Trichinellosis is a parasitic disease caused by eating the raw or undercooked meat of animals infected with Trichinella. Trichinella infections are common in wild, meat-eating animals such as bears and cougars as well as some other meat and plant-eating animals like wild hogs. People usually become infected by consuming raw or undercooked meat that is infected, especially from bear and wild hogs. Most animals infected with Trichinellado not show any signs of illness.
People infected with Trichinella can have a variety of symptoms depending on the amount of parasite ingested and how strong their immune system is. The first symptoms of trichinellosis include nausea, vomiting, diarrhea, and abdominal pain. Infected people may then develop facial swelling and flu-like symptoms such as headache, fever, chills, and muscle pain. In very severe infections, people can lose control of their movements and have heart and breathing problems. Trichinella can cause death if severe infections are left untreated.
Prevent trichinellosis from wildlife by thoroughly cooking game meat.
What is trichinellosis?
Trichinellosis, also called trichinosis, is caused by eating raw or undercooked meat of animals infected with the larvae of a species of worm called Trichinella. Infection occurs commonly in certain wild carnivorous (meat-eating) animals such as bear or cougar, or omnivorous (meat and plant-eating) animals such as domestic pigs or wild boar.
What are the signs and symptoms of a trichinellosis infection?
The signs, symptoms, severity and duration of trichinellosis vary. Nausea, diarrhea, vomiting, fatigue, fever, and abdominal discomfort are often the first symptoms of trichinellosis. Headaches, fevers, chills, cough, swelling of the face and eyes, aching joints and muscle pains, itchy skin, diarrhea, or constipation may follow the first symptoms. If the infection is heavy, patients may experience difficulty coordinating movements, and have heart and breathing problems. In severe cases, death can occur.
For mild to moderate infections, most symptoms subside within a few months. Fatigue, weakness, muscle pain, and diarrhea may last for months.
How soon after infection will symptoms appear?
Abdominal symptoms can occur 1-2 days after infection. Further symptoms usually start 2-8 weeks after eating contaminated meat. Symptoms may range from very mild to severe and relate to the number of infectious worms consumed in meat. Often, mild cases of trichinellosis are never specifically diagnosed and are assumed to be the flu or other common illnesses.
How does infection occur in humans and animals?
When a human or animal eats meat that contains infective Trichinella cysts, the acid in the stomach dissolves the hard covering of the cyst and releases the worms. The worms pass into the small intestine and, in 1-2 days, become mature. After mating, adult females lay eggs. Eggs develop into immature worms, travel through the arteries, and are transported to muscles. Within the muscles, the worms curl into a ball and encyst (become enclosed in a capsule). The life cycle repeats when meat containing these encysted worms is consumed by another human or animal.
Am I at risk for trichinellosis?
If you eat raw or undercooked meats, particularly bear, pork, wild feline (such as a cougar), fox, dog, wolf, horse, seal, or walrus, you are at risk for trichinellosis.
Can I spread trichinellosis to others?
No. Infection can only occur by eating raw or undercooked meat containing Trichinella worms.
What should I do if I think I have trichinellosis?
See your health care provider who can order tests and treat symptoms of trichinellosis infection. If you have eaten raw or undercooked meat, you should tell your health care provider.
How is trichinellosis infection diagnosed?
A blood test or muscle biopsy can show if you have trichinellosis.
How is trichinellosis infection treated?
Several safe and effective prescription drugs are available to treat trichinellosis. Treatment should begin as soon as possible and the decision to treat is based upon symptoms, exposure to raw or undercooked meat, and laboratory test results.
Is trichinellosis common in the United States?
Infection used to be more common and was usually caused by ingestion of undercooked pork. However, infection is now relatively rare. During 2008–2012, 15 cases were reported per year on average. The number of cases decreased beginning in the mid-20th century 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. Cases are less commonly associated with pork products and more often associated with eating raw or undercooked wild game meats.
How can I prevent trichinellosis?
- The best way to prevent trichinellosis is to cook meat to safe temperatures. A food thermometer should be used to measure the internal temperature of cooked meat. Do not sample meat until it is cooked. USDA recommends the following for meat preparation.
- For Whole Cuts of Meat (excluding poultry and wild game)
- Cook to at least 145° F (63° C) as measured with a food thermometer placed in the thickest part of the meat, then allow the meat to rest* for three minutes before carving or consuming.
- For Ground Meat (excluding poultry and wild game)
- Cook to at least 160° F (71° C); ground meats do not require a rest* time.
- For Wild Game (whole cuts and ground)
- Cook to at least 160° F (71° C).
- For All Poultry (whole cuts and ground)
- Cook to at least 165° F (74° C), and for whole poultry allow the meat to rest* for three minutes before carving or consuming.
*According to USDA, “A ‘rest time’ is the amount of time the product remains at the final temperature, after it has been removed from a grill, oven, or other heat source. During the three minutes after meat is removed from the heat source, its temperature remains constant or continues to rise, which destroys pathogens.”
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- For Whole Cuts of Meat (excluding poultry and wild game)
- Curing (salting), drying, smoking, or microwaving meat alone does not consistently kill infective worms; homemade jerky and sausage were the cause of many cases of trichinellosis reported to CDC in recent years.
- Freeze pork less than 6 inches thick for 20 days at 5°F (-15°C) to kill any worms.
- Freezing wild game meats, unlike freezing pork products, may not effectively kill all worms because some worm species that infect wild game animals are freeze-resistant.
- Clean meat grinders thoroughly after each use.
To help prevent Trichinella infection in animal populations, do not allow pigs or wild animals to eat uncooked meat, scraps, or carcasses of any animals, including rats, which may be infected with Trichinella.
Risk Factors
People acquire trichinellosis by consuming raw or undercooked meat infected with the Trichinella parasite, particularly wild game meat or pork. Even tasting very small amounts of undercooked meat during preparation or cooking puts you at risk for infection. Outbreaks occur in settings where multiple people consume the same Trichinella-infected meat.
In the United States, trichinellosis cases are reported to CDC much less commonly now than in the past (Figure 1). During the late 1940s, when the U.S. Public Health Service began counting cases of trichinellosis, 400 cases in the United States were recorded each year on average. During 2008-2010, 20 cases were reported to CDC each year on average. The overall number of cases reported has decreased because of improved pig-raising practices in the pork industry, commercial and home freezing of pork, and public awareness of the danger of eating raw or undercooked meat products. The number of cases associated with raw or undercooked wild game meats has remained relatively constant over time (Figure 2). Over the past 40 years, few cases of trichinellosis have been reported in the United States, and the risk of trichinellosis from commercially raised and properly prepared pork is very low. However, eating undercooked wild game, particularly bear meat, puts one at risk for acquiring this disease.
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