Dog flu is a contagious respiratory disease in dogs caused by a specific Type A influenza virus referred to as a “canine influenza virus.” This is a disease of dogs, not of humans.
The “canine influenza virus” is an influenza A H3N8 influenza virus (not a human influenza virus) that was originally an equine (horse) influenza virus. This virus has spread to dogs and can now spread between dogs.
The H3N8 equine influenza virus has been known to exist in horses for more than 40 years. In 2004, however, cases of an unknown respiratory illness in dogs (initially greyhounds) were reported. An investigation showed that this respiratory illness was caused by the equine influenza A H3N8 virus. Scientists believe that this virus jumped species (from horses to dogs) and has now adapted to cause illness in dogs and spread among dogs housed in kennels and shelters. This is now considered a dog-specific lineage of H3N8. In September of 2005, this virus was identified by experts as “a newly emerging pathogen in the dog population” in the United States.
The signs of this illness in dogs are cough, runny nose and fever, however, a small proportion of dogs can develop severe disease.
The percentage of dogs infected with this disease that die is very small. Some dogs have asymptomatic infections (no signs), while some have severe infections. Severe illness is characterized by the onset of pneumonia. Although this is a relatively new cause of disease in dogs and nearly all dogs are susceptible to infection, about 80 percent of infected dogs will have a mild form of disease.
Canine influenza virus can be spread to other dogs by direct contact with aerosolized respiratory secretions from infected dogs, by uninfected dogs coming into contact with contaminated objects, and by moving contaminated objects or materials between infected and uninfected dogs. Therefore, dog owners whose dogs are coughing or showing other signs of respiratory disease should not expose other dogs to the virus. Clothing, equipment, surfaces, and hands should be cleaned and disinfected after exposure to dogs showing signs of respiratory disease.
Testing to confirm canine influenza virus infection is available. Your veterinarian can tell you if testing is appropriate. The tests can be performed using respiratory secretions collected at the time of disease onset or using two blood samples; the first collected while the animal is sick and the second 2 to 3 weeks later.
Treatment largely consists of supportive care. This helps the dog mount an immune response. In the milder form of the disease, this care may include medication to make your dog more comfortable and fluids to ensure that your dog remains well-hydrated. Broad spectrum antibiotics may be prescribed by your veterinarian if a secondary bacterial infection is suspected.
To date, there is no evidence of transmission of canine influenza virus from dogs to people and there has not been a single reported case of human infection with the canine influenza virus. While this virus infects dogs and spreads between dogs, there is no evidence that this virus infects humans.
However, human infections with new influenza viruses (against which the human population has little immunity) would be concerning if they occurred. Influenza viruses are constantly changing and it is possible for a virus to change so that it could infect humans and spread easily between humans. Such a virus could represent a pandemic influenza threat. For this reason, CDC and its partners are monitoring the H3N8 influenza virus (as well as other animal influenza viruses) very closely. In general, however, canine influenza viruses are considered to pose a low threat to humans. As mentioned earlier, while these viruses are well established in horse and dog populations, there is no evidence of infection among humans with this virus.
Schedule an appointment with your veterinarian so that they can evaluate your dog and recommend an appropriate course of treatment.