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Canine Influenza H3N2 Updates

About the Virus

Influenza A virus can cause infection in many mammalian and avian species and exists in multiple subtypes. CIV was first identified as a factor in canine respiratory disease in 2004. This virus is a genetic variant of the H3N8 equine influenza virus that gained the ability to infect dogs. The key change in the virus was the ability for transmission of the virus from dog to dog. The Asian H3N2 virus is derived from an avian strain that also gained the ability to infect dogs and be transmitted from dog to dog. As is the case with all influenza viruses, there is the opportunity for changes in the virus that could affect transmission rates and increase or decrease the ability of the virus to cause respiratory illness.

Transmission and Symptoms

CIV is transmitted by close contact with an infected dog, often in a restricted space such as an animal shelter, day care center, or boarding kennel. Casual contact is less likely to be a factor mainly due to the relatively low amount of virus shed by an infected dog. Virtually all dogs are susceptible regardless of age or breed.

Influenza virus infection in dogs follows a similar pattern to infections in other species. The onset of clinical signs will be 2-3 days post infection. Peak of virus shed is 3-4 days post infection. Longer shedding times of up to 24 days have been identified in dogs infected with H3N2. Because of the differences in the time dogs may shed virus, the quarantine of 7 days is recommended for dogs with H3N8 influenza, while a 21 day quarantine is recommended for dogs with H3N2 influenza. Dogs may continue to cough for several weeks following recovery from acute infection. While in the past CIV infections in and of themselves have not shown a significant mortality rate, CIV infections as well as other respiratory viruses compromise the normal defenses of the lung permitting secondary bacterial pneumonias.

Testing Offered at the AHDC

The AHDC Online Test Catalog provides detailed information about available tests for CIV.

In addition to the Influenza Virus Matrix PCR test that will detect any influenza variant currently circulating that may infect dogs or other species, the AHDC offers a more broadly diagnostic Canine Respiratory PCR Panel. This panel includes canine adenovirus, canine distemper virus, canine parainfluenza virus, canine respiratory coronavirus, canine pneumovirus, Bordetella bronchiseptica, and Mycoplasma cynos along with Influenza Virus Matrix PCR. 

It is difficult to determine solely by clinical signs which respiratory pathogen is present in the dog; the respiratory panel is the best option. It is common to find multiple viruses in these environments and this panel will assist in finding those agents.

As with all respiratory viruses, it is critical to take samples for agent detection within a day or two of the onset of clinical signs which include runny nose, low grade fevers, and coughing. It is very uncommon, but this virus can be fatal in some dogs. Dogs showing clinical signs for >7 days should be tested for CIV by an antibody test as the virus itself is often undetectable in later stages of illness, as is true for most respiratory viral infections.

Testing Later in the Course of the Disease

Testing for antibodies specific for influenza virus is generally done using the standard influenza virus test of hemagglutination inhibition (HI). Antibodies to CIV develop rapidly and by 10 days post infection there is a significant antibody titer. In the absence of a history of vaccination, the presence of CIV antibodies following a clinical illness is highly correlated with CIV being part of the clinical event.

The ADHC at Cornell offers serologic assays that detect antibodies to the H3N2 virus and to the H3N8 virus. Veterinarians and pet owners should submit acute and convalescent serum samples and request Canine Influenza Virus HI H3N8 - (CIVHI). Samples from dogs with respiratory disease will be tested for both H3N8 and H3N2-specific antibodies. Results will be provided for both assays for the same cost as the original H3N8 assay.

Sampling and Shipping Information

For rRT-PCR (real time PCR) or virus isolation, nasal or pharyngeal swabs are the samples of choice. Do not place swabs in bacterial transport media unless you are attempting to isolate a bacterial or mycoplasma infection. To detect viruses, swabs can be placed into a red-top blood collection tube with a few drops of sterile saline or viral transport media if available. If any animal should die from suspected influenza fresh lung tissue is the tissue of choice.

Samples should be shipped on packs and arrive chilled using a next day delivery.


Vaccines do exist for CIV. All of products offered are killed vaccines and are specific for the H3N8 or the H3N2 strain of influenza A and can be administered separately. A vaccine combining the two virus strains into a single vaccine is now also available. Two doses of the vaccines are necessary to develop an effective immune response. Animals previously administered CIV vaccines are expected to have detectable antibodies to the variants of virus in the administered vaccine(s). Therefore, it is important to include vaccination history when requesting CIV HI antibody testing for dogs with respiratory illness.

Additional Information

Contact the AHDC if you have additional questions.