Canine influenza virus (CIV) is a respiratory tract disease that mimics Bordetella bronchiseptica infection (kennel cough). It is a highly contagious virus that was identified in Florida in 2005 when it caused several severe respiratory outbreaks in racing greyhounds. Since it is a relatively new virus, almost all dogs are susceptible to infection when they are first exposed because they have not built up natural immunity. Most dogs that develop CIV infection have a mild illness, but some dogs get very sick and require treatment. The disease appears to occur most frequently in high-density dog populations. The disease is thought to have originated as a mutation of an influenza strain that affects horses and is not related to typical human influenza strains or the avian flu.

Transmission :
The virus is efficiently spread between dogs by aerosol, direct transmission, and transmission of respiratory secretions via fomites. Common fomites include toys, chew toys, bedding, etc. The actual virus persists for less than one week in the environment and is easily killed with bleach and other common disinfectants. No known transmission to humans has occurred.

There does not appear to be a carrier state of the disease, and no one knows how long immunity lasts after natural exposure. Influenza viruses can change over time, allowing them to evade host defenses, but it is unknown if this will happen with canine influenza. All previously unexposed dogs are susceptible, regardless of age, sex, breed, or vaccination status, but the disease is more likely to become clinically apparent in dogs that are housed in populations such as animal shelters, boarding facilities or day care settings.

Clinical Signs :
60-80% of infected dogs develop clinical signs. There is a 2-5 day incubation period post infection. Nasal virus shedding peaks during this time. Clinical signs generally do not become apparent until day 5-7 and in most cases shedding wanes by 7-10 days after infection. Clinical signs are generally very mild to inapparent during peak viral shedding. A soft, moist, sometimes-productive cough is seen. The cough often persists for several weeks, even with appropriate therapy. Dogs may lose their appetite, develop a fever, and produce a pus-like nasal discharge. Up to 10% of dogs may develop a more severe form of illness, with high fever, lethargy, rapid breathing, and secondary bronchopneumonia. Dogs at higher risk for a more severe form of canine influenza include those that are in poor condition and/or are debilitated, concurrently exposed to other pathogens, very young or very old patients. The fatality rate related to pneumonia/bronchopneumonia is reported to be around 5-8% in selected high-risk populations. Acute, fatal hemorrhagic pneumonia tends to occur only in greyhounds. After day five, approximately 10-20% of affected dogs have no symptoms but are still shedding infectious virus.

Distinguishing CIV from other causes of acute respiratory disease based on clinical signs can be difficult.

Diagnosis :
Diagnosis includes physical examination, blood tests looking for antibodies to the disease, virus isolation, thoracic radiographs, etc.

Treatment/Management :

  • Mild cases are often self-limiting, and may require only isolating the dog and providing supportive care, such as nutrition, rest, prevention of dehydration, and so on. Uncomplicated cases should resolve within 10-14 days.
  • Dogs with severe clinical signs, treatment is aimed at preventing secondary infection and is also largely supportive. Fluid support is important. Antimicrobials that target secondary bacterial infections are needed, and are ideally chosen based upon culture and sensitivity tests.
  • It is generally recommended to NOT use human antiviral drugs that are neuraminidase inhibitors like Tamiflu. They require use early in the course of influenza infection when it is unlikely that disease will even have been noticed; there are no efficacy or safety studies done on animals; and there are potential resistance mechanisms that could develop with implications for human medicine.

Preventive of CIV:
Control of CIV relies primarily on reducing the spread of virus between dogs. If CIV is established in a boarding facility the kennel should be evacuated for 1-2 weeks and be disinfected.
CIV is best prevented by vaccination prior to boarding. Although vaccination may not prevent infection, it tends to reduce the severity and duration of the disease. The vaccine is first administered twice within a 3 week period then annually.
Please contact us at Brooklyn Veterinary Group to schedule an appointment to have your pet vaccinated against canine influenza virus.