Canine influenza (CI, or dog flu) is caused by the canine influenza virus (CIV), an influenza A virus. It is highly contagious and easily spread from infected dogs to other dogs by direct contact, nasal secretions (through barking, coughing or sneezing), contaminated objects (kennel surfaces, food and water bowls, collars and leashes), and by people moving between infected and uninfected dogs. Dogs of any breed, age, sex or health status are at risk of infection when exposed to the virus.
Currently, two strains of CIV have been identified in the U.S. The H3N8 strain of canine influenza was first identified in 2004 in Florida. Since then, it has been found in several other states. In 2015, the H3N2 virus strain was identified as the cause of an outbreak of canine influenza in Chicago. The virus was known to exist in Asia, but the 2015 outbreak was the first report of the H3N2 virus affecting dogs outside of Asia.
Canine influenza can occur year round. So far, there is no evidence that canine influenza infects people.
Canine influenza and cats
In early 2016, a group of cats in an Indiana shelter were infected with H3N2 canine influenza (passed to them by infected dogs). The findings suggested that cat-to-cat transmission was possible. Cats infected with H3N2 canine influenza show symptoms of upper respiratory illness, including a runny nose, congestion, malaise, lip smacking and excessive salivation.
Canine influenza symptoms and diagnosis
The symptoms of a CIV infection resemble those of canine infectious tracheobronchitis ("kennel cough"). Dogs infected with CIV develop a persistent cough and may develop a thick nasal discharge and fever (often 104-105oF). Other signs can include lethargy, eye discharge and reduced appetite. Canine influenza infections can cause mild to severe illness in dogs. Some infected dogs may not show any signs of illness, but can still be contagious and able to infect other dogs
Most dogs recover within 2-3 weeks. However, some dogs may develop secondary bacterial infections which may lead to more severe illness and pneumonia. Anyone with concerns about their pet’s health, or whose pet is showing signs of canine influenza, should contact their veterinarian.
Laboratory tests are available to diagnose both H3N8 and H3N2 CIV. Consult your veterinarian for more information regarding testing for CIV.
Transmission and prevention of canine influenza
Dogs infected with CIV are most contagious during the two- to four- day virus incubation period, when they shed the virus in their nasal secretions but do not show signs of illness. The virus is highly contagious and almost all dogs exposed to CIV will become infected. The majority (80%) of infected dogs develop flu-like illness. The mortality (death) rate from CIV is low (less than 10%).
To reduce the spread of CIV, isolate dogs that are sick or showing signs of a respiratory illness, and isolate dogs known to have been exposed to an infected dog.
Isolate dogs infected with H3N2 canine influenza for at least 21 days and dogs infected with H3N8 CIV for at least 7 days. Practice good hygiene and sanitation, including hand washing and thorough cleaning of shared items and kennels, to reduce the spread of CIV. Influenza viruses do not usually survive in the environment beyond 48 hours and are inactivated or killed by commonly used disinfectants.
Vaccines are available for both the H3N8 and H3N2 strains of canine influenza virus. The CIV vaccination is a "lifestyle" vaccination, recommended for dogs at risk of exposure due to their increased exposure to other dogs – such as boarding, attending social events with dogs present, and visiting dog parks. Your veterinarian can provide you with additional information about the vaccines and whether you should consider vaccinating your dog.
Frequently Asked Questions (for pet owners)
Canine Influenza reference page (for veterinarians)
Canine Influenza (Center for Food Security and Public Health, Iowa State University)
H3N2 Frequently Asked Questions (Cornell University College of Veterinary Medicine)
Doginfluenza.com (Merck Animal Health)