What is canine influenza (dog flu)?

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 canine 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.

Can canine influenza viruses infect humans?

To date, there is no evidence of transmission of canine influenza viruses from dogs to people and there has not been a single reported case of human infection with a canine influenza virus.

However, 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. Human infections with new influenza viruses (against which the human population has little immunity) are concerning when they occur. Such viruses could present pandemic influenza threats. For this reason, CDC and its partners are monitoring the canine influenza H3N8 and H3N2 viruses (as well as other animal influenza viruses) closely. In general, canine influenza viruses are considered to pose a low threat to humans.

Where did canine influenza viruses come from and how long has it been around?

Canine influenza H3N8 virus originated in horses, has spread to dogs, and can now spread between dogs. The H3N8 equine influenza (horse flu) 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 in the United States. An investigation showed that this respiratory illness was caused by the equine influenza A H3N8 virus. 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 H3N8 virus. In September 2005, this virus was identified by experts as a “newly emerging pathogen in the dog population” in the United States.

The H3N2 canine influenza virus is an avian flu virus that adapted to infect dogs. This virus is different from human seasonal H3N2 viruses. Canine influenza A H3N2 virus was first detected in dogs in South Korea in 2007. This virus seems to have been an avian influenza virus that adapted to infect dogs and has since been reported in China and Thailand. H3N2 canine influenza has reportedly infected some cats as well as dogs. It was first detected in the United States in April 2015. The canine H3N2 virus is genetically different from human seasonal H3N2 viruses. It is not known how canine H3N2 virus was introduced into the United States.

What are signs of canine influenza infection in dogs?

The signs of this illness in dogs are cough, runny nose, and fever, but not all dogs will show signs of illness. The severity of illness associated with canine flu in dogs can range from no signs to severe illness resulting in pneumonia and sometimes death.

How serious is canine influenza infection in dogs?

The percentage of dogs infected with this disease that die is very small. Some dogs have asymptomatic infections (no signs of illness), while some have severe infections. Severe illness is characterized by the onset of pneumonia. This is a relatively new cause of disease in dogs and nearly all dogs are susceptible to infection.

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