What we know about a mysterious illness making dogs sick and how to keep your pets safe

There is a new warning about a mystery illness affecting dogs, with cases being reported nationwide.

Here is what we know about the unknown respiratory illness affecting hundreds of dogs nationwide and what veterinarians are recommending.

"There was just far more coughing dogs coming into the emergency room than in years past," said Amanda Cavanagh, the section head at Small Animal Emergency Service at Colorado State University Veterinary Teaching Hospital.

While research is still underway, vets are saying the illness is highly contagious, and in some cases, fatal. Most reported symptoms are similar to those of a typical kennel cough, including coughing, sneezing, nasal and/or eye discharge and lethargy.

"Instead of that dry cough where the dog felt good, it was now this wet cough where the dog felt sick," Cavanagh said.

First reported in Oregon back in August, the state's Department of Agriculture received over a hundred written reports from vets about the illness. Cases eventually spread even further west, with the San Diego Humane Society temporarily pausing intake of owner-surrendered dogs until next month to help prevent further spread.

"He's never been sick a day in his life," said Wendy Brown, an Idaho dog owner.

Brown said her three golden Retrievers Bridge, Dooley and Lulu each started showing symptoms earlier this month.

"Dooley started doing kind of this huffing and also seem to feel quite lethargic. Not too long after, Bridge began to exhibit the symptoms. But he and his were louder, more boisterous. It was like, I thought it was his stomach because he made like a retching sound," Brown described.

At first, Brown thought it was just a typical kennel cough but when the symptoms didn't go away, she knew it was something more serious.

"The vet started him on a ten-day cycle of doxycycline. Today was day ten and he is not a lot better. So quite a bit of concern for us there," Brown said.

While her dogs are slowly starting to show signs of recovery, Brown said she's still in the dark as to what caused the illnesses in the first place.

"They go swimming usually once a week -- could be there. All three dogs have participated in all of those activities. We've all gone to the dog park. I don't know how you nail down which one of those things might have been the culprit in terms of contracting it," Brown said.

Experts say dogs showing any signs of consistent coughing is a good reason to get them checked out.

"Let the vet fully evaluate," Cavanagh recommends. "We can ultrasound the lungs to see if there is a problem that is related to pneumonia or the contagious pneumonia that seems to be going around. That early vet visit can be so important to establish that relationship with your vet and have them help you take care of your dog and then track how this illness is going to progress."