Like influenza viruses that infect other mammals, canine influenza virus causes an acute respiratory infection in dogs. It is one of several viruses and bacteria that are associated with canine infectious respiratory disease, or what is commonly referred to as "kennel cough." Because canine influenza is a novel virus to the canine population, dogs lack preexisting immunity to the virus. Virtually all dogs that are exposed become infected with the virus; and approximately 80% develop clinical signs of disease. The 20% of infected dogs that do not exhibit clinical signs of disease can still spread the infection. The virus is most likely to spread in facilities where dogs are housed together and where there is a high turnover of dogs in and out of the facility. As with other respiratory pathogens, the virus is spread primarily by direct contact with infected dogs and by aerosols generated by coughing and sneezing. The virus can also contaminate kennel surfaces, food and water bowls, collars and leashes, and the hands and clothing of the people who handle infected dogs. Fortunately, the virus is easily made inactive by washing with soap and water, or the use of a 5% bleach solution to clean the facilities. Unlike human influenza, canine influenza is not a "seasonal" infection, but can occur year round.
Canine influenza cannot be diagnosed by clinical signs because all of the other respiratory pathogens cause similar signs of coughing, sneezing and nasal discharge. Canine influenza virus causes clinical disease that mimics kennel cough. As a result, infection with the virus is frequently mistaken for infections of kennel cough. A full serological workup is required to definitively diagnose canine influenza.
The majority of infected dogs (80%) exhibit the mild form of canine influenza. In the mild form, the most common clinical sign is a cough that persists for 10 to 21 days despite treatment with antibiotics and cough suppressants. Most dogs have a soft, moist cough, whereas others have a dry cough that is similar to that induced by Bordetella bronchiseptica/parainfluenza virus infection (kennel cough). Many dogs have a nasal discharge and a low-grade fever. The nasal discharge is usually caused by secondary bacterial infections.
Some dogs are more severely affected with clinical signs of pneumonia, such as a high-grade fever (104°F to 106°F) and increased respiratory rate and effort. Canine influenza has not shown to have a high mortality rate. Only about 1-1.5% of dogs infected have died and most of these where older dogs or dogs with other health problems.
Since canine influenza is a viral infection, treatment consists mainly of supportive care while the virus runs its course, much like for human influenza. Good husbandry and nutrition may assist dogs in mounting an effective immune response. Dog owners should consult with their veterinarians if they think their dog has canine influenza. The veterinarian can determine what type of supportive care is needed, including whether antibiotics should be given for secondary bacterial infections. Dogs with pneumonia most likely require more intensive care provided in a hospital setting under the supervision of a veterinarian.
