What is Trichinosis?
Trichinosis is an infection caused by a roundworm Trichinella spiralis or another species of Trichinella. Symptoms of this infection are diarrhea, abdominal cramps, muscle pain, and fever.
Transmission occurs through consumption of contaminated raw or undercooked meat.
Initially, the person suffers from nausea, diarrhea, abdominal cramps, then muscle pain, weakness, fever, headache and sometimes inflammation in other organs appear.
A few weeks after the onset of the initial infection, the diagnosis can be confirmed by testing a blood sample for antibodies to Trichinella.
Cooking meats well can kill Trichinella larvae, and freezing pork (except meat from wild animals) usually kills the larvae.
Antiparasitic drugs, such as albendazole, can kill these worms in the intestines but not the larvae in the muscles, and pain relievers are needed to relieve muscle pain.
Trichinella larvae live in the muscles of animals, typically pigs, wild boars, foxes, walruses, and many other carnivores. Sometimes the muscle tissue of horses fed meat supplements contains these larvae.
Humans develop trichinosis when they eat raw, undercooked, or improperly squared meat from an animal that carries the parasite. In most cases, infection is due to the consumption of pork meat, especially in areas where these animals are fed raw meat scraps and rubbish, or from the consumption of wild boar meat, from bear or walrus.
Worldwide, an estimated 10,000 cases of trichinosis occur each year. In the United States, fewer than 20 cases are reported each year.
When meat containing Trichinella cysts is eaten, the cyst lining is digested, and the larvae released quickly develop into adult worms which reproduce immediately in the intestine. After mating, the male worms die and no longer play a role in the infection. Females, on the other hand, burrow into the intestinal wall and, after several days, begin to lay the larvae there.
This larval production continues for about 4 to 6 weeks. Then the female either dies or is excreted from the body. The larvae are transported throughout the body by lymphatic and blood vessels. They enter the muscles and cause inflammation. Within 1 to 2 months, they form cysts that can live in the body for years. The dead larvae eventually get absorbed or calcify (harden).
Some muscles, such as those of the tongue, eye and intercostal muscles, are more frequently infected. The larvae rarely form cysts in the heart muscle, but in about a quarter of people with trichinosis, an electrocardiogram (ECG) shows evidence of heart inflammation.
Symptoms of trichinosis
Symptoms of trichinosis vary depending on the stage of infection, the number of infesting larvae, the tissues involved and the general condition of the person. Many people with this condition are asymptomatic.
Symptoms of trichinosis appear in 2 stages:
- Stage 1: The intestinal infection appears 1 to 2 days after eating contaminated meat. Symptoms may include nausea, diarrhea, abdominal cramps, and a slight fever.
- Stage 2: Symptoms of larval invasion of muscles usually begin about 7 to 15 days later. Symptoms are muscle pain and tenderness, fatigue, fever, headache, and swelling of the face, especially around the eyes. The pain is often more intense in the muscles used to breathe, cough, speak, chew and swallow. A non-itchy rash may appear. In some people, the whites of the eyes turn red, the eyes burn and become sensitive to bright light.
In the presence of a large number of larvae, inflammation of the heart, brain, and lungs may develop. It can be responsible for heart failure, cardiac arrhythmias, seizures and serious breathing problems. The death is exceptional.
If left untreated, most symptoms go away by the third month of infection, although vague muscle pain and asthenia may persist longer.
Diagnosis of trichinosis
- Blood tests to look for antibodies against the parasite
- Trichinosis cannot be diagnosed by microscopic examination of the stool. Testing a blood sample for antibodies to Trichinella spiralis is fairly reliable, but the test is not positive until 3 to 5 weeks after symptoms appear. If the results are negative, the doctor will base his diagnosis of trichinosis on the symptoms and on the increased level of eosinophils (a type of white blood cell) in the blood. The test for antibodies is repeated weekly for several weeks to confirm the diagnosis.
- A muscle tissue biopsy (in which a sample of tissue is taken and examined under a microscope), taken after the second week of infection, may show larvae or cysts, but is rarely necessary.
Prevention of trichinosis
Trichinosis is prevented by properly cooking meats, especially pork and pork products, at a temperature above 71 ° C, until they are golden all over. Alternatively, in domestic pigs that are less than 15 cm thick, the larvae can be killed by freezing the pig at -5 ° C for 20 days. Freezing is not recommended for meat from wild animals, as they can be infected with Trichinella species that are not killed by low temperatures.
Smoking, curing, or cooking in the microwave is not entirely effective in killing the larvae.
Meat grinders and other items used to prepare raw meat should be thoroughly cleaned. It is also important to wash your hands with soap and water.
Also, do not feed pigs raw meat.
Mebendazole or albendazole (antiparasitic drugs that kill adult worms)
For muscle pain, analgesics
For severe infections, corticosteroids
Oral treatments with mebendazole or albendazole kill adult worms in the intestines but do not have much effect on cysts in the muscles.
Pain relievers (such as nonsteroidal anti-inflammatory drugs [NSAIDs]) can relieve muscle pain.
To reduce inflammation during severe infections, corticosteroids (such as prednisone) may be prescribed.
Most patients with trichinosis recover completely.
Key points of trichinosis
- Humans are infected with Trichinella by eating meat that is raw, undercooked, or prepared from infected animals, most commonly pork, wild boar, or bear.
- The larvae disencyst in the small intestine, enter the mucosa and develop into adults which release live larvae; the larvae migrate through the bloodstream and lymphatics and become encysted in striated skeletal muscle cells.
- Symptoms begin with gastrointestinal irritation followed by periorbital edema, muscle pain, fever, and eosinophilia.
- Manifestations gradually subside by about month 3, when the larvae are completely encysted, although relative muscle pain and fatigue may persist.
- Diagnose by enzyme immunoassay.
- Treat symptoms (eg, with pain relievers and prednisone for allergic manifestations or for central nervous system involvement); anthelmintics kill adult worms, but once the larvae encyst in the skeletal muscle, treatment may not eradicate them or eliminate the associated symptoms.
- Thorough cooking of pork and wild animal meat can prevent trichinosis.
Photo description: Trichinella spiralis. Shows muscle tissue infected with Trichinella spiralis larvae, the nematode parasite that causes trichinosis. The largest larva shown here has a rope length of about 22.5 micrometers, and a diameter of about 5 micrometers.