Trichinosis

Date Updated: 05/29/2020

Overview

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. These parasites primarily infect meat-eating animals (carnivores) such as bears and foxes, or meat- and plant-eating animals (omnivores) such as domestic pigs and wild boars. 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 small 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.

Symptoms

Signs and symptoms of trichinosis infection and their severity vary depending on the number of larvae consumed in the infected meat. Abdominal symptoms can occur one to two days after infection. Other symptoms usually start two to eight weeks after infection.

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:

Diarrhea
Abdominal pain
Fatigue
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
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 might not need medical attention. If you experience gastrointestinal problems or muscle pain and swelling about a week after eating pork or wild-animal meat, talk to your doctor.

Causes

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 of trichinosis in humans 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

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 — particularly those with access to wild-animal carcasses — have higher rates of infection. Wild animals, such as bears and walruses, are still common sources of infection.

Complications

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

Prevention

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

Avoid undercooked meat. Be sure to thoroughly cook cuts of meat until brown. Cook pork and meat from wild animals to an internal temperature of 160 F (71 C) throughout. For whole cuts and ground varieties of poultry, cook to a temperature of at least 165 F (74 C). Don't cut or eat the meat for at least three minutes after you've removed it from the heat.

Use a meat thermometer to ensure that the meat is thoroughly cooked.
Freeze pork. Freezing pork that is less than six inches thick for three weeks will kill parasites. However, trichinella parasites in wild-animal meat are not killed by freezing, even over a long period.
Know that other processing methods don't kill parasites. Other methods of meat processing or preserving, such as smoking, curing 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.

Diagnosis

Trichinella larvae travel from the small intestine through the arteries to bury themselves inside muscle tissue, so stool sample tests don't often show evidence of the parasite. Your doctor can diagnose trichinella infection by performing a physical exam and discussing your signs and symptoms such as 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 a 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.

Treatment

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. Your doctor may prescribe medications depending on your symptoms and the severity of infection.

Anti-parasitic medication. Anti-parasitic medication is the first line of treatment for trichinosis. If the trichinella parasite is discovered early, albendazole (Albenza) or mebendazole (Emverm) can be effective in eliminating the worms and larvae in the intestine. You may have mild gastrointestinal side effects during the course of treatment.

If the disease is discovered after the larvae bury themselves in muscle 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, your doctor may prescribe pain relievers to help relieve 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.

Preparing for an appointment

You're likely to start by seeing your family doctor. 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 goes with 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 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, 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?