DVM: Why is canine influenza an emerging threat?
Crawford: We have not recognized previously that dogs were susceptible to infection by influenza viruses. This virus was first reported in dogs and associated with the occurrence of respiratory infections in 2004. So, just five years ago, it was first reported, and I would say that it is now a recently recognized viral infection of dogs as opposed to newly emerging virus.
DVM: How serious is the virus, especially for animals boarded at animal hospitals?
Crawford: Canine influenza is a community-acquired infection. It occurs in facilities where dogs are housed together and there is a high frequency of movement in and out of the facility. So dogs that are in shelters, boarding or training facilities, day-care centers, veterinary clinics, pet stores and grooming parlors are at highest risk for exposure to canine influenza virus, especially if the facilities are in communities where the virus is prevalent.
Like influenza viruses in other species, canine influenza virus causes an acute respiratory infection in dogs. The clinical signs are very similar to respiratory disease caused by other viruses and bacteria known to cause kennel cough. The term kennel cough is well recognized by dog owners and used by veterinarians to describe a cough that a dog develops while boarding, visiting the grooming parlor or after purchase from a pet store.
The clinical illness is very flu-like. It’s very similar to what humans experience when they are infected with an influenza virus. They experience a cough, which is the primary sign, sneezing and a runny nose. The cough can persist for two to three weeks.
Most dogs recover from the flu-like illness, and they recover just fine after two to three weeks without further health complications. However, some progress to pneumonia, usually due to secondary bacterial infections. The pneumonia likely will require more intensive care in a hospital setting under veterinary supervision. And this pneumonia has been life-threatening in several cases. Fortunately, the mortality rate for dogs with canine influenza is low. It can be higher in dogs that develop secondary bacterial pneumonia if they are not treated appropriately.
DVM: When an outbreak occurs, what’s the next step for practitioners?
Crawford: First, I recommend diagnosis. It is very hard to know how to manage an outbreak of respiratory disease if you don’t know what is causing it. There are many other viruses and bacteria that can cause respiratory-disease outbreaks, not just canine influenza virus. All of these viruses and bacterial pathogens may have different properties that will affect how the outbreak is managed. I think diagnosis will help direct treatment and management and prevent further outbreaks.
DVM: Is the threat of an outbreak more serious now because it can spread between dogs?
Crawford: Dog-to-dog transmission ensures the horizontal spread of the virus through a population of dogs. So, yes, it is easily spread. It is highly contagious, just like influenza viruses are generally.
We have lab confirmation of infected dogs now in 30 states and the District of Columbia. Five years ago, we detected the virus in dogs in only one state, Florida. But as we began looking at more and more dogs across the country, the numbers increased to thousands and many more states.
So the virus is slowly spreading, probably through the canine population in the United States over the past five years. It’s very hard to estimate the number of dogs that have been infected because there is no central reporting agency collecting that data from veterinarians.
However, this is an influenza virus, and one of its properties is unpredictability. So as more and more dogs become infected with canine influenza virus, the virus can become more virulent or, alternatively, it could become less virulent. Influenza viruses have been known to wax and wane in a community. At times they are more prevalent, at other times it appears they may not be circulating. So these are all hallmarks of influenza viruses in general, and certainly canine influenza virus fits into that type of behavior.
We have not recognized a seasonality pattern to canine influenza. The real pattern is that it occurs in facilities with frequent movement of dogs in and out. This is the same pattern that exists for other respiratory pathogens for dogs, namely Bordetella bronchiseptica bacterium or the adenovirus, other viruses that cause respiratory infections in dogs. The likelihood of exposure and infection is increased for dogs that are housed in a kennel-like setting together.