Canine influenza, also known as dog flu, is a highly contagious respiratory disease caused by two type A influenza virus strains: H3N8 and H3N2. H3N2, which originated as an avian influenza, was first detected in dogs in South Korea in 2007 and first appeared in the US in 2015. 

Most dogs in North America have no preexisting immunity to the virus, making them susceptible to infection. Outbreaks are most common in places where dogs are in close contact with each other, such as dog parks, boarding facilities, animal shelters, and grooming salons. Most infected dogs experience mild illness, and the mortality rate is low. 

Symptoms of dog flu caused by the H3N2 virus appear two to four days after exposure. A dog can transmit the virus one to five days after they become infected, so they may pass it on to other dogs even if they appear to be healthy.

Common symptoms of H3N2 canine influenza include:

Some dogs will show no signs of illness, while others will develop severe illness resulting in pneumonia and sometimes death.

H3N2 is derived from an avian virus that gained the ability to infect canines. Almost all dogs are susceptible to infection regardless of age, breed, or health status. Infection can occur at any time of year, and outbreaks are most common when dogs are in close contact with each other, especially indoors.

The H3N2 virus spreads through the following ways:

While H3N2 can survive on surfaces and objects for 12 to 24 hours, it is easily killed by common disinfectants and handwashing with soap and water. 

If you suspect your dog has the H3N2 flu virus, call your vet first. It's recommended to call before going to the clinic, as your dog may have a highly contagious infection. When you call, tell your vet your dog's symptoms, when they started, and if your dog has been to a daycare or boarding facility, dog park, grooming salon, or another place with other dogs within the past week.

Your vet will provide instructions on when and how to see your dog. When you arrive at the clinic, they may ask you to wait in the car first before bringing you in through a separate entrance. 

Because dog flu looks like many other infectious respiratory illnesses, certain tests are needed to confirm if your dog is infected with canine influenza. If your dog has been sick for less than three days, your vet may collect nasal or pharyngeal swabs for PCR testing. If they've been sick for more than a week, your vet may collect a blood sample, for more accurate results.

A blood test is considered the most reliable way to confirm canine influenza virus infection. However, it requires two samples collected a few weeks apart in order to be accurate. Thus, PCR testing is preferred, but it may result in false-negatives after four days of illness. Both types of tests take time to run as they need to be submitted to an outside laboratory.

There is no specific treatment for canine influenza; the goal is to support the dog as their immune system fights off the viral  infection. Treating dog flu mostly consists of supportive care and may include: 

Rest and fluids keep your dog comfortable and well-hydrated. Water is needed in every important bodily function, including moving nutrients into cells and regulating body temperature.

Dogs with very little appetite can benefit from a recovery diet, which is high in calories, protein, and fat. This means your dog still gets the nutrients they need even if they eat less. 

Coupage is a technique that's performed by gently striking the chest with cupped hands. Nebulization is the delivery of fine mist, which may consist of plain water or saline solution, to the lungs. Both treatments help loosen lower airway secretions.

Antibiotics may be prescribed to dogs with complications such as pneumonia or a secondary bacterial infection. 

Non-steroidal anti-inflammatory medications may be given to reduce fever and inflammation, keeping dogs more comfortable during recovery.

Fortunately, most dogs recover from canine influenza at home without any complications within two to three weeks. However, they can remain contagious for up to four weeks, so it's recommended to isolate them from other dogs (and cats) for four weeks after they began showing symptoms to keep the virus from spreading. 

And while there is a vaccine for the H3N2 virus, vaccination is generally only recommended in certain circumstances, such as in areas where the virus is known to be circulating or when a dog travels. Routine vaccination is not recommended. 

Good hygiene and infection control practices can reduce your dog's risk of contracting the H3N2 dog flu virus.