Canine Influenza


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How Important is Vaccination?

Between December 27, 2017 and February 12, 2018, there were 413 confirmed cases of canine influenza in California, most of them in the San Francisco Bay Area. During the last half of March and the end of April, 2018, 65 percent of cases reported nationwide were in California. If we include Nevada (primarily the Reno area), that number jumps to 87 percent. And, because most cases are not definitively diagnosed, the actual number of dogs infected is almost certainly much higher.

Since 2015, California has seen sporadic cases of canine flu, but nothing that approaches the significance of the outbreak we are seeing now. It has brought us to the forefront of a renewed nationwide discussion about the nature of the threat, as well as the best way to protect our pets from it. People ask me about canine flu every day, with a frequency that suggests it has become an important topic of discussion in our own community, as well.

Here are some thoughts to consider when deciding if your dog should receive a vaccination.

People ask me about canine flu every day, with a frequency that suggests it has become an important topic of discussion in our own community.


There are two known strains of canine flu: H3N8 and H3N2. H3N8 was discovered in Florida in 2004 in a group of racing greyhounds. Research determined that it was a horse virus that mutated and jumped species to dogs. Deeper investigation revealed that it may have been present as far back as 1999, but prior to that time canine influenza didn’t exist. The virus subsequently caused a number of small outbreaks among greyhounds at racetracks in several states and a significant outbreak among all breeds in New York in 2005. A vaccine against H3N8 was introduced in 2009. Even so, it has since appeared in nearly every state and become endemic in many parts of the country.

Outside the United States, concerns began to surface in 2007 when H3N2 was discovered in South Korea. Its precise origin is unclear, but we know it was an avian virus that jumped from birds to dogs, possibly through exposure in markets in other parts of Asia. Any remaining complacency about canine flu disappeared in March 2015, when H3N2 turned up in Chicago (nobody knows exactly how) and caused a major outbreak. By the end of the year, it had been identified in several other states, causing smaller outbreaks in Atlanta in the summer/fall of 2015, and in Seattle in early 2016. As is typical with flu vaccines, the H3N8 vaccine is ineffective against H3N2. A vaccine against H3N2 was not available until the end of 2015, but its use has only gradually increased, and cases have continued to appear. Unlike human flu, there is no seasonal variation in the transmission of canine flu.

While there is still a lot we don’t know about canine influenza, it seems possible that, even though both strains cause similar illness, H3N2 may be more easily transmitted than H3N8, or at least carriers may be contagious for a longer period of time. For the last three years, H3N2 has been the dominant strain in every area where multiple cases have been confirmed, although H3N8 hasn’t gone away. Currently, vaccines are available that protect against both strains. Because canine influenza is a newly emerged virus, there is no natural immunity to it, so vaccination has become a key component in efforts to control both the spread of the disease and the severity of outbreaks where they occur.


In a general sense, dogs catch canine flu the same way people catch human flu. (Fortunately, people don’t get dog flu.) The virus is contained in aerosolized droplets of saliva or respiratory secretions and is usually transmitted through coughing, sneezing, and barking. But it is also easily passed by contact with contaminated surfaces, like chew toys, water bowls, or kennels, and even people’s clothing and hands. Studies have shown the virus remains viable for up to 48 hours on surfaces, 24 hours on clothing, and 12 hours on hands.

Because no population immunity exists, we can assume every unvaccinated, exposed dog will become infected. Of those infected, as many as 20 percent may show no obvious symptoms, but 80 percent will become ill. Even those who don’t become sick can still transmit the virus. Transmission is most likely to occur in the first 2 to 3 days after infection, at a point where some dogs have few symptoms, so they may be most contagious when their condition is least obvious. After that relatively short window of high infectivity, the virus becomes difficult to detect through the most commonly used diagnostic tests. As a result, many cases of canine flu are never accurately diagnosed, which means that the number of confirmed cases reported may represent only a portion of the total number of dogs affected.

Symptoms and Treatment

There is another reason statistics on the number of dogs with flu probably don’t represent the true number of cases. The symptoms can be very similar to other respiratory diseases, often described as “kennel cough”: coughing, sneezing, nasal discharge, loss of appetite, and lethargy, which are similar to the symptoms most humans experience. Like humans, most dogs will recover from flu with supportive care using fluids, nutrition, possibly antibiotics, and sometimes anti-inflammatories and cough suppressants. However, they may continue to cough for 2 to 3 weeks, and a few (probably under 5 percent) will develop pneumonia and die from flu. Most of those who develop serious illness have other, predisposing conditions, like tracheal collapse, heart disease, or a suppressed immune system, that make them more susceptible to secondary infections. Such especially vulnerable individuals, therefore, have the most to benefit from vaccination.


We still have things to learn about canine flu, and, to a great extent, it’s a lack of familiarity that concerns us most. Some of us remember that before the late 1970s, canine parvovirus didn’t exist. It mutated from a cat virus, and since no dog was immune to it, the results were devastating. Nowadays, no one considers not vaccinating against parvovirus.

Fortunately, canine influenza virus will never have an impact like parvovirus because the mortality rate is so much lower. As a disease agent influenza virus is more analogous to Bordetella, the organism most closely associated with the “kennel cough” syndrome, and one we routinely vaccinate against. As with many upper respiratory pathogens, including Bordetella among others, exposure to influenza can be somewhat controlled through lifestyle adjustments. Avoiding contact with other dogs and places where they come together (like boarding, grooming, and daycare facilities) can reduce the risk significantly. A key difference with influenza is the extreme ease of transmission that is compounded by a lack of population immunity. Although in time it may become just another risk among many, at the moment it seems to warrant special attention.

In a broader, more altruistic sense, vaccination provides an additional, general benefit by inducing a greater immunity in the local population, which reduces each individual’s risk of encountering a contagious dog, and especially protects dogs with pre-existing health conditions, who are the most vulnerable members of our community.

VCA Rancho Mirage Animal Hospital located at 71-075 Highway 111, Rancho Mirage, CA. 760-346-6103. Visit


Canine influenza is a recently emerged disease, so virtually every dog exposed to it will become infected.

Some infected dogs will never show symptoms, but most will show variable combinations of sneezing, coughing, listlessness and loss of appetite.

A small percentage of dogs will develop significant disease, and some will die. Most of them have pre-existing health conditions.

There are two known strains of canine influenza. Vaccinations against each strain are available.

Canine influenza is non-seasonal. Infections can occur any time of year.

Transmission occurs through respiratory secretions from sneezing, coughing, barking, or by contact with contaminated surfaces.

The virus stays viable on surfaces for up to 48 hours, on clothing for up to 24 hours, and on hands for up to 12 hours. Routine disinfection, laundering, or hand washing will inactivate it.

Any dog that shares an indoor space, or has close contact with another dog outdoors, including sharing of toys or water bowls, is potentially at risk.

The incubation period is 2 to 8 days. Most transmission occurs in the first 2 to 3 days, often before symptoms are noticed. Coughing may continue for up to three weeks.

Dogs suspected of infection should be isolated for a month.

Testing can confirm the virus, but to be reliable, should be performed in the earliest stages of infection.

Treatment is supportive, using fluids, nutrition, antibiotics, anti-inflammatories, and sometimes cough suppressants.

In a few rare cases, cats have contracted canine influenza, but they seem less severely affected than dogs. There is no vaccine for cats.

There are no reported incidents of people catching canine influenza.

Live help
Robert Reed, DVM, MSES, MPA
Robert Reed, DVM, MSES, MPA
Dr. Reed received his veterinary degree from Texas A&M University in 1993 and his master degrees in environmental science and public affairs from Indiana University in 1987. Prior to beginning his veterinary career, he worked as a teacher, and as a wildlife biologist in Michigan, Alaska, and Tamaulipas, Mexico. He is a former research fellow with World Wildlife Fund and The Conservation Foundation. Dr. Reed practiced veterinary medicine in Texas, Utah, and Nevada before establishing roots in the Coachella Valley in 2003. As Medical Director he seeks to maintain a standard of exceptional patient care, a strong commitment to client service, and a dedication to involvement with the community of Rancho Mirage.


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