Canine influenza (CI, or dog flu) in the U.S. is caused by the canine influenza virus (CIV), which is H3N8 influenza A, and was first discovered in 2004. Although seasonal flu in people is caused by influenza A viruses, canine influenza virus is a different virus and so far does not infect people. Unlike seasonal flu in people, canine influenza can occur year round. Dogs of any breed, age, sex or health status are at risk of infection when exposed to CIV.
CIV is highly contagious and easily spread from infected dogs to other dogs through direct contact, nasal secretions (through coughing and sneezing), contaminated objects (kennel surfaces, food and water bowls, collars and leashes), and people moving between infected and uninfected dogs. Dogs are most contagious during the two- to four-day incubation period for the virus, when they are infected and shedding the virus in their nasal secretions but are not showing signs of illness. Almost all dogs exposed to CIV will become infected, and the majority (80%) of infected dogs develop flu-like illness. The mortality (death) rate is low (less than 10%).
CIV infection resembles canine infectious tracheobronchitis ("kennel cough"). More common causes of kennel cough include infections are caused by Bordetella bronchiseptica/parainfluenza virus complex. The illness may be mild or severe, and infected dogs develop a persistent cough and may develop a thick nasal discharge and fever. Lethargy, nasal or eye discharge, and reduced appetite may also be observed. Most dogs recover within 2-3 weeks. Secondary bacterial infections can develop, and may cause more severe illness and pneumonia.
CIV can be diagnosed early in the illness (less than 4 days) by testing a nasal or throat swab. The most accurate test for CIV infection is a blood test that requires a sample taken during the first week of illness, followed by a second sample 10-14 days later.
The spread of CIV can be reduced by isolating ill dogs as well as those who are known to have been exposed to an infected dog and those showing signs of respiratory illness. Good hygiene, such as hand washing and thorough cleaning of shared items and kennels, and good sanitation also reduce the spread of CIV. Influenza viruses do not usually survive in the environment beyond 48 hours and are inactivated or killed by commonly used disinfectants.
There are vaccines against CIV available for use. The vaccines may not completely prevent infection, but appears to reduce the severity and duration of illness. It also reduces the period of time than an infected dog may shed the virus in its respiratory secretions, as well as the amount of virus shed - making them less contagious to other dogs. The CIV vaccination is a "lifestyle" vaccination, recommended for dogs at risk of exposure due to their increased exposure to other dogs -Â such as boarding, attending social events with dogs present, and visiting dog parks.