The Canine Flu: What You Need to Know

Canine Flu is in the news media this week and will probably continue to be for several weeks. So I decided that our practice better stay ahead of the curve, educate our clients, and make decisions on preventative care.

The common canine flu is the H3N8 strain.  I’m sure these numbers and letters look familiar because they are the same nomenclature used in defining strains of human flu. Odd as it may seem, the H3N8 strain was an equine (horse) flu that mutated to infect dogs. Recently, a new strain was introduced to the Great Lakes region from Asia, H3N2.  This is the outbreak that is currently spreading in Chicago and into Indiana and Wisconsin. Cases have also been reported in Ohio. This is a reportable disease, meaning that if a case is suspected it must be verified by blood tests and reported to federal officials for tracking. In other words, if reported, these cases are real. they are not cases that look like or may be flu, they are Influenza.


The obvious method of transmission is aerosol; sneezing and coughing from infected dogs. Also, the virus can survive for up to 2 days on surfaces outside of the animal. This includes clothes, water and food bowls, cage surfaces, grooming tables, etc.  

Once exposed, the incubation period before symptoms develop is about 2 days. During this time the dog is very contagious. This certainly aids in the spread as your dog may be around an apparently healthy dog that is really incubating and shedding the virus. An exposed dog will continue to shed the virus for up to 10 days.

Spread in the dog population is further enhanced by the fact that this is a new virus and no dogs carry a natural immunity. Virtually all dogs exposed will be infected when exposed.

Furthermore, unlike human flu strains, the dog strains are non-seasonal. Outbreaks have occurred any time of the year.


Think human flu.  On exposure, all dogs become infected. However, about 20% of exposed dogs do not develop symptoms. Super Man immune symptoms, I suppose. However these dogs will shed the virus like sick dogs do.  

The other 80% have symptoms ranging from a mild upper respiratory infection/sinusitis, to bronchitis, to a raging viral pneumonia with fevers of 104 to 106 degrees. Secondary bacterial infections are a major  complication that can lead to life threatening pneumonia. Symptoms last for up to 2 weeks in uncomplicated cases. Mortality is reported to be up to 10%.


A vaccine for H3N8 has been available for several years. It has been used successfully in areas of outbreaks in Florida, and on the East and West Coast. The vaccine is not full proof. It has been shown to be effective in preventing infection in most dogs or to dramatically reduce symptoms if infection does occur. Also, these dogs are much less likely to shed the virus.

Now for the catch. The outbreak in chicago is the H3N2 variety and there is no reported research to date of the vaccine efficacy against this strain. Sound familiar?  This is the same dilemma human doctors deal with every winter with the multitude of strains that develop worldwide.  

Our Recommendations and Requirements

Until research reports are published as to the efficacy of the vaccine versus H3N2 we will strongly recommend vaccinating using the current vaccine. However we will not consider it a core vaccine*.  If you take your dog to a grooming parlor, dog park, boarding facility, dog shows, or agility competition, chance of exposure is obviously greater. Therefore we strongly recommend vaccinating.  We also recommend vaccinating service dogs and immune compromised dogs. Immune compromised dogs can be super-geriatrics, dogs on chemotherapeutic drugs, dogs taking corticosteroids (prednisone), or other immune suppressing drugs for variable diseases. We will require all dogs using our boarding or grooming facility to be vaccinated for their protection and the rest of our patients.

Will this protect them against both strains of canine flu? We certainly hope so. In reality we just do not know at this time. But we certainly do not want to be in a situation where an outbreak occurs and the vaccine is determined to be effective and we did not protect our patients. This is our job, to make health decisions regarding our patients. We want to offer them the best care possible.

*For a description of core vaccines refer to the blog post on vaccines.

To learn more about the vaccination protocol for the canine flu please click here.

Information in this blog post has been sourced from the AVMA's most recent report on the current outbreak in Chicago. April 12th, 2015.

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