Canine Influenza Virus (Dog Flu)


The canine flu virus, also referred to as Canine Influenza Virus, Greyhound Disease, and Race Flu, is considered highly contagious respiratory infection of dogs.

It was originally identified in 2005 and last years news of it flooded the internet and news. There are possible cases being documented by veterinarians in almost every state but there is not a good communication system between states to determine the full extent of the virus. The virus can cause coughing, high fevers, nasal discharge and a fatal pneumonia.. In the spring of 2015, and outbreak affecting over 1,000 dogs occured in the Chicago area and Midwest. This outbreak was caused by a different strain of the canine influenza virus (CIV).

It has been suggested that 80% of dogs exposed to the virus will develop an infection. Most dogs will only have mild coughing however puppies and older dogs are at greatest risk for fatalities associated with the virus. The number of dogs at risk from dying from this virus may be anywhere from 1 to 10%.

According to Dr. Dick Slemons, an authority on influenza viruses at the Ohio State University College of Veterinary Medicine, the disease is associated most often with dogs housed in a high-density population or boarding kennel. The infectious agent is transmitted by direct contact with respiratory secretions through the air or by contact with contaminated surfaces. It can be spread by people moving between infected and uninfected dogs with contaminated objects.

The virus has been primarily documented in shelters, boarding facilities, pet stores and dog tracks.

The incubation period (time from exposure to symptoms) is estimated to be 2 -5 days.

The canine influenza virus is an influenza H3N8 influenza virus that was originally a horse virus. It is not a human virus nor is it contagious to humans. The H3N8 equine virus has been known to exist in horses for 40 years. It is believed by scientists for the virus to have adapted from horses to cause illness in dogs.

The virus was discovered by Dr. Cynda Crawford, an immunologist at the University of Florida College of Veterinary Medicine, who began investigating the first outbreak at a racetrack in Jacksonville, FL in January 2004. The virus made national media attention after Dr. Crawford and colleagues published an article in the September 26, 2005 edition of Science Magazine entitled “Transmission of Equine Influenza Virus to Dogs”.

It is often mistaken for infections caused by kennel cough (Bordetlla bronchiseptica/parainfluenza virus complex. The virus may appear similar to kennel cough, which is a highly contagious inflammation of the trachea (windpipe) and bronchial tree caused by a contagious virus (adenovirus, parainfluenza virus, canine distemper virus) or bacterium (Bordetella bronchiseptica). However, with most cases of kennel cough, a mild to moderate cough without other symptoms is usually self-limiting; however, occasional cases become lingering and cause chronic bronchitis. With this new virus, the cough is often associated with high temperatures, coughs and nasal discharge.


Previous to the 2015 outbreak, there was no evidence that the dog virus can spread to humans, cats or other animal types.  It was believed that the virus is species specific and only spread dog to dog. However, with the 2015 outbreak, researches at Cornell University found that the new strain caused infection and respiratory illness in cats.

What to Watch For

Watch for a variety of symptoms that can vary in severity.

  • Signs of upper respiratory problems such as conjunctivitis (irritated eyes), rhinitis (runny nose) or sneezing may be observed.
  • Cough. The classic symptoms are coughing that worsen with activity or excitement and can persist for minutes. If secondary bacterial pneumonia develops, the dog often shows signs of illness such as loss of appetite, depression, or fever.
  • Fever (high as 106 degrees F)
  • Difficulty breathing
  • Loss of appetite
  • Depression
  • Runny nose
  • No symptoms. Some dogs have asymptomatic infections.

    Any of these signs should prompt a visit to see your veterinarian in order to be certain pneumonia has not set in. Symptoms can last for up to four weeks.



    A complete medical history may help to reveal recent exposure to a kennel or other dogs. However, it will be difficult in some situations to differentiate this virus from the common “Kennel Cough” virus mentioned above. Diagnostic tests are needed to recognize it and exclude other diseases. These tests may include:

  • A chest X-ray may be recommended to determine if pneumonia is present.
  • Routine laboratory blood tests-a complete blood count (CBC) or blood chemistry panel is not necessary unless your pet is showing signs of generalized illness, fever or loss of appetite.
  • A fecal flotation should be done to exclude intestinal parasites.
  • Blood titers – Testing for the virus is being done through veterinary diagnostic centers. The test can be performed by using testing respiratory secretions at the time of disease onset or by blood samples.

    According to Dr. Crawford, blood testing recommendations include that a sample be submitted during the first week of illness (acute sample) followed by another sample 2 – 3 weeks later (convalescent sample). Diagnosis is based on a four-fold increase in antibody titers from acute to convalescent phase. They need 1/2 ml of serum for this test. For more information about sample submission, talk to your veterinarian (also, they can go to With the sample, the lab is also requesting additional information to help them characterize the disease and locations. Antibodies are generally not detectable during the first week of clinical signs but are detectable after the first week and for up to 2 years after infection. If an acute sample is not available, exposure can be confirmed by the presence of antibodies in a convalescent sample.

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