Canine influenza, commonly referred to as dog flue, is caused by varieties if the Influenza A virus capable of creating influenza in dogs and other canines. Among these varieties, the qquine influenze virus H3N8 is generally considered to be the most important one.

During an outbreak of H5N1, a completely different type of influenza, a dog in Thailand caught the disease by eating an infected duck. (H5N1 is also known as avian flu.)

Canine influenza background

The H3N8 influenza virus was discovered in 2004 after an outbreak on a racetrack in Florida. The virus is believed to have spread from horses to Greyhounds, since both animals competed on the same tracks. This was the first time in history that influenza A could be scientifically proven as causing influenza in dogs. Further investigations of serum taken from racing Greyhounds between 1984 and 2004 did however show dogs infected with canine influenza virus (CIV) as far back as 1999.

By analysing the genome of the canine influenza virus, scientists have confirmed that H3N8 was transmitted from horses to dogs and then adapted to dogs through point mutations in the genes.

Since influenza A has not occurred in dogs until the end of the 20th century (at least as far as we know), dogs have no natural immunity. When the virus enters a group of dogs, e.g. on a dog show, it normally spreads very quickly and a lot of dogs become infected. Thankfully, very few of the infected dogs die – especially not if they receive treatment for the secondary infections that can develop.

The influenza A virus is a enveloped negative sense single-stranded RNA virus. It is roughly 80-120 nanometres wide and 200-300 nm long. There are no known instances where canine influenza has spread from a dog to a human, a cat, or a horse.

Dog flu symptoms

When dogs become infected with canine influenza, roughly 80 percent of them develop noticeable symptoms. The incubation time is 2-5 days. A majority of the dogs develop only mild symptoms, but there are exceptions. Dog influenza can for instance lead to pneumonia (normally accompanied by high fever).

These are the most common symptoms of canine influenza in dogs:
- A cough that lasts for 10-30 days
- Greenish nasal discharge
- Fever  

Canine influenza diagnosis

For a definite diagnosis, the vet can take a serum sample from the dog and send it to a laboratory that carries out a PCR test for canine influenza viruses. In many cases, upper respiratory disease in a dog proved to be vaccinated against the major causes of kennel cough will make the vet suspect canine influenza, especially if other dogs in the area has been diagnosed with it.

Canine influenza prevention

Unfortunately, there is no canine influenza vaccine available. Research indicates that a canarypox-vectored vaccine for equine influenza virus might be useful, but much more studies and tests are necessary.

The viruses behind canine influenza can be easily killed with common disinfectants, e.g. household bleach solutions.

A dog suffering from canine influenza should ideally be separated from other dogs, because it can release viruses for 7-10 days after showing the first symptoms. There are no known instances where a dog has become a persistent carrier of the disease.

Canine influenza treatment

There is no cure for canine influenza and the vet can only focus in alleviating the symptoms. If secondary bacterial infections set in, antibiotics can become necessary. If the dog develops pneumonia, the survival chance can be lower than 50% if you do not take it to a vet and provide it with correct care. Autopsies performed on dogs that died after having contracted canine influenza showed that they had developed severe hemorrhagic pneumonia and/or vasculitis.

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