Trichinellosis - Fact Sheet
What is trichinellosis?
Trichinellosis (trichinosis) is a disease that can affect both animals and humans. It is caused by small nematodes (roundworms) of the Trichinella species. Infective larvae are transferred (from host-to-host) by the consumption of raw or undercooked infected meat.
In many countries human trichinellosis has been associated with the consumption of improperly or uncooked meat from infected swine. Regulations to detect and control trichinellosis in swine have been in place in many countries for more than 100 years.
Globally, outbreaks of human trichinellosis associated with pork from abattoirs operating under modern inspection systems rarely occur; however, cases which are associated with the consumption of undercooked meat from wild boars, horses, wildlife species such as walrus and bear, and outdoor-reared and home-processed swine continue to be reported.
Is trichinellosis a risk to human health?
The risk to public health is considered to be low. This risk assessment is based on several factors including:
- surveillance results;
- modern farm management techniques; and
- the absence of outbreaks.
Provincial abattoirs must report suspected cases for Canadian Food Inspection Agency (CFIA) follow-up.
In Canada, the primary risk for acquiring trichinellosis is through the consumption of undercooked or raw meat from wildlife species such as bears and walruses.
The risk of infection can be eliminated through the proper cooking of meat. All wild game meat, pork and horse meat should be cooked to an internal temperature of at least 71°C. Curing (salting), drying, smoking or microwaving the meat does not consistently kill infective larvae.
What are the clinical signs of trichinellosis?
Clinical signs of trichinellosis in animals are not easily recognized.
The severity of human trichinellosis is dependent upon the number of infected larvae ingested, the species of Trichinella, and the immune status of the human host. Commonly observed signs, which appear 5 to 15 days after exposure, may include:
- abnormal fear of light;
- facial swelling;
- gastrointestinal upset;
- muscle pain; and
- skin rash.
Inflammation of the heart muscle and the brain, if they occur, are serious and may be life-threatening.
Where is trichinellosis found?
Trichinella have a worldwide distribution and are common in many wildlife populations.
All mammals are susceptible to infection, but the number of larvae required for infection varies according to the genetic makeup of the parasite and the host species. There are a few Trichinella species that can affect birds and crocodiles.
The most recent Canadian occurance of trichinellosis in swine occurred in January 2013 in a pig raised on a non-commercial farm. It was slaughtered and consumed on the farm. No product entered the commercial food system.
How is trichinellosis transmitted and spread?
Trichinellosis is acquired by eating raw or undercooked meat that contains Trichinella larvae. Domestic animals can be infected by the consumption of infected raw tissues. In poorly managed farm operations, cycles of transmission can easily be established. Wild animals become infected through scavenging infected domestic or wild animals.
How is trichinellosis diagnosed?
Most infections in animal species (domestic and wild) are undiagnosed. In Canada, post-slaughter testing of individual animal carcasses for food safety and export certification is conducted using a scientifically validated analysis carried out under an internationally recognized quality assurance system.
How is trichinellosis treated?
The objective, in humans and animals, is to prevent the ingestion of viable Trichinella cysts.
Treatment of trichinellosis in animals is not practical. Treatment in humans is unpredictable, but consists of using antihelmintics (a group of drugs targeted at the adult worm) as well as corticosteroids (steroidal anti-inflammatories). Treatment must occur within a short timeframe of ingestion of infected meat in order to target the adult worm. The later the treatment occurs, the higher the probability that the person will harbour viable larvae in their muscles for years.
What is done to protect Canadian livestock from an outbreak of trichinellosis?
The CFIA administers a Trichinella control program which includes surveillance, regulation and testing.
The CFIA conducts two ongoing surveillance programs on a statistically representative population of Canadian swine. Approximately 18,000 slaughtered swine are tested annually and every three to five years, 16,000 sows are tested. This is done to ensure that there has been no introduction of disease to the domestic swine population and to demonstrate to importing countries that Canada's commercial swine herd is Trichinella-free.
CFIA inspection staff at federally inspected meat plants enforce meat processing regulations for cooking, curing and freezing pork to ensure the destruction of Trichinella larvae. All horses slaughtered in CFIA-regulated abattoirs for human consumption are tested for trichinellosis at the point of slaughter to meet export requirements. It is important to note that most species of Trichinella found in wildlife are resistant to freezing, and, therefore are not eliminated using the freezing guidelines developed for pork; instead this meat needs to be well cooked.
The CFIA also prohibits the feeding of meat and meat by-products to swine through the Health of Animals Regulations.
How would the CFIA respond to an outbreak of trichinellosis in Canada?
Trichinellosis is a “reportable disease” under the Health of Animals Act. This means that all suspected cases must be reported to the CFIA for immediate investigation by inspectors.
Canada's emergency response strategy in the event of an outbreak of trichinellosis would be to:
- investigate the source of infection and eradicate the disease; and
- re-establish the country's disease-free status as quickly as possible.
In an effort to eradicate trichinellosis, the CFIA may employ some or all of the following disease control methods:
- the humane destruction of all infected and exposed animals;
- surveillance and tracing of potentially infected or exposed animals;
- strict quarantine to control the slaughter and meat distribution of potentially infected animals; and
- strict decontamination of infected premises.
Owners whose animals are ordered destroyed may be eligible for compensation.
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