Trichinosis (trik-ih-NO-sis), sometimes called trichinellosis (trik-ih-nuh-LOW-sis), is a type of roundworm infection. Roundworm parasites use a host body to live and reproduce. Infection occurs primarily among meat-eating animals (carnivores) such as bears and foxes, or meat- and plant-eating animals (omnivores) such as domestic pigs and wild boar. The infection is acquired by eating roundworm 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 adult worms then produce larvae that travel 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.
Abdominal symptoms can occur one to two days after infection. Other symptoms usually start two to eight weeks after infection. The 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 signs or symptoms. Symptoms can develop with moderate or heavy infestation, sometimes progressing as the parasite travels 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 wall of the small intestine, where they mature into adult worms and mate. At this stage, you may experience:
- Abdominal pain
- Nausea and vomiting
Later signs and symptoms
About a week after infection, the adult female worms produce larvae that go through 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
- Sensitivity to light
- Pink eye (conjunctivitis)
When to see a doctor
If you have a mild case of trichinosis with no symptoms, you might not 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.
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. Cattle don't eat meat, but some 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, even fatal, 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
- Pneumonia — an inflammation of your lungs
The best defense against trichinosis is proper food preparation. Follow these tips to avoid trichinosis:
Avoid undercooked meat. Be sure whole cuts of meat other than poultry and wild game are 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. Cook ground pork and beef to at least 160 F (71 C). They can be eaten immediately after cooking.
Using a meat thermometer is the best way to ensure the meat is thoroughly cooked.
- Avoid undercooked wild game. For both whole cuts and ground varieties, cook to an internal temperature of at least 160 F (71 C).
- Avoid undercooked poultry. For whole cuts and ground varieties, cook to a temperature of at least 165 F (74 C). For whole cuts, let the poultry sit for three minutes before cutting or eating.
- Have wild-animal meat frozen or irradiated. 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.
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 might use these tests:
- Blood tests. Your doctor may take a blood sample and test it for signs suggesting trichinosis — an increase in the number of a certain type of white blood cell (eosinophils) or the formation of antibodies against the parasite after several weeks.
- Muscle biopsy. While the blood test typically is enough to establish a diagnosis, your doctor might also recommend a muscle biopsy. A small piece of muscle is removed and examined under a microscope to look for trichinella larvae.
Trichinosis usually isn't serious and often gets better on its own, usually within a few months. However, fatigue, mild pain, weakness and diarrhea may linger for months or years. Symptomatic infections may respond to treatment with medication.
Anti-parasitic medication. Anti-parasitic (anthelminthic) medication is the first line of treatment against trichinosis. If the trichinella parasite is discovered early, in the intestinal phase, albendazole (Albenza) or mebendazole can be effective in eliminating the intestinal worms and larvae. You may have mild gastrointestinal side effects during the course of treatment.
If the disease is discovered after the larvae bury themselves in tissues, the benefit of anti-parasitic medications is less certain. Your doctor might prescribe one if you have central nervous system, cardiac or respiratory problems as a result of the invasion
- 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 might prescribe a corticosteroid to control inflammation during larval migration.
You're likely to start by seeing your family doctor or a general practitioner. In some cases, you may be referred to an infectious disease specialist.
Here's some information to help you prepare for your appointment.
What you can do
- Be aware of pre-appointment restrictions. When you make the appointment, ask if there's anything you need to do in advance, such as restrict your diet.
- Write down your symptoms, including any that seem unrelated to the reason for which you scheduled the appointment.
- Write down key personal information, including major stresses or recent life changes.
- List all medications, vitamins and supplements you take.
- Take a family member or friend along, if possible. Someone who accompanies you can help you remember the information you get.
- Write down questions to ask your doctor.
Preparing a list of questions will help you make the most of your time with your doctor. For trichinosis, some basic questions to ask your doctor include:
- What is likely causing my symptoms or condition?
- What are other possible causes?
- What tests do I need?
- Is my condition likely temporary or chronic?
- What is the best course of action?
- What are the alternatives to the primary approach you're suggesting?
- I have these other health conditions. How can I manage them together?
- Is there a generic alternative to the medicine you're prescribing?
- Are there brochures or other printed material I can take? What websites do you recommend?
Don't hesitate to ask other questions.
What to expect from your doctor
Your doctor is likely to ask you a number of questions, including:
- When did your symptoms begin?
- Have you eaten raw or rare or unusual meat such as game lately?
- Have your symptoms been continuous or occasional?
- How severe are your symptoms?
- What, if anything, improves your symptoms?
- What, if anything, worsens your symptoms?