Reducing Your Dog’s Exposure to Canine Influenza

What it is, and what you can do to reduce your dog’s exposure.
By Sara Greenslit DVM, May 2019
Canine Influenza

Photo-illustration by Tim Carpenter

In the very large universe of microorganisms, viruses are particularly crafty. For example, during the two-to four-day incubation period before dogs show any signs of illness, the Type A influenza virus that causes dog flu, or CI, can spread through such commonplace activities as being patted on the head, sharing a tennis ball or a water bowl, or a nose-to-nose greeting. And unlike those that cause human flu, the CI virus is active year-round.

As is the case with all microbes, the CI virus can only be seen with an electron microscope. Zoom in, and the hemagglutinin (HA) and neuraminidase (NA) proteins that spike up from its round surface are immediately visible. Influenza viruses are named for the way HA and NA combine, and CI comes in two forms, or strains: H3N8 and H3N2. Only 80 percent of affected dogs show flu-like signs, and the fatality rate is less than 10 percent.

The H3N8 strain that first appeared in Florida in 2004 was suspected to have jumped from racehorses to Greyhounds. Then, in 2015, dogs with H3N2 were seen in Chicago; previously known to exist only in South Korea, China and Thailand, the strain is thought to have been transmitted to dogs by infected birds found in live Asian bird markets, then possibly brought to the U.S. via imported dogs.

Dog flu targets the cells in the respiratory tract, from the nose to the small airways of the lungs, and causes mild to severe inflammation; recovery takes two to three weeks (see box for symptom details). While a dog of any age or breed can contract CI, some may be at bigger risk, particularly puppies, pregnant bitches, dogs with concurrent respiratory disease or tracheal collapse, and those on immunosuppressive medication.


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Ask your veterinarian about yearly H3N2 and H3N8 vaccines, particularly if your dog spends time at a kennel; goes to daycare, a groomer, dog parks or dog-friendly festivals; or if a human in the house works around dogs. Vaccination may not prevent an infection, but it can reduce its severity and duration. A bivalent vaccine that offers protection against both strains is also available.

Other strategies for thwarting this sneaky virus: Maintain your dog’s core vaccines (DHPP and Bordetella), which will help him avoid a secondary respiratory infection. Bring your own water to the dog park. When you come home, take your shoes off at the door and wash your hands first thing (yes, before you greet your pets; it’s also a good practice for your own health). Leave leashes and dog coats at the door as well. CI tends to survive no longer than 48 hours in the environment and can be inactivated by common cleaners, such as a 1:30 bleach-to-water solution. Fabric items that have come in contact with sick dogs should be washed in hot water with regular detergent.

If, despite all your precautions, your dog shows signs of CI, take him to your veterinarian. To reduce its spread, ask the reception staff if they’d like you and your dog to stay in the car until ready to be seen, and enter and exit by a side door if possible.

Dogs with influenza often spike fevers; using a rectal thermometer, take your dog’s temperature every four to six hours to make sure it’s staying below 103°F. (Don’t forget to mark the thermometer as the dog’s!) A high-grade fever (104°F to 106°F) and increased respiratory rate and effort could mean that your dog is developing pneumonia; your vet will most likely recommend chest x-rays to screen for this.

Treatment is supportive. Based on your dog’s exam and signs, it may include antibiotics for secondary infections, fluid therapy, nutritional support, appetite stimulants and dog-specific fever-reducing NSAIDs. (Don’t share yours; aspirin, ibuprofen, acetaminophen and other human NSAIDS can be toxic for dogs.) Keep your sick dog home for at least four weeks; if you have multiple dogs, even those who seem healthy should also be restricted to home base.

Currently, there’s no data to suggest that the CI virus is zoonotic—that it can spread from dogs to humans—but since dogs may carry other viruses that are, it makes sense for young, elderly, pregnant or immunocompromised people to avoid contact with ill animals.

What if yours is a multispecies household? In 2016, cats in an Indiana shelter contracted H3N2, and dog-to-cat transmission was suspected. Sick cats show signs like nasal discharge, congestion, fatigue, lip-smacking and excess salivation. To date, no cats have died from CI and no vaccine is yet available for them.

So far, there is no indication that H3N8 can be transmitted from dogs to horses, ferrets or other animal species. However, there is some proof that guinea pigs and ferrets can become infected with H3N2. Contact your veterinarian if you have more questions.

Like most infectious diseases, when it comes to dog flu, prevention is key. For both our dogs’ benefit and our own, washing our hands frequently, keeping up-to-date on vaccines and staying home when sick go a long way toward keeping those pesky flu microbes at bay.

Symptoms of Canine Influenza

A caveat: not all dogs will display all symptoms.

  • A soft, dry cough that persists for 10 to 21 days despite treatment. It can be mistaken for kennel cough (aka infectious tracheobronchitis). Bacteria like Bordetella and Mycoplasma and viruses such as parainfluenza, canine distemper and canine adenovirus-2 present similarly.
  • Nasal congestion and/or thick nasal discharge
  • Fever
  • Lethargy
  • Poor appetite
Article first appeared in The Bark, Issue 97: Spring 2019

Sara Greenslit, DVM, CVA, is a small-animal  veterinarian and writer who lives and practices  in Madison, Wisc.