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Mystery Canine Respiratory Illness: What You Need to Know

Updated: Feb 26

This article will continue to be updated as more information becomes available. Last updated: 2/26/24

Most recent update from the AVMA:

"The most likely explanation for last year’s canine respiratory disease outbreak is a commensal bacterium that possibly plays a role in some disease but has been overlooked, says Dr. Scott Weese, a professor at the University of Guelph Ontario Veterinary College.

“It doesn’t seem like anything remarkable is going on at the moment,” Dr. Weese said, adding that a periodic spike in CIRDC cases in various regions is to be expected.

Dr. Michael Lappin, an internal medicine specialist and director of the Center for Companion Animal Studies at Colorado State University (CSU), said in a press release, “Why that trend is occurring is unknown but may be related to our pets spending less time in social situations that might include ill dogs during the winter months.”

What is this Mystery Illness?

Unfortunately, at this time, the cause remains a mystery as there have not been enough thoroughly investigated cases to confirm a cause. Over the last two years, there have been several reports from across the United States about this illness, but there has been extra buzz amongst pet owners after all of the media coverage that came out in November 2023, so we hope to calm some fears by sharing all the information that we can find. Up to the most recently published update to this article (stated above), there have been no official reports of this illness in our area.

The common mild to moderate symptoms include: coughing, sneezing, nasal and/or eye discharge, and lethargy for several weeks with severe cases developing into potentially life-threatening pneumonia. These symptoms are very similar to other commonly spread upper respiratory infections like Bordetella (kennel cough) and Canine Flu, but they last considerably longer than either of these infections and occur in patients that are well vaccinated for both. There are, however, some anecdotal reports of a specific infection called Streptococcus equi subsp. zooepidemicus also known as Strep zoo potentially being the cause and increased reports of this illness began in January of this year. If this is the case, it's important to note that this illness has been present for quite some time and only just now got explosive media coverage, which quickly caused mass panic.

Update from the American Veterinary Medical Association: 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

In a News Release from the American Veterinary Medical Association published 12/6/23, pathobiology professor Dr. Scott Weese weighed in on the situation.

"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. 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.”

What Should You Do to Protect Your Dog?

  • If your dog has any signs of coughing, sneezing, nasal and/or eye discharge, inappetance, or lethargy, contact your primary Veterinarian immediately and keep your dog at home until they can be examined. Do not come to CROC, even if you have other pets in your household without symptoms.

  • Per Southern California Veterinary Medical Association's recommendations, sick dogs should be isolated at home for a minimum of 28 days past the first onset of illness. Exposed, but otherwise healthy dogs, for 14 days to monitor them for symptoms.

  • Keep your dog up to date on all vaccinations where possible. While this illness does not appear to be preventable with currently available vaccines, having your dog up to date on vaccinations can help your Veterinarian to treat your pet quickly and more effectively should they become ill. In some specific instances, vaccinated dogs that become ill may have diagnostics or treatment reimbursed by vaccine manufacturers.

  • If your dog becomes ill, it is recommended to pursue diagnostics such as a Respiratory PCR panel or Culture to help pinpoint the cause of your pet's illness.

  • Avoid traveling with your dog unless absolutely necessary.

  • Avoid high traffic areas or areas where your dog might be exposed to many other dogs. This includes boarding kennels, doggie daycare, and dog parks.

  • Routinely wash and disinfect your pet's toys, food and water bowls, bedding, and any other gear.

How is CROC Responding?

  • The safety of our patients is paramount to anything else. For that reason, any patients with any of the above listed symptoms (or those living with symptomatic housemates) will not be allowed to participate in therapy until they have been cleared by their veterinarian. There are no exceptions and this has always been CROC's policy, even prior to this outbreak.

  • There have been no known cases in any of CROC's current or recent patients and there are no official reports of this illness in our area.

  • Water bowls and toys have been removed from all common areas of our facility to reduce chances of any possible transmission of this infection. If your pet requires water before or after their therapy, please bring your own bowl and water and give these to your dog outside of our building or in your vehicle if possible.

  • The entire clinic is being thoroughly disinfected multiple times a day with pet-safe but effective cleaning agents. Every patient is given a cubby that has been disinfected and set up with freshly laundered bedding so that no common resources are being shared without being disinfected/sanitized first.

  • The Underwater Treadmills are frequently sanitized throughout the day and the water is treated, filtered, and replaced often.

  • CROC patients that are not from the same household are not allowed to interact with each other on our premises, inside or outside. All efforts are being made to spread patients out among our patient cubbies to maintain as much distance as possible between patients.

  • The CROC Team is thoroughly washing their hands between patients.

  • Maximal ventilation is being utilized to reduce transmission of any airborne particles thanks to our expansive treatment area, many windows, and custom temperature control and ventilation equipment.

  • We are vigilantly watching for any and all updates on this illness and will continue to post updates on our Facebook and Instagram whenever they are available and adjust our protocols for maximum patient safety.

When Should You Worry?

Unless your pet is traveling frequently or spending a lot of time in a kennel or playgroup environment, their risk for this illness is low. This illness has likely always been around, recently became more prominent in the canine population via overcrowded shelters, and then suddenly received an explosion of media coverage. There have been no known cases of this in any current or previous CROC patients. Nearly all of the above listed sanitation protocols have always been in place at CROC, though we are taking some extra steps just to be safe, like removing water bowls from the lobby and other shared areas.

This mystery illness is something that your pet has a slim possibility of catching and that we want you to be aware of, but the issue for which your pet is being rehabbed is something that your pet is actively dealing with and delaying therapy now can have long term consequences for your pet. Many conditions that we frequently treat can quickly decline with just a 2-3 week break from therapy, sometimes even just a week. If we're lucky, we can regain lost ground, but several conditions have only a limited window of time during which to recover as much as possible. Even if we can regain lost ground, that delay in recovery often causes extra expense for you and unnecessary discomfort for your pet in the meantime. Keep this in mind when making plans for your pet.

We want you to be as well informed as possible so that you can take action to protect your dog and know that we are taking all available measures to minimize transmission of any illness at CROC. If you have any questions or concerns, feel free to email us at

Additional sources of information include:

While we wouldn't consider this the most reliable source, there are several quotes from reliable sources within this article, so we figure it doesn't hurt to share it:

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