How to tell if your dog has canine flu

Published: Aug. 3, 2018 at 5:17 PM EDT
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Michigan health officials are reporting 49 cases of dog flu in the Lower Peninsula since mid-July. That's a dramatic increase from 2017, when nine case were reported during the entire year.

Our NewsCenter 16 Saturday Morning Pet Vet Dr. David Visser say the spike doesn't mean the illness is more severe. However, if dogs are in close proximity with an infected dog, the risk of exposure to dog flu increases.

"Fortunately, as significant as it is for a respiratory disease, and as highly infectious as it is, it's typically not deadly," said Visser. "But as a respiratory condition, it can certainly lead to things like pneumonia, which can become much more severe.

The following information was written by Dr. Visser.

Symptoms include fever, lethargy, coughing, and nasal and/or eye discharge.

Most cases of canine influenza are mild and last a few weeks, but some are more severe. H3N8 has an incubation period of 1 to 5 days, with clinical signs in most cases appearing 2 to 3 days after exposure. Dogs infected with H3N2 may start showing respiratory signs between 2 and 8 days after infection. Dogs are most contagious during the incubation period and shed the virus even though they are not showing clinical signs of illness. Some dogs may show no signs of illness, but have a subclinical infection and shed the virus.

Virtually all dogs exposed to canine influenza virus become infected, with approximately 80% developing clinical signs of disease. The approximately 20% of infected dogs that do not exhibit clinical signs of disease can still shed the virus and spread the infection.

The most common clinical sign is a cough that persists for 10 to 21 days despite treatment with antibiotics and cough suppressants. Some dogs are more severely affected and exhibit clinical signs of pneumonia, such as a high-grade fever (104°F to 106°F). Although most dogs recover without incident, deaths due to H3N2 have been reported.

Species affected

Dogs and to lesser extent cats. There is no evidence that either strain of canine influenza (H3N8 or H3N2) can infect humans.

Exposure risks and prevention steps

Facilities where dogs are brought together for care, grooming and more are advised to prevent the spread of disease by keeping sick dogs away, cleaning and disinfecting thoroughly and recommending that dogs are vaccinated before arrival.

Dogs in close contact with infected dogs in places such as kennels, groomers, day care facilities and shelters are at increased risk of infection. Canine influenza can be spread indirectly through objects (e.g., kennels, food and water bowls, collars and leashes) or people that have been in contact with infected dogs.

It is important to clean and disinfect objects that have been in contact with an infected dog to avoid exposing other dogs to the virus. Likewise, people who have been in contact with an infected dog should wash their hands and clean their clothing to avoid spreading the virus.

The virus can remain viable (alive and able to infect) on surfaces for up to 48 hours, on clothing for 24 hours, and on hands for 12 hours.

There is no “season” for canine influenza, and infections can occur any time of the year.


PCR may be the most reliable test for the diagnosis of canine influenza.


Treatment for canine influenza, as for most viral diseases, is largely supportive. Good husbandry and nutrition may help dogs mount an effective immune response. Most dogs recover from canine influenza within 2-3 weeks.

If signs call for additional medical treatment:

• Antimicrobials may be used if there are known or suspected

secondary bacterial infections.

• Nonsteroidal anti-inflammatory medications as needed to reduce

fever and inflammation.

• Fluids to help correct dehydration or maintain hydration.

• Antiviral drugs (like Tamiflu®) to treat influenza are approved for use in humans only. Little is known about their use, efficacy and safety in dogs. Veterinarians who use approved drugs in a manner not in accord with approved label directions (e.g., use of an antiviral drug only approved for use in humans) must follow the federal extralabel drug use regulations of theAnimal Medicinal Drug Use Clarification Act (AMDUCA).


To prevent transmission of the virus, dogs infected with canine H3N2 influenza as well as other dogs in the household should be isolated for 4 weeks.

In veterinary, boarding, and shelter facilities, the canine influenza virus appears to be easily killed by disinfectants commonly used in those facilities. Dogs exposed to CI or exhibiting respiratory symptoms should not be brought to locations where other dogs are present such as training classes, shows or events, day care, and boarding and shelter facilities until the isolation period is completed.

Vaccines are available for both H3N8 and H3N2 canine influenza. A bivalent vaccine offering protection against both strains is also available. Currently, there are no canine influenza vaccines approved for use in cats. Vaccination can reduce the risk of a dog contracting canine influenza. Vaccination may not altogether prevent an infection, but it may reduce the severity and duration of clinical illness.

In general, the vaccine is intended to protect dogs at risk for exposure to the canine influenza virus, which includes those that participate in activities with many other dogs or are housed in communal facilities, particularly where the virus is prevalent. Dogs that may benefit from canine influenza vaccination include those that receive the kennel cough (Bordetella/parainfluenza) vaccine, because the risk groups are similar. Dog owners should consult with their veterinarian to determine their dog’s risk of exposure to the canine influenza virus and if vaccination is appropriate for their dog.

US Data – General history

At present, two strains of canine influenza virus have been identified in the United States: H3N8 and H3N2. Influenza viruses are able to quickly change and give rise to new strains that can infect different species. Both strains of canine influenza identified in the U.S. can be traced to influenza strains known to infect species other than dogs. At some point, these viruses acquired the ability to infect dogs and be transmitted from dog to dog.

Canine H3N8 influenza was first identified in Florida in 2004 in racing greyhounds. It is thought this strain developed from an equine H3N8 influenza strain that jumped from horses to dogs. Since being detected in 2004, canine H3N8 influenza has been identified in dogs in most U.S. states and the District of Columbia.

Canine H3N2 influenza was first identified in the United States in March 2015 following an outbreak of respiratory illness in dogs in the Chicago area. Prior to this, reports of canine H3N2 influenza virus were restricted to South Korea, China and Thailand. It was initially identified in dogs in Asia in 2006-2007 and likely arose through the direct transfer of an avian influenza virus – possibly from among viruses circulating in live bird markets – to dogs.

Following the initial diagnosis in Chicago, additional cases of canine H3N2 influenza were reported in a number of states. In early 2016, a group of shelter cats in Indiana were diagnosed with H3N2 canine influenza. It is believed the virus was transmitted to them from infected dogs.

In May 2017, canine H3N2 influenza was diagnosed in dogs in Florida, Georgia, North Carolina, South Carolina, Texas, Kentucky, Tennessee, Missouri, Louisiana, and Illinois. This was the same strain of H3N2 involved in the 2015 outbreak in Chicago.

Credits for the notes:

David A. Visser, DVM – compiling, edits, comments

Michigan Department of Agriculture and Rural Development website

American Veterinary Medical Association website

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