I watched anxiously as my 80-pound doodle trotted off to his regularly scheduled doggy daycare, blissfully unaware that he'd soon be swapping all manner of germs with his buddies.

I wondered, does this constitute a high-risk situation? This was the same small circle of dogs he played with every week, but I had no clue where the others spent their time.

Would he come home with more than a healthy dose of slobber? Maybe, even, a new and poorly-understood pathogen?

Reports of respiratory illness afflicting dogs have put many dog owners like myself on edge in recent weeks.

Social media is filled with increasingly distressing headlines and anecdotes of otherwise healthy pets coming down with a raft of symptoms, everything from a hacking cough to sometimes life-threatening complications.

Most concerning, veterinarians say they're unable to identify what's making the dogs ill and the go-to treatments for canine respiratory illness, generally called "kennel cough," appear to be ineffective.

The list of states with suspected cases of a "mystery illness" has grown to include most regions of the country.

The uncertainty is worrying for the 65 million households with a dog — especially those whose pets have fallen sick. In rare cases, dogs have died.

But veterinarians who study infectious diseases say this may, in fact, not be an outbreak of a singular illness at all. There's still scant evidence connecting these cases with any common pathogen, let alone to an altogether new one.

"It's entirely possible that there are just a ton of different bugs and viruses causing disease in different parts of the country," says Dr. Jane Sykes, a professor at UC Davis School of Veterinary Medicine who focuses on infectious disease. "We just have to be a bit careful about panicking."

Because the U.S. doesn't have a robust surveillance system for infectious disease in dogs, it's hard to track these cases and discern whether anecdotes and scraps of data add up to widespread and concerning patterns.

"Two things keep getting mixed up," says Dr. Scott Weese, an infectious disease veterinarian at the Ontario Veterinary College. "Do we have more disease? And do we have something new? Because those are not necessarily connected."

Poor clinical understanding of 'atypical' illness

Weese says it seems that certain parts of the country are experiencing an uptick in canine respiratory illness. However, it's possible the deluge of media coverage and attention on social media has created the appearance of a nationwide outbreak that may not exist in reality.

"I get an email a couple of times a week saying, 'hey, are we seeing more respiratory disease in dogs?" he says, "But I've been getting that email for like five years."

Despite all the attention on individual cases, there's nothing at this point "that would indicate there's a national outbreak, anything that would indicate these are all medically connected to each other," says Dr. Silene St. Bernard, a regional medical director for VCA Animal Hospitals, which runs more than a thousand hospitals in the U.S. and Canada.

Of course, none of this skepticism rules out the possibility that there is a new pathogen starting to spread.

For example, researchers in New Hampshire have identified an odd bacteria that could be relevant, although they haven't yet confirmed this is actually what's causing illness in some dogs.

"The three choices are: There is not a new disease out there. There is a disease whose incidence is particularly high right now and it's a known agent," says Dr. Kurt Williams, who directs the Oregon Veterinary Diagnostic Laboratory, "Or there's truly something new and novel out there."

While there's no official tally, there are now hundreds of cases of an "atypical canine respiratory disease," according to state health officials and medical organizations in more than a dozen states.

However, Williams cautions this framing can be misleading because it gives the impression that a clearly defined disease is spreading. "We have a very poor understanding of the cases clinically," he says.

Generally speaking, the unifying symptom of the cases that are being reported seems to be a persistent cough that doesn't resolve as would be expected with typical cases of kennel cough. In the worst cases, dogs can come down with life-threatening pneumonia, which sometimes develops rapidly.

Negative tests may not rule out known pathogens

Similar to veterinarians in other states, Dr. Melissa Beyer says she's not seeing dogs with an unidentified illness dying in high numbers. What's puzzling is they can't identify the causes of their illness.

"We've been running respiratory panels to check about 20 different viruses and bacteria," says Beyer, who runs South Des Moines Veterinary Center, "A lot of them are coming back negative."

This observation by veterinarians around the country has raised the specter of a new pathogen, but there's actually many reasons why the PCR tests used for canine respiratory illness could come back negative, says Sykes of UC Davis.

The sample collected could simply be too small, or taken from the wrong part of the body; the levels of the pathogen can change from day to day, or the dog's body might have stopped shedding it by the time the sample was collected.

Even if it's a well-known bug, the genetic sequence might be different enough that the PCR test fails to detect it.

"For some of these organisms, negative results are even more common than positive test results," she says.

Sykes, who founded the International Society for Companion Animal Infectious Diseases, says the observations that dogs are resistant to standard treatment is thorny because many dogs are treated unnecessarily with antibiotics, when, in fact, they have a viral illness.

"What's actually being said here by veterinarians in these different locations is really that dogs are taking a long time to recover," she says.

Symptoms could be caused by a 'pathogen soup'

Of the many possibilities, she suspects one could be a "pathogen soup," essentially a mixture of co-occurring infections that are making dogs especially sick and prolonging their recovery.

Respiratory disease in dogs wax and wane and the last few years have seen more "dramatic swings" where outbreaks last longer and take place across broader areas, says Dr. Weese.

The epidemiology around this illness is especially hazy because there's already some mix of the usual suspects, like Bordetella and canine respiratory coronavirus (not related to COVID-19), with outbreaks of canine flu layered on top of that.

The uptick in illness doesn't happen in a vacuum, either: Dog ownership in the U.S has gone up steadily, vaccinations have been disrupted in recent years, and the holiday season has led more people to board their dogs or bring them on travel and mingle them with other pets.

Pathologist search for clues in the lab and in lungs

Still pathologists are keeping an open mind as they collect samples from sick dogs and search for clues.

"I do trust veterinarians," Williams says, "If they say we are seeing increased numbers of cases and they're behaving clinically differently than we're used to, we need to pay attention."

In New Hampshire, a team of researchers have used genetic sequencing to turn up evidence of what appears to be a new bacteria, similar to Mycoplasma.

While they haven't been able to culture the bacteria, they've identified it in samples collected from dogs who fell ill in New Hampshire last year and from dogs in neighboring states this year.

"We think this may be a pathogen," says David Needle, a pathologist at the New Hampshire Veterinary Diagnostic Laboratory, "We don't think it itself is responsible for mortalities very often, but it may allow for secondary infections that could cause mortalities."

Needle is analyzing samples from other states to see if they can find the same genetic material in sick dogs there.

While intriguing, Weese points out that Mycoplasma can commonly be found in dogs with and without respiratory disease. He says it's way too soon to assume this is behind any of these outbreaks.

"We just don't know at this point," he says.

In Oregon, Williams is skeptical that would explain what he's seeing in his state, saying it's possible something distinct is happening in the Pacific Northwest.

In fact, he's in the early stages of examining the lungs of dogs who died from the atypical respiratory illness that has sickened more than 200 dogs in Oregon. So far, he's finding acute injury in the small air sacs, called alveoli, and bleeding from that into the lungs.

"I don't want to get out over my skis here, but I've looked at a lot of dog lungs in my career, and these are a little bit different," he says, "So it makes me think, maybe, there's something out there."

Take precautions but don't succumb to fear

For now though, veterinarians tell NPR it's wise for dog owners to take common-sense measures, like avoiding contact with sick dogs and making sure your dog is up to date on its vaccine.

Ultimately, Weese says it will depend on your situation.

"If there are a lot of sick dogs in your area, then it is reasonable to be more restrictive. If you've got a dog that's at high risk for disease, be more restrictive," he says.

Some people may want to steer clear of "high traffic" public places like dog parks and if possible, boarding facilities, groomers and other crowded settings, says Dr. Ashley Nichols, president of the Maryland Veterinary Medical Association.

"Those are the activities that if you're nervous about exposure, I would avoid because that's where dogs with many backgrounds, many immunization levels and things like that mix," she says.

Nichols worries about the exponential rise in fear among some pet owners. She and her colleagues have noticed it's led some to skip routine health care, worried their dog might catch something at the clinic.

"I understand people's concerns. I think avoiding the vet clinic is not the way to go," she says.

And if your pet does get sick, get them seen immediately. Ashley Dozier, a vet tech in Virginia Beach, initially wasn't too worried when her young golden retriever started coughing earlier this fall. That changed as his condition deteriorated, though.

"I brought him in to work and he was diagnosed with pneumonia," says Dozier. "He went a total of nine weeks on three different types of antibiotics and a round of about three to four weeks of steroids."

Now off the steroids, she says he's finally starting to bounce back.