by Barry B. Burtis D.V.M.
In recent months we have read and heard a great deal about avian influenza. Medical authorities warn of the very real risk that this disease, at present affecting birds in various places in the world, could trigger a human influenza pandemic. Although not in any way related to the avian influenza threat, veterinarians and dog owners have recently learned that a new canine influenza virus has been identified as a new cause of disease in dogs.
Canine influenza is caused by a type A influenza virus in the Orthomyxovirus family. Canine influenza virus (CIV) is closely related to equine influenza virus and is an example of transmission across species (i.e. horse to dog). The virus, having adapted to dogs, now can spread from dog to dog, easily spreading the disease. This, of course, is exactly what is feared could happen when the avian influenza virus causes infection in people and may then develop the ability to spread from person to person. It should be noted that neither the CIV nor the equine influenza virus from which it is derived, has ever been demonstrated to infect humans.
The first recognized outbreak of canine influenza occurred in racing greyhounds in January 2004 at a track in Florida. CIV infection was reported at 14 tracks in 6 other states before the end of that year. In 2005 it continued to cause disease at a number of other dog racing tracks in the United States. Canine influenza has now been confirmed to have infected family dogs in Florida and New York State. At the time I write this column, in the first week of November, a spokesperson at the Animal Health Laboratory in Guelph, told me there have not yet been any confirmed cases in dogs in Canada. The Guelph laboratory can test for the canine influenza virus and therefore will be able to assist veterinarians in the diagnosis of the problem in any canine patients under their care.
Canine influenza is spread via respiratory secretions transmitted through the air or on inanimate objects or people moving between infected and uninfected dogs. The incubation period is usually two to five days. Infected dogs shed virus for four to seven days after clinical signs develop. It is likely inevitable that dogs in our area will eventually be infected. Because this is a new disease, all dogs, regardless of breed or age are susceptible to infection and have no natural or vaccine-induced immunity. Virtually all dogs that are exposed to the virus become infected. It is reported that up to 20% of infected dogs do not show signs of the disease but still shed the virus and therefore can spread the infection. Fortunately, although the disease is easily spread, most dogs recover without complications.
CIV causes a disease very similar to infectious tracheobronchitis or kennel cough. The disease may be mild or severe. In the mild form, a persistent, soft, moist cough is noticed. This cough may last for 10-30 days and appears quite resistant to medications usually used in the treatment of kennel cough. Many dogs have a purulent nasal discharge and run a low grade fever. The nasal discharge is usually caused by secondary bacterial infection. Some dogs are more severely affected with signs of pneumonia, a high fever and increased respiratory rate and effort. In dog shelters, morbidity or the number of animals affected can be as high as 80%. If treated, mortality or animals that die of the disease can be decreased to 5% of those infected.
Treatment, as for most viral diseases is largely supportive. Good nursing care and proper nutrition may help animals mount an effective immune response to the virus. Antibiotics and other antimicrobial agents are necessary to control bacterial infections complicating the disease. Intravenous fluids may be necessary to maintain proper hydration in sick dogs.
At this time there is no vaccine available to protect against canine influenza. Vigilance must be exercised by all persons handling dogs to reduce the risk of spreading the disease. Boarding kennels, animal shelters and veterinary hospitals will need to be attentive to proper cleaning and disinfecting protocols in order to kill any virus in such facilities. Dog owners need to be aware of the danger posed by this infection and consult their veterinarian with any questions regarding their pet.