Canine Influenza H3N2 Virus Updates

By on
Canine Influenza H3N2 Virus Updates

On April 9, 2015, I reported that five dogs had passed away from canine influenza out of 1,000 known cases in the Chicagoland area. Chicago is densely populated with dogs and provides a rich resource of social opportunities for them, so these factors would contribute to the flu spreading so quickly. Most of us assumed the influenza strain was the H3N8, which is common in the United States.

A few days later, Cornell University stated it was a different flu strain, H3N2, that was first found in Asia. Rumors have circulated that the virus was introduced to the U.S. through dogs rescued and imported from Asia, but there is still no evidence to confirm these rumors.

For the month preceding the announcement, panicked pet parents were having their dogs vaccinated with the H3N8 vaccine, which offers no cross-immunity to the H3N2 strain. I completely empathized with the panic. We have to remember the source fueling the anxiety: sensationalist journalism in an attempt to grab attention. Don’t get me wrong, media outlets are a necessary part of society because they distribute vital news and information.

But, put canine influenza in perspective compared to your office environment. You have 10 people who all have the same symptoms and are out for a few days. 30 people who have mild symptoms who can still make it to work. 20 people who never come down with the disease because of natural immunity. 10 people with stellar immune systems. 5 who were vaccinated. But, your colleague, Larry, develops pneumonia.

So, in instances like the Chicago outbreak of 2015, I implore you to refer to professionals like myself, the American Veterinary Medical Association (AVMA), the American Animal Hospital Association (AAHA), or a collegiate research institution before vaccinating your companion animal for any flu strains.

Statistical Perspective


In February 2016, Cornell University released a H3N2 testing summary compiled from twelve reputable laboratories across the nation.

  • Time period: March 8, 2015 – February 2, 2016.
  • Sample size: 13,900 United States dogs tested for H3N2.
  • 12,228 (88%) tested negative for H3N2.
  • 1,672 (12%) tested positive for H3N2.
  • A positive nasal swab PCR test could indicate the dog is in the midst of illness.
  • A positive serum test could indicate the dog has recovered from an H3N2 infection and will have a titer against the H3N2 virus.

This is not the entire dog population tested or exposed, but the sample size is significant. These statistics demonstrate that the virus may not be spreading as quickly as we had previously thought or to the degree the media has touted.


The AVMA reports that the fatality rate is less than 10% (low) for any strain of canine influenza at this time. Others like myself estimate 2-3% as the 10% includes older data. Indeed, when I reported the five dogs that unfortunately passed away, they only represented 0.5% of the known cases of H3N2 infection in Chicago.

Developing Symptoms

The veterinary community categorizes the symptoms by either mild or severe. Most dogs exposed will only develop mild symptoms.

Mild Symptoms (Common):

  • Soft, moist cough that persists for 10 to 30 days
  • Lethargy
  • Reduced appetite
  • Fever
  • Sneezing and discharge from the eyes and/or nose

Severe Symptoms (Rare):

  • High fevers
  • Clinical signs of pneumonia, such as increased respiratory rates and effort
  • Pneumonia (Streptococcus) may develop in about 2% of cases due to a secondary bacterial infection

If a dog does pass away from influenza, he is probably malnourished, parasitized or otherwise debilitated. Also, if he is one of the few dogs that harbors Streptococcus organisms in his upper respiratory tract or lungs (uncommon), then the combination with canine influenza virus can be serious and even fatal.

Dealing with an Outbreak

An outbreak occurs because several dogs in one area have never been exposed to a virus and do not have natural immunity to it. We need to consider the severity of what has “broken out”. Is it a cat running out of the house or a tiger escaping the zoo?  

When you hear about an influenza outbreak in your area, please:

  • Take a deep breath;
  • Start preventative measures such as avoiding dog parks, dog beaches, doggy daycares, grooming facilities, dog-friendly businesses, daycares and just saying “hello” to the neighbor dogs;
  • Provide your dog immune boosters like curcumin (found in turmeric);
  • Clean and disinfect clothing, equipment, surfaces, and hands after exposure to dogs showing signs of respiratory disease; and,
  • Use portable water bowls during walks and do not allow him to drink from communal water bowls.


A vaccine is available for H3N2, as well as combination one that covers both H3N2 and H3N8. I am pleased that many veterinarians are not promoting this vaccine at their practices because it may take several weeks to be effective. They, too, are advocating the preventative measures listed above. The majority of dogs that are infected from exposure, will then have natural immunity and will not need to be vaccinated. Naturally generated immunity is preferred to vaccination for influenza.  

In fact, if an outbreak is in your area and then you decide to give him the required two doses/three weeks apart (plus annual booster), viral loads may have decreased by the time the vaccine is effective and your dog may have already been exposed to the virus. Some of my colleagues may argue that the first vaccine may lessen the effects of possible flu symptoms, but again the majority of dogs develop only mild symptoms. 

W. Jean Dodds, DVM
Hemopet / NutriScan
11561 Salinaz Avenue
Garden Grove, CA 92843


Becker, Karen, DVM. “Canine Influenza Infects Almost 100% of Dogs Exposed to It.” Healthy Pets., 9 Sept. 2015. Web. 22 May 2016.

” Canine Influenza.” American Veterinary Medical Association, n.d. Web. 22 May 2016.

“Canine Influenza Diagnostic Frequently Asked Questions.” (2015): 1-408.Animal Health Diagnostic Center. Cornell University, 16 Apr. 2015. Web. 22 May 2016.

“ Canine Influenza FAQ.” American Veterinary Medical Association, n.d. Web. 22 May 2016.

“Canine Influenza Virus Surveillance Network Recent H3N2 Testing Summary.” (n.d.): n. pag. Feb. 2016. Web. 22 May 2016. 

Dodds, W. Jean, DVM. “Canine Influenza Outbreak – Chicago 2015.” Dr. Jean Dodds’ Pet Health Resource Blog. 9 Apr. 2015. Web. 22 May 2016.

“Key Facts about Canine Influenza (Dog Flu).” Centers for Disease Control and Prevention, 22 Apr. 2015. Web. 22 May 2016.


Share this message: