Dr. Dodds Discusses the Mystery Illness in Dogs

Mystery Dog Illness in Dogs

Dr. Dodds and Hemopet have been monitoring the “Mystery Illness in Dogs” that has been appearing around North America. Thankfully, it appears to be waning at this point in time. Overall, the concerted effort and collaboration amongst academia, veterinary practitioners, veterinary associations, and government agencies is commendable and should be praised.

Of course, we seem to go through this situation every couple of years with some so-called “mystery illness in dogs.” In 2022, Michigan had a parvovirus outbreak. In 2015, a newly introduced strain of canine influenza to North America hit Chicago especially hard. The current mystery turns out to be atypical Canine Infectious Respiratory Disease Complex (CIRDC; aka a new type of Kennel Cough). CIRDC also caused a panic in 2017.

While there appears to be consensus amongst the experts regarding the latest outbreak, a few debates continue to linger and we have opinions as well. Before we delve into the debates, let’s review CIRDC and the latest outbreak.


  • CIRDC is a cocktail of approximately 12 pathogens that are both bacteria and viruses.
  • A mixture of 2 or more pathogens is typically needed before developing into the clinical illness of CIRDC.
  • Clinical signs are most often mild, transitory and self-limiting. They include coughing, sneezing, nasal and/or eye discharge, and lethargy.
  • Vaccines are available against several pathogens within the complex: Bordetella (bacterium), canine parainfluenza (CPiV), and adenovirus-2 (CAV-2). CAV-2 provides cross-protection against canine infectious hepatitis (CAV-1).

CIRDC Outbreak 2023

In 2022, New Hampshire state officials started noticing an uptick in this “mystery” illness. However, that did not receive much attention until cases with similar symptoms started appearing in Oregon, Colorado, and a handful of other states and provinces.

The reported cases of 2023 appeared to fall within three general clinical categories according to Oregon Department of Agriculture (ODA):

  • Chronic mild to moderate tracheobronchitis with a prolonged duration of 6 to 8 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 to 36 hours.

The San Diego Humane Society identified an outbreak of Streptococcus, but that has not been identified as the driving cause in other places.


All of these debates are interconnected. Let’s begin with diagnostic testing.

Hemopet agrees with the American Veterinary Medical Association, which stated, “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.”

Many experts raise salient arguments against testing for CIRDC such as:

  • Several of the known pathogens of CIRDC show up on PCR panels. So, which pathogens are causing the severe clinical signs?
  • University of Wisconsin-Madison has the position, “In nearly all shelters, the funds required to do this much testing would be better allocated for other purposes, provided the disease observed appears to be at normal levels in terms of number of ill dogs, severity of clinical signs and time to recovery.” However, they have shifted their thoughts in light of the current outbreak.
  • Jane Sykes was attributed this comment in an article by NPR, “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.”

Our argument for CIRDC testing:

  • A larger number of dog samples submitted for diagnostic tests will potentially help determine a cause faster;
  • It can help rule out or in potential diseases that present with similar symptoms, like canine influenza or distemper;
  • Diagnostic testing needs to use a standardized procedure in veterinary care for all infections and diseases;
  • It can help identify the direction for diagnostic test improvement; and,
  • Many of the dogs infected in 2023 lived in a household and not a shelter environment.

The ODA made public their findings mentioned above. The ensuing headlines immediately jumped to “antibiotic resistance.” However, the ODA did not have or provide data on the number of dogs that had PCR tests for viruses and bacteria or bacterial cultures.

We are not dismissing the hypothesis of antibiotic resistance, but the predominant facts in these cases are that the majority of dogs apparently were not tested and were immediately prescribed antibiotics. As many of us know, antibiotics will not treat a viral infection.

So, why not prescribe an antiviral? In short, viruses often mutate and escape antiviral medications quickly, and none are indicated so far for dogs with CIRDC.

In a recent webinar, infectious disease expert Dr. Michael Lappin of Colorado State University wavered on PCR testing for CIRDC, but was unequivocal that at least a bacterial culture needs to be taken so that we are prescribing the right antibiotic against the offending bacterium or bacteria.

On the other side of the country, the Veterinary Diagnostic Laboratory at University of New Hampshire revealed evidence of a potential novel bacterial respiratory pathogen. However, this pathogen is not showing up in all of the samples the laboratory has received from around the country.

There is speculation that this is a strain of Mycoplasma, which is one of the recognized pathogens of CIRDC. Additionally, some have suggested that this may not be new pathogen, but just newly recognized by us. The bottom line is that we would not have known about it without genetic testing.

A Positive Shift

Dr. Scott Weese of the University of Guelph (Dr. Dodds’ alma mater) has a well-known blog called Worms and Germs. In a December 2023 post he stated:

“We have good vaccines against canine parainfluenza virus and Bordetella bronchiseptica, two important causes of respiratory disease in dogs. Protection is much better with ‘mucosal’ vaccines that are given directly into the nose or mouth, so that’s the kind we want to use routinely for these pathogens. The vaccines won’t protect against all types of infectious respiratory disease, but reducing the risk of some major ones is still very helpful. Intranasal and oral vaccines are given once, then re-dosed annually. There’s currently nothing indicating we should re-vaccinate dogs more frequently than this.”

Did you notice what is missing? CAV-2 vaccine.

Why did he not mention CAV-2? His reasoning may be that the majority of dogs are already vaccinated against CAV-2, which provides sterilizing immunity for five-seven years. Granted, the American Animal Hospital Association recommends that revaccination against CAV-2 should be every three years. Regardless, CAV-2 is considered a ‘core’ vaccine along with canine distemper and parvovirus.

The vaccines against Bordetella and CPiV are considered lifestyle (non-core) vaccines and confer immunity for approximately one year.

Additionally, this distinction about CPiV vaccine is welcomed because it is often contained in the same vial with the three ‘core’ vaccines.

Another important aspect Dr. Weese mentioned was the method of vaccine delivery: intranasal and oral. Both areas of entry to the body produce localized (in the mucosal membrane) and systemic immunity, whereas injectables work by providing a systemic immune response.

If you are wondering, we prefer the oral vaccines against Bordetella and CPiV, as they do not tend to spray around the face like the intranasal vaccines.

Further Research

According to Colorado Public Radio, Colorado State University (CSU) researchers plan to release findings from samples collected in Fort Collins, Denver, Colorado Springs, and Grand Junction for signs of the viruses or bacteria known to cause CIRDC and whether those pathogens mutated or if there are novel causes revealed there.

We are encouraged by that news and are eager to find out their discoveries, and plans to incorporate and implement their findings.

Our Wish

We would love to know the following about the dogs diagnosed with CIRDC in 2023.

  • Age and breed type
  • Complete medical and family history
  • Vaccination history – frequency, vaccines given, type of vaccine
  • Diagnostic testing
  • Treatments
  • Outcome of treatments
  • Places of possibly exposure
  • Ventilation at places of possible exposure
  • Cleanliness of places of possible exposure
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