Making sense of the mystery illness found across the US

Updated December 7, 2023

As of early December, cases of canine infectious respiratory disease complex (CIRDC) have been seen by veterinarians in multiple states. The exact number remains unknown as requirements for veterinarians to report CIRDC to their state animal health officials are highly variable. Further hampering reporting is that several bacteria and viruses can contribute to CIRDC, and that, by the time a dog does get tested, if the causative agent is a virus, it may have already passed the point of being detectable.

So, while nationwide numbers are not known, Colorado, New Hampshire, and Oregon officials are working with state and federal veterinary diagnostic laboratories to determine the underlying cause or causes.

The Oregon Department of Agriculture (ODA) has received more than 200 case reports from veterinarians since the middle of August. The ODA, which has been investigating the pathology of CIRDC, says the illness presents with the following clinical syndromes:

• Mild-moderate tracheobronchitis with a prolonged duration (six to eight weeks or longer) that is minimally or not responsive to antibiotics.
• Chronic pneumonia that is minimally or not responsive to antibiotics.
• Acute pneumonia that rapidly becomes severe and often leads to poor outcomes in as little as 24-36 hours.

At this time, there are no indications of a connection between these CIRDC cases and an outbreak of Streptococcus equi subsp. zooepidemicus at the San Diego Humane Society, which resulted in four dogs being euthanized.

Vaccination and socialization factors

The pet insurance company Trupanion hosted a virtual Q&A on November 30 featuring a panel of veterinarians who fielded questions and offered their insights into CIRDC. The panelists were Dr. Scott Weese, a pathobiology professor at the University of Guelph Ontario Veterinary College and director of the university’s Centre for Public Health and Zoonoses; Dr. Michael Lappin, a professor at Colorado State University College of Veterinary Medicine & Biomedical Sciences; Dr. Steve Weinrauch, chief veterinary and product officer of Trupanion; and Dr. Carrie Journey, a veterinary neurologist and practice owner at Remedy Veterinary Specialists in San Francisco and president of nonprofit Not One More Vet.

The big question at the moment, according to Dr. Weese, is whether the recent CIRDC cases are a result of changes in how dogs have been cared for and managed or something else. He suspects it’s the former. So much relating to dog ownership changed during COVID, Dr. Weese explained. Dog ownership increased, veterinary care was disrupted, and canine vaccinations may have dropped. People—and thus, their pets—socialized less as a safety precaution. Working from home became the norm, meaning doggy daycare wasn’t needed, and associated vaccinations such as Bordetella and canine parainfluenza, fell off.

“What the net result could be is we’ve got more dogs that have a lower level of resistance because they’ve been exposed to other dogs less over the last couple of years, and they’ve had less vaccinations. That means, just with our normal respiratory diseases that are always circulating, we’ll see more spikes in disease cases,” Dr. Weese said.

“Of course, we’re always worried about a new bug,” he said, but added that “most times the strange cases we see are just the usual suspects behaving a little bit differently.”

In a follow-up post on Dr. Weese’s blog, he said if some of these cases turn out to be a new pathogen in dogs, most likely it will be a “new to us pathogen” versus a “new pathogen” scenario.

“By that, I mean that it’s more likely that it’s a longstanding cause of disease that we’ve never diagnosed before, versus a new bug that’s recently emerged and is starting to spread,” he wrote. “The current disease patterns don’t really fit with emergence of a new highly transmissible pathogen.

“I’m open to new evidence and other opinions, but at this point, if I had to make a somewhat informed guess, I’d go with the assumption that we have patchy but significant increases in disease in some areas across parts of North America, but driven by our normal bacterial and viral causes.”

Snippets of data

While uniform data from state and national laboratories, which would show a much clearer picture of CIRDC, is lacking, the panel referenced insurance claims that may shed some light on the illness. Dr. Lappin, who is also director of the Center for Companion Animal Studies, showed a chart of respiratory-related claims made to Trupanion between 2021 and 2023 in the state of Colorado.

Notably, respiratory-related claims in Colorado trended slightly higher in 2021 than in 2022, but a bit lower than in 2023. Things changed around June of each year, however. That’s when, for instance, 2021 claims hit a high of close to 70. Claims in 2022 hit a high of approximately 80 in August before dropping while 2023 claims shot upward to 132 before falling off down into the 80s.

Panelists advised pet owners not to panic if their dog coughs, but to remain vigilant about the pet’s health and contact their veterinarian if they have concerns. Signs that warrant a visit to the veterinarian include a lingering cough, weakness, loss of appetite, difficulty breathing, worsening of illness, and a cough that is sufficiently severe that it causes the dog to vomit or makes it hard for the animal to breathe.

Additionally, the webinar panelists said it is especially important to see a veterinarian if the dog is old, very young, brachycephalic (short nosed or flat faced), immunocompromised, pregnant, or has underlying heart or respiratory disease.

Taking proper precautions

In a time not so far removed from the SARS-CoV-2 pandemic, questions have arisen regarding the zoonotic potential of a new infectious animal disease.

“We have been asked by journalists whether humans can catch this illness from dogs,” AVMA President Rena Carlson acknowledged in a statement. “In general, the risk of people getting sick from dogs with canine infectious respiratory disease is extremely low. However, because we don’t know yet exactly what agent or agents is or are causing the current outbreak, it’s a good idea to thoroughly wash your hands after handling your or other dogs.”

The AVMA also strongly urges owners to keep their dog’s vaccines updated, she added. While the efficacy of existing vaccines against current cases is uncertain, maintaining overall health through routine vaccinations can help support a dog’s immune system in combating disease, she said. Optimal protection against common respiratory infections includes an annual intranasal vaccine against Bordetella, canine adenovirus type 2, and canine parainfluenza vaccine. Where canine influenza is known to be circulating, the injectable canine influenza vaccine also is recommended.

Practitioners presented with dogs with clinical signs consistent with CIRDC are encouraged to pursue diagnostic testing immediately, during the acute phase of disease and before starting treatment, to assist in determining an etiology.

For addition information about CIRDC from Trupanion, visit K9illness.trupanion.com.