Modern Medicine, Old-Fashioned Care

Apr 21, 2015 | General Health

Canine Influenza: The Dog Flu

Here’s what you need to know about the canine influenza virus:

We’re all familiar with the human influenza virus that makes the rounds every winter. We sneeze, cough, have a runny nose and suffer from chills and fever. Your dog can catch the flu as well, and although the symptoms are similar to human flu, the virus is not the same one that infects people. In 2004, the horse influenza virus mutated to a form known as H3N8, and began to infect dogs for the first time. The virus quickly spread from its original location in Florida and has now been verified in most of the United States. In 2015 a variant of the virus, H3N2, appeared in the Midwest. It is believed that this form was brought into the country with infected dogs from Asia.

The Signs

The signs of Canine Influenza Virus (CIV) are virtually identical to those caused by many other viruses and bacteria that cause Canine Cough or the Canine Infectious Respiratory Disease (CIRD) complex. A dog will develop:

  • low grade fever
  • soft moist cough
  • possible nasal discharge

Although most dogs will recover without complications, a small percent may develop life-threatening pneumonia. Young puppies, old dogs, and dogs with pre-existing heart or respiratory conditions are at higher risk. Because the clinical signs of CIV closely resemble those of other canine respiratory diseases, any dog showing symptoms should be seen by a veterinarian.

CIV spreads quickly among dogs for a few reasons

First, most dogs are naive to the virus. In other words, their immune systems have never “seen” CIV and thus almost 100% of exposed dogs will become infected. In addition, the 2 to 4 day incubation period from exposure to the development of clinical signs is when dogs are at their most contagious. Peak viral shedding takes place when a dog is either showing no signs of disease or, at most, a slight runny nose. Finally, diagnosis of CIV is tricky. The most reliable time to test for canine flu is during the period before clinical signs are apparent. Testing outside of this window is complicated and false negative test results are common.

The Vaccine

The good news is that there is a safe and effective vaccine for the H3N8 strain of CIV. While the vaccine does not completely prevent infection, it reduces the symptoms to a mild form and greatly decreases transmission of the virus. The vaccine may also provide some benefit against additional strains, but at this time the level of protection is not known. The vaccine is administered as a series of two injections, two to four weeks apart, and is strongly recommended for any dog that has a social life. Respiratory viruses can be encountered at dog parks, grooming salons, pet care facilities, veterinary clinics, on your pet sitter’s clothing or on walks around your neighborhood. Most quality pet care facilities will recommend or require this vaccine in order to protect the dogs in their care.


If your dog develops signs of respiratory disease, schedule an appointment with your veterinarian. Treatment for most cases of CIV consists of keeping your dog in a warm and dry environment, feeding high quality food, and offering plenty of fluids. If your veterinarian is concerned about secondary bacterial infections, an antibiotic may be prescribed. Your dog should be kept at home for two weeks in order to avoid exposing other dogs. Since the virus is not contagious to people, you can safely provide the love and care that will help your dog return to full health.

Doylestown Veterinary Hospital offers protection to all dogs that have a “social life” by administering this vaccine. Holiday House Pet Resort & Training Center requires the canine influenza vaccine for doggie daycare and lodging.

Dr. Laura Weis practices veterinary medicine in Bucks County, PA, where she and her husband, Dr. Ransome Weis, own Doylestown Veterinary Hospital and Holiday House Pet Resort.