Pet Boarding & Daycare

Canine Influenza H3N2

Canine Influenza H3N2

What We've Learned

By Jill Lopez, DVM, MBA

The H3N2 canine influenza virus is of avian origin and was first isolated from sick dogs in China in 2006 and South Korea in 2007(1) The first reported incidence of Canine Influenza H3N2 in the United States was documented in March 2015. Canine H3N2 influenza virus has been associated with severe respiratory signs and other clinical signs such as fever, reduced body weight, and interstitial pneumonia.(1)


An H3N2 Task Force was created to help track the disease spread. The first cases of Canine Influenza H3N2 in North America were identified by IDEXX from two samples that were tested on March 4, 2015.(2) One of the dogs was from Chicago, Illinois and the other was from Grand Rapids, Michigan. As of July 11, 2016, H3N2 has been diagnosed in 30 states. (3)

Clinical Signs

According to an informal survey conducted by Merck Animal Health, of 81 H3N2 confirmed infected dogs from the initial Chicago outbreak, the incidence of clinical signs was as follows:

The two most probable sources of infection, based on history and onset of clinical signs, were doggie day cares (42%) and boarding kennels (40%.) Clinical signs of illness were noted within 24-72 hours within 46% of the dogs.(4)


Since many other infectious respiratory disease pathogens can cause similar clinical signs, this virus cannot be diagnosed by clinical signs alone. The best approach to diagnose cases of Canine Influenza and other infectious respiratory diseases is through viral isolation, PCR and serology.


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 facility. H3N2 is considered highly infectious and according to a study conducted by the University of Wisconsin, dogs have been shown to shed H3N2 virus for up to 24 days.(5) Sanitation and isolation procedures will help stop the spread but have no effect on the shedding.

Cats are also at risk for Canine Influenza H3N2. The University of Wisconsin recently discovered that several cats in an Indiana shelter with a H3N2 outbreak became ill with H3N2 despite being housed in separate areas than infected dogs.(6) Clinical signs of H3N2 seen in cats are similar to those seen in dogs.


Vaccination is key to helping prevent the spread of canine influenza.  “Dogs at risk should be vaccinated at least yearly with both influenza strains, H3N8 and H3N2, in addition to the other causes of ‘Canine Cough’,” says Dr. Ronald Schultz, Professor of Pathobiological Sciences at the University Of Wisconsin School Of Veterinary Medicine and member of the 2016 Pet Business Consensus Statement Panel.

For more information, please visit:

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.

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

Canine Influenza Virus Surveillance Network—updated July 2016.

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

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, Vol 248, No 9, May 1, 2016.

Cats Sickened by Canine Influenza, JAVMA NEWS, May 2, 2016


Dr. Jill Lopez is a veterinarian with Merck Animal Health. She started her career as a small animal practitioner in West Virginia and has worked in various segments of the Animal Health Industry for over 15 years.  She has particular interests in pet safety, infectious disease,  and general health issues.