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But the illness is distinct from kennel cough because symptoms will include a wet, rather than a dry cough, experts have said.
“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 Good Morning America.
Vets have also warned that the mystery illness is highly contagious and could potentially be fatal.
Some cases of the pneunomia progress quickly, making dogs very sick within 24 to 36 hours.
The Oregon Department of Agriculture has documented more than 200 cases of the disease since mid-August.
Wendy Brown, from Idaho, told Good Morning America her three golden retrievers — Bridge, Dooley and Lulu —started showing symptoms of the mystery illness earlier this month.
“Dooley started doing kind of this huffing and also seemed to feel quite lethargic,” she said. “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.”
Ms Brown said she initially thought her dogs had kennel cough, but after the coughing did not subside, she knew it was more serious.
She said after 10 days and a dose of doxycycline from the vets, her beloved pets are still not feeling much better.
Ms 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,” she said.
She also recommended keeping any dogs showing symptoms away from other dogs during the length of their illness, as well as for two weeks after the cough goes away.