Dog Illness Mystery Explained: What We Know, What We Don't

Cases of a mystery respiratory illness in dogs reported across the U.S. have been confirmed by officials and researchers who are still determining its cause, severity, and spread.

Reports of the illness have cropped up across a number of states, including: California, Colorado, Oregon, New Hampshire, Rhode Island, Massachusetts, Florida, Idaho, Indiana, Illinois, and Georgia.

Dogs that come down with the illness are said to develop symptoms including a cough, fever, and lethargy. Some can contract pneumonia, and some cases can lead to death.

The illness was spotted in Oregon in August and increased in incidence, though local dog medics told Newsweek earlier this month that there was little evidence of a widespread outbreak. There had been anecdotal reports nationally as far back as a year earlier.

Newsweek examined the confirmed data and spoke to researchers and pet groups to see what they know so far.

Advice for Dog Owners

The Oregon Department of Agriculture said that as of November 21 it has received more than 200 reports of what it has called atypical canine infectious respiratory disease.

It has said dog owners should exercise caution rather than worry, noting that the number of reported cases represented a "very small" percentage of Oregon's dog population.

The American Kennel Club told Newsweek it had warned dog owners about the potentially higher risk of infection over the Thanksgiving weekend.

"With higher numbers of pets boarded during holiday travel, there are increased numbers of dogs in close proximity and the potential for spread," Stephanie Montgomery, CEO of the AKC Canine Health Foundation, said. "Owners should consider risk factors for the pet and a there is a canine influenza vaccine available."

What We Know

David Needle, pathology section chief at the University of New Hampshire's Veterinary Diagnosis Laboratory (NHVDL), told Newsweek on Tuesday that the illness, a respiratory syndrome, has been resistant to standard treatments and does not result in positive tests for common respiratory pathogens.

The initial investigation into the illness began in late summer 2022. After providing swabs to local clinics, tests found 21 of 31 had segments of DNA "predicted to belong to a likely non-culturable bacterium that has been minimally studied and is not well characterized."

Researchers from the laboratory told NBC News that it genetically sequenced samples from an initial group of 30 dogs in New Hampshire and then another 40 from Rhode Island and Massachusetts.

"Based on what we know it is probable that these are part of the normal community of bacteria and other microorganisms that live in the respiratory tract," Needle told Newsweek.

"For some reason they gained the ability to be associated with disease."

What We Don't Know

Should the illness be identified as a pathogen, Needle said it was likely that the bacteria would be "host-adapted with long histories of colonizing dogs," later developing a "virulence-associate gene/trait."

Needle said that there was no evidence the infection had the potential to pass between animals and humans but there was "no evidence to dismiss this possibility completely."

The NHVDL has not yet found a way to determine which breeds might be most at risk.

In rare cases, animals had developed an "an acute and sometimes fatal pneumonia after the longer chronic disease," Needle said.

How Fast Is the Dog Disease Spreading?

Outside of Oregon, Los Angeles health officials said Tuesday it had recorded 10 cases, since November 16, of dogs with respiratory illness that tested negative for common viruses and bacteria seen in dogs with similar symptoms.

The Colorado Department of Agriculture stated that it had received calls over the past two months, "reporting an elevated number of canine respiratory disease cases in the state."

"Veterinarians are currently reporting that they are seeing double the number of cases than what is typically seen during a canine infectious respiratory disease outbreak," it added.

The Illinois College of Veterinary Medicine stated as of Tuesday "our clinicians at the Veterinary Teaching Hospital in Urbana and the Medical District Veterinary Clinic in Chicago had not seen an uptick in canine respiratory cases."

It added: "Right now, we don't know the true extent of illness or deaths because we don't have sufficient data as the symptoms overlap with other causes of lung disease, and the presumed infectious agent (or agents) driving disease remains unknown.

"At this time, too few positive bacterial and viral samples have been collected nationally to clarify the lung pathology, and what leads some dogs to recover and others to succumb to the disease."

Miami-Dade County Animal Services Department also stated as of Tuesday that there had been "no reported cases" in Florida but was closely monitoring the situation.

More samples arrived at the NHVDL from Oregon last week, with more expected from Colorado, Illinois, and other states. It has said preventive measures were the same as other respiratory infections, such as avoiding contact with other dogs, ensuring your dog is up to date on all vaccinations recommended by your vet, and contacting your vet has clinical signs of the disease.

Newsweek has contacted health officials in Florida, Illinois, Georgia, Idaho and Indiana, as well as the U.S. Department of Health and Human Services, and the U.S. Department of Agriculture via email for further information.