Merck Manual

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Pet Owner Version

Canine Influenza (Flu)


Ned F. Kuehn

, DVM, MS, DACVIM, Michigan Veterinary Specialists

Reviewed/Revised Jun 2018 | Modified Oct 2022

Canine influenza (flu) is caused by the canine influenza virus. Similar to the influenza virus of people, different versions (called strains) of the virus are found. Two strains of the virus have been identified in dogs: H3N8 and H3N2. The virus causes a respiratory infection in affected dogs. Because it is highly contagious, outbreaks are most common when dogs are in close contact with each other, for example at kennels, shelters, and dog parks. The virus is spread from one dog to another through respiratory secretions (transferred by coughing, sneezing, or barking), contaminated objects (such as water bowls or leashes), and on the hands and clothes of people that have been around an infected dog. It typically takes 2–4 days for dogs to show signs after being exposed to the virus. Dogs usually spread the disease to others when they are showing signs, but around 20% of infected dogs can still spread the virus without showing any signs.

After exposure to the virus, most dogs (80%) develop a mild respiratory infection and have a cough that lasts 1–3 weeks. The cough may be similar to the cough seen in dogs with "kennel cough" (canine infectious tracheobronchitis Infectious Tracheobronchitis of Dogs (Kennel Cough) Tracheobronchitis is a sudden or longterm inflammation of the trachea and bronchial airways; it may also extend into the lungs. It often occurs in dogs already affected by respiratory disease... read more ), which is typically a harsh, dry cough that may be followed by gagging. Other signs include discharge from the eyes and nose, sneezing, fever, lethargy, and loss of appetite. Some dogs become severely sick, with a high fever (104º–106ºF), pneumonia, and an additional bacterial infection. Less than 10% of affected dogs die because of the flu.

Veterinarians diagnose canine influenza virus in dogs that have been sick for less than 3 days by taking samples from the nose or the back of the throat. Blood tests can be done on dogs that have been sick for longer than a week. Both of these types of tests take time to run because they need to be submitted to a laboratory. To confirm the diagnosis, it may be necessary to perform an additional blood test that is collected after the dog improves.

There is no specific treatment for the flu in dogs. Treatments are aimed at supporting affected dogs while their immune system fights the infection. Dogs that have complications (such as pneumonia or a bacterial infection at the same time) may need antibiotics or other medications. Vaccines are available to prevent canine influenza. It is imperative that facilities that house groups of dogs use good hygiene, infection control practices (such as separating sick dogs from healthy ones), and disinfectants to help minimize the spread of the flu. Fortunately, there is no evidence to suggest that canine influenza virus can spread from dogs to people.

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