Veterinarians are sounding the alarm as they see a growing number of coughing dogs.
Wendy Brown's three golden retrievers — Bridge, Dooley and Lulu — are among the dogs who started showing symptoms earlier 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."
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.
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, 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," 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.