Canine influenza virus

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Clinical appearance of a dog with influenza virus, characterized by nasal discharge and rhinitis[1]

Canine influenza is a viral disease of dogs that is highly contagious, potentially deadly but with low seroprevalence across the northern hemisphere[2].

The canine influenza virus replicates in the epithelial tissue lining the nasal passages, trachea, bronchi, and bronchioles.

Viral replication results in epithelial cell necrosis and exposure of the basement membrane, which predisposes to secondary bacterial infection, which commonly progresses to pneumonia.

Spread is by aerosol and foment transfer, and has emerged transcontinentally due to the high frequency of transport of dogs across state borders for transnational dog shows and stud programs.

Strains which have been reported as pathogenic to dogs include:

  • H5N2[3] - mild upper respiratory signs only
  • H3N8[4] - common in shelter dogs
  • H3N2[5] - transmissible to cats

Recent outbreaks of H3N8 have been recorded in the greyhound, which quickly spread across the United States to domestic dogs. Affected dogs died rapidly from hemorrhagic pneumonia and the etiological agent was isolated on postmortem.

This virus is a novel type A orthomyxovirus similar to a known H3N8 equine influenza virus[6]. It is less prevalent than kennel cough but can cause fatal pneumonia in less than 10%[7].

Serologic evidence indicates that there is a sustained horizontal transmission of canine influenza H3N8 virus between dogs in the United States and the United Kingdom. Seroprevalence is higher in shelter dogs[8] and those vaccinated rather than unvaccinated[2]

CIV causes similar respiratory disease symptoms to other “kennel cough” pathogens, including Bordetella bronchiseptica, canine adenovirus, and canine parainfluenza virus.

Naïve dogs are susceptible and high morbidity rates (60-80%) are expected. The onset of clinical signs is typically less than 5 days after infection. Peak viral shedding occurs 2 - 4 days after infection, meaning that dogs may be at their most infectious prior to showing signs of disease.

Affected dogs are have symptoms of lethargy, anorexia, low grade fever, serous/mucoid/mucopurulent nasal discharge and rhinitis.

The most common sign is a persistent dry cough that lasts for several weeks, despite treatment. After the first week of coughing, 10 - 20% of dogs progress to more severe signs, including fever, dyspnea and secondary pneumonia.

Diagnosis is based on presenting clinical signs and isolation of virus using PCR assays from nasal swabs[9].

Cultures have revealed a variety of bacteria including Staphylococcus spp, hemolytic and nonhemolytic Streptococcus spp, Pasteurella multocida, Klebsiella pneumoniae, Escherichia coli, and Mycoplasma spp[10].

Treatment is usually supportive and may include broad-spectrum antimicrobials such as cephalosporins and amoxycillin/clavulanate[11].

A canine influenza vaccine is available in the United States made from inactivated virus.

The vaccine has been shown to reduce the incidence and severity of lung lesions, as well as the duration of coughing and viral shedding, and is administered by subcutaneous injection in two doses, two to four weeks apart.


  1. Shelter Medicine
  2. 2.0 2.1 Wiley CA et al (2013) The Seroprevalence of Canine Influenza Virus H3N8 in Dogs Participating in a Flyball Tournament in Pennsylvania in 2010: A Follow-Up Study. J Vet Intern Med 27(2):367-370
  3. Song QQ et al (2012) Dog to dog transmission of a novel influenza virus (H5N2) isolated from a canine. Vet Microbiol Aug 3
  4. Crawford, A et al (2007) Canine Influenza: Diagnosis, Clinical Disease, and Epidemiology. NAVC Proceedings
  5. Jeoung HY et al (2013) A novel canine influenza H3N2 virus isolated from cats in an animal shelter. Vet Microbiol Apr 6
  6. Hutsell, S & Camus, MS (2003) Canine Influenza: An Emerging Disease
  7. Crawford PC, Dubovi EJ, Castleman WL, et al (2005) Transmission of equine influenza virus to dogs. Science 310(5747):482-485
  8. Anderson TC et al (2013) Prevalence of and exposure factors for seropositivity to H3N8 canine influenza virus in dogs with influenza-like illness in the United States. J Am Vet Med Assoc 242(2):209-216
  9. Pecoraro HL et al (2013) Evaluation of virus isolation, one-step real-time reverse transcription polymerase chain reaction assay, and two rapid influenza diagnostic tests for detecting canine Influenza A virus H3N8 shedding in dogs. J Vet Diagn Invest Mar 27
  10. Daly JM, et al (2008) Transmission of equine influenza virus to English foxhounds. CDC Emerging Infectious Diseases 14(3):461-464
  11. Dubovi EJ & Njaa BL (2008) Canine Influenza. Veterinary Clinics of North America Small Animal Practice: Emerging and Reemerging Viruses of Dogs and Cats 38(4):827-835