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Ask the Vet: Canine Influenza by Dr. Stefanie Wong
May 18, 2016

Canine influenza, also known as the dog flu, is a highly infectious virus that has been confirmed in 40 states across the United States, including California.  There are currently two strains that have been identified - H3N8 and H3N2.  H3N8 was first identified in Florida among racing greyhounds in 2004.  H3N2 was first identified in an outbreak affecting dogs in Chicago and the surrounding Midwest region in 2015.  In March 2016, multiple cats in an animal shelter in the Midwest were also confirmed as infected with H3N2, suggesting that cats are also susceptible to the virus.  As it's continued its trek across the United States to California, we at Bishop Ranch feel it is of the utmost importance that our clients be educated about this potential threat to pet health.

How is it spread?

Canine influenza is spread via direct nose-to-nose contact as well as via aerosolized droplets from coughing, sneezing and barking.  Contaminated droplets can also land on surfaces such as floors and walls, food and water bowls, collars and leashes.  It can also spread via people travelling between the sick and healthy animals.  The virus (if it's not killed by cleaning agents) remains alive on surfaces for 48 hours, clothing for 24 hours and on hands for 12 hours.

The incubation period (the time before an animal is showing symptoms of the disease) is 2-4 days from when they are exposed.  Unfortunately, dogs are most highly contagious during this time frame.  Dogs continue to remain contagious for up to 7 days in most cases although in some cases they can be contagious for several weeks.  Therefore the recommendation set forth by the American Veterinary Medical Association (AVMA) is to keep pets isolated and quarantined from other animals for at least 21 days.

Virtually all dogs that are exposed will become infected with the virus - but only 80% will develop outward signs of disease.  20% are asymptomatic, however they can continue to shed the virus and spread disease.

At this time, there is no evidence of transmission of canine influenza from dogs to people and no reported cases of canine influenza in humans.

What are the symptoms?

There are two forms of canine influenza: mild and severe.

Thankfully, the majority of dogs will contract the mild form of canine influenza, which is often self-limiting.  The most common symptom is a cough that can stick around for up to 21 days despite treatment with antibiotics and cough suppressants.  Nasal discharge, ocular discharge, sneezing, lethargy and decreased appetite can also be seen.

Dogs who are more severely infected will often develop pneumonia.  Symptoms of pneumonia include fever, yellow or green nasal discharge, increased respiratory rate and effort, severe lethargy and anorexia.  The severe form of canine influenza can be fatal, although thankfully mortality rates are low.  Pneumonia is diagnosed by taking chest x-rays.

Cats affected by H3N2 often can show nasal discharge, congestion, lethargy, lip smacking and excessive salivation.

It is important to note that the symptoms listed above are not exclusive to canine influenza.  We can see symptoms like these in many different upper respiratory infections of dogs and cats.  For example, kennel cough in dogs can cause very similar symptoms.  The only way to know if your pet has canine influenza is through testing.

How do you diagnose canine influenza?

The most reliable way to confirm infection is via a paired blood test measuring antibodies (which the body produces as a response to infection).  We would draw a first blood sample within the initial 7 day window of your pet showing symptoms, and then draw a second blood sample 14 days later.  The infection is diagnosed by comparing the samples - the second sample should show a marked increase in the number of antibodies, reflecting the body's response as it fights off the infection.

Another option is taking nasal and throat swabs for PCR testing - this needs to be taken within 3 days of the dog showing illness to be accurate.  If this test is performed 4 days or more after symptoms have arisen, this test becomes less able to detect the virus.

How do you treat it?

Treatment is mostly supportive - because canine influenza is caused by a virus, there is no medication available to treat it directly.  Supportive treatment is often used to help them feel more comfortable and also to give them a better chance of fighting off the virus with their immune system.  These treatments will be determined on a case-by-case basis.  Examples of treatments include: antibiotics to fight off secondary bacterial infections and fluids if dehydration is present.  In severe cases with pneumonia, often hospitalization is needed.

How do you prevent it?

Canine influenza vaccinations are available for H3N8 and H3N2.  As H3N2 is the newest strain, this is the vaccine that Bishop Ranch will be carrying.  This vaccine is important for dogs that will be at boarding facilities, grooming facilities, going to dog shows, going to dog parks or traveling to the Midwest.  Please reach out to your veterinarian to help you decide if your pet should be vaccinated.  With any flu vaccine (just like the ones people receive), there is always a chance that it will not be 100% protective, however it provides benefit in that often the symptoms will be less severe and the window in which their symptoms are present is often shortened.  The vaccine is given as two boosters given 2-4 weeks apart.  While vaccine reactions are always possible with any vaccine, we have not seen any increased evidence with this particular one.  Unfortunately at this time there is no vaccine available or approved for use in cats. 

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