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Canine Influenza: The Dog Flu in St. Louis (H3N8 and H3N2)

Dog with a bag of cold water on his head

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. More recently another strain identified as H3N2 has also been identified. Although the virus has yet to be verified in the state of Missouri, it has been identified in all surrounding states and we anticipate its spread to Missouri highly probable.

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 a low grade fever, a soft moist cough and possibly 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 can result.


The good news is that there is a safe and effective vaccine for the H3N8 form of CIV, the most common form in the United States. There is also evidence that the vaccine may be helpful to minimize symptoms in dogs exposed to the H3N2 new Influenza virus. The vaccine may not completely prevent infection in all dogs. Yet vaccinated dogs showing symptoms will likely have a mild form which also greatly decreases viral shedding. The vaccine is administered as a series of 2 injections, two to four weeks apart. This vaccine is now required for all dogs visiting Petropolis for lodging, day care, grooming and training. Since CIV has yet to be diagnosed in our area, Petropolis will initially make some exceptions accepting unvaccinated dogs if the urgency of Petropolis services prevent prior vaccination.


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.

For more information, contact Petropolis Pet Resort at 636.537.2322

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