Dog Flu Facts

Canine flu spreads in one of two ways: movement of infective dogs between communities and movement of contaminated people between dogs.

Dogs transmit it to each other through direct contact with respiratory secretions delivered by barking, coughing, or sneezing. They also can acquire the virus through contact with contaminated surfaces or items such as food or water bowls. Dr. Dubovi said there is some evidence that dogs infected with H3N2 shed the virus for longer periods than dogs with H3N8.

Boarding kennels, dog daycare centers, dog parks, and animal shelters offer other opportunities for the virus to spread. The trend of people bringing their dogs to public spaces, workplaces, hotels, and restaurants with outdoor seating or traveling cross-country with them by plane, car or recreational vehicle contributes as well.

Although the disease in most cases is mild, it’s highly contagious and can spread rapidly any timelarge groups of dogs gather in one place. Dog shows are a prime example. Last year, the virus blew through the dog show community, sickening hundreds of dogs and killing several. Because bothstrains are relatively new, many dogs haven’t been exposed to or vaccinated for the viruses.

Diagnosis and management

Canine influenza can’t be diagnosed on clinical signs alone. It is most accurately tested for byswabbing the nasal and pharyngeal cavities of suspect dogs and submitting the swabs to a diagnostic laboratory that offers the PCR test for both H3N8 and H3N2 canine influenza, Dr. Crawford said. The test is most accurate when swabs are collected in the first few days of illness.

Practices in areas where the virus is prevalent need a plan for managing dogs with acute respiratory infections without putting other dogs at risk. That may include examining those dogs while theyremain in the owner’s vehicle and, if they need hospitalization, keeping them in a secure isolationspace with tight biosecurity precautions. Clothing, including shoes, equipment, surfaces, and hands should be cleaned and disinfected after exposure to dogs showing signs of respiratory disease.


In mild cases, dogs display typical clinical signs of coughing, sneezing, and nasal discharge for two to three weeks or as long as 30 days. The viruses compromise the natural defense systems of the upper respiratory tract, and some dogs infected by either virus will progress to severe and even life- threatening pneumonia.

Preventing secondary bacterial pneumonia is a key part of treatment, Dr. Dubovi said. Catching canine influenza early and providing supportive care is essential.

Whether to vaccinate

Any dog without immunity conferred by a prior infection or vaccination can develop canine flu, but very young or old dogs, dogs with chronic health conditions, or dogs with certain anatomic features are at higher risk for consequences from the disease. That risk group includes brachycephalic breeds such as bulldogs, pugs, and Pekingese. Their flat faces make it difficult for these dogs to breathe under normal circumstances, and an upper respiratory infection exacerbates the problem.

The newest vaccine is Vanguard, a bivalent vaccine released in December by Zoetis that protects against both strains known to be circulating in the United States: H3N2 and H3N8.

Dogs also can receive individual vaccines for each flu strain. Merck makes a killed-virus vaccine against H3N8 as well as a bivalent vaccine. Zoetis produces a killed-virus vaccine against H3N2.

While the vaccines induce immunity, they don’t necessarily prevent infection in an individual. But a dog who has received the vaccine is likely to experience a less severe and less lengthy form of the disease, Dr. Dubovi said.

“The vaccines under the best of conditions are not going to prevent infection,” he said. “They rarely would ever do that, but what they will do is reduce the amount of clinical signs associated with theinfection and reduce the period of time of the virus being shared from one dog to another.”

More important, said Dr. Crawford, the canine vaccine has been shown to protect against pneumonia. The newer strain, H3N2, may cause more severe disease and pathology in the lungs. A higher percentage of dogs with H3N2 develop pneumonia, so the vaccine can be protective in that way.

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