Pigs that feed on garbage containing uncooked meat acquire trichinosis in the same way.

When humans ingest 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. Trichinella roundworms are most widespread in rural areas and in warm climates throughout the world. In the United States, they're most commonly found in hog-producing regions.

If you have mild trichinosis, you may have no symptoms or only mild stomach or muscle aches. When your body is infested with hundreds of worms, though, more serious symptoms and complications can occur.

Trichinosis can be treated with medication. It's also easy to prevent.

Mild cases of trichinosis — those with only a small number of parasites in your body — may cause no symptoms. Symptoms can develop with moderate or heavy infestation, sometimes progressing as the parasite migrates through your body. The trichinella roundworm enters your body as larvae encased in a cyst. Your stomach's digestive juices dissolve the cyst, releasing the parasite into your body. The larvae then penetrate the intestine, where they mature and mate. At this stage, you may experience:

• Diarrhea
• Abdominal cramps
• Malaise

About a week after infection, the adult female worms produce larvae that penetrate the intestinal wall, enter the 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)

People get trichinosis when they eat infected meat — such as bear, walrus, horse or pork — that is undercooked. In nature, carnivores are infected when they feed on other infected animals. Pigs and horses can become infected with trichinosis when they feed on uncooked 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, pigs are now a less common source of infection. In recent years, bear meat has become the most common cause of trichinosis in the United States.

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.

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 undercooked pork or wild-animal meat, consult your doctor. There is no satisfactory treatment to eliminate trichinella once larvae invade tissue. At that point, treatment is for symptoms until the larvae eventually die.

Trichinella larvae bury themselves inside muscle tissue rather than remain in the intestine as in other roundworm infections, so stool sample tests don't often show evidence of the parasite. The initial diagnosis relies on the classic signs and symptoms — swelling around the eyes, muscle inflammation and fever. To confirm the diagnosis, your doctor may use these tests:

• Blood tests. Your doctor may take a blood sample and test it for signs of trichinosis.
• Muscle biopsy. While the blood test typically is enough to establish a diagnosis, your doctor may also need to do a muscle biopsy. A very small piece of muscle, weighing about 1 gram, is removed and examined under a microscope to look for trichinella larvae.

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

• Myocarditis
• Encephalitis
• Meningitis
• Bronchopneumonia
• Nephritis
• Sinusitis
• Pneumonia

Trichinosis usually isn't serious and often gets better on its own. Symptomatic infections may respond to treatment with medication.

• Anti-parasite medication. Anti-parasite (antihelminthic) medication is the first line of treatment against trichinosis. If the trichinella parasite is discovered early, in the intestinal phase, albendazole (Albenza) or mebendazole (Vermox) can be effective in eliminating the intestinal worms and larvae. You may have mild gastrointestinal side effects during the course of treatment, and you may need to take repeat doses to get rid of the infestation completely. If the disease is discovered after the muscle invasion stage, anti-parasite medications are no longer effective in eliminating the parasite.
• Pain relievers. After muscle invasion, pain relievers may be given for muscle aches. Eventually, the larvae cysts in your muscles tend to calcify, resulting in destruction of the larvae and the end of muscle aches and fatigue.
• Corticosteroids. Some cases of trichinosis cause allergic reactions when the parasite enters muscle tissue or when dead or dying larvae release chemicals in your muscle tissue. Your doctor may prescribe a corticosteroid to control inflammation during larval migration.

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 the meat is cooked to an internal temperature of 150 degrees F throughout before eating it.
• 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 several days 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.