Overview

Canine influenza is an important illness that poses an emerging threat to all dogs.

Influenza A virus is a highly contagious enveloped virus that causes respiratory illness and pandemics in humans. It has a wide host species range, and specific subtypes cause disease in birds, cats, horses, and dogs. Influenza viruses usually exhibit species-specific infectivity.⁴ However, the influenza A virus is one of the most mutable among the influenza viruses. The H3N8 subtype of canine influenza virus (CIV) is genetically similar to the type that causes influenza in horses and is believed to have jumped to Greyhound dogs at racing facilities in the United States in 2003.^2,4

Canine influenza is easily spread and is now considered to be a community-acquired illness that has been documented in a variety of breeds in the general canine population throughout the United States.² The prevalence is increasing, and outbreaks have been reported in dog-racing facilities, veterinary offices, pet stores, shelters, and kennels.^4-8 A major concern is that virtually 100% of newly exposed dogs are susceptible because CIV is a novel pathogen and there is no preexisting immunity. Dogs of any breed, age, and those that have been vaccinated for other pathogens that cause canine respiratory infections (eg, canine cough, infectious tracheobronchitis) are susceptible to CIV infection.²

CIV is part of the constellation of canine infectious respiratory disease (CIRD) complex, which is often referred to using the terms infectious tracheobronchitis, or canine cough, interchangeably. However, these two terms are misleading because the complicated syndrome of CIRD complex is not limited to the trachea, nor does it always present as coughing. CIRD complex may be caused by CIV, or other viral (eg, parainfluenza, adenovirus, canine respiratory coronavirus, canine herpesvirus) or bacterial (eg, Bordetella bronchiseptica, Mycoplasma spp., Streptococcus equi subsp zooepidemicus) pathogens. Secondary bacterial infection may be an important factor leading to more severe systemic manifestations.⁹

CIV infection can be difficult to differentiate from these other acute respiratory conditions because it presents with similar clinical signs, including mild, low-grade fever, cough (productive or dry) lasting between 10 to 30 days, and potentially thick, purulent, and/or bloody nasal discharge.⁸ Therefore, canine influenza should be suspected in any dog that has signs of respiratory infection, and as for other contagious respiratory infections, precautions should be taken to isolate the dog to prevent spread to other dogs in the population.^2,8

Of those dogs exposed:⁸

• Between 80 to 90% will develop clinical infection
• Up to 20% of dogs with CIV infection will develop a more severe systemic form of canine influenza that manifests with a high fever (104-106°F) and pneumonia
• About 10 to 20% of dogs will contract the infection but not show clinical signs

It is important to note that dogs that do not show clinical signs can still pass the infection to other dogs. The mortality rate of canine influenza has been reported to range from 1 to 8% in puppies and older dogs.² Serology can be performed to confirm a diagnosis of CIV infection; however, samples must be sent out, so this diagnostic test does not help acute management.⁸

There is no treatment specifically for CIV infection; treatment consists of supportive therapy. Intravenous fluids may be helpful. Antibiotics may be indicated in the case of secondary bacterial infection, with selection guided by culture and sensitivity testing.^2,6

The pattern of a sudden increase in the prevalence of acute respiratory disease, severity of illness, or a lack of response to antibiotic therapy is one of the first warning signs of a CIV outbreak. It is important to recognize this pattern so that appropriate isolation and other precautions can be taken to minimize the spread of this highly contagious virus. In addition, a veterinarian should be consulted to ensure that appropriate treatment is implemented.

As with any infectious disease outbreak, management of canine influenza requires breaking the cycle of transmission among dogs that are infected and those that are exposed through:

• Early recognition, treatment, and isolation of infected or potentially infected dogs
• Environmental control procedures
• Education of veterinary professionals, kennel owners, shelter managers, and dog owners
• Vaccination

An effective vaccine for canine influenza is now approved and USDA-licensed specifically for use in dogs - Nobivac^® Canine Flu H3N8.
Note: The equine vaccine should not be used in dogs.