Trichinosis is an infection caused by the roundworm (nematode) Trichinella spiralis or another Trichinella species.
People acquire the infection by eating undercooked, contaminated meat.
At first, people may have nausea, diarrhea, and abdominal cramps, followed later by muscle pain, weakness, fever, headache, and sometimes inflammation of other organs.
Repeat blood tests are done to detect antibodies to Trichinella spiralis.
Treatment includes medications used to treat worm infections and medications to relieve muscle pain.
Thoroughly cooking pork and meat from wild animals can kill Trichinella larvae, and freezing pork (but not meat from wild animals) usually kills the larvae.
Helminths are parasitic worms that can infect humans and animals. There are 3 types of helminths: flukes (trematodes), tapeworms (cestodes), and roundworms (nematodes). Trichinella spiralis and other Trichinella species are roundworms.
Trichinella larvae live in the muscle tissue of animals, typically pigs, wild boars, foxes, bears, walruses, and many other carnivores.
People develop trichinosis if they eat undercooked meat from an animal that carries the parasite. In most people, infections result from eating pork, particularly in regions where pigs are fed uncooked meat scraps and garbage, or from eating wild boar, bear, or walrus meat.
Worldwide, approximately 10,000 people are infected each year. In the United States, approximately 15 people are reported each year.
(See also Overview of Parasitic Infections.)
Transmission of Trichinosis
When a person eats undercooked meat containing live Trichinella cysts, the cyst wall is digested, releasing larvae that quickly mature to adulthood and mate in the intestine. After the male worms mate, they die and thus play no further role in infection. The females burrow into the intestinal wall and, after several days, begin to produce larvae.
Production of larvae continues for approximately 4 to 6 weeks. Then, the female worm dies or is excreted from the body. The larvae are carried through the body through the lymphatic vessels (tubes that carry a fluid called lymph through the body) and bloodstream. The larvae penetrate muscles, causing inflammation. In 1 to 2 months, they form cysts that can live for years in the body. Eventually, dead larvae are absorbed or become hard (calcified).
Image from the Centers for Disease Control and Prevention, Global Health, Division of Parasitic Diseases and Malaria.
Symptoms of Trichinosis
Trichinosis symptoms vary, and many infections are mild. Many people have no symptoms.
When people do have symptoms, they may develop during the first week after eating contaminated meat. Symptoms include nausea, diarrhea, and abdominal cramps.
Once the larvae penetrate the muscles, people may develop other symptoms such as muscle pain and tenderness, weakness, high fever, headache, and swelling of the face, particularly around the eyes. The pain is often most pronounced in the muscles used to breathe, speak, chew, and swallow. In some people, the whites of the eyes become red, and their eyes hurt and become sensitive to bright light. These symptoms start approximately 1 to 2 weeks after infection.
If many larvae are present, the heart, brain, and lungs may become inflamed. Heart failure, abnormal heart rhythms, seizures, and severe breathing problems may result. Death can occur but is rare.
Without treatment, most trichinosis symptoms disappear by the third month of infection. Vague muscle pains and fatigue can last for many months.
Diagnosis of Trichinosis
Blood tests
Doctors do blood tests to detect antibodies to Trichinella spiralis. These antibodies are often not detectable until 3 to 5 weeks after symptoms start, so doctors repeat the antibody test at weekly intervals for several weeks to confirm the diagnosis. If antibodies are not detected, doctors usually base an initial diagnosis on the person's symptoms and on the presence of elevated levels of eosinophils (a type of white blood cell) in a blood sample.
Doctors may do a biopsy of muscle tissue (in which a sample of tissue is removed and examined under a microscope), but this procedure is usually not necessary.
Treatment of Trichinosis
Medications used to treat worm infections (anthelmintics)
Pain relievers
Sometimes corticosteroids
To eliminate adult worms from the intestine, a doctor prescribes albendazole or mebendazole. These medications are known as anthelmintics, and they are taken by mouth. These medications do not eliminate cysts in the muscles.
People can take pain relievers (such as nonsteroidal anti-inflammatory drugs, or NSAIDs) to help with muscle pain.
Doctors prescribe corticosteroids (such as prednisone) to reduce inflammation in people who have a severe infection or who have inflammation in their heart or brain.
Most people with trichinosis recover fully.
Prevention of Trichinosis
Trichinosis is prevented by thoroughly cooking meats, especially pork and meat from wild animals, to a temperature higher than 160° F (71° C), until they are brown throughout. Alternatively, larvae can be killed in pork that is less than 6 inches (15 centimeters) thick by freezing the pork at -15° F (-5° C) for 20 days. Freezing is not recommended for meat from wild animals because they may be infected with Trichinella species that are not killed by low temperatures.
Smoking, salting, or microwave cooking does not reliably kill the larvae.
Meat grinders and other items used to prepare raw meat should be thoroughly cleaned. Washing the hands with soap and water is also important.
Domestic pigs should not be fed uncooked meat.
