Canine Flu Update – Vaccines and More

Published: December 14, 2015
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Flu season is upon us, at least in the world of human medicine. Despite the fact that canine influenza doesn’t seem to be nearly as seasonal as human influenza, I thought I’d take the opportunity to update you on some recent changes in the landscape of dog flu.

First of all, veterinarians and owners now have two types of dog flu to deal with. H3N8 strains of the virus were first diagnosed in dogs in 2004, developing after the equine influenza virus mutated and gained the ability to spread from dog to dog. Earlier this year, a new strain—H3N2—arrived in the U.S. from Asia and started wreaking havoc, particularly in the Midwest. Both the H3N8 and H3N2 strains of dog flu are now being diagnosed across large parts of the country.

The symptoms of dog flu are typical of many different respiratory infections. Some combination of coughing, sneezing, a runny nose, poor appetite, lethargy, and a fever are usually seen. It is impossible to tell which virus or bacteria (or combination of viruses or bacteria) is to blame for a dog’s symptoms without laboratory testing. Many veterinary diagnostic labs offer respiratory panels that will identify what pathogens are present. In particular, Cornell University’s Animal Health Diagnostic Center recommends a panel that includes polymerase chain reaction (PCR) tests for “canine adenovirus, canine distemper virus, canine parainfluenza virus, canine respiratory coronavirus, canine pneumovirus, Bordetella bronchiseptica, and Mycoplasma cynos along with matrix influenza PCR. Influenza A positive samples will be further characterized as H3N8 or H3N2 at no additional cost.”

Panels like this one are best run within a day or two of the dog developing signs consistent with a respiratory infection since PCR tests look for the presence of the pathogens themselves. If a dog is to be evaluated later in the course of the disease, antibody tests may be a better option, although previous vaccination can complicate interpreting the results.

Which brings me to the topic of vaccination. An H3N8 dog flu vaccine has been around for a while, but just a couple of weeks ago Merck Animal Health announced that their new H3N2 vaccine received a conditional license from the FDA and is now available to veterinarians.

According the U.S. Department of Agriculture, conditional licenses “are used to meet an emergency condition, limited market, local situation, or other special circumstance.”

The data required for conditional licensure are reduced from that needed for full licensure in that there needs only to be a “reasonable expectation” of efficacy…. Conditionally licensed products must meet the same safety and purity requirements as fully licensed products.

The decision of whether or not to vaccinate a dog against canine influenza can be complicated (even when we’re not dealing with a conditionally licensed product). The flu can make dogs quite sick, a few individuals will even die, but most recover uneventfully. Also, flu vaccines don’t actually prevent infection with the virus. They are designed to decrease the severity of the illness that results and reduce the spread of the virus. This last point may be especially important with regards to the H3N2 dog flu virus. As a Merck news release states:

According to clinical studies by researchers at the University of Wisconsin, the CIV [canine influenza virus] H3N2 may be shed for an extended period of time – up to 24 days, which is far longer than what is seen with CIV H3N8.2 As a result, the infection can spread quickly among social dogs in inner cities, doggie daycares, boarding facilities, dog parks, sporting and show events and any location where dogs commingle.

"Based on experimental studies in Asia and the rate of spread we've observed, I would estimate that H3N2 produces 10 times more virus than H3N8, which makes it far more contagious," said Edward Dubovi, Ph.D., Professor of Virology and Director, Virology Laboratory, Animal Health Diagnostic Center, College of Veterinary Medicine, Cornell University. "Preventing the transmission of the disease through vaccination is highly recommended for those dogs that have lifestyles that put them at greater risk."

Talk to your veterinarian about the pros and cons of vaccinating your dog against H3N8 and/or H3N2 dog flu.

Dr. Jennifer Coates