Canine Influenza- An Emerging Disease

By Mark Hale, DVM

Bolivar, MO

            With all the talk concerning human flu now, I thought it might be pertinent to discuss the canine flu virus. This disease is caused by influenza A subtype H3N8 virus, which was discovered in 2004 in racing greyhounds at a Florida track. This virus is a mutated equine influenza virus that now infects only canines. From June to August of 2004, outbreaks of influenza respiratory disease were reported at 14 tracks in 6 states. Since then, canine influenza has been documented in 30 states and Washington DC. These include our neighboring states of Arkansas, Kansas, and Iowa.

            Canine influenza is spread via aerosolized respiratory secretions and contaminated objects (food and water bowls, collars and leashes) and people moving between infected and uninfected dogs. The virus can remain viable for up to 48 hours in the environment. The time from exposure to becoming sick (incubation period) is usually 2-4 days. A complicating factor is that dogs are most contagious during the time before they become sick, which makes it hard to stop or control an outbreak. Viral shedding decreases after that, but may continue for up to 7 days in most dogs. Because there had never been an influenza virus of canines, all dogs are susceptible to infection as they have no natural immunity. If the virus enters a kennel or other closed group, a high percentage of the dogs become infected. About 20% will not show signs of disease, but will shed the virus to others. Most dogs will have a mild form and recover. These dogs typically have a cough that persists for 10-21 days, a green or yellow nasal discharge, and a low-grade fever. However, some will develop a severe pneumonia and a high fever, and may die even with aggressive treatment.

            Canine influenza cannot be diagnosed solely by clinical signs because these signs are similar to other respiratory pathogens. Cornell University has developed a test to confirm the virus' involvement. Samples must be obtained early in the disease for accuracy.

            Treatment is similar to other respiratory diseases. Antibiotics for secondary infections, IV fluids, and nebulizer treatments may all be necessary. Recovery may take 2-3 weeks. Fatality rates in exposed animals have been reported from 1-8%. 

            Prevention of this disease is similar to other flu viruses. Proper hand washing, disinfection of areas shared by dogs, and limiting exposure to possibly sick dogs are ways to help protect your pet. In May 2009, the USDA approved the conditional licensure of the first influenza vaccine for dogs, developed by Schering Plough Animal Health Corporation. This vaccine contains an inactivated whole virus, so it cannot cause the disease, as some people may fear. Although it may not completely prevent the disease, the vaccination has been shown to significantly reduce the severity and duration of clinical signs. In addition, vaccination decreases the amount of virus shed, thereby helping to control its' spread to other dogs. Vaccination is not recommended for every dog. In general, dogs that are most at risk and therefore candidates for vaccination are involved in activities with other dogs, such as shows, boarding kennels, and dog parks.

            At this time, to the best of my knowledge, no canine influenza has been diagnosed in Missouri yet. That will likely change in the near future. When this happens, you will need to discuss with your veterinarian if the vaccine is the right choice for your pet.