Canine Influenza

by Bruce W. Little, DVM



As the saying goes, I hate to keep barking up the same tree; but canine influenza virus is showing its ugly face again, or still, across much of America. Canine influenza has now been diagnosed in more than 40 states in the United States. It all started in March 2015 in and around the Chicago area when more than a thousand dogs were diagnosed with canine influenza. A dozen or so died. In the beginning, it was thought that outbreak was being caused by the H3N8 virus that had been around since being discovered by the University of Florida in 2004 at various greyhound race tracks and had sporadically infected susceptible dogs in any location in which the local dog population had not been exposed to the virus in order to develop passive immunity. However, much to the chagrin of veterinarians and pet owners alike, the virus that infected thousands of dogs in the Chicago area was due to the H3N2 virus that had been isolated only in Asia prior to the Chicago outbreak. A vaccine for H3N8 influenza virus had been developed and approved for use in 2009; however, no vaccine for H3N2 had been developed at that time and the virus was extremely virulent, meaning it spread to all susceptible dogs quite easily. When the virus enters a community where there has never been exposure and all dogs are susceptible, it will cause symptoms in more than 80% of those dogs with as many as 10% of those infected developing into much more serious conditions including pneumonia. A small number of those dogs die from their infection. Since the outbreak in Chicago a little over a year ago, two veterinary pharmaceutical companies have developed and have received USDA Food and Drug Administration licenses to distribute the H3N2 vaccine to veterinarians who have used it to vaccinate tens of thousands of dogs.

Canine influenza is transmitted from dog to dog through respiratory secretions by way of coughing, sneezing and barking and through contaminated objects including water and food bowls, collars, leashes and people moving between infected and uninfected dogs. The virus can remain viable on surfaces for up to 48 hours, clothing up to 24 hours and on people’s hands for 12 hours. A recent study conducted by Merck Animal Health determined that approximately 80% of dogs were infected at boarding kennels and day care facilities, while animal hospitals and animal shelters account for most of the other transmissions from dog to dog. It is possible, and I am sure has happened, that dog sitters can transmit the virus from an infected dog to a susceptible dog if they do not take preventive steps to keep from transmitting the virus. It is very important for these facilities that house dogs take precautionary steps to eliminate the viable viruses from their countertops, kennel spaces, cages and equipment before admitting another dog to that space. The incubation period is usually two to four days from exposure to onset of clinical signs. Although most dogs have a milder form of canine influenza and recover without complications, some may develop severe respiratory symptoms leading to pneumonia. Approximately 25% of infected dogs are expected to remain asymptomatic or not show any signs of disease, but can still shed the virus and spread the disease.

The majority of dogs exhibit the mild form of canine influenza. In the mild form, the most common clinical sign is a cough that persists for 10 to 21 days despite treatment with antibiotics and cough suppressants. The cough can be either a soft, moist cough or a dry cough similar to that induced by kennel cough. Nasal discharge or matter from the eyes may be observed along with sneezing, sore throat, lethargy and lack of appetite or the desire to drink water. Some dogs are more severely affected with clinical signs of pneumonia, such as a high fever that may go as high as 104-105⁰ F. These signs will persist at different levels of severity for one to three weeks and the dog will slowly regain its ability to move about and eat and drink with enthusiasm.

Canine influenza can be diagnosed only by submitting a blood sample and/or nasal swabs to a laboratory where tests for antibodies are conducted. Many times a second test is required to measure the antibody concentration using the first test as a base-line determination used for comparison. In the event of epidemic outbreaks of canine influenza in a localized area, veterinarians may not submit samples for diagnosis because they know by experience and awareness they are dealing with this virus and want to commence supportive therapy as quickly as possible before secondary bacterial infections can gain a foothold.

Your veterinarian will establish the best course of treatment or treatment options if your dog is diagnosed with canine influenza. As is the case for all viral diseases, treatment is mostly supportive with loving care and nutrition that can assist dogs in developing an effective immune response to the disease. The presence of secondary bacterial infection as evidenced by fever, dehydration and nasal discharge may need a course of antibiotics, fluids to correct and maintain hydration and/or anti-inflammatory medications to reduce fever. Your dog should be kept isolated from other dogs in the house and in the neighborhood during the course of the disease.

Preventing your dog from contracting canine influenza is the best scenario possible. Talk to your veterinarian about the risk factors that may affect your dog. Find out if there are widespread cases of canine influenza in the area in which you live or in places that you are contemplating visiting. Make sure boarding kennels, dog day care facilities, groomers and dog-sitters are aware of the potential for your dog regarding canine influenza, and that they take all precautions necessary to keep the disease contained as well as possible. Ask your veterinarian if your dog should be vaccinated against canine influenza as there has been government approved vaccines against both H3N8 and H3N2 influenza viruses. The vaccine for your dog may not stimulate a total preventative for the disease; however, records show it provides complete immunity to approximately 90% of the dogs who receive it. It also relieves the severity and duration of the illness. The vaccine reduces the period of time that an infected dog may shed the virus in its respiratory secretions, as well as the amount of virus shed, thus making them less contagious to other dogs. The vaccine is given in two doses, two to four weeks apart, and the dog does not have immunity until as much as four weeks after the second injection. Therefore, one cannot wait to vaccinate their dog after the influenza outbreak occurs amongst the dog population in your locality. Your veterinarian will advise you whether or not there is the threat of canine influenza in your area and what steps should be taken to prevent your dog from contracting the disease. Most veterinarians will advise their clients to vaccinate if their dog is exceptionally social while visiting dog parks, grooming parlors, boarding facilities or even out for an evening walk. If your dog likes to approach other dogs and/or people you may be advised to have the dog vaccinated. If your dog never goes outside your own home and yard, and if there are no stray dogs or other visiting dogs coming into your home environment, your veterinarian may advise you that your dog does not need the vaccine.

It has been determined recently that the H3N2 canine influenza virus can and has infected cats. There is no vaccine available for cats at this time. Also at this time, there is no evidence of transmission of H3N8 canine influenza from dogs to horses, ferrets, or other animal species including humans. The H3N2 strain, however, has been reported in Asia to infect cats, and there’s some evidence that guinea pigs and ferrets can become infected. In early 2016, cats in an Indiana shelter were infected with H3N2 canine influenza (spread to them from infected dogs) and investigators found evidence that cat-to-cat transmission is possible. Stay tuned for further information on whether the canine influenza viruses are a threat to cats and other animals. Remember, of course, that all viruses are prone to mutate in order to make themselves a threat to any mammalian species.

Seek out and follow the advice of your veterinary professional and canine influenza can be mitigated or contained altogether. Canine influenza, like human influenza, can make a dog very sick for a period of time. Prevention is always better than treating the disease once it has infected your dog. Your dog deserves the very best of care, and will continue to show its unconditional love regardless.



Bruce W. Little, DVM