Canine Influenza Virus

Canine influenza is a highly contagious respiratory infection caused by influenza A subtype H3N8 virus. Influenza A viruses are RNA viruses (family Orthmyxoviridae) which are naturally maintained in aquatic birds, occasionally transfer to mammals to cause individual infections or outbreaks of disease, and sometimes go on to cause epidemics and pandemics in their new hosts. Influenza viruses can also transfer between different mammalian host species, as has recently been observed in the case of swine-origin pandemic H1N1 influenza A virus that emerged in 2009 in humans.8 In kennels and shelters, the infection rate may reach 100 percent. Dogs of all ages are susceptible to infection with canine influenza virus (CIV) and prior vaccination against canine distemper, adenovirus type 2, parainfluenza virus, and Bordetella brochiseptica does not diminish introduction and spread of CIV within a kennel.3,6

The A/H3N8 canine influenza virus (CIV) is a new pathogen of dogs, which resulted from the transfer of an intact A/H3N8 equine influenza virus (EIV) to the dog. CIV was first isolated from the lungs of racing greyhounds that died from pneumonia during outbreaks of acute respiratory disease at tracks in Florida in 2003 and 2004. Infections occurs through inhalation of airborne viral particles or oral contact with contaminated surfaces. Most cases have a history of group housing: kennels, day care centers, rescue shelters, or contact with dogs that have recently been in group housing. These dogs are also at great risk of exposure to other respiratory pathogens, such as Streptococcus equi subsp. zooepidemicus, which has been isolated from shelter dogs with acute fatal hemorrhagic pneumonia.7

Early signs are almost indistinguishable from signs of kennel cough. Most dogs develop a relatively mild form of the disease, which is characterized by a cough that may persist for weeks in spite of treatment. Many dogs recover without any complications, while in others the cough is accompanied by fever and nasal discharge. A few dogs develop pneumonia with bleeding in the respiratory tract, but this is quite rare.1 The virus may also cause lymphocytic and neutrophilic rhinitis.4 Animals with influenza are usually treated with supportive care and rest. Antibiotics may be used to control secondary bacterial infections.5

The first influenza vaccine for dogs (an inactivated vaccine containing CIV subtype H3N8), was conditionally approved by the U.S. Department of Agriculture (USDA) for licensure in May 2009 and fully licensed in June 2010. To achieve protection, it is important that dogs are vaccinated at least 3 weeks before exposure to CIV. Immunity can be expected approximately 7 days after the second dose. To ensure protection, dogs at risk for CIV, such as those that routinely spend time in multidog facilities, such as dog day care, boarding facilities, and dog shows, should be given 2 doses of CIV (H3N8) vaccine 2 weeks apart and then held for 7 days before being placed in contact with other dogs.7

Influenza virus H1N1
Virions from a Novel Flu H1N1 (source: Cynthia Goldsmith, CDC)


  1. Anna Rovid Spickler, James A. Roth, Jane Galyon, Jeanne Lofstedt. Emerging and Exotic Diseases of Animals
  2. C. Greene. Infectious Diseases Of The Dog And Cat.
  3. Lila Miller, Kate Hurley. Infectious Disease Management in Animal Shelters
  4. Michael Schaer. Clinical Medicine of the Dog and Cat
  5. Glenda Dvorak, Anna Rovid Spickler, James A. Roth (editors). Handbook for Zoonotic Diseases of Companion Animals
  6. Larry P. Tilley, Francis W. K. Smith, Jr. (editors). Blackwell's Five-Minute Veterinary Consult: Canine and Feline
  7. Efficacy of the Canine Influenza Virus H3N8 Vaccine To Decrease Severity of Clinical Disease after Cochallenge with Canine Influenza Virus and Streptococcus equi subsp. zooepidemicus
  8. Microevolution of Canine Influenza Virus in Shelters and Its Molecular Epidemiology in the United States

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