Scientists search for cause of mysterious dog respiratory illness as vets rush to treat it

Veterinarians across the country are scrambling to treat the rising number of dogs sick with a severe type of respiratory illness. At the same time, scientists are trying to figure out what’s causing the current outbreak, how widespread it is, and how many previously healthy pups have become seriously ill or died.

Maple was a happy, healthy 7-month-old Australian shepherd until last Saturday, when she began coughing. Her owner, Adrianna Deffenderfer of Fontana, California, became scared when the pup’s cough progressed quickly, keeping Deffenderfer up through the night.

“I was just holding her, trying to comfort her as best as I could,” said Deffenderfer, 23. “I could tell that she was scared, too.”

At the vet the next morning, the young dog was tested for various respiratory illnesses, all of which eventually came back negative.

“The vet called me and he said, basically because there’s no definitive proof of this illness yet, we don’t know really what’s causing it,” said Deffenderfer.

Maple was treated for bronchitis, given a nebulizer and a steroid shot, and had the secretions cleared from her lungs. She was also sent home with two different antibiotics.

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Maple, a 7-month-old Australian shepherd, is recovering from a severe respiratory illness.Courtesy Adrianna Deffenderfer

Canine respiratory infections, especially dog flu, are common, often causing outbreaks in shelters and doggy day cares. The current surge has been spreading in areas of the U.S. and Canada over the last year. This outbreak is different from garden-variety respiratory illness, experts say, because of the large number of cases serious enough to lead to pneumonia.

In Colorado, the number of canine pneumonia cases rose by 50% from September through November of this year, compared to the same months in 2022, said infectious disease expert Dr. Michael Lappin, director of the Center for Companion Animal Studies at the Colorado State University School of Veterinary Medicine. According to Trupanion, a pet insurance company, claims data suggests that the number of dogs with severe respiratory illness is on the rise in a number of states.

More dogs may be getting severely ill because they have been infected with multiple pathogens at the same time — including canine influenza, Bordetella (kennel cough) and mycoplasma pneumonia — said Dr. Deborah Silverstein, section chief of emergency medicine and critical care at the Ryan Veterinary Hospital at the University of Pennsylvania —similar to the tripledemic of Covid-19, influenza and RSV that affected people last fall and winter.

Is it a new bug?

There could be a number of reasons for the uptick. Many dogs may have lower resistance to infections because pandemic-era restrictions kept them out of day cares or boarding facilities and they weren’t exposed to circulating viruses or bacteria, experts note. There have also been reported decreases in canine vaccination rates. A recent study found that nearly half of dog owners are hesitant about vaccinations for their pets.

“We’ve got more dogs that have a lower level of resistance because they’ve been exposed less over the last couple of years and they’ve had less vaccination,” Dr. Scott Weese, an infectious disease veterinarian at the Ontario Veterinary College, said during an online briefing Thursday. “So that means just with our normal respiratory disease that’s always there and always circulating around, we can see more disease and more spikes.”

Silverstein said it’s possible that any of these factors could explain the increased incidence of a disease making some dogs deathly ill.

“It’s more than likely that some bug may have changed in its virulence,” Silverstein said. “Just like Covid strains can be milder or more severe.”

Still, there is a possibility there is a new bacteria circulating.

Scientists at the University of New Hampshire recently identified a novel bacterium as a possible culprit. The findings are based on a small number of cases from New England states, so the results need to be confirmed in a larger and more geographically diverse sample of dogs.

Researchers at other centers, including Oregon State University,  Colorado State University and the University of Pennsylvania are also trying to identify the cause of the outbreak.

One big factor slowing down research in the U.S. is that there is no single group keeping track of pet illnesses. For example, scientists at CSU are coordinating with the state veterinarian’s office, the U.S. Department of Agriculture and other researchers to get more insight into what’s happening in Colorado.

Another hurdle is that many owners can’t afford to take a sick dog to a veterinary hospital or specialty center or even pay for diagnostic testing. According to Dr. Steve Weinrauch, chief veterinary officer at Trupanion, “For less frequent, but severe cases where multiple day hospitalization and supportive care is necessary, costs can range from $15,000 to $20,000.”

Which dogs are at increased risk?

Usually, brachycephalic or flat-faced dog breeds such as French bulldogs or pugs, senior dogs or dogs with underlying lung disease are more at risk of developing pneumonia from a respiratory infection.

But at Texas A&M School of Veterinary Medicine, Dr. Kate Aicher treated a cluster of cases of atypical canine respiratory disease in young, vaccinated dogs in March and April of this year. What Aicher and her colleagues were seeing was a sudden onset of fever and a wide range of severity.

“You don’t expect 1- and 2-year-old dogs who are well conditioned and healthy to end up with pneumonia so severe that they need to be put on a ventilator and then die,” said Aicher. “You don’t expect dogs to die despite aggressive care.”

About 75% of the dogs at Texas A&M tested positive for a known pathogen. But in 25% there was nothing at all on the tests, Aicher said.

Then, for Aicher, it all suddenly became personal.

Her 2-year-old Labrador retriever developed a high fever and a disturbing cough. Aicher’s dog was hospitalized and, fortunately, recovered with treatment. The pup is now back at home “running around being her normal Lab self.”

Sadly, a dog of the same age and breed that came to the hospital for treatment didn’t make it, she said.

Aicher recalled that while on a walk, her dog had made some subtle snuffling noises and coughed once.

“In hindsight, those were probably the first signs and they didn’t trigger any alarm bells,” she said.

It underscores the importance of owners knowing their dogs and recognizing when things seem off.

Symptoms of canine respiratory infection include:

  • Coughing.
  • Sneezing.
  • Red, runny eyes.

Many dogs will recover on their own. But if the dog has difficulty breathing or stops eating, it could be a more serious problem and the dog should be taken to a vet.

With all the attention the unidentified illness is getting in the news, and especially on social media, Dr. Cynda Crawford, a chair in shelter medicine at the University of Florida College of Veterinary Medicine, worries that owners will panic when there don’t yet seem to be that many cases overall.

Nevertheless, “vets working on the front lines in private practice are seeing higher numbers of dogs with respiratory illness, and some of those dogs are progressing to pneumonia,” Crawford said. “They are reporting that the dogs are not responding as well or as quickly to the normal standard of care.”

Meanwhile, Maple, the Australian shepherd, appears to be improving and is due for another chest X-ray to make sure the antibiotics are working.

“She can sleep through the night, she can take naps,” said Deffenderfer. “We can do a little bit of training.”