Canine influenza, sometimes referred to as dog flu, is a highly contagious respiratory disease caused by two specific type A influenza viruses known to infect dogs. One is an H3N8 virus, and the other is an H3N2 virus.
Most dogs in North America have no preexisting immunity to canine influenza virus, making them highly susceptible to infection. The majority of canine influenza cases in dogs have been reported in association with multicentric, non-sustaining outbreaks.
Infection with the H3N2 canine influenza virus has been occasionally diagnosed in cats, with cats in animal shelters at highest risk. There is no evidence that canine influenza is contagious to people.