Trichinellosis (Trichinosis)

What is trichinellosis? 
Trichinellosis is a parasitic disease caused by eating raw or undercooked meat of animals infected with the larvae of a type of worm called Trichinella. Infection occurs commonly in certain wild carnivorous (meat-eating) animals but can also occur in domestic pigs. On the Continent, there have been a number of recent outbreaks associated with eating undercooked horse meat. Trichinellosis is a notifiable disease in Ireland.

How common is trichinellosis in Ireland?
Trichinellosis is a very rare infection in Ireland and no cases had been reported prior to 2007. In June 2007, an outbreak of trichinellosis in Poland led to the identification of the illness in Ireland in people who had travelled to Poland.

How severe a disease is trichinellosis?
That generally depends on the numbers of larvae eaten. Trichinellosis can be very mild; so mild it goes unnoticed. Most cases are unpleasant and resolve fully with proper treatment. Very occasionally, it can be so severe that it is fatal. 

What are the symptoms of trichinellosis?
Symptoms vary considerably. The first symptoms can involve swelling of the eyes. This will often be accompanied by gastroenteritis symptoms such as diarrhoea, vomiting, and abdominal discomfort. There may also be fatigue, fever headaches, shivering, cough, aching joints and muscle pains. If the infection is severe, patients may have difficulty coordinating movements, and have heart and breathing problems. In the most severe cases, death can occur.

For mild to moderate infections, most symptoms subside within a few months. Fatigue, weakness, and diarrhoea may last for a number of months.

How soon after infection will symptoms appear?
Symptoms of illness including eye symptoms and muscle symptoms usually appear 1-2 weeks after eating infected meat (although they may not appear for up to 6 weeks). Gastrointestinal symptoms can appear within a day or two of eating infected meat. Quite 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 releasing the larvae which pass into the small intestine and, in a couple of days become mature. Adult females lay eggs that develop into larvae, travel through the arteries, and are transported to muscles. Within the muscles, the larvae curl into a ball and encyst (become enclosed in a capsule). Infection occurs when these encysted larvae are consumed in meat. Proper cooking kills the encysted larvae.

How common is the infection in animals and food in Ireland?
In animals trichinellosis rarely presents as a clinical disease, so it requires special tests in order to detect it. All pigs slaughtered for human consumption have to be tested and shown to be free from this worm, and there have not been any cases detected in Irish pigs for several decades. Surveys of Irish wildlife have found the worm present at very low levels in Irish foxes.

Who is at risk of trichinellosis?
Anyone who eats raw or undercooked meats is at risk. The worm can potentially affect most animal species but is generally present at higher levels in wild meat-eating animals. The meats most commonly implicated in the EU include wild boar meat, cured fermented pork-based sausage, and horse meat. In other parts of the world, bear, wild cat (such as cougar), fox, dog, wolf, seal, or walrus have been implicated.

Can trichinellosis spread from an infected person to other people?
No, infection can only occur by eating raw or undercooked meat containing Trichinella larvae.

What should I do if I think I have been exposed to trichinellosis?
You should contact your doctor if you are worried. Let your doctor know if you have eaten raw or undercooked meat.

How is trichinellosis diagnosed?
The presence of gastroenteritis, myalgia (muscle aches), facial oedema (swelling), or subconjunctival haemorrhages (bleeding into the whites of the eye), and an increase in eosinophils (a type of white blood cell) levels would suggest trichinellosis. It can be difficult to differentiate trichinellosis from diseases such as influenza and typhoid. A simple blood test usually confirms the diagnosis. If diagnosis is proving difficult, occasionally a sample of muscle from the shoulder (muscle biopsy) is taken.

How is trichinellosis infection treated?
There is a range of safe and effective antiparasitic medications to cure trichinellosis.

How can it be prevented?
Effective ways of removing risk from food

  • Cook meat products until the juices run clear
  • Freezing pork less than 6 inches thick for 20 days at -15oC will kill any larvae
  • Freezing wild game meats, unlike freezing pork products, is not guaranteed to kill all larvae.

Dealing with known high-risk categories of meat

  • Pork-based fermented meat products (traditional sausage products) should be bought from an approved reliable source, and ideally cooked prior to consumption.
  • Wild game meat, including wild boar meat should be handled hygienically while raw, and cooked thoroughly prior to consumption. 

Methods which are not effective in removing risk for food

  • Curing (salting), fermenting, pickling, drying, smoking, or microwaving meat does not consistently kill infective worms.

Click here to see factsheet in Polish.


Created on: 19 June 2007

Last reviewed: 10 January 2008