Encountering new diseases

Does your dog have the H3N8 virus?

Does your dog have some strange symptoms? – Photo courtesy Twitter

In 2004, 22 greyhounds at a Florida racetrack came down with fever and cough. Outbreaks of respiratory disease in such close-quarter environments are often caused by a variety of infections we lump together and call canine infectious tracheobronchitis. You know it as kennel cough, a typically mild and self-limiting disease. But eight of those greyhounds developed pneumonia and died. By June, similar outbreaks were occurring elsewhere, affecting thousands of greyhounds. University veterinarians, in collaboration with the Centers for Disease Control, eventually determined the cause: a new influenza virus (H3N8), closely related to the equine influenza virus. The theory was that the equine virus mutated, then jumped species, from horse to dog. By 2005, sporadic cases had been diagnosed throughout the country, not just at race tracks, and not just in greyhounds. Shelters, pet stores, boarding kennels, and veterinary clinics were beginning to see confirmed cases of canine influenza.

Because it was a newly emerging disease, no dogs had natural immunity. There was concern about possible epidemics with high mortality rates sweeping the country. It’s been 11 years now. Those dire fears have not been realized, but outbreaks do occur, and they usually hit the news, raising alarm in dog owners. This May, such an outbreak occurred in Chicago, but just like human flu has different varieties, so does canine influenza. The Chicago outbreak was caused by a newly introduced strain of dog flu (H3N3) coming from Asia, specifically South Korea, Thailand, and China, and originally derived from avian virus, not equine.
When a dog is infected with either strain of canine influenza, there is a two- to five-day incubation period, during which there are no signs but the dog sheds virus from its nose and can infect other dogs. Clinical signs generally appear within five to seven days. Viral shedding ends after seven to 10 days. Symptoms vary greatly. Some animals never show any signs. The vast majority experience mild disease, with a soft, moist cough lasting 10 to 30 days. Other symptoms may include lethargy, reduced appetite, fever, sneezing, and discharge from eyes and/or nose. Occasionally the cough is dry, like typical “kennel cough.” One to 10 percent of dogs develop severe disease with high fever, pneumonia, and increased respiratory rate and effort.
Treatment is largely supportive and tailored to the specific case. Remember, antibiotics do not kill viruses, and influenza is a virus. Overuse of antibiotics when not truly indicated only increases the problem of antibiotic-resistant bacteria worldwide. But if secondary bacterial infections are suspected, or an individual is at high risk for complications, then antibiotics are needed. Severely affected dogs need intravenous fluid therapy to keep hydrated, aggressive antibiotics for secondary bacterial infection, and medications to reduce inflammation and fever. The mortality rate in the general population is less than 1 percent, rising to 5 to 8 percent in high-risk dogs like the elderly, very young, or those with other illnesses such as heart disease, cancer, or compromised immune systems.

Dogs that develop a cough after being kenneled or in contact with many other dogs can be tested for influenza either by blood samples or nasal swabs. Multiple tests may be needed to confirm or rule out the diagnosis. While awaiting results, coughing dogs should be isolated, and owners should observe routine sanitation practices, such as frequent hand washing, to limit spread. The virus can be transported on clothes and objects like food bowls, but is easily killed with bleach or most disinfectants. Transportation of “rescue dogs” around the country may spread canine influenza, so if you adopt a dog from another part of the country, remember an infected animal can shed virus for a week while not showing any clinical signs of illness. Keep newly arrived dogs isolated from other dogs for 14 days to be sure they are healthy.
In 2009, a vaccine was approved for H3N8 canine influenza in the United States, requiring two initial injections (two to four weeks apart) and an annual booster. Vaccination does not actually prevent infection, but does lessen severity of symptoms if a dog does get exposed. Will the H3N8 vaccine protect a dog against the new H3N3 influenza? We just don’t know. Should you have your dog vaccinated? Most veterinarians consider this a “lifestyle” decision. If Rover is not frequently exposed to large numbers of dogs and doesn’t travel, the risk of exposure is extremely low here in Massachusetts. In 2014 there was a small H3N8 outbreak on the North Shore associated with a single kennel. There have been a few other isolated cases reported throughout the state. This May, a dog traveling here from the Chicago area tested positive for H3N2, and was immediately isolated. Two other local dogs were exposed to that dog, but are doing fine. There have been no other reports of H3N2 in Massachusetts at this time.

The low incidence of confirmed Massachusetts cases, combined with uncertainty about vaccine efficacy, makes routine vaccination of Island dogs questionable. On the other hand, we do get dogs visiting from all over the country. Take basic precautions. Don’t let Rover drink from communal water bowls. Avoid contact with dogs you don’t know. If you have visitors coming from the Chicago area, ask them to consider having their dog tested before they arrive. If you are worried, talk to your veterinarian.

I personally do not carry the H3N8 vaccine. (The manufacturer requires purchase of 25 [expensive] doses at a time, far more than I can use.) But on rare occasions, for clients traveling with high-risk animals to high-risk locations, we have figured out how to arrange access to the product. All dogs that cough do not have canine influenza. That old culprit “kennel cough” is still a far more common, and less worrisome, cause of respiratory disease. It is up to us veterinarians to watch for sudden changes in the prevalence and severity of suspicious cases of coughing in our area. So far, so good, but summer is almost here.