Canine Influenza

Canine influenza is an emerging disease. No influenza viruses circulated in dogs until genetic changes in an equine influenza virus allowed this virus to spread efficiently in the canine population. Canine influenza was first reported in racing greyhounds, and initially seemed to be confined to this breed. Beginning in 2004, outbreaks of respiratory disease occurred at greyhound kennels and racetracks in a number of U.S. states. The canine influenza virus was found to be responsible for some outbreaks, and is thought to have been involved in others. Serologic evidence suggests that this virus has been circulating among greyhounds since at least 1999. Recently, it has also caused respiratory disease in a variety of breeds in the general canine population. All dogs regardless of breed are now considered to be susceptible. Because this is the first influenza virus to circulate in dogs, they are not expected to have any immunity to canine influenza. If the virus enters a kennel or other closed group, a high percentage of the dogs will probably become infected, and most of these dogs will be symptomatic. Approximately 20-25% of infected dogs are expected to remain asymptomatic, but can still shed the virus and disseminate the disease. Although most dogs have a milder form of canine influenza and recover, some may develop severe pneumonia. Deaths occur mainly in dogs with the severe form of disease; the mortality rate is thought to be 1-5% or slightly higher. Higher case fatality rates have been reported in small groups of greyhounds that developed hemorrhagic pneumonia during outbreaks. In 2007, a different influenza virus caused an outbreak of canine respiratory disease in Korea. This virus appears to be entirely of avian origin, but can be transmitted between dogs. As of 2009, it has been reported only from a limited geographic area.