Mystery dog disease is spreading in at least 14 states as laboratories race to isolate the pathogen – these are the symptoms pet owners should look out for

A “mysterious” disease spreading among dogs has now reached at least 14 states, health officials said.

Since August, hundreds of dogs have tested positive for the disease, and several have died – although these are thought to be huge underestimates due to a lack of awareness and testing.

The disease initially resembles the common 'kennel cough' virus, but can quickly turn into pneumonia when the infection spreads to the lungs and causes breathing problems, fatigue and discharge from the eyes and nose.

The American Veterinary Medical Association (AVMA) is now asking veterinarians to report cases as labs work to isolate the pathogen.

Colorado, California, Indiana, Washington, Georgia and Oregon are among the states that have reported cases

Colorado, California, Indiana, Washington, Georgia and Oregon are among the states that have reported cases.

So far, more than 200 dogs in Oregon have tested positive.

The Oregon Department of Agriculture described the mystery illness as an “atypical infectious respiratory disease of dogs.”

Reported symptoms of the disease include coughing that can last for weeks, watery eyes and sneezing.

The disease can progress and lead to pneumonia, which can lead to death within 36 hours.

The disease has been shown to be resistant to common respiratory treatments, such as antimicrobial drugs.

Although several dogs are believed to have died from the virus, experts say deaths do not appear to be a major consequence.

Health officials are urging people to make sure their dogs are up to date on all vaccines and to reduce contact with other dogs

However, without a clear way to define or test for the disease, it is difficult to determine how many dogs actually have the virus and how many have died from a severe form of the infection.

Although the disease remained a mystery for the first few weeks after its appearance, researchers at the University of New Hampshire believe they may have identified the bacteria that causes the disease.

Dr. David Needle, a veterinary pathologist who led the research, said it was a 'funky' organism – which has not yet been named – and had not been seen before.

His team discovered the bacteria by conducting forensic tests on 70 dogs that had developed the tell-tale symptoms over the past two years.

Speak with NBC Newshe said this was “new as a potential cause of disease, but it is likely – or evolved from – part of the dog microbiome (millions of bacteria found in the intestines of animals).”

He also described the bacterium as smaller than other species and said it had few specific genetic characteristics, making it harder to detect.

The disease is spread through airborne droplets when dogs sneeze, cough or bark. No cases of the disease spreading to humans have been reported.

Dr. Rena Carlson, president of AVMA, said, “We just don't know if it can jump to other species, whether they're humans or cats. We're keeping a close eye on that.'

Vets have advised owners to avoid large gatherings with unfamiliar dogs, especially if the dogs appear ill. This includes daycare centers, parks, grooming salons and boarding houses.

Shared water bowls should also be avoided, and extra caution should be taken if traveling with dogs during the holidays.

The Oregon Veterinary Medical Association said it advises “caution rather than worry” but urged pet owners to make sure their dog has received all vaccinations, including against canine flu, Bordetella and parainfluenza.