It was the summer of 2022 when veterinarian David Needle first started hearing rumblings of a canine respiratory illness spreading in New Hampshire.

The dogs were sneezing, they'd develop a cough and discharge from their eyes, and the illness would drag on for weeks.

"The cough is pretty significant and it's resistant to normal treatment," says Needle, senior pathologist at the New Hampshire Veterinary Diagnostic Lab.

Even more puzzling, the dogs tended to test negative for the bacteria and viruses that are usually responsible for a respiratory syndrome often described by the umbrella term "kennel cough."

"In our experience, this is not a high mortality syndrome, but there is a subset of animals, it appears, that will develop acute and severe pneumonia and can die," he says.

Needle set out to find what was behind the strange illness, collecting samples from clinics and using genetic sequencing techniques to identify a possible pathogen.

At first, his search turned up nothing.

"We found no known DNA or RNA viruses, no bacterial pathogens, no fungal pathogens," says Needle, "We were sort of at a breaking point."

Until finally, a clue: A short segment of DNA belonging to what — as far as Needle can tell — appears to be bacteria that no one has ever described before.

"We think this may be a pathogen," he says, "It's something novel. It's in a proportion of the cases. It's funky."

Specifically, it appears similar to a genus of bacteria called Mycoplasma, which lack cell walls.

A respiratory illness pops up in more states

Needle didn't expect to share any of this information publicly – at least not so soon.

The cluster of cases happened during a few months last year. His team at the University of New Hampshire is still busy trying to sequence more of the genome and hasn't been able to culture the bacteria yet.

"If it wasn't for the fact that there were newer, potential outbreaks of a similar respiratory syndrome, we really wouldn't have come forward," he says.

This past summer, Needle learned that a similar illness was in neighboring states. He received a handful of samples from Rhode Island and Massachusetts that turned up signs of the same bacteria.

"The fact that we were able to see it in two other states a year after we first saw it was significant," he says.

Now, veterinarians and state health officials around the country are wrapping their heads around what appear to be hundreds of cases of a yet-to-be-identified respiratory illness. While there's no official count, cases are being investigated in a handful of states, including Colorado, Oregon and Illinois.

The situation is still murky though.

It's not yet clear how many cases are actually related to what Needle has identified in New England.

"Until we can put the dots together in the coming weeks to month, there is no certainty at all that what we've seen is even what's going on in the other places," says Needle.

Some vets recommend precautions

Still, some veterinarians are concerned enough that they're recommending dog owners think about how to reduce their pets' potential exposure.

Dr. Amanda Cavanagh, an emergency and critical care veterinarian at Colorado State University, advises scaling back visits with other dogs and avoiding doggy daycares, boarding facilities and dog parks.

"Just anecdotally, the chatter among veterinarians is that there are hot spots all over the country where some people are seeing an increase in respiratory cases," says Cavanagh.

In her state, the uptick in canine respiratory illness is obvious. Cavanagh says her hospital has about three to four dogs a day coming in — a clear increase from years past.

"We're very much in the information gathering stage," she says.

Unlike kennel cough that typically lasts about a week to 10 days, some of the dogs Cavanagh has treated had a cough for weeks to even months.

"We're noticing that more dogs are getting secondary bacterial pneumonia," she says.

This is why it's also important for dog owners to make sure their pets are up to date on vaccines, especially those that guard against canine influenza and Bordetella, she says.

An outbreak in the Pacific Northwest raises more questions

Meanwhile, Oregon state health officials have reported more than 200 cases of an "atypical canine infectious respiratory disease" since late summer. The illness generally doesn't respond to antibiotics and in some cases progresses to severe pneumonia quickly.

"It was a little scary in the beginning because of how sick some of these young otherwise healthy dogs were getting," says Hannah Marshall, a critical care specialist at DoveLewis, an animal hospital in Portland, Ore.

"This is lasting a lot longer than we would expect. This isn't responding to the normal antibiotics, or we're having to do really intensive, aggressive therapy, even surgery for these animals," she says.

Marshall says the numbers of dogs coming into their hospital with this respiratory syndrome — especially the severe cases of pneumonia — seems to have tapered off since the summer.

She says basically none of the animals have been testing positive on the standard infectious disease panels the hospital uses.

"We don't want it to be blown out of proportion, but it's something that we think is important enough to monitor closely," she says.

Cases also have been detected in Illinois and Iowa, a spokesperson for the Illinois State Veterinary Medical Association tells NPR.

Scientists expect to learn more soon

It could be an old strain of influenza or another bug that's driving at least some of these illnesses, says Colorado State's Cavanagh, who notes veterinarians at her hospital are starting to test the animals that come in.

"It could be a new virus," she says. "We just won't know until we have that testing."

While it's possible this is a new infectious agent, Dr. Colin Parrish says it may actually be multiple outbreaks with different causes, since dogs aren't traveling as much as humans.

"Respiratory diseases in dogs, that's commonplace," says Parrish, a professor at the College of Veterinary Medicine at Cornell University, but "they tend not to sort of show up in a lot of places in relatively close succession."

But New Hampshire veterinarian Needle is keeping his mind open to the possibility they are connected. He's already testing samples from dogs in Oregon and soon will be receiving some from Colorado.

He expects to know a lot more in a few weeks. His advice to the worried dog owners whose emails are filling up his inbox?

"I think caution, not fear," he says, "If you can be conservative in spreading your dog around with other dogs, you're probably going to put yourself in a better position to not have to deal with this."