Swine influenza is a respiratory illness caused by the type A influenza virus. It regularly causes outbreaks in pig herds. The main swine flu virus subtypes circulating in Québec are H1N1, H3N2 and H1N2.

Though rarely, the swine flu virus can be transmitted between pigs and humans or other animals. Preventing this transmission, particularly between species, continues to be important for protecting animal health and public health. It limits the risk of a new virus developing that could impact pig populations or cause a pandemic.

At-risk animals

Swine flu primarily affects domestic pigs raised on farms or kept as pets. It can also be transmitted to wild boars. In rare cases, it is also possible for the virus to spread to other animal species, like birds.

Signs of the disease

Some animals infected with swine flu may not show any symptoms, while others may show signs of acute illness, like:

  • Fever
  • Weakness
  • Loss of appetite
  • Weight loss
  • Difficulty breathing
  • Coughing
  • Sneezing
  • Nasal discharge
  • Reduced fertility
  • Abortion
  • Eye redness or inflammation

Although the disease can affect entire pig herds, it has low mortality rates.

Transmission and incubation period

Pig herds can be contaminated by other infected pig herds or by a human- or bird-borne virus. Swine flu can be introduced into a herd through the arrival of an infected animal, contact with a sick human or contact with contaminated hands, boots or equipment.

After one to three days, clinical signs appear and last less than a week, unless the pig contracts another infection or develops complications. Pigs become contagious 24 hours after infection and remain contagious for 7 to 10 days.

Viral shedding occurs through respiratory droplets, which are spread by coughing, sneezing and nasal discharge. The virus can be found on surfaces and in the air as aerosols at the time of shedding.


There is no specific treatment for swine influenza.

Supportive treatment can be administered to treat the symptoms of the disease. For example, an anti-inflammatory can be administered to fight off fever. Antibiotics can also be used as needed to control secondary bacterial infections, like pneumonia.

Protection and prevention

Several measures can help prevent swine flu in animals.

  • Wear herd-specific clothing and boots.
  • Wash your hands regularly.
  • Develop and implement a herd-specific biosecurity program with the help of your vet.
  • Vaccinate pigs for swine flu.
  • Watch your pigs for signs of the flu.
  • Avoid contact between people with flu-like symptoms and pigs to reduce risk of human-to-pig transmission. If not possible, require people to wear medical-grade masks, like surgical masks sold in pharmacies.
  • Prevent contact with wild birds and material contaminated by wild birds, like equipment or surface water.

Swine industry workers must be especially well informed about what measures to take. That’s why it’s recommended to put up this poster about influenza This hyperlink will open in a new window. (in French only) in the workplace.

Vaccinating workers against the seasonal human flu can limit the risk of spreading the virus to animals. There is very low risk of contracting the flu through food products.

In humans

Swine influenza symptoms are similar to seasonal flu symptoms.

Cases of swine flu in humans are rare, most often occurring in workers who come in close contact with pigs or their immediate surroundings.

There is no evidence that the virus can be transmitted to humans through properly prepared and cooked pork or pork products. Continue to follow standard guidelines to prevent food poisoning (in French only).

Prevent pig-to-human transmission

To prevent transmission, it is important to wash your hands with soap and hot water after any contact with a pig. If you are unable to, clean your hands with an alcohol-based hand rub.

On farms, measures taken by workers to protect pigs from swine flu also help to reduce the risk of pig-to-human transmission.

Proper personal protection measures include wearing clean clothes and boots on the farm, as well as changing them and then washing your hands after leaving a building. If you have a wound on your hand, bandage it and wear gloves.

If any of your pigs show signs of swine flu, wear gloves, goggles and an N95 mask.


In Québec, the réseau porcin (in French only) conducts swine influenza surveillance. Veterinarians are invited to submit samples for analysis from any pigs showing signs of the disease.

Last update: June 2, 2023


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