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Understanding Canine Influenza

Drs. Foster & Smith Educational Staff
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Did you know that your dog could get the flu? Canine influenza, also known as dog flu, is a contagious respiratory disease in dogs caused by specific Type A influenza viruses known to infect dogs. Dog flu originates from 2 different influenza A viruses - H3N8 and H3N2.

The H3N8 Type A Influenza Virus

H3N8 causes disease in dogs but not humans. Originally a horse influenza virus identified more than 40 years ago, H3N8 adapted/mutated to cause disease in dogs and now transmits easily between dogs. In fact, experts now consider this mutated virus a dog-specific H3N8 virus. H3N8 was first reported in US dogs in 2004. While originally diagnosed in racing greyhounds in Florida, H3N8 has since spread nationwide throughout dogs of all breeds, especially those housed in kennels and shelters.

The H3N2 Type A Influenza Virus

A more recent discovery in the United States, the canine influenza A H3N2 virus caused a Chicago-based outbreak of canine influenza in spring 2015 that sickened thousands of dogs and killed at least 5 dogs. Originally an avian flu virus that mutated/adapted to infect dogs, the canine influenza A H3N2 virus also differs genetically from human seasonal H3N2 viruses. The canine influenza A H3N2 virus, first detected in dogs in South Korea in 2007, was first detected in US canines in April 2015. Experts do not know exactly how the canine H3N2 virus infiltrated the United States.

To date, no recorded cases of humans becoming infected with canine influenza viruses exist.

Dog Flu Symptoms & Infection Risk

Dogs infected with either the H3N8 or H3N2 canine influenza virus will generally start to show symptoms of disease 2-4 days after they are exposed to the virus.

  • 80% of infected dogs who develop dog flu will exhibit mild symptoms that include sneezing, runny nose, a fever, and a persistent cough that does not respond to treatment. These signs may be very similar to those of kennel cough, another common and highly contagious canine disease.
  • Approximately 20% of infected dogs will show no signs of disease, yet still be able to spread the virus.
  • In the remainder of infected dogs, canine influenza can become very serious, developing into pneumonia with labored breathing and other respiratory signs.

Dog flu's course of infection lasts 2-4 weeks, and any dog unvaccinated for influenza may become infected. Canine influenza is a relatively new/emerging disease. Therefore, few dogs are immune to it (unless they have been vaccinated against it), and most dogs are at risk of infection.

Frighteningly Simple Flu Transmission

Canine influenza spreads between dogs as they emit airborne viruses through respiratory secretions (coughing and sneezing), just like human flu spreads between people. The virus can also be transmitted when a flu-free dog:

  • Directly contacts an infected dog - dogs can spread the virus for up to 10 days, with the highest levels of aerosolized respiratory secretions occurring 2-4 days after being exposed to the virus.
  • Contacts contaminated items - the virus can remain alive and infective on surfaces for up to 48 hours, and on clothing for 24 hours.
  • Contacts people who may be carrying the virus on their hands or clothing - the virus can also survive on hands for 12 hours.

Veterinary Diagnosis is Crucial

Unfortunately, dog flu cannot be diagnosed solely on clinical signs. To properly diagnose dog flu, a veterinarian must perform a specific antibody test on 2 separate blood samples - 1 taken when the dog is first suspected to have the flu, and another taken 10-14 days later. The presence of a specific antibody in the second blood test will confirm that a dog does indeed have the flu. Microscopic examination of nasal secretions within 72 hours of symptom onset may also reveal the flu virus. A veterinarian may also take chest X-rays depending on a dog's specific symptoms.

Treatment Through Supportive Care

Unfortunately, dog flu has no specific treatment. Instead, supportive care - giving fluids to prevent dehydration, feeding healthy food, and giving medications to relieve specific symptoms - helps your dog build an immune response sufficient to allow recovery from canine influenza. Your dog may also receive broad-spectrum antibiotics to prevent or treat any secondary infection, especially if flu has progressed to pneumonia or nasal discharge is very thick or green in color. Seriously ill dogs may also need supplemental oxygen and long-term hospitalization.

A Relatively Good Prognosis

Symptoms of dog flu range from non-existent to severe. Most dogs with mild symptoms recover fully. Severe illness usually results in the onset of pneumonia. Death occurs mainly in dogs with the severe form of disease; however, the mortality rate is thought to be less than 10%.

Experts believe that dog flu immunity lasts at least 2 years. Therefore, in rare cases, a dog may become re-infected with canine influenza, even after fully recovering from it.

H3N8 Canine Influenza Vaccine Available

The United States Department of Agriculture (USDA) approved a vaccine for the H3N8 canine flu virus in 2009. Currently, several vaccine manufacturers produce the H3N8 vaccine, but it is available only from a veterinarian. While the H3N8 vaccine does not treat the disease or entirely prevent it, it may help decrease the severity of dog flu in an infected dog. The vaccine also decreases the amount of H3N8 virus shed into the environment, so vaccinated dogs are less likely to transmit the virus to other dogs. There is also a vaccine available for the H3N2 strain, which became available late in 2015. Additionally, experts do not believe that the H3N8 vaccine protects against the H3N2 canine flu virus. The H3N2 vaccine does not protect against H3N8 strain.

Veterinarians do not recommend vaccinating every dog against canine influenza. Instead, veterinarians recommend vaccinating specific groups of dogs who are at higher risk of contracting the virus:

  • Dogs who reside in a shelter, even for a short time
  • Dogs boarded in a kennel or day care, even for a few days
  • Dogs who frequently attend dog shows or dog parks
  • Dogs who otherwise interact with a large number of other dogs

These aforementioned dogs should also receive a kennel cough vaccine, since its transmission occurs in the same situations. Ask your veterinarian whether the canine influenza vaccine is appropriate for your dog(s). The kennel cough vaccine does not protect against canine influenze.

No Current Reported Infection Risk to Humans

To date, experts have reported no cases of human infection with either canine influenza virus. While the H3N8 and H3N2 viruses infect dogs and spread between dogs, there is no scientific or medical evidence that either virus transmits to or infects humans.

However, influenza viruses constantly change/mutate, and human infection with a canine influenza virus (and subsequent transmission between humans) could occur in the future. To prevent potential threats to the human population, the US Department of Health & Human Services Centers for Disease Control and Prevention (CDC) closely monitors the canine influenza H3N8 and H3N2 viruses (as well as other animal influenza viruses) for mutations.

Easily Prevent Canine Influenza from Affecting Your Dog(s)

To keep dog flu from making your dog(s) miserable, follow these simple steps:

  • Isolate any dog showing signs of a respiratory infection from other dogs for at least 2 weeks. Ideally, use a totally separate room/location.
  • Thoroughly clean and disinfect any clothing, equipment, or surfaces that could be contaminated with respiratory secretions. A 10% bleach solution or a commercial disinfectant is ideal.
  • Wash your hands thoroughly with soap and water before AND after having contact with a dog showing signs of a respiratory disease.
  • Do not allow your dog to share toys or dishes with other dogs grouped together.
  • Routinely monitor your dog(s) and any other dog(s) with whom he regularly interacts for signs of illness.

In Conclusion, NEVER Ignore Respiratory Signs

If your dog suddenly starts coughing, sneezing, gagging, or having difficulty breathing, don't just assume it's an allergy or some other occurrence that will "simply pass." These respiratory symptoms are extremely indicative of dog flu. Call your veterinarian immediately to schedule an appointment for evaluation, testing, and treatment if needed. Also, alert your veterinarian to the possibility of dog flu; he or she may wish to take precautions - such as meeting you at your vehicle when you arrive - to avoid the possibility of contaminating the clinic and unnecessarily transmitting the virus to other canine patients. Your veterinarian and veterinary team will be grateful for your concern and conscientiousness. Remember, ANY time your dog seems to be in respiratory distress, contact your veterinarian to keep dog flu and its potentially devastating symptoms from becoming an unhappy reality in your home.

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