Canine influenza (also known as dog flu) is a contagious respiratory disease in dogs caused by specific Type A influenza viruses known to infect dogs. These are called “canine influenza viruses.” Dog flu is a disease of dogs. No human infections with dog influenza have ever been reported. There are two different influenza A dog flu viruses: one is an H3N8 virus and the other is an H3N2 virus.
Two Types of Canine Influenza
Influenza H3N8
Canine influenza H3N8 viruses originated in horses, spread to dogs, and can now spread between dogs. H3N8 equine influenza (horse flu) viruses have been known to exist in horses for more than 40 years. In 2004, cases of an unknown respiratory illness in dogs (initially greyhounds) were reported in the United States. An investigation showed that this respiratory illness was caused by equine influenza A(H3N8) viruses.
Scientists believe this virus jumped species (from horses to dogs) and has adapted to cause illness in dogs and spread among dogs, especially those housed in kennels and shelters. This is now considered a dog-specific, or canine, H3N8 virus.
In September 2005, this virus was identified by experts as a “newly emerging pathogen in the dog population” in the United States. It has now been detected in dogs across much of the United States.
Influenza H3N2
Canine influenza H3N2 viruses originated in birds, spread to dogs, and can now spread between dogs. Transmission of H3N2 canine influenza viruses to cats from infected dogs has been reported also. H3N2 canine influenza viruses were first detected in the United States in April 2015, and has now been found in more than 30 states.
Two Forms of Canine Influenza
Two clinical syndromes have been seen in dogs infected with the canine influenza virus—a mild form of the disease and a more severe form that is accompanied by pneumonia.
Mild form
Dogs suffering with the mild form of canine influenza develop a soft, moist cough that persists for 10 to 30 days. They may also be lethargic and have reduced appetite and a fever. Sneezing and discharge from the eyes and/or nose may also be observed. Some dogs have a dry cough similar to the traditional “kennel cough” caused by Bordetella bronchiseptica/parainfluenza virus complex. Dogs with the mild form of influenza may also have a thick nasal discharge, which is usually caused by a secondary bacterial infection.
Severe form
Dogs with the severe form of influenza develop high fevers (104ºF to 106ºF) and have clinical signs of pneumonia, such as increased respiratory rates and effort. Pneumonia may be due to a secondary bacterial infection. Along with permanent scare tissue and possible death.
Don’t Wait To Vaccinate!
There are multiple canine influenza vaccines available that vaccinate for either H3N8 or H3N2, as well as combination products that vaccinate for both H3N8 and H3N2. Dog influenza vaccines are considered “lifestyle” vaccines, meaning the decision to vaccinate is based on a dog’s risk of exposure. Dog owners should consult their veterinarian to determine whether vaccination is needed.
