Dogs, like their human companions, are vulnerable to infectious diseases. The dog flu, also known as canine influenza, has become a national concern in recent years. In 2007, veterinary health officials reported outbreaks in two U.S. states. However, in 2019, nearly every state in the country was reporting not just one, but two strains of dog flu. Understanding the contagious nature of the virus, the symptoms, and ways to prevent it is important for protecting your pet’s health.1
What is Canine Influenza?
Canine influenza (CI) is an illness that results from the canine influenza virus, an influenza A virus. It is a respiratory type of infection. The type A influenza virus is capable of causing large outbreaks because coughing and sneezing spread the infection. The canine flu is a fairly new virus, so most dogs in the U.S. have no immunity to it and are susceptible to infection. CI is highly contagious. Veterinarians often misinterpret its symptoms as another type of infection. Sometimes the flu exhibits mild symptoms; other times, they are severe.2
The Two Strains of Canine Influenza
There are two strains of CI, both of which appear in dogs across the U.S. The first strain of CI started in 2004 as an H3N8 influenza A virus, identified when an outbreak occurred among racing Greyhounds in Florida. H3N8 was closely related to an equine virus that has been around for more than 40 years. Researchers believe that this equine influenza mutated, jumped species, and became the canine influenza strain.
Then, in 2015, H3N2, a new canine influenza virus, arrived on the scene. Although it was genetically identical to a previous H3N2 strain found in Asia, this new influenza strain was the result of avian influenza that likely started in live bird markets. This new strain is responsible for canine flu outbreaks in the Midwest part of the U.S. in 2015 and 2016 and then spread across the U.S.3
How Your Dog Can Catch Canine Influenza
Kennels, grooming parlors, and shelters are prime locations for a dog to catch CI. Dog flu spreads easily because it is airborne. When an infected dog coughs, sneezes, or barks, it sends respiratory secretions into the air, and other dogs breathe them in. They can also catch the canine flu through objects, such as collars and kennel surfaces. Or, an uninfected dog can also get sick if he eats or drinks out of a water bowl that a dog who has the canine flu used previously. Dogs can pass CI to another through licking, kissing, or nuzzling each other as well. Humans who interact with an infected dog can pass the virus to uninfected dogs through touch.4
Symptoms of Canine Influenza
Dogs exhibit a variety of symptoms if they contract CI, similar to those that humans experience when they have the flu. The most common symptom is a persistent cough. Most owners will see reduced energy levels and a loss of appetite as well. Many dogs also run a fever and have a throbbing headache, just like humans do. There are signs you can look for to determine if your dog has a headache. Your pet may avoid loud noises or show no desire to play. They may rub their head against your leg. Some dogs seek out quiet, cool, dark places like closets or under beds to sleep and find relief.5
Two Clinical Forms of Canine Influenza in Infected Dogs
There are two forms of canine influenza: the mild form, which is most common, and the severe form. Dogs who experience the mild form usually have a soft, moist cough that continues for up to 30 days. You may notice the dog sneezing, which could also be accompanied by both an eye discharge and a thick nasal discharge. Discharges may be a sign of secondary bacterial infections. With severe forms of canine influenza, dogs develop a high fever of up to 106 degrees. They often have increased respiratory rates, difficulty breathing, and may develop pneumonia.6
Incubation Periods for Canine Influenza
Dogs are most contagious during the incubation period, but the problem is, in most cases, they aren’t showing any symptoms at this time. Veterinarians say that just about any dog that comes into contact with canine influenza will contract the virus. Not all will show symptoms, however, and about 20 percent of these asymptomatic dogs pass the disease to other dogs. The incubation period begins within two to four days after exposure to the influenza virus, but those with H3N2 are contagious for around 26 days. Vets recommend a 21-day isolation period for dogs with H3N2. Dogs with H3N8 are contagious for around ten days and should remain in isolation for a minimum of seven days.7
The Dog Flu Isn’t Usually Fatal
Few dogs die from canine flu. In most cases, they recover from their symptoms within two to three weeks. Many dogs who contract CI show no signs of the illness while others experience more severe symptoms. However, dogs are more likely to become seriously ill if they develop pneumonia as a result of canine influenza. Even then, less than 10 percent die from the illness. If you suspect that your dog has had interactions with an infected canine, you should consult your veterinarian.8
Can Humans Catch Canine Influenza?
According to the Centers for Disease Control, it is unlikely that humans can contract the dog flu from their pet. There have been no such cases reported in the U.S. or around the globe. However, due to the nature of influenza viruses, the CDC says there is a chance that these viruses could change at some point and then pose a threat to humans. The World Health Organization monitors any human flu infections contracted through influenza A viruses that originate with animals. An example of this type of influenza would be the swine flu or the avian flu. Additionally, dogs cannot get influenza from their human companions.9
H3N2 and Cats
In 2016, veterinarians diagnosed cats in an Indiana shelter with the H3N2 strain of canine influenza. Researchers discovered that eight cats were infected through contact with infected dogs even though they had no direct contact with the dogs. These cats then infected other cats in the shelter. Their symptoms included non-specific signs of upper respiratory infections. Some of the cats had increased lip-smacking behaviors, while others experienced hyper-salivation. However, veterinary professionals say the risk of this type of infection in cats is rare.10
Prevention, Diagnosis, and Treatment
Before boarding your pet at a kennel, ask the facility’s operators if there have been any outbreaks of dog flu. If your dog has a cough, it is important to have them examined by a vet, because this can be a symptom for a variety of ailments. The vet may conduct testing using throat or nasal swabs to verify whether or not your dog has CI, but the results generally take a few days to come back. If the dog has canine flu, the treatment is generally for symptom relief. There are no medications that can cure canine flu. Vets may prescribe additional fluids, along with non-steroidal and anti-inflammatory medications. In most cases, the vet will recommend quarantining your dog and will also provide instructions for disinfecting the dog’s living areas. Vaccinations against both strains of canine influenza are available.