Dog Flu (Canine Influenza)

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Dog flu, or the canine influenza virus (CIV), is a highly contagious viral infection that can strike at any time. It is an infectious respiratory disease caused by an influenza A virus, similar to the viral strains that cause human influenza. For dogs, there is no specific “flu season”; infection can occur any time of the year.

Two different strains of canine influenza virus (CIV), H3N2 and H3N8, have been confirmed here in the United States. The incubation period is anywhere from 2 to 4 days from initial exposure. Dogs infected with the H3N8 strain remain contagious for up to 10 days after exposure, and those infected with H3N2 will remain contagious for up to 26 days after initial exposure.

Influenza is an airborne virus that can be spread through a number of ways. Most dogs exposed to the virus will contract it, but not all who become infected will exhibit symptoms, though they can still spread the disease (this is referred to as a “subclinical infection”). Dog flu can range from being mild and asymptomatic to very severe, in which case it may result in pneumonia or even death. While the survival rate is extremely high, it’s important to be in tune with your dog’s health and seek out treatment at the first sign of dog flu.

Signs & Symptoms of Dog Flu

Cases of dog flu can range from mild to severe. Common symptoms include the following:

  • Coughing (either moist or dry)
  • Sneezing
  • Nasal discharge
  • Runny eyes
  • Fever
  • Lethargy / lack of energy
  • Difficulty breathing
  • Decreased or absent appetite

It’s important to note that some of the symptoms related to dog flu can also resemble other respiratory diseases, including bordetella (“kennel cough”) and distemper.

Not all dogs infected with canine influenza will show symptoms, but that doesn’t mean they aren’t contagious. Approximately 10–20% of dogs who contract dog flu are asymptomatic, while the remaining 80–90% develop a clinical infection. Up to 20% of those infected with dog flu will contract a more severe form that manifests with a high fever and pneumonia.

The mortality rate for canine influenza is low, but in cases where secondary bacterial infections present themselves, there’s an increased chance of a more severe illness and/or pneumonia, which can be life-threatening without proper treatment.

H3N8 versus H3N2
Both strains cause respiratory infections in dogs. H3N8 originated in horses; H3N2 originated in birds.

The incubation period for each strain is slightly different. For H3N8, the period is anywhere between 1 to 5 days, with clinical signs appearing 2 to 3 days after exposure. In dogs infected with the H3N2 strain, signs of infection can appear anywhere between 2 and 8 days after infection and shed intermittently for up to 26 days.

While these are the only two strains of dog flu currently confirmed in the US, as with all types of viruses, there is always the risk of new strains emerging.

How Did My Dog Get Dog Flu?

Canine influenza is an airborne virus that spreads rapidly. It can be found in places like boarding facilities, groomers, dog daycare centers, dog parks, shelters, and other spots where dogs are co-mingling. If dog flu is discovered in any one of these places, owners should err on the side of caution and assume their dog was not only exposed to the virus but is likely infected.

Exposure can also occur via direct contact with respiratory discharge from an infected dog, by way of a cough, bark, or sneeze. Dog bowls, toys, bones, clothing, collars, leashes, and even people who have handled infected dogs but have not been properly disinfected can also spread the virus.

Canine influenza can remain viable on hard surfaces for up to 48 hours, on clothing for 24 hours, and on hands for 12 hours. People who have come in contact with an infected dog, or suspect they have, must wash their hands, clothes, and anything else they’ve touched to prevent the virus from spreading.

Diagnosing Dog Flu

Because the signs and symptoms associated with canine influenza can also be indicators of other respiratory illnesses, a diagnosis cannot be made by symptoms alone. The best way to confirm a flu diagnosis is with testing. Your veterinarian will take a collection of nasal swabs and serum samples.

Swabs are used for detection of the virus when the dogs start coughing, and serum samples for detection of CIV-specific antibodies in dogs that have been ill for more than 7 days.

For dogs that have been ill for fewer than 4 days, nasal and oral swabs can be collected and sent out for diagnostic testing at a laboratory that offers a validated PCR (polymerase chain reaction) test for canine influenza. While a positive result means that the dog is infected, a negative result may be false if the swabs were taken before or after the period of peak viral shedding.

The most reliable way to diagnose dog flu is paired serologic testing on two blood samples – one that is taken during the first week of illness and the second taken 2 to 3 weeks later.

Treating Your Dog for the Flu

Because dog flu is a viral illness, treatment consists mainly of supportive care, which can include the administration of fluids, non-steroidal anti-inflammatory medications to reduce fever, and possibly antibiotics if a secondary infection develops. Good nutrition is always important, and something you should discuss with your veterinarian. Most dogs will recover within 2–3 weeks. Secondary bacterial infections can take longer to clear up, and may require additional testing and treatment.

In order to prevent transmission of the virus, an infected dog should be quarantined; how long depends on which strain was contracted. Your vet should also be able to recommend a disinfectant solution to help kill the virus in your home.

Is There a Cure for Dog Flu?

There is no cure for canine influenza. The flu is a viral infection that needs to run its course in order for your dog to feel better. In cases where a secondary infection presents itself, such as pneumonia, then an antibiotic is required.

Is Dog Flu Contagious for Humans or Other Pets?

Canine influenza is highly contagious between dogs. Dogs who have become infected with the flu should be kept away from other dogs until they are no longer contagious.

As of now, there is no evidence that either strain of the virus (H3N2 or H3N8) can be passed from dogs to humans or other animals. However, flu viruses are constantly changing, so it is possible this may change one day. People who have been in contact with infected dogs should wash their hands and clothing to avoid spreading the virus.

What Is the Cost for Treating Canine Influenza?

The cost to treat the flu depends on the route you take. A dog flu vaccine can range between $30–$55 (possibly higher, depending on your geographic area). An office visit to the vet, either to have your dog examined or to administer the vaccine, will be a separate charge.

Recovery and Management of Dog Flu

During your dog’s recovery from canine influenza, ensure he is drinking plenty of fluids to prevent dehydration. Since it’s so contagious, it’s best to quarantine your dog until he’s no longer contagious; this is especially true for people who have more than one dog.

If a trip to the vet is required, the best way to prevent other dogs from contracting the virus is to either remain outside or in the car until the vet is ready to see you. You can also inquire as to whether there is a separate entrance you can use to ensure your dog doesn’t cross paths with any other animal there.

Preventing Dog Flu

Good sanitary practices by dog owners can help prevent the spread of dog flu. Here are some common-sense tips:

  • Wash your hands with soap and water after touching other dogs.
  • Change and wash your clothes after interacting with other dogs.
  • Consider vaccinating. While it’s not mandatory, like the rabies vaccine, the flu vaccine ought to be considered if your dog is going to be in places where there’s a risk of contamination (dog parks, kennels, boarding houses, etc.).
  • Keep hard surfaces sanitized.
  • Both you and your dog should stay away from dogs showing symptoms of dog flu, and steer clear of areas with reported breakouts.

Is There a Vaccine for Dog Flu?

Vaccines are available for both strains of canine influenza. Depending on your dog’s lifestyle, your veterinarian may recommend vaccinating. While vaccines may not stop your dog from contracting the virus, they can help reduce the severity and length of the flu if contracted.


Dog flu is a highly contagious viral infection, similar to strains that cause human flu. Common symptoms include coughing, sneezing and breathing difficulties. While most cases are mild, some may become serious, leading to a high fever and pneumonia. Vaccines can help protect your dog from dog flu; speak to your veterinarian about whether the canine influenza vaccine is appropriate for your dog.

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