Canine Influenza H3N2 Updates


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. It is for this reason that the AHDC continues to track and monitor the changes in the virus over time.


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.