Canine influenza, also called “dog flu,” has been making the news on and off for the past year or so. A new strain, imported from Asia earlier this year, has sickened thousands of dogs in the United States, and as outbreaks have spread from state to state, some of the local headlines have sounded dire, with terms such as “deadly,” “contagious” and “epidemic.”
So when you hear your dog starting to cough one night, naturally, you’re worried. Ordinarily, when one of your animals seems a little sluggish, you’d “wait and see” for a day or two before calling the veterinarian. But is this a time to rush your dog to the emergency clinic?
Not necessarily—at least it’s not an emergency. Even if your dog has contracted influenza, chances are he will be just fine. Still, it is a good idea to get him to a veterinarian sooner rather than later.
“The golden rule, if you are seeing a respiratory illness in your dog, is that he ought to be seen by a veterinarian and maybe be treated with an antibiotic before it gets worse,” says virologist Edward Dubovi, PhD, of Cornell University. “Mortality is not great as a result of the virus, but the difficulty with respiratory infection in dogs isn’t with the initial viral infection; it can be complicated by secondary bacterial infections that, once entrenched, can be difficult to treat.”
Researchers are still gathering data and working to understand all of the risk factors for canine influenza. In the meantime, your best bet for protecting your dog is limiting his exposure to situations where he might come into contact with the virus. Here’s what you need to know.
So far, two different strains of canine influenza virus have been identified: H3N8 and H3N2.
First detected in January 2004 among racing greyhounds in South Florida, H3N8 had caused outbreaks at 20 tracks in 11 states by spring of 2005. H3N8 was originally an equine influenza strain that “jumped species” and is now well established among dogs. The virus has now been seen in 30 states and is considered endemic to Colorado, Florida, New York and Pennsylvania.
H3N2, originally an avian flu, was first found in dogs in 2007 in South Korea. The virus was first identified in the United States in the Chicago area, and by April 2015 an estimated 1,000 dogs had been affected in Illinois and nearby areas. By July, H3N2 was found in multiple states, including Alabama, California, Texas, Georgia, North Carolina, Pennsylvania, Ohio, Massachusetts, New York, Wisconsin, Michigan, New Jersey, Iowa and Indiana. How the virus reached the United States is not known.
Both strains of influenza pass readily from dog to dog via nasal secretions. This can happen through direct nose-to-nose contact, by way of airborne secretions and through contact with shared objects, such as food and water bowls and kennel surfaces. People can also transfer the virus between dogs on their skin and clothes. According to the American Veterinary Medical Association (AVMA), flu virus can survive on surfaces for 48 hours, on clothing for 24 hours and on hands for 12 hours. It spreads most readily among dogs kept in close quarters, such as kennels, shelters, daycare centers and boarding facilities.
Neither H3N2 nor H3N8 causes illness in people, but horse owners ought to be aware of the possibility of one type of cross-species infection: The strain of H3N8 that causes equine influenza may also infect dogs. “So if your horse sneezes on your friendly dog, the dog can get ill,” Dubovi says. “But that strain of the virus doesn’t transfer on to other dogs. And the canine H3N8 does not go from dogs back to horses.”
H3N2 is not known to affect horses, but it can cause respiratory illness in cats. “If you have dogs and cats in your home, and your dog gets sick, it could spread to your cats,” says Dubovi.
When a dog is exposed to canine influenza, the infection incubates for two to four days before signs of illness appear. During this time, he will shed large amounts of the virus—in other words, dogs may be contagious before they get sick. They may continue shedding the virus for up to three weeks after infection.
The viruses cause inflammation of the lining of the respiratory tract, potentially from the dog’s nose all the way to the bronchioles in the lungs. The severity of influenza varies, depending on the dog:
• The majority (more than 70 percent) develop a mild illness. According to the AVMA, the primary sign is a persistent cough that lasts for 10 to 21 days. Other signs include nasal discharge, sneezing, lethargy, loss of appetite and a low-grade fever.
• A small number of dogs (maybe 3 to 5 percent) will develop a more severe form of illness, including a high fever (104 to 106 degrees), labored breathing and pneumonia, according to the AVMA. Some cases may be fatal.
• A significant number (20 to 25 percent) of dogs will become infected with the virus but will never show any outward signs of illness. Still, they are able to pass the virus to others.
All of these percentages, including the mortality rate, are approximations—researchers don’t have all the data they need. “In Chicago, we think 3,000 to 5,000 dogs were exposed, with only six dying, but we really don’t know for sure,” says Dubovi. “We’ve had no centralized data collection.”
It’s also not clear whether some dogs might be more susceptible than others. “We have no data to suggest age or breed differences,” says Dubovi. “There may be some out there, but we don’t have enough data to draw any conclusions, so it’s best to assume all dogs may be susceptible.”
Because the clinical signs of canine influenza are similar to other respiratory diseases, a definitive diagnosis requires clinical testing. Within the first week of exposure, before the dog has built up antibodies to the virus in his blood, the most effective diagnostic test is to analyze nasal swabs via polymerase chain reaction (PCR) to identify the presence of the virus. After that, blood tests—to look for antibodies in the dog’s serum—become the more accurate method.
The only treatment for canine influenza is supportive care. Nonsteroidal anti-inflammatory medications may be used to alleviate fever and inflammation, and IV fluids may be necessary to prevent dehydration. Antibiotic medications may be prescribed if the dog has developed secondary bacterial infections. According to the AVMA, most dogs recover within two to three weeks.
Two vaccines are available to protect dogs against H3N8; there is currently no vaccine available for H3N2. However, Dubovi expects there will eventually be one: “Rumors are that the biologics companies are working on a vaccine. They ought to be able to come out with a multivalent vaccine [which combines both viruses into one formula] with fewer regulatory hurdles than it would take to create a whole new one.” It is not known whether the H3N8 vaccine will also protect a dog against infection with H3N2.
The dogs most at risk of encounter-ing canine influenza viruses are those who congregate in large numbers in confined spaces, such as at kennels, shelters, daycare facilities, dog parks and similar venues. Rural dogs on the whole may be less at risk of exposure, but contagion is still possible—for example, if you regularly take your dog to a boarding barn and he socializes with dogs there, some of whom might also frequent dog parks.
If you’ve heard that canine influenza outbreaks are in your area, exercise caution and ask questions before bringing your dog into contact with others. “If 100 dogs are congregating in one place, and 70 of them come down with a respiratory illness, chances are it’s influenza,” says Dubovi. “The only safe bet is to keep your dog away from other dogs.”
This article first appeared in EQUUS issue #457, October 2015.