USA - Veterinarians and researchers across the US are working to figure out what's causing an infectious respiratory disease among dogs. In a few rare cases, the mysterious disease has been deadly.

Cases of a mysterious canine illness have been recently found from New Hampshire, Illinois, Colorado, and Oregon, according to CNN.

The Oregon Department of Agriculture describes it as an "atypical canine infectious respiratory disease." They say symptoms include coughing, sneezing, eye or nose discharge, and even lethargy in pets. Vets are urging caution as the number of cases continues to increase.

Vets in Oregon have reported more than 200 cases of the disease since August, as clinics in Washington have also seen an increase.

It's not yet clear what triggers the disease, and it has yet to be identified.

Researchers are comparing DNA samples from around the US to identify the pathogen.

"If what we have identified is a pathogen, it is likely that the bacteria is host-adapted bacteria with long histories of colonizing dogs," pathologist Dr. David B. Needle told CNN.

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Sadly, the mysterious illness appears to be resistant to the more common treatments. In rare cases, secondary infections have caused dog deaths.

Vets are urging pet owners to give them a call if their pooch starts coughing or shows other signs of a respiratory infection. They are also advising pet owners to limit their dog's contact with other animals, especially other dogs for the time being.

Sick or symptomatic dogs should also be kept away from other canines.

Though the mysterious disease is concerning, veterinarians suggest caution over worry.