Canine Influenza


Influenza A viruses are divided into subtypes and numbered according to two proteins found on the virus’ surface: hemagglutinin (H) and neuraminidase (N).1 Currently, two canine influenza virus strains (or mutations) of Influenza A viruses previously found in other animals have been identified: H3N8 and H3N2.

Canine Influenza Virus (CIV) H3N8

The first clinically apparent canine influenza virus (CIV) was a strain of the equine subtype of Influenza A virus H3N8.234 While this CIV was first isolated in 2004, following a Canine Infectious Respiratory Disease (CIRD) outbreak in Florida;2 the mutation is thought to have occurred as early as 1999, when racing greyhounds in the United States became infected.567 Although it is uncertain what caused the mutation to occur, there is speculation viral mutation may have been facilitated through feeding dogs raw horse meat.89

Canine Influenza Virus (CIV) H3N2

In April, 2015; an outbreak of canine influenza virus infection in the Chicago area was found to be caused by a different subtype of Influenza A virus, previously not found outside of Asia.10 This newer strain of CIV, thought to have emerged in Asia in the mid-2000’s, is a strain of the avian subtype of Influenza A virus H3N2.11 This outbreak signifies the first introduction of this more-recently identified CIV into the United States.10

At least two (2) dogs were tested for CIV H3N2 in Connecticut during the outbreak, but neither tested positive.12 For comparison: In Illinois, at the epicenter of the outbreak; more than half of over four-hundred (400) dogs tested for the virus were confirmed positive.12




As with Kennel Cough, recent outbreaks of canine influenza virus H3N8 infection have prompted many local boarding and/or grooming facilities, and some public parks, to require vaccination for CIV H3N8.

CIV H3N8 vaccines are administered according to the following schedule:

Schedule Vaccine
(Initial Vaccination) Initial CIV H3N8 Vaccination
Two (2) to Four (4) Weeks Later CIV H3N8 Vaccine Booster
Every Year Thereafter CIV H3N8 Vaccine Booster

CIV H3N8 vaccines are administered in series, starting at six (6) weeks of age or older. The initial vaccine and booster must be administered two (2) to four (4) weeks apart; if not, the series must be restarted.


The CIV H3N8 vaccine only provides limited protection against CIV H3N2,13 which necessitated the development of a CIV H3N2-specific vaccine.

In November 2015; conditional licenses were granted for a CIV H3N2 vaccine;1415 while efficacy and potency study data were pending,14 as such licensing allows.16 As of late 2016, however; those vaccines are fully-licensed.


The most common symptoms of CIV infection stem from a mild respiratory disease similar to that of CIRD, and include lethargy, anorexia, fever, purulent nasal discharge, cough; and other signs of pneumonia in more severe cases.917


Testing for CIV H3N8 and/or H3N2, as part of our outside Laboratory services, indicates viral presence using pharyngeal and conjunctival (inner eyelid) swabs.

Additional Resources

Visit (presented by Merck Animal Health) for more information regarding canine influenza virus infection.


  1. ^ Types of Influenza Viruses. Centers for Disease Control and Prevention. Updated August 19, 2014.
  2. ^ a b Dubovi EJ, Njaa LB. Canine influenza. Vet Clin N Am-Small. July 2009; 38(4): 827-835. doi:10.1016/j.cvsm.2008.03.004.
  3. ^ Payungporn S, Crawford PC, Kouo TS, et al. Influenza A virus (H3N8) in dogs with respiratory disease, Florida. Emerg Infect Dis. June 2008; 14(6): 902-908. doi:10.3201/eid1406.071270.
  4. ^ Von Grotthuss M, Rychlewski L. Influenza mutation from equine to canine. Science. March 2006; 311(5765): 1241.
  5. ^ Crawford PC, Dubovi EJ, Castleman WL, et al. Transmission of equine influenza virus to dogs. Science. 2005; 310: 482-485.
  6. ^ University of Florida. UF Researchers: Equine Influenza Virus Likely Involved In Recent Respiratory Disease Outbreak In Racing Greyhounds. University of Florida. Published April 22, 2004.
  7. ^ Yoon K-J, Cooper VL, Schwartz KJ, et al. Influenza virus infection in racing greyhounds. Emerg Infect Dis. December 2005; 11(12): 1974-1976. doi:10.3201/eid1112.050810.
  8. ^ Beeler E. Influenza in dogs and cats. Vet Clin Am-Small. March 2009; 39(2): 251-264. doi:10.1016/j.cvsm.2008.10.011.
  9. ^ a b Vahlenkamp TW, Greene CE, Hartmann K. Influenza Virus Infections. In: Greene CE, ed. Infectious Diseases of the Dog and Cat 4th ed. St. Louis, MO: Elsevier; 2012: 209.
  10. ^ a b Schwartz J. Midwest Canine Influenza outbreak caused by new strain of virus. Cornell University. Published April 12, 2015.
  11. ^ Zhu H, Hughes J, Murcia PR. Origins and evolutionary dynamics of H3N2 canine influenza virus. J Virol. May 15, 2015; 89(10): 5406-5418. doi:10.1128/JVI.03395-14.
  12. ^ a b Emergency Disease Monitoring: Canine Influenza Virus (H3N2). Ithica, NY: Cornell University College of Veterinary Medicine; May 2015.
  13. ^ Nogales A, Rodriguez L, Chauche C, et al. Temperature-sensitive live-attenuated canine influenza virus H3N8 vaccine. J Virol. January 31, 2017. doi:10.1128/JVI.02211-16.
  14. ^ Canine Influenza Virus H3N2 | Killed Virus. Zoetis Inc. Published November 2015.
  15. ^ Merck Animal Health. Merck Animal Health Pioneers H3N2 Canine Influenza Vaccine. Published November 20, 2015.
  16. ^ United States Department of Agriculture Animal and Plant Health Inspection Service. Conditional licenses. Fed Regist. April 7 1987; 54: 11026. Codified at 9 CFR 102.6.
  17. ^ Iowa State University College of Veterinary Medicine. Canine Influenza. Published December 2009.