Canine influenza, also known as dog flu, is a highly contagious respiratory infection caused by a specific Type A influenza virus known to infect both cats and dogs. Currently, two strains of canine influenza virus have been identified in the U.S.: H3N8 and H3N2. These viruses can change quickly and create new strains that can infect other species. However, there is no evidence that either strain (H3N8 or H3N2) can infect humans.

How is it transmitted?

Canine influenza is transmitted from coughing, barking, and sneezing of infected dogs. The illness tends to spread most among dogs staying in kennels, groomers, and shelters. The viruses can be transmitted indirectly through objects such as food and water bowls, collars and leashes, or even people that have been in contact with infected dogs. The virus is alive and able to infect on surfaces for up to 48 hours, on clothing for 24 hours, and on hands for 12 hours. For this reason, we highly suggest cleaning and disinfecting any objects that have been in contact with an infected dog to avoid exposure to other dogs. If you notice your dog coughing or showing other signs of respiratory disease, try to limit your pet’s exposure to other dogs to prevent further spread of infection as well.

Signs of Canine Influenza

Dogs infected with these viruses usually begin showing symptoms between 2 and 8 days after exposure. The most contagious period is during incubation (1st – 5th day) when the animal sheds the virus even though there may be no visible symptoms. The virus infects and replicates inside cells from the nasal lining to the airways. The response to the infection causes rhinitis, bronchitis, and bronchiolitis. This process kills the cells lining the respiratory tract which then exposes the respiratory tract to other bacterial infections that can cause nasal discharge and coughing.

Essentially all dogs exposed to canine influenza virus become infected, with 80% showing clinical signs of the virus. However, the other 20% of infected dogs that don’t show signs can still shed the virus and spread the infection. There is no exact “season” for canine influenza so infections can occur at any time of the year. Frequently, the symptoms of canine influenza resemble kennel cough which is caused by 1 or more bacterial or viral infections.

The majority of infected dogs display the mild form of canine influenza with the most common sign of a cough that lasts for 10-21 days despite use of antibiotics or cough suppressants. Dogs with canine influenza will usually have a wet or dry cough, nasal or ocular discharge, sneezing, and lethargic or anorexic behavior. Many dogs develop a fever of 104-105 degrees and nasal discharge caused by secondary bacterial infections. Cats infected with H3N2 virus exhibit signs of upper respiratory disease, such as nasal discharge, congestion, discomfort, lip smacking, and excessive salivation.

Dogs that are more severely affected usually exhibit sign or pneumonia, including a high fever of 104-106 degrees and an increased respiratory rate. Chest x-rays may reveal consolidation of lung lobes and although the majority of dogs recover without any incident, some deaths have been reported due to H3N2 virus.


Canine influenza cannot be diagnosed merely by clinical signs (coughing, sneezing, or nasal discharge) because we see these same signs with other respiratory illnesses. However, there are tests available to diagnose and identify the strains of canine influenza. You can reach out to our office and make an appointment to have your dog tested for the virus.

This virus is not widespread in the canine population and many dogs have never been exposed to the virus. The number of exposed animals that develop the disease is approximately 80%. The mortality rate is low at less than 10%. Death occurs mainly in dogs with the most severe form of disease.


The treatment for canine influenza, similar to most viral diseases, is mostly supportive. Good care and nutrition can help dogs develop an effective immune response. Antiviral drugs to treat influenza are only approved for human use as there is little known about their efficacy and safety in dogs. Most dogs recover from the infection within 2-3 weeks, however, secondary bacterial infections, pneumonia, dehydration, or other health factors may require additional diagnostics and treatments. These additional treatments may include fluids to improve hydration, nonsteroidal inflammatory medications to reduce fever and inflammation, or antimicrobials for bacterial infections. Modifications should be made if needed based on your pet’s response to treatment or other health factors and care capabilities of the owner.

Prevention and Control

To prevent transmission of the virus, dogs infected with H3N2 virus and any other dogs in the household should be isolated for 4 weeks with a separate air supply. In veterinary boarding and shelter facilities, the canine influenza appears to be easily killed by disinfectant solutions frequently used in those facilities. Dogs exposed to this virus should not be brought to locations where other dogs are present including training classes, veterinary waiting rooms, shows, events, day care, boarding, or parks until the isolation period is complete. When handling ill dogs or cats, wear protective equipment such as a gown and gloves to avoid contaminating clothing.

Vaccines are available for both H3N8 and H3N2 canine influenza. There is also a vaccine offering protection against both strains. Unfortunately, there are no canine influenza vaccines approved for use in cats at this time. However, vaccination can reduce the risk of your dog contracting the virus. Vaccines may not completely prevent an infection, but it can reduce the severity and duration of the illness.

In general, the vaccine is intended to protect dogs at risk for exposure to the virus, which includes dogs that participate in activities with many other dogs or those who are housed in facilities like shelters and kennels, especially where the virus is prevalent. Dogs that have received the kennel cough vaccine may benefit from the canine influenza vaccination because the risk groups are similar. Please consult with one of our doctors to determine your dog’s risk of exposure to the virus and if vaccination is an appropriate decision for your dog.