Canine Influenza H3N2—One Year Later

Canine influenza is an infectious respiratory disease that was first identified in the United States in 2003. The CIV H3N8 strain mutated from horses to dogs. In 2015, a new strain, CIV H3N2, emerged, which is of avian origin and was first isolated from sick dogs in Asia in 2006.1 Both strains are not closely related, so dogs should be vaccinated against both strains for best protection.

The first cases of Canine Influenza H3N2 in North America were identified by IDEXX from two samples that were tested on March 4, 2015—one from Chicago, Illinois and the other from Grand Rapids, Michigan.2 In less than a year, H3N2 had been diagnosed in more than half the country.3

CIV H3N2 is considered to cause high morbidity. Researchers at the University of Wisconsin found that CIV H3N2 can shed for more than 20 days.4 Since the initial outbreak, there have been many accounts of kennels, doggie day cares, and veterinary clinics becoming overwhelmed with cases of H3N2 in their facilities.

Infection can spread quickly in areas where dogs comingle. According to a survey of confirmed cases from the initial Chicago outbreak, the two most probable sources of infection were doggie day cares (42%) and boarding kennels (40%). Also, clinical signs of illness were noted within 24–72 hours in almost half the cases with the incidence of clinical signs as follows: coughing (95%), lethargy (70%), inappetence (63%), fever (58%), nasal or ocular discharge (49%), gastrointestinal signs (27%), and pneumonia (20%).5

While sanitation and isolation procedures may help stop the spread, they have no effect on the shedding. Fortunately, vaccination can help prevent the disease. Nobivac® Canine Flu Bivalent contains inactivated strains of CIV H3N2 and H3N8. The vaccine may be administered to puppies as young as 7 weeks of age. Nobivac® Canine Flu Bivalent is administered as a 1 mL subcutaneous injection followed by a second dose 2–4 weeks later.6 An annual booster with one dose is recommended.

Despite the prevalence of cases and seriousness of the disease, many pet owners are still unaware that their dogs are at risk for canine influenza. For this reason, Merck Animal Health launched If This Dog Could Talk, a campaign to raise awareness among pet owners of canine influenza. Conducted in partnership with The Dogist photographer Elias Weiss Friedman, the campaign helped encourage pet owners to speak with their veterinarians about the right protection for their dogs.

The If This Dog Could Talk events were held in three cities—Chicago, Atlanta and Charlotte—all areas hit with H3N2 canine influenza outbreaks in 2015. During the events, pet owners had their dogs photographed by The Dogist while they learned about lifestyle factors that could place their dogs at increased risk. The campaign concluded with an event hosted by the Arizona Animal Wellness Center in Gilbert, Arizona—the winner of the If This Dog Could Talk contest.

The photos and stories of dogs will be memorialized in an e-book produced by The Dogist in 2017. To learn more about canine influenza, please visit

This content was provided by Intervet Inc., doing business as Merck Animal Health, a subsidiary of Merck & Co., Inc.


1. Kang et al., H3N2 Canine Influenza Virus Causes Severe Morbidity in Dogs with Induction of Genes Related to Inflammation and Apoptosis. Veterinary Research 2013,44:92. 

2. IDEXX, Important Diagnostic Update. Influenza A virus: the virus that reinvents itself. July 2015.

3. Canine Influenza Virus Surveillance Network – updated July 2016.

4. Newbury S, et al, Prolonged intermittent virus shedding during an outbreak of canine influenza A H3N2 virus infection in dogs in three Chicago area shelters: 16 cases (March to May 2015). JAVMA 2016 May; 248(9): 1022-1026.

5. CIV Patient Survey, Merck Animal Health, data on file.

6. Nobivac® Canine Flu Bivalent (H3N8, H3N2) Product Insert. 

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