Canine influenza (CI, or dog flu) is caused by the canine influenza virus (CIV), an influenza A virus. It is highly contagious and easily spread from infected dogs to other dogs by direct contact, nasal secretions (through barking, coughing or sneezing), contaminated objects (kennel surfaces, food and water bowls, collars and leashes), and by people moving between infected and uninfected dogs. Dogs of any breed, age, sex or health status are at risk of infection when exposed to the virus.
Currently, two strains of CIV have been identified in the U.S. The H3N8 strain of canine influenza was first identified in 2004 in Florida. Since then, it has been found in several other states. In 2015, the H3N2 virus strain was identified as the cause of an outbreak of canine influenza in Chicago. The virus was known to exist in Asia, but the 2015 outbreak was the first report of the H3N2 virus affecting dogs outside of Asia.
Canine influenza can occur year round. So far, there is no evidence that canine influenza infects people.
In early 2016, a group of cats in an Indiana shelter were infected with H3N2 canine influenza (passed to them by infected dogs). The findings suggested that cat-to-cat transmission was possible. Cats infected with H3N2 canine influenza show symptoms of upper respiratory illness, including a runny nose, congestion, malaise, lip smacking and excessive salivation.