What’s Causing Mysterious Respiratory Illness in Dogs?

A severe respiratory illness appears to be spreading in dogs in at least 15 states, according to recent reports. Veterinarians compare it to “kennel cough,” a term used to describe several viral and bacterial infections that can cause a sudden, honking cough in dogs. But whereas kennel cough usually clears up, the recent infections have resulted in pneumonia and even death. One research team has pinpointed a bacterium with an odd genome as a potential source.

“In some of these places the dogs that are affected are more severely affected than what we would normally experience” in a typical respiratory season, says Kathleen Aicher, a veterinarian who specializes in internal medicine for dogs and cats at Texas A&M University. “Even if that’s a fairly isolated thing, for the veterinarians who are seeing those dogs and for the families that love those dogs, that is pretty darn scary.”

While plenty of dogs seem to clear the infection with treatment, others aren’t responding to typical treatments and develop long-term symptoms or secondary infections, Aicher says. Some of these dogs can deteriorate frighteningly quickly. She points in particular to reports of cases in which vets have needed to put dogs on ventilators or to surgically remove sections of infected lung tissue—both of which are extremely unusual measures—particularly for dogs that had previously been young and healthy, as some of these are, Aicher notes. “In the areas of the country that are reporting this right now, they’re really going through a difficult time,” she says.

Although the mysterious illness is now making headlines nationally, cases remain patchy, with reports coming from the states of Oregon, Colorado, California, Illinois, Florida, Georgia, Indiana, Massachusetts, Washington, Vermont, Maryland, Idaho, New Hampshire, Rhode Island and Pennsylvania. That said, it’s not yet clear whether the same infection is responsible for all these cases, Aicher says.

Veterinary investigators are having trouble tracking down the organism—or organisms—responsible for these strange illnesses, says David Needle, a veterinary pathologist at the New Hampshire Veterinary Diagnostic Laboratory and a clinical associate professor at the University of New Hampshire, who since late 2022 has led the process of trying to identify the cause of infections in New Hampshire.

He first heard about the illness last year, but in the early days, he had no samples—neither nasal swabs nor…