Cases of mystery dog illness reported in 2 more states

A mysterious respiratory illness among dogs appears to be spreading with cases being reported in two more states.

This week, Nevada and Pennsylvania reported cases of atypical canine infectious respiratory disease complex. Overall, 16 states have reported cases of the illness.

While the cause of the respiratory illness is unknown, some veterinarians are advising owners not to expose their dogs to other dogs who are coughing, to make sure their dogs are up to date on their vaccinations and to take extra precautions when traveling this holiday season.

Last month, veterinarians began sounding the alarm as they saw a growing number of coughing dogs.

Dog owner speaks out about mystery illness

Wendy Brown's three golden retrievers -- Bridge, Dooley and Lulu -- are among the dogs who started showing symptoms this November.

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

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Initially, Brown thought her pets had a typical kennel cough but when their symptoms didn't subside, she knew it was something more serious.

"The vet started him on a 10-day cycle of doxycycline. Today was day 10 and he is not a lot better," Brown said.

Brown, an Idaho resident, said she's still not sure what could have caused her dogs' illness in the first place.

What are the symptoms of the mystery respiratory illness in dogs?

While research is underway, veterinarians say the mystery illness is highly contagious and can be fatal. Reported symptoms so far have also been typical of a kennel cough and they include coughing, sneezing, difficulty breathing, lethargy, fever, nasal and/or eye discharge and a loss of appetite.

"Instead of that dry cough where the dog felt good, it was now this wet cough where the dog felt sick," Amanda Cavanagh, the section head of the urgent care service at Colorado State University Veterinary Teaching Hospital, told "GMA."

Experts like Cavanagh said any dogs showing signs of consistent coughing should be brought to a vet to be examined.

"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," Cavanagh said.

Cavanagh also recommends keeping any coughing dogs away from other dogs and for two weeks after the cough goes away.