Spoiler alert: there’s not a lot new to say about the ongoing situation with canine infectious respiratory disease in North America. Most of this I’ve said before. Talk seems to be dying down in a lot of areas, but whether that’s because there are fewer cases or people are just getting bored of talking about it is unclear. It’s probably a combination of both. Based on some data I posted last week and talking to people on the ground in different regions, it seems like most areas that have had a (real or perceived) increase in canine infectious respiratory disease complex (CIRDC) cases are returning back to baseline. Presumably, there are some other areas where disease is ramping up, as usual. However, there are still a few questions worth bearing in mind at this stage:

Is this really an outbreak?

I’d say it’s not so much an “outbreak” as a gradual increase in the incidence of CIRDC over the past couple of years, with typical periodic spikes of disease superimposed over top of it. We have fairly clear evidence of more cases in some areas, usually following the typical outbreak pattern where cases go up, then return back to baseline levels. We also have areas where there’s really nothing too different happening.

Is there a “mystery virus” causing the increase in cases?
This is commonly reported in news headlines, but there’s no evidence of that. There’s a lot of viromics work underway, where they sequence any and all viral bits present in a sample to look for anything new. Since nothing has been found (or at least reported) thus far, it’s becoming less and less likely that there’s a new virus causing any substantial number of cases. I’d also expect a bit of a different disease pattern with a new, highly transmissible virus. More time and more testing will provide more details but at this point, I don’t think we have a reasonable suspicion of a new pathogen.

What about that strange little bacterium reported by the lab in New Hampshire?

This bug needs to be investigated more, but it’s not looking like a leading candidate at this point. It hasn’t been found to be a potential important cause of respiratory disease elsewhere (although I’ve only heard of one place that’s said they’ve looked and failed to find it). We need to learn more about this bacterium, but I’d guess that it’s either just part of the normal bacterial microbiota in dogs or it’s a potential cause of disease that’s been around for a long time, we just didn’t know (and therefore didn’t test for it). I doubt it’s a new bug that’s just recently emerged and spread in dogs in North America.

Are the reported cases of CIRCD more severe?

I don’t think so. Concerns about severe disease in dogs are probably more of a media effect. With typical CIRDC, we expect a small percentage of dogs to get pneumonia, and an even smaller percentage to have serious disease and die. That’s always been the case. When the number of dogs with CIRDC goes up, the number of dogs with severe disease will go up proportionately. So, we’d expect to see more cases of severe disease when we have an more cases during outbreaks, not because the disease itself is more severe, but simply because there’s more overall illness. If we have 100 dogs with CIRDC, we’d expect maybe 1-2 severe cases. If we have 1000 dogs with CIRDC, our severe case numbers jump to 10-20, even if the disease itself is no different.

What about treating dogs with CIRDC with Paxlovid?

Ugh. Horrible headline writing has driven requests to use this drug in dogs with CIRDC.

Please don’t.

We have inadequate dosing data and little understanding of safety for Paxlovid in dogs, and no evidence that its use is necessary (or effective) in any of these cases

What about treating dogs with CIRDC with chloramphenicol?

UGH X2. Chloramphenicol is an antibiotic. It’s a great drug, but (as for all antimicrobials) should only be used when it’s really needed. This drug has fairly important animal and human health risks (even just handling the drug), so we should not be using it routinely; however, if I have a multidrug-resistant bacterial infection in an animal, and chloramphenicol appears to be the best option to treat it, I’ll use it. Standard treatments still apply for routine cases of CIRDC. If we start using Paxlovid and chloramphenicol routinely (be it out of fear, panic or just the desire to do “something”), I have little doubt that we’ll harm more dogs than we’ll help.

Is “kennel cough” vaccination in dogs worthwhile?

Yes. 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.

Are some dogs at increased risk of infection with respiratory pathogens?

Risk of infection depends heavily on risk of (and amount of) exposure. Dogs that encounter a lot of other dogs, especially transient groups of dogs of unknown health status, are at increased risk of pathogen exposure. The more dogs encountered, the closer and more prolonged the contact, and the less certain the health status of the dogs involved, the greater the risk.

Reducing the overall number of dog contacts, particularly contacts with groups of dogs of unknown health status (e.g. random groups of dogs at an off-leash park, versus a small consistent group of known dogs at a day care or play group) is an important control measure.

Are some dogs at increased risk of severe respiratory disease?

Generally yes. We know there are some dogs that have a greater risk of severe respiratory disease or death if they get infected, so we want to be extra cautious with them, including avoiding exposure, vaccination and getting them to a veterinarian sooner if the dog gets sick. High-risk dogs include older dogs, very young puppies, dogs with pre-existing heart or lung disease, dogs with compromised immune systems, and brachycephalic breeds (i.e. flat-faced breeds like bulldogs).

Why might CIRDC rates be increasing?

It’s just a guess, but we could have a pandemic-associated confluence of factors that have led to more dogs with greater susceptibility to respiratory infection.

Changes in how we have interacted over the past few years, and how often dogs go to kennels or daycare (which is often the trigger for getting a kennel cough vaccine) could plausibly have reduced overall vaccination coverage in the dog population. Also, if fewer dogs were exposed to respiratory viruses over the past few years, there may be more dogs that are susceptible to them now. I try to stay away from the “immunity debt” discussion, since that’s more political than scientific, and it’s triggering for some people (my inbox is a testament to that). Nonetheless it’s quite logical that less immune protection from less vaccination and less infection over the past couple years could mean more susceptible dogs. It’s not “debt,” it’s just deferred exposure.

From a severe disease standpoint, changes in the popularity of different dog types could be playing a role too. The French bulldog, a higher risk breed, is now the most popular dog in the US. That’s plausibly going to increase the number of cases of severe disease just based on numbers.

What should the average dog owner do?

• Breathe. This is not a doggie plague sweeping across the nation.
• Consider your dog’s risk of exposure and whether you can do things to reduce it, while not being unnecessarily disruptive to life in general (e.g. if your dog needs to go to day care for you to work, send your dog to day care).
• Consider your dog’s risk of severe disease when deciding whether to change your behaviours and how much to change.
• Talk to your veterinarian about respiratory disease vaccines.