Influenza is a viral respiratory illness that can infect several animal species, including domestic and wild:

  • birds
  • pigs
  • dogs
  • horses
  • bats
  • mink
  • seals
  • whales

In certain circumstances, the virus can be transmitted to humans. The spread of influenza can be prevented through strong biosecurity measures.


There are 4 types of influenza virus: A, B, C and D.

Type A virus is the most important due to its ability to infect different animal species and humans.

Type A

Influenza A viruses are divided into subtypes based on 2 proteins located on the surface of the virus structure:

  • hemagglutinin (H)
  • neuraminidase (N)

There are 18 different H subtypes and 11 different N subtypes that can combine, change over time and, in rare instances, can lead to the development of a new influenza subtype.

Most influenza A viruses infect a single species, while others can infect more than one species (such as birds, pigs and humans).

Wild birds represent the primary natural reservoir for all subtypes of influenza A viruses and are considered a source of influenza A virus infection for all other animals.

Clinical signs

Outbreaks of influenza usually occur suddenly and spread rapidly, although sometimes the disease is extremely mild.


There are 3 main subtypes responsible for influenza infections in pigs (H1N1, H1N2, and H3N2), with multiple strains within each subtype.

The infection typically presents either as a severe (acute) respiratory disease or as an ongoing (chronic) form that affects mostly growing pigs.

Clinical signs include fever, depression, nasal and ocular discharge, cough, short or laboured breathing and loss of appetite.

Most affected animals recover from the disease within 1 to 3 weeks, but weight drop in affected pigs may be significant, resulting in economic loss.


Equine influenza is caused by 2 subtypes of influenza A virus, (H3N8 and H7N7).

Clinical signs include fever, nasal discharge and dry cough.

Sporadically, influenza can cause pneumonia in young foals and donkeys, as well as encephalitis in horses.


There are 2 known strains of influenza A that infect dogs, H3N2 and H3N8.

The signs of infection can range from mild to severe, with severe disease more likely to occur in dogs with other illnesses or respiratory problems.

Common signs include coughing, sneezing, nasal discharge, ocular discharge, loss of appetite and fever.

Most dogs recover fully within 2 to 3 weeks, with an ongoing cough that can persist after the virus has been eliminated.


The influenza A viruses that affect birds are divided into multiple subtypes (H5N1, H5N3, H5N8, H7N9) and their genetic characteristics evolve rapidly.

The clinical signs and mortality rate in infected birds depend on 2 major factors:

  • Pathogenicity: Low pathogenic strains (LPAI) target respiratory and digestive tracts, often presenting as depression, appetite and weight loss, ruffled feathers, reduction in egg production and low mortality, making the diagnosis in the field difficult. Highly pathogenic strains (HPAI) affect all organs, including respiratory, digestive, reproductive, nervous and urinary systems, leading to systemic disease. Birds infected with HPAI present as a drop in egg production with abnormal-shelled eggs, coughing and sneezing, depression, diarrhea, purple-blue discolouration of comb and wattles, neurological signs and high mortality.
  • Species: The HPAI virus causes severe clinical disease and high mortality in gallinaceous birds such as chickens and turkeys. While infections in ducks and most other waterfowl often do not cause clinical signs, the new H5N1 subtype (1996 Gs/GD lineage) has been responsible for mass die-offs in wild waterfowl and other birds. This strain has also been reported in several species of terrestrial and aquatic mammals, including dogs and cats.


Animals diagnosed with influenza need supportive care with adequate rest, food, water and bedding or shelter. A veterinarian may prescribe medication to help control secondary infections.

In the event of an outbreak of H5 or H7 avian influenza, the Canadian Food Inspection Agency (CFIA) will lead the response, as these types are reportable diseases under the Health of Animals Act.

To prevent the spread of the disease and to limit the economic impact, response may include the establishment of quarantines and zones, humane euthanasia of the infected birds followed by disposal, cleaning and disinfection.

Prevention and management

Strong biosecurity practices remain the most important measure to prevent the introduction or spread of the disease. These include:

  • a veterinary designed or reviewed biosecurity program with measures including cleaning, sanitation and segregation (please contact your veterinarian)
  • adequate training of farm and company personnel in biosecurity and disease prevention
  • minimizing visits to other production sites and avoiding any commingling
  • avoiding exchanging and sharing equipment with other production sites or farms
  • preventing the introduction of contaminants by providing dedicated clothing and footwear for each barn
  • ensuring all vehicles and farm equipment that access the barn vicinity are properly washed, disinfected and thoroughly dried before use
  • ensuring that laneways are restricted and secured
  • preventing wild bird and rodent entry to barns and related facilities
  • ensuring that bedding is free of contaminants (such as feces from wild animals)
  • keeping all domestic poultry indoors during the high-risk period of spring and fall migration
  • avoiding events where animals from different locations are brought together, including shows, fairs, swaps, sales, educational programs and sporting events. Commingling animals from various locations increases the risk of spreading diseases such as influenza.
  • washing hands and covering your mouth when coughing and sneezing

In some species, vaccination can help minimize clinical signs and reduce the spread of the disease. Booster vaccinations are recommended regularly to help maintain protection against the disease.

Transmission to humans

While it is highly uncommon for humans to get influenza infections directly from animals; globally, there have been sporadic human infections and outbreaks caused by certain Influenza A viruses, including subtypes (H5N1, H7N9, H9N2, H1N1, H1N2 and H3N2). The subtypes mentioned are either low or highly pathogenic strains.

Adequate public health measures and disease awareness remain critical as close contact between animals, stress, environmental and meteorological factors have been shown to contribute to influenza virus spread.

Some precautions to consider when working with animals include:

  • If you are sick with a cold or flu, stay home and have someone else look after your animals.
  • Use additional protective equipment around animals diagnosed with influenza or other diseases, including wearing gloves and an N-95 respirator mask. Always wash your hands after working with or handling animals.
  • When handling manure from swine or poultry, or spray washing livestock housing or vehicles, wear an N-95 respirator mask and eye protection.
  • Get vaccinated for influenza every year.


All avian H5 and H7 influenza A subtypes are reportable diseases under the federal Health of Animals Act. Influenza A virus detected in other species in Ontario is immediately notifiable and veterinary laboratories are required to report to the Office of the Chief Veterinarian for Ontario. The Ministry of Agriculture, Food and Rural Affairs monitors and responds as appropriate.