What Is Dog Flu? Vets Warn Against Highly Infectious Virus Spreading in U.S.

Veterinarians are once again warning pet owners about a rash of canine influenza, commonly known as dog flu, after seeing an increase in reported cases of the highly infectious virus.

Veterinarians in San Francisco, New York and Florida have said more pets are testing positive for the virus than is seasonally typical. If left untreated, the flu could have disastrous consequences for the suffering animal, especially if the dog already has a compromised immune system.

The cases are especially severe in Brooklyn, where multiple vets have said they've seen an uptick in reported cases. Heather Thomson, doctor of veterinary medicine at Brooklyn Heights Veterinary Hospital, told Newsweek that up to 16 cases have popped up within the past month at her clinic. She recommended avoiding dog parks and other places where infected animals might come into contact with one another.

"We definitely have not had this many cases of canine influenza before," she said. "There has been a progressive spread. We're seeing it acutely right now."

Veterinarians in Northern California and Florida also said more pets have been coming into the doctor's office with symptoms that could be dog flu, though more tests are needed to confirm the cases. The earlier symptoms include coughing, lethargy, fever and nasal discharge. The virus causes acute respiratory infection in dogs and, more rarely, cats.

According to the American Veterinary Medical Association, the virus has a mortality rate of about 10 percent in dogs, but treatment is typically successful. There have been no feline deaths attributed to the virus, the association said.

"With treatment, most of the dogs—if not all—are going to recover from it and are doing fine," Thomson said. She advised pet owners to vaccinate their pets against the two strains of canine influenza virus that have been identified in the United States: H3N8, which researchers say originated in horses, and H3N2, which doctors think is an adaptation of bird flu.

Canine influenza cannot infect humans, but pet owners can spread the airborne virus through contact with infected dogs. The virus can live on surfaces for up to 48 hours, on clothing for 24 hours and on hands for 12 hours, the American Veterinary Medical Association notes on its website. Because dogs have no natural immunity to the virus, it spreads rapidly from dog to dog.

"Virtually all dogs exposed to canine influenza virus become infected, with approximately 80 percent developing clinical signs of disease," the association reported. "The approximately 20 percent of infected dogs that do not exhibit clinical signs of disease can still shed the virus and spread the infection."

There has been a considerable dispute regarding the earliest cases of infection. According to the Centers for Disease Control, the first cases of dog flu stemming from H3N8 were reported around 2003 or 2004, at greyhound racing facilities in Florida. Cases attributed to an adaptation of H3N2 sprouted later, with a rash of cases appearing in the United States in 2015. Some form of dog flu has been reported in all states, except for North Dakota, Nebraska and Alaska, according to a report from Cornell University.

The University of Florida College of Veterinary Medicine advised pet owners to call the veterinarian before heading to the vet's office with a suspected case of dog flu. While some dogs eventually recover at home, other pets may need hospitalization, the statement said.

A dog looks out from its cage during the dog meat festival at a market in Yulin, China, on June 22, 2015. In the United States, an increase of dog flu cases has been reported in major urban areas. Johannes Eisele/AFP/Getty Images