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H3N2 Canine influenza virus

Canine influenza virus

Canine influenza virus (CIV) is a type of influenza A that is adapted to dogs. Influenza virus strains are named based on their hemagglutinin (H) and neuraminidase (N) types. There are two different CIVs in North America.
H3N8 CIV was first identified in Florida in the early 2000s and was the result of adaptation of an equine influenza strain to dogs. This virus is still present in the US but the incidence of disease appears to be relatively low.
H3N2 CIV is a more recently encountered strain in North America. It is believed to have originated in Asia as a result of direct transmission of an avian H3N2 virus to dogs. Canine H3N2 was likely introduced to the US in 2015 through importation of dogs from South Korea. It has spread widely in the US, causing outbreaks in many regions.

CIV in Canada

Until recently, CIV activity has not been clearly documented in Canada. H3N2 CIV was first identified in southwestern Ontario in late December 2017.


Transmission involves direct contact, short-distance aerosol transmission and indirect transmission from contaminated fomites. Direct contact poses the highest risk. Humans can potentially act as fomites through short-term carriage of CIV on their bodies or clothing, with subsequent exposure of a dog.

Infected dogs can start shedding CIV before the onset of disease (usually- 24th before), so clinically normal dogs can be a source of infection. Shedding of H3N2 CIV has not been well investigated, but H3N2 CIV appears to have a relatively long period of infectivity. A study of a shelter outbreak showed that shedding most often stopped with 14d, yet intermittent positive PCR results were obtained in some dogs for up to 24 days. Whether that reflects intermittent shedding. Prolonged low level shedding or re-exposure is difficult to discern

Clinical disease

H3N2 influenza causes disease that is indistinguishable from other causes of canine infectious respiratory disease complex (CIRDC, also referred to as kennel cough). Dogs of any age can be affected, although disease is more likely to be serve in very young and old dogs, as well as brachycephalic breeds.
Coughing, sneezing, nasal discharge, ocular discharge, decrease appetite and fever are the main signs. Fever is often transient and may not be present by the time of veterinary examination. Cough can persist after elimination of active infection, and cough is not a good indicator of risk of viral shedding. Most dogs fully recover within 2-3 weeks.
Complications are uncommon but the true incidence of severe disease associated with H3N2 CIV is not well understood. Secondary bacterial pneumonia is the main concern. Fatal infections are rare but can occur. High or persistent fever, increase respiratory rate and effort, anorexia and purulent nasal discharge are indicators of more sever disease and/or secondary bacterial infection.


Diagnosis usually involves detection of CIV by PCR from nasal swabs. Nasopharyngeal or oropharyngeal swabs can also be collected but nasal swabs are preferred. Ocular swabs can also be tested but are lower yield. PCR testing can broadly detect influenza A or target specific influenza types (e.g H3N2), PCR testing detects viral shedding and is highest yield early in disease.

Serological testing can be performed but is of limited use clinically. In areas where CIV has not been present, a single positive antibody titre is suggestive of infection in dogs that have not been previously vaccinated or traveled to a region where CIV is present. However, definitive diagnosis requires detection of a 4-fold increase in antibody titre in samples collected 2-4 weeks apart. It is preferable to test the acute and convalescent samples at the same time, so serological diagnosis of CIV is retrospective. Virus isolation can also be performed but is less common.


There are no specific treatments. Supportive care (e.g. cough suppressants) should be provided, as needed. Antibiotics are note indicated for CIV infection, but occasionally may be needed if a secondary bacterial component develops, as is described in recent respiratory infection guidelines.


Commercial vaccines are available. These may be against H3N8 of both H3N8 and H3N2. Vaccination is not 100% effective but can reduce the risk and potentially severity of infection. A minimum of 2 doses is required, 2-4 weeks apart. CIV vaccination is a non-core vaccine that should be considered base on the risk of exposure and the risk of complications of infection.

Infection control in veterinary facilities

CIV is highly transmissible in veterinary clinics, particularly in areas where CIV is new, because of the high transmissibility of the virus and the naïve canine population. Various exposure risks and sources may be present, including mixing of dogs in waiting rooms, contamination of waiting room, examination and treatment room environments, aerosol transmission in ward and treatment areas and indirect transmission through veterinary personnel or equipment.

Control of CIV in veterinary clinic is dependent on prompt recognition of the potential for CIV and use of enhanced infection control practices, along with good potential for CIV and use of enhanced infection control practices, along with good adherence to general principles of infection control.

  • Front office staff should flag any acute respiratory disease cases at the time of appointment booking. Owners can be directed to call from their vehicle upon arrival or come into the clinic initially without their dog. The dog can then be admitted directly to an examination room or isolation area and personnel can start the appointment wearing additional personal protective equipment (gown or lab coat that will be used just for that appointment, gloves). Routine use of mask and eye protection is not required, but should be considered in situations where someone’s face will be in close proximity to a potentially infected dog, especially if the dog is coughing. In that event, goggles and mask, or a face shield, should be used.
  • Infected (or suspected) cases should be housed is an isolation area and handled with enhanced precautions (as described above).
  • Potentially contaminated items (e.g. stethoscopes) should be cleaned and disinfected after use on a CIV suspect, potentially contaminated consumable materials should be disinfected or discarded. 
  • Routine disinfectants, used properly, will inactivate CIV, Prompt and careful disinfection of potentially contaminated environments is required.
  • Veterinary personnel should pay close attention to hand hygiene. Hands should be washed or an alcohol-based hand sanitizer should be used after patient contact (including after removing gloves). Alcohol-based hand sanitizers will effectively inactivate CIV.

Zoonotic Potential

H3N2 CIV is different than the common H3N2 human (seasonal) influenza virus. There is currently no evidence that H3N2 CIV can infect people. However, potential for human infection cannot be discounted. Of greater concern is the potential for re-assortment of human influenza and CIV, if a dog (or person) is infected with both strains at the same time, as occasional infections of dogs with human H3N2 or H1N1 influenza viruses have been identified. Re-assortment of influenza viruses is of concern because it can potentially result in a virus that is readily able to infect people but is different enough from other human influenza viruses that people have no immunity from previous influenza infection or vaccination.


As of January 1, 2018, Ontario veterinarians are veterinary laboratories are required to immediately report known or suspected infections with ‘novel influenza viruses’ to their local Medical Officer of Health. This includes influenza viruses not known to be circulating in Ontario, which would include H3N2 CIV at this time.

Other species

H3N2 CIV can infect cats. But the incidence appears to be low. Ferrets are susceptible to a range of influenza viruses and are also susceptible to H3N2 CIV