Search results for: dog respiratory

As concerns about canine infectious respiratory disease in the US have taken up most of my time lately, let’s merge that issue with what I had hoped to be the focus of the week: World Antimicrobial Resistance (AMR) Awareness Week.

test

Despite lots of media attention and associated fear, we’re still not sure what’s going on with all these coughing dogs, or even if there’s really a story at all. This could be something new, but more likely, it’s the usual suspects doing their usual thing (possibly at higher rates in some areas, as fairly commonly occurs periodically).

In the unlikely event this is something new, it’s likely viral. It’s much less likely to be something bacteria.

Either way, we have to think about how that might impact treatment. The short answer is: it probably doesn’t affect our treatment approach.

Viral respiratory illness can’t be treated with antimicrobials. Some affected dogs will develop secondary bacterial pneumonia, and antimicrobials are indicated in those cases. But it doesn’t matter what virus triggered it.

Primary bacterial respiratory infections in dogs are less common. The bacterium Bordetella bronchiseptica is typically the number 2 or number 3 overall cause of canine infectious respiratory disease complex (CIRDC), after canine parainfluenza virus and maybe canine respiratory coronavirus. Streptococcus zooepidemicus is a rare cause of CIRDC and usually causes sporadic but really nasty (often rapidly fatal) disease, most often in shelters or other high stress settings. Secondary infections (i.e. things that move in after a virus has already caused some damage) can be caused by a variety of different bacteria.

When considering antimicrobial therapy, we need to think about the disease we’re targeting. Cough isn’t a disease. It’s a sign of disease. Cough can be triggered by infection, be it bacterial or viral, and often persists even after the infection is over. Too often, we get into a mindset of “the dog is coughing really badly” or “the cough isn’t going away” and we unnecessarily reach for antimicrobials, hoping they will somehow help, when in reality we just need to give the dog more time to fully recover, or we can use other approaches to decrease inflammation and suppress the cough if that’s the part that’s still a problem.

Our 2017 Antimicrobial use Guidelines for Treatment of Respiratory Tract Disease in Dogs and Cats from the International Society for Companion Animal Infectious Disease are a good start for thinking about how to manage these sick dogs. We’re starting a revision, and I think we’ll see a few changes to the guideline, but most of the original content still applies. Some newer approaches to care of these cases are already incorporated into the antimicrobial use guidelines available to veterinarians through the Firstline app (see image below).

Here are some of the basic recommendations:

Basic upper respiratory tract infection: cough, runny eyes and nose, maybe a fever and a bit quiet, but dog is usually pretty bright overall.

  • No antibiotics.
  • This is likely viral, and if it’s bacterial, it’s mild and should resolve on its own. Tincture of time and supportive care are recommended.

More serious upper respiratory tract infection that is probably bacterial: more advanced signs of disease, mucopurulent (yellow, goopy) nasal and ocular discharge, but lungs are clear.

  • Consider antibiotics but most cases probably don’t need them.
  • As these cases are more severe it’s easier to justify antibiotics, but I can often go either way and have a fairly high threshold to say “start antibiotics” (at least right away). However, it’s not unreasonable in many cases.
  • Doxycycline is the drug of choice for treatment. It’s lower tier, effective, safe and works against the main bacterial pathogens of concern.
  • If there’s no response to initial treatment, we need to back up and think about whether that’s because it’s a bacterial infection is not responding, or whether what we’re seeing is more likely viral or non-infectious. That’s often hard to sort out, but we need to consider it carefully rather than just jumping to another drug every time we don’t get the response we expect on the first try.

Mild/moderate pneumonia: Varying upper respiratory signs, but with signs of lung involvement, such as audible crackles and wheezes, and radiographic evidence of pneumonia. These dogs are sicker but are stable. They are breathing reasonably normally, are quiet but alert and do are not crashing.

  • Antibiotics are definitely indicated.
  • Doxycycline is still the drug of choice. Along with the points listed above, it achieves good drug levels in the lung and is a great first line choice for pneumonia. If it’s a rare, milder or earlier Strep zooepidemicus pneumonia (mainly we’d suspect this because it’s part of an outbreak), amoxicillin would be fine instead, but usually we want a broader spectrum drug than that and one that gets better levels in the lung.
  • Some people are suggesting that enrofloxacin seems to work better in some of the more recently reported cases. That could be a true reflection of better activity against certain bugs, or issues with resistance to other drugs, but could also just be a function of using enrofloxacin as a second line option later in disease (where its use corresponds to natural resolution of disease, versus a true effect of the drug). It’s a good observation and I don’t dismiss anecdotes like that, I want to explore it more to try to tease out the reasons versus making a full switch to regularly using a higher tier drug like that. It could be that enrofloxacin is a better drug (overall or in specific areas), but given the potential issues with use of this higher tier drug, we’re best to be cautious and try to make sure we really have a firm indication that it’s necessary. If we put every dog with pneumonia on a fluoroquinolone like enrofloxacin, we won’t be able to use the drug for long because resistance will quickly become an even bigger problem.
  • Azithromycin is another option for treatment of pneumonia, as it also achieves great levels in the lung.
  • The more convinced I am of a true treatment failure, and the more severe the disease, the more I’d escalate, but sometimes we can be mislead by our observations. If it’s clear that doxycycline isn’t working in one area but another drug is, it’s logical to use that other drug, but we want to make sure we’re limiting changes in approaches and use of higher tier drugs as much as we can, because the more we use them, the quicker we lose them.

Severe/septic pneumonia

  • One of my big considerations when deciding whether to use more broad spectrum treatment in any patient is “What’s likely to happen if my drug choice is wrong?” If the answer is “the animal will probably die,” I can justify using a higher tier drug or combination to help ensure it’s effective on the first try. For the cases above, I wouldn’t typically jump to a broader spectrum combination, but with severe septic pneumonia we are dealing with a subset of dogs that are really sick with significant lung disease. They are not oxygenating well. They have low blood pressure or other signs of severe systemic inflammation. They’re at risk of crashing hard and fast, and I need to get the infection under control pronto. So, I can justify a broad spectrum antimicrobial – nothing crazy (e.g. not meropenem), but a broad spectrum drug/combination that’s higher tier and something I generally avoid, but am comfortable using in a situation like this.
  • Intravenous clindamycin & enrofloxacin, ampicillin & enrofloxacin, or an intravenous 3rd generation cephalosporin (e.g. ceftiofur, cefotaxime) would be reasonable choices in these cases.

How long do we treat a dog with pneumonia?

We have very little duration of treatment data for most infections we deal with in veterinary medicine, especially companion animals. We tend to be quite risk averse and therefore default to really long antimicrobial treatment courses.  Based on the short durations of antimicrobial use in people with similar conditions (where there’s lots of evidence that shorter is better), and even in cattle (where there’s lots of evidence and desire for shorter courses because it’s a hassle treating them), we need to be aim for shorter courses of antimicrobials in pets too.

  • Five days is what I’m recommending now. We don’t have data for that, but we also don’t have data for using any longer duration of treatment, and since we have good comparative data from other species, increasing anecdotal evidence and a duty to consider a “least harm” approach, I’m happy with five days. We can always go longer if needed, based on patient response and complicating factors, but short durations are often effective, come with fewer adverse event risks, and are cheaper and easier for owners (who, realistically, often don’t complete long treatment courses when their pet is doing well anyway).

We have to remember that antibiotics are there to help resolve bacterial infection, but eliminating the infection doesn’t immediately fix everything. Signs like cough and radiographic changes can linger, and more antibiotics don’t help those things resolve any faster.

So, while we’re not sure what’s going on with all the coughing dogs in the US right now, we can be reasonably confident we know how to treat them. Our usual approaches will still work. We need to be conservative with antimicrobials, but also ready to use appropriate drugs (including broad spectrum, higher tier drugs) when indicated. The right drug at the right dose for the right patient still applies.

test

This wasn’t on my bingo card for 2023, but it looks like I need to comment on the use of Paxlovid in dogs with respiratory disease. I guess I shouldn’t be surprised, but there’s been a lot of buzz about a single report of a veterinarian using Paxlovid to treat one dog with respiratory disease – in the absence of any definitive diagnosis as to what was making the dog sick.

Some media reports are claiming Paxlovid cured the dog. Did it?

Probably not. I suspect the dog got better on its own despite Paxlovid (not because of it), but can’t say for sure. However, I can say that I don’t see any evidence that we should be using this drug in dogs, and I have a variety of concerns about its use in this manner.

Concerns about Paxlovid use in dogs (quick version)

Paxlovid is an antiviral that we know basically nothing about in dogs. We don’t have dosing or safety info in dogs, and we don’t have evidence that the respiratory disease we’re currently seeing in dogs in North America is caused by a virus that’s susceptible to Paxlovid. So, I don’t think its use is appropriate in such cases, and I suspect widespread use of Paxlovid in dogs would result in harming more dogs than it would help.

Concerns about Paxlovid use in dogs (longer version)

Using a human drug in a pet isn’t rare in veterinary medicine, and often it can be appropriate. Veterinarians often need to use drugs in an extra-label manner, since many important drugs are not licensed for use in animals. When we know how to use the drug, its safety and that it’s likely to work in an animal, this kind of extra-label use can be appropriate.

  • The less we know about things like dosing and safety in animals (which can be very different across species), the greater the risk.
  • The less we know about efficacy, the lower the value.

Treatment is typically a cost-benefit decision, based on assessing potential risks, potential unknowns and potential beneficial effects.

Paxlovid is a combination of two antiviral drugs, nirmatrelvir and ritonavir, which are both protease inhibitors, neither of which are used in dogs. The combination has been shown to be beneficial for treating COVID-19 in some types of people, in some circumstances, with the right timing. That’s based mainly on study of Paxlovid use in unvaccinated people. In Canada, it’s licensed for use in people with mild to moderate COVID-19 who are at increased risk of severe disease. It’s not meant for everyone, and it’s meant for early treatment. There are different opinions about whether it’s really of much use at this point in the pandemic, but I won’t get into that.

What do we know about Paxlovid in dogs?

Pretty much nothing. I’m not aware of any dosing or safety information.  The only thing I can find is a study that looked at Paxlovid in serum of different animal species, including dogs (i.e. they added the drug to serum in a tube, but they did not give the drug to the live animals) and did a pharmacokinetic study on just two healthy research dogs (Greenfield et al 2023). That’s a start, but the small number of dogs (2) means it still doesn’t tell us too much. The researchers reported some pretty major differences between species, including between dogs and people. They concluded that “Some species (rabbit,dog) demonstrated high plasma protein binding (PPB) that was concentration-dependent, whereas others (human, monkey, rat) did not. This can have a major impact on understanding concentration-effect relationships for both efficacy and safety endpoints. As such, it is important to consider PPB when selecting animal species for studies aimed towards understanding efficacy and safety in humans.”

My take home message from that study is it can’t tell us anything about how/if we can and should use Paxlovid in dogs, and we can’t assume safety and efficacy data in people apply to dogs.

Sometimes we use the same doses in people and dogs for a specific drug, but sometimes, the doses are quite different.

Some drugs that are useful in people also work in dogs, but some drugs do not.

Some drugs that are relatively safe in humans are relatively safe in dogs, but some human drugs are highly toxic to dogs.

If we don’t know dosing and safety in a particular species, it’s really hard to consider use of a particular drug if there isn’t a huge potential upside, e.g. because we need to treat a severe disease and we have no other options, and where the drug has a strong chance of working. That’s not the case here with canine respiratory disease and Paxlovid.

Could Paxlovid work in dogs?

Paxlovid could have an impact on some viral causes of canine infectious respiratory disease complex (CIRDC), such as canine respiratory coronavirus (which is a completely different virus than SARS-CoV-2, despite the similarity in name). However, even IF Paxlovid has effects on canine respiratory coronavirus, or other relevant viruses, that may not really mean a lot clinically. It might shorten disease and/or might reduce the risk that secondary complications developing, but that would probably still be dependent on very early treatment, something that is not likely to happen in a lot of dogs when illness is still mild, particularly given the cost of Paxlovid.

Could use of Paxlovid in dogs hurt?

Absolutely. We have no idea if the drug is safe in dogs. There are various known side effects in people, and the drug interacts with a lot of other medications. If we’re going to apply a cliché, it should be “above all, do not harm” vs “it can’t hurt.” The latter is not likely true.

What about developing resistance to Paxlovid?

There’s probably very little risk of viral resistance to Paxlovid increasing due to use in dogs. The concern would mainly be about development of resistance in viruses that can affect people, since that’s where the drug is most often used and where resistance is most likely to have a significant impact. Dogs can be infected with SARS-CoV-2, but for resistance to be a risk, a dog would have to be infected with SARS-CoV-2 at the time it had respiratory disease (likely unrelated, since SARS-CoV-2 is unlikely to cause clinical respiratory disease in dogs based on what we know) AND resistance would have to develop while the dog was infected AND that resistant virus would have to be transmitted back to a person. Dogs seem to pose very limited risk for transmission of SARS-CoV-2 to humans, so it’s fair to assume that the health risks posed to humans from use of Paxlovid in dogs are very low to negligible.

However, we understand little about antivirals and antiviral resistance in animals, and the precautionary principle would have us remain pretty conservative with their use, and to only do so after a thorough risk assessment.

At this point, my assumption is that widespread use of Paxlovid in dogs would harm more dogs that it would help.

In contrast, there’s a different story about another COVID-19 drug in cats. We have some good data about the antiviral drug Remdesivir in terms of dosing, safety and efficacy for feline infectious peritonitis, which is otherwise a pretty much invariably fatal disease. This is a drug we should be using in cats, but we still can’t get (legal) access to it in North America. We’re working on that, so it will probably be the topic of a post in the near future. Good or bad news? I don’t know yet.

There’s been a lot of discussion about canine infectious respiratory disease complex (CIRDC) going around in dogs in the US recently. In the last week, I’ve already covered this from a few different angles, including what might really be going on with all the reports of sick dogs, reports of the potential involvement of a potential novel canine respiratory pathogen and when and when not to treat dogs with respiratory disease with antimicrobials. I’ll try to get another post done soon about the data we have (and don’t have). This post will address the most common questions dog owners are asking.

What should dog owners do?

Relax. It seems like there’s more respiratory disease in dogs in some areas, but that’s something we often see. Serious disease is being reported in a small subset of infected dogs, but that’s also something we regularly see. So, being aware is good, being anxious is bad, freaking out is definitely unnecessary.

The vast majority of dogs that get CIRDC recover uneventfully. That’s as true now as it was a year or 10 years ago. However, severe disease can occur so we don’t want to be too dismissive.

My dog is sick. What should I do now?

The default answer is “talk to your veterinarian if you’re concerned.”

However, the answer is not “if your dog coughs, it must be taken to a veterinarian ASAP.” A dog should be taken to a veterinarian if it’s really sick, deteriorating quickly, not getting better over the course of several days (but remember dogs may still cough after they’re feeling better), if there might be complications, or if it’s unclear what’s going on.  If the dog just has mild upper respiratory infection, it rarely needs to be seen by a veterinarian. If it has pneumonia, it definitely needs to see a veterinarian.

Think about it in terms of how we react when we get sick or our kids get sick. If you had a cough and felt a bit run down, you probably wouldn’t go to a doctor unless you had underlying risk factors for severe disease. The same applies to dogs – if they’re pretty bright and alert, are eating and breathing normally, but just have a cough and runny nose or eyes, it’s very unlikely they need to be examined (in part because it’s very unlikely that they need any specific treatment or testing, and because a visit to the veterinary clinic might just cause more stress for the dog and risk exposing other animals.) If you felt like you could barely drag yourself out of bed or you were having a hard time breathing, you’d go to the doctor. That’s also the same for dogs.

While I want to avoid being too prescriptive about who should or shouldn’t see a veterinarian (since there are lots of exceptions and grey areas), if the following signs are present, a prompt visit to the veterinary clinic is indicated:

  • Weakness, severe depression (meaning the dog is really quiet, not engaged and just lies around, doesn’t get up when you’d expect it too (like for food))
  • Loss of appetite
  • Difficultly breathing (breathing faster and harder even when not exercising)
  • Rapid worsening of illness
  • Cough that is causing significant problems such as vomiting or making it hard for the dog to breathe

It’s especially important to see the veterinarian if these signs occur in a high-risk dog, including:

  • Elderly
  • Very young
  • Pregnant
  • Immunocompromised (by disease or treatment)
  • Underlying heart or respiratory tract disease
  • Brachycephalic (i.e. squishy-faced) breeds

What will happen when I take my dog to the veterinary clinic?

That’s depends on a lot of things, so it’s hard to say what you should expect.

  • The first thing the staff should do is assess whether it looks like your dog has infectious respiratory disease, and how stable your dog is (in terms of its lung function). Most dogs with CIRDC don’t need anything but time and TLC; so, if your veterinarian says your dog looks stable and no treatment is needed at this point, take that as a good sign. Don’t ask for unnecessary treatments like antimicrobials “just in case.”
  • If your dog’s cough is disruptive, then a cough suppressant may be warranted (but that depends on a few things).
  • If your dog has signs of pneumonia, radiographs of the chest and bloodwork will likely be needed. If pneumonia is confirmed, antimicrobials are indicated.
  • If your dog is really sick, hospitalization with intensive care, antimicrobials and oxygen therapy may be required. That’s uncommon but it happens, and when there’s more respiratory disease activity in an area at a given time, there will be more cases of severe disease too just based on numbers (e.g. 1% severe disease rate in 1000 infected dogs is more really sick dogs than 1% in 100 infected dogs).

The severity of your dog’s illness, the type of illness, what the clinic can offer and (unfortunately) sometimes budget limitations will influence what’s ultimately done.

Additionally, sick dogs should be kept away from other dogs to help reduce the risk of disease transmission. That includes no going to day care, parks or any other places where non-household dogs would be encountered. For how long? That’s hard to say without a diagnosis but I’d aim for at least 2 weeks.

My dog is healthy. What should I do?

Let’s try to keep your dog healthy by limiting its contact with other dogs, especially large numbers of different dogs with unknown health status. Contact with small, stable groups (e.g. an established walking group, a small day care with the same dogs that don’t see a lot of other dogs) is lower risk. Logically, dogs should be kept away from any obviously sick dogs.

What about vaccines for my dog?

Vaccines are available for some of the causes of CIRDC. For any dogs that have frequent contact with other dogs, vaccination against Bordetella bronchiseptica and canine parainfluenza virus is important. Mucosal vaccination (intranasal is preferred, oral is second best) should be done whenever possible. Critically, it is important to use a vaccine that covers both Bordetella and parainfluenza. I suspect that loss of parainfluenza protection because of increased use of Bordetella-only oral vaccines might be driving some of the issues we’re seeing.

Canine influenza (flu) vaccination can be considered too, but it can be hard to get (there are currently some production and backorder issues) and canine flu is a pretty sporadic disease.

My dog is healthy but higher risk for disease or complications (see high risk list above). What should I do?

Take the same precautions described above for non-high risk dogs, but with more rigour. I’d also be quicker to recommend respiratory disease vaccines for these dogs, irrespective of how much contact they have with other dogs.

My own two dogs probably fall into those two risk categories. Both have fairly cloistered lifestyles from an exposure standpoint. Their dog contacts are largely restricted to a small number of well known and similarly low risk dogs.

The young pest, Ozzie, is a one-year-old, healthy Labrador, and is therefore at low risk of exposure and low risk for serious disease. He got an intranasal Bordetella/parainfluenza vaccine this summer so he could go to day care when we were away at a cottage (to give us some Ozzie-free afternoons to relax). The old guy, Merlin, is an 11-year-old Labrador who’s on chemo for chronic lymphoid leukemia. His exposure risk is low but he’s probably at some degree of greater risk for serious disease if he gets infected. There doesn’t seem to be anything remarkable going on locally compared to normal, so it’s status quo for them, but I’d be quicker to vaccinate Merlin if I decided vaccination might be warranted, especially if influenza hit the area.

As with any emerging issue, the current situation in the US is fluid, and we’re trying to sort out more about what’s happening. At the moment, for your average dog owner, it’s still just a matter of some common sense precautions and good dog care.

test

I’ve held off writing about this but since I’ve been answering many emails about it every day, here we go.

The questions I keep getting (as usual) are “What’s going on with this reported outbreak of respiratory disease in dogs in the US? What new disease is this?”

I’m not sure there’s a new disease here. I’m not even sure there’s a major outbreak (or any outbreak).

Various groups in different areas of the US are reporting cases of respiratory disease in dogs (which we refer to as canine infectious respiratory disease complex, or CIRDC) in dogs in various parts of the US. There’s always limited info about true numbers, and the disease description is vague and quite familiar (coughing dogs, some that get pneumonia, a few that die).

The issue is, that largely describes the every day status quo when it comes to CIRDC. This syndrome is endemic in dogs and has a variety of known causes (e.g. canine parainfluenza virus, Bordetella bronchiseptica, canine respiratory coronavirus, canine pneumovirus, canine influenza virus, Streptococcus zooepidemicus… roughly in that order of occurrence, and maybe the enigmatic Mycoplasma as well). There are also presumably a range of other viruses involved that have been present for a long time but that we don’t diagnose.

We see CIRDC all the time, anywhere there are dogs. There’s a background level of disease that usually flies under the radar, alongside periodic clusters of cases. I get lots of emails every week asking whether there’s more or more severe CIRDC activity at the moment, but I’ve been getting those reports for years, from across North America. To me, that reflects the fact that CIRDC is always circulating, but we notice it more at certain times than others, either because of local clusters or, increasingly, local increases in awareness, often due to media coverage. Media and social media can drive outbreak concerns. They can be great to get the word out and help sort out issues, but often, they lead to false alarms.

  • For example, we might have 100 dogs with CIRDC every week in Guelph (a complete guess since we have no way to track this). Usually, only a few people hear about it. The dogs typically get better and life goes on. However, if someone starts talking about it on social media, we might hear about 50 of those 100 cases. All of a sudden, we have an “outbreak of a disease affecting dozens of dogs” when in reality, we might just have our normal background level of disease that people are actually noticing.

The same thing can happen on a larger scale. There are thousands of coughing dogs in the US every day, since there are millions of dogs. Once people start talking about it, some of these go from “Oh, my dog is coughing. I guess he picked up something at the park. Whatever.” to “OMG, my dog has this new disease that’s sweeping the nation, I need to tell someone!” With the first approach, no one but the owner usually knows or cares. Once we hit the panic button, many owners start to tell everyone about it.

We don’t have any idea if the current stories reflect:

  • A multistate outbreak caused by some new bacterium/virus
  • A multistate outbreak caused by our usual suspects, for some reason
  • Unconnected sporadic local outbreaks caused by usual suspects
  • A slight increase in baseline disease
  • Our normal disease activity with an outbreak of media attention.

I suspect it’s one of the last two. My perception is that we have been seeing a bit more CIRDC activity over the past couple of years, and that we are now seeing a somewhat greater incidence of severe cases. However, with more cases, we see more severe disease, so those are linked. Also, with the explosion of breeds like French bulldogs that are much more likely to have severe outcomes from any respiratory disease (since a large percentage of them have been bred to have completely dysfunction respiratory tracts), increases in deaths could be linked to dog factors, not disease factors.

I never outright discount reports of something potentially new, and we continue to try (futilely so far) to get a better handle on what’s happening with regard to CIRDC activity in different areas. It’s tough, since there’s no effective surveillance system, the voluntary reporting that we’ve tried tends not to get much buy-in (understandably knowing veterinary clinics are swamped by other priorities), testing of sick dogs is expensive and rarely impacts how we care for an individual animal (great for surveillance but harder to justify the cost to an individual owner), and we have little to no funding to do much with companion animal infectious diseases at all.

My guess is this is simply an outbreak of media attention piggybacked on a somewhat increased rate of CIRDC cases that we’ve seen over the past year.

I might be wrong, which is why we’re still trying to collect more data, but I don’t currently see a reason for extra concern.

If you’re worried about canine respiratory disease:

  • Limit your dog’s contacts, especially transient contacts with dogs of unknown health status
  • Keep your dog away from sick dogs
  • If your dog is sick, keep it away from other dogs
  • Talk to your veterinarian about vaccination against canine parainfluenza virus (CPIV) and Bordetella bronchiseptica (plus canine influenza, but influenza is much more sporadic (especially in Canada) and vaccine availability is still an issue).

And, at risk of a flurry of emails, I’ll add… consider health when choosing a dog. That doesn’t mean no Frenchies, but get one that looks like they used to – one with a nose, not the current popular version of the breed.

For the past year or more, we’ve been trying to track infectious upper respiratory tract disease (officially known as “canine infectious respiratory disease complex (CIRDC)” but more commonly called “kennel cough”). It’s a tough thing to do since testing is limited, the disease is always present to some degree in the dog population, and there’s no formal reporting system. Enquiries about CIRDC in different areas seem to fill my inbox in waves, but that’s probably more related to reporting (especially social media rumours) vs actual frequency of illness. This week’s been busy so far  with a dozen or so emails asking about things like “new” respiratory diseases, or specific things like canine influenza (and it’s only Monday…).

We’re still not sure what’s going on. It does seem like there’s increased CIRDC activity over a lot of North America right now, and it’s been going on to some degree for quite a while. When we think about increases in respiratory disease reports, there are a few  potential causes (as I have mentioned many times before):

Increased disease caused by the usual suspects

  • This is my main guess at this point for what’s currently going on. Common things occur commonly, and that’s particularly true for the variety of bacteria and viruses that cause CIRDC in dogs.
  • A few potential reasons for the increased disease from these pathogens can be postulated. One is there’s more dogs mixing with each other now as people start to increase activity and get together post-lockdowns, and as people prioritize safer outdoor activities (often with their dogs). Combine that with a surge in new dogs and potentially decreased vaccination (due in part to overloaded veterinary clinics and access difficulties from earlier restrictions), and it’s easy to see how we might have more disease.
  • Another potential dynamic is increased use of oral “kennel cough” vaccines, as they are easier to administer to some dogs compared to intranasal vaccines. The problem is oral vaccines only protect against one cause of CIRDC (Bordetella bronchiseptica) while intranasal vaccines protect against Bordetella and canine parainfluenza virus (CPIV). That’s important because CPIV is the most commonly diagnosed cause of CIRDC in many areas.

Increased disease caused by a new pathogen

  • We’re always on the lookout for something new, but nothing is apparent yet. With a new virus, we’d be more likely to see widespread transmission in exposed groups, since no dogs would have any immunity. We’re not really seeing that. The cases being reported are more sporadic, as we’d expect with our typical causes of CIRDC. However, we can’t rule out a new pathogen completely, and there are undoubtedly various causes of CIRDC (mainly viral) that we simply haven’t identified yet.  I don’t think it’s the explanation for the current situation, though.

Increased reporting of disease

  • This is probably part of what we’re seeing. There’s more social media use these days so word spreads quickly. One voice can be amplified disproportionately and unsubstantiated claims can be disseminated easily. Further, it feeds on itself. When there’s more buzz about sick dogs, more people that otherwise wouldn’t have said anything chime in. So, we probably hear about a greater percentage of sick dogs simply because people are talking about them when they otherwise wouldn’t have.
  • Also, as more people are at home with their dogs, we probably hear more about the typical mild cases of CIRDC, because owners pay more attention when the dog is coughing beside them all day.

What about SARS-CoV-2?

  • SARS-CoV-2 is very unlikely to be playing a role. We can never say never, since the COVID-19 pandemic is a dynamic situation and we don’t know much about recent variants in animals. However, what we know so far is that infection of dogs and cats with SARS-CoV-2 is quite common, but disease is uncommon in cats and rare in dogs.

What about canine influenza?

  • Canine flu certainly can cause large outbreaks of respiratory disease in dogs. It spreads quickly because of limited immunity in the dog population. There has been some canine flu activity in a couple places in the US in the past few months, but these seem to have burned out (or at least burned down) relatively quickly.
  • There have been social media reports of canine flu outbreaks in Ontario. As far as I know, that’s false. Canine flu is reportable in Ontario, and no such reports have been received from any lab. We haven’t seen canine flu in Ontario since we eradicated it in 2018. I’m always on the lookout for it, but I’m most concerned about flu when there’s an outbreak that has a very high attack rate, including dogs that have had intranasal kennel cough vaccine. We’re still looking but I doubt canine flu is playing a role currently.

What can people who are worried about their dogs do?

  • Reduce contacts with large numbers of unknown dogs. Just like with other respiratory pathogens, the more contacts, the greater the risk of encountering someone that’s infectious.
  • Reduce contact with sick dogs. This can be harder but it’s common sense: if a dog looks sick (e.g. coughing, runny nose, runny eyes), keep your dog away from it.
  • Keep sick dogs at home. (Duh… but you’d be surprised.)
  • Avoid things like communal water bowls in parks that are shared by multiple dogs.
  • Get your dog vaccinated (ideally intranasally) against kennel cough if it tends to encounter other dogs regularly. My dog doesn’t get this routinely since we live in the country and he has a very limited number of other dogs with which he interacts. If I was in town and/or going to dog parks or other places where he’d mix with lots of dogs of unknown status, I’d vaccinate him (especially as he’s getting older now).
  • Consider testing your dog if your dog gets sick. Testing is useful to help figure out what’s going on and maybe to help control things. However, it rarely tells us something that influences care for the individual dog (since we don’t have specific treatments). So, the cost of testing is (understandably) hard to justify for some.

We’re also still tracking cases so people with sick dogs can provide information by filling out our quick survey here:
https://uoguelph.eu.qualtrics.com/jfe/form/SV_eP6E6AzIiJfnDlY

test

As H5N1 avian influenza continues to spread in wild birds and spills over into domestic birds and mammals of many kinds, we’re becoming more aware of the risks to domestic mammals and there are more questions about test selection and interpretation. Fortunately, testing for H5N1 influenza is relatively straightforward.

  • For cats and dogs, the recommended samples for testing are typically oropharyngeal swabs, plus or minus nasal swabs (plus or minus other tissue samples of the animal is deceased. 

What tests are currently being run by veterinary diagnostic labs?

PCR is the most accessible and useful test; diagnostic labs basically offer two types of influenza PCR: matrix / pan-influenza A PCR, and strain-specific PCRs (see below). Different commercial labs offer different tests or combinations of these tests, and the tests offered may also vary by species (i.e. what’s routinely done for dogs can be different from cats). Test offerings may also change over time as labs adapt to the ever-changing situation with flu in different populations. If influenza is a consideration in your patient, check with your lab regarding which tests they will run (particularly if you are submitting samples for a respiratory PCR panel) and how to interpret the results, including whether or not the test will detect H5N1 flu if that’s a concern.

Influenza A matrix PCR (aka pan-influenza A PCR)

This test will detect RNA from any / all influenza A viruses. A positive test confirms that flu virus is present, but not the strain (and not that the virus present is necessarily viable). Knowing the strain is important to understand how the animal might have been exposed and transmission risk. It’s a good first screening step, but if it’s positive we need more testing. If a cat was positive, it could mean it has a human seasonal flu strain (people sometimes infect their cats, and ’tis the season), or it could have H5N1 influenza, or another flu strain (e.g. a low pathogenicity flu strain which can cats sometimes get from wild birds, or potentially a swine flu virus if they have contact with pigs). Really rarely, but importantly, an animal could be infected with a combination of different flu viruses. Our concerns about and responses to these different scenarios are really different, so it’s important information to get. 

Strain-specific influenza PCR

These tests target specific influenza strains in different species, like canine H3N2, canine H3N8, avian H7N2 (found sometimes in cats) and human H1N1 (which can spill over sometimes into dogs and cats). It’s important to be aware that these are strain-specific tests, so an animal that just has H5N1 influenza will test negative on the H3N2 test, for example.

H5N1-specific influenza PCR 

As the name suggests, this test is specifically for H5N1 influenza, and we can be more confident in the result if that’s the strain for which we’re looking. The downside is that it won’t detect co-infections with multiple flu strains. The odds of a dog having H3N2 canine flu or H1N1 human flu and H5N1 avian flu at the same time are REALLY low, but that would be a REALLY concerning situation, so it would be nice to know. It’s more relevant when there’s higher non-H5N1 flu activity in the area as well, since that would mean there’s a greater chance of a hidden co-infection.

In order to provide the best possible information without over-testing every sample, labs will sometimes perform different tests in sequence: 

Run matrix PCR; if positive, then test for H5N1

This adds a step, but it’s usually a quick one, and we find out whether the animal has a flu virus and if so, whether its H5N1. The same issue with not identifying co-infections applies here, because there’s no testing for other flu strains.

Run matrix PCR, then test for non-H5N1 strains; if negative, then test for H5N1 

This works too. It adds a bit of extra time/work, and the more steps that are required, the greater the chance of a test error, but it gets to the same result pretty quickly and gives us a specific H5N1 result. The main theoretical issue is that we could still miss a coinfection (in this case because the H5N1 test isn’t run if any of the other strains are detected). 

Run matrix PCR, then test for non-H5N1 strains; if negative, then refer to another lab for H5N1 testing

This slows things down more and adds in some uncertainty as it requires sending the sample out for follow-up testing, which is another step where human error could affect things. It also misses co-infections.

Run matrix PCR, then test for non-H5N1 strains, then test for H5N1; if negative, stop and call it a generic influenza A positive

This isn’t ideal but still tells us a lot. In most cases nowadays, if the sample is matrix positive and negative for all the other main flu strains, it’s probably H5N1 flu, but pets can get spillover infection of other strains that aren’t included in strain-specific tests. If they stop here, it’s functionally okay but not ideal. I’d want to try to get followup testing of any matrix positive, type-specific negative samples (and would treat them as H5N1 positive until proven otherwise).

Any of these combinations would be okay for testing an animal in which there’s suspicion of H5N1 flu exposure / infection, but I’d rather have a quick H5N1-specific result in these cases, and I’d want to make sure that the lab will forward any positive sample for further genomic testing, so we can better understand the situation with H5N1 flu. 

Take home message

  • Talk to your lab to know what they can (and can’t) do in terms of testing for H5N1 flu, and follow up testing.
  • We can’t just stop at “flu positive.” Any such result needs to be scrutinized to make sure we know the strain (or strains) involved.
test

TLDR: Nope.

These days I commonly get the question ”Does vaccination of dogs with available canine influenza vaccines protect them from H5N1 avian flu?” While we don’t have any hard data on this, we still have a pretty good idea of the answer.

One of the challenges with flu vaccination (in any species, including humans) is the lack of good cross protection between strains (e.g. H3N2 vs H1N1 vs H5N1). In general, we assume there’s little to no cross-protection, and organizations such as CDC, Public Health Agency of Canada and WHO have stated that seasonal flu vaccines don’t offer any protection to people against H5N1 flu. 

That said, theoretically there there may be a bit of protection, though it’s hard to have confidence in that based on data from older lab animal studies. One study (Rockman et al. J Virol 2013) showed that ferrets vaccinated with human seasonal flu vaccine had partial protection against challenge with H5N1 flu. They determined that this was from the H1N1 component of the vaccine, and was predominantly from the neuraminidase (N) part (H5N1 and H1N1 have the same N1). While we typically pay more attention to the H component for vaccination, the similarity in N may be useful. That means there may be some protection of people from H5N1 flu if they’re vaccinated for seasonal flu, but not a lot, and we have to be careful extrapolating too much from older studies using different types of H5N1 in lab animal models. 

Canine flu vaccines target H3N2 canine flu, plus or minus H3N8 canine flu strain. (Realistically we only care about H3N2 now, since H3N8 appears to have disappeared as of a few years ago.) Those are quite different from H5N1 avian flu in flu terms.  Since there’s no overlap in the Hs or Ns, we wouldn’t expect to even have that small theoretical cross-protection benefit. If we had an H1N1 canine flu strain, maybe there’d be some protection, but (thankfully!) we don’t.

Does canine flu vaccination help protect against flu recombination? 

Recombination (mixing) of different flu strains in the same host (human or animal) to create a new, more problematic strain is certainly a concern. We don’t want someone to be infected with seasonal flu and H5N1 flu at the same time, as that creates the potential for a new flu strain to emerge that has the hallmarks of a human flu (readily infected people, effective human-to-human transmission) but has picked up enough H5N1 bits that we don’t have protection from previous exposure or vaccination and may can cause more severe disease. So even though seasonal flu vaccines in people don’t protect against H5N1 flu, there is still benefit from reducing the human seasonal flu burden, as it in turn reduces the risk that a person will be infected with multiple flu strains at the same time, which reduces the chances of recombination.

Does the same principle apply to vaccination of dogs against canine flu? It’s a stretch. There could be some potential benefits for canine health, but probably not much benefit for public health. Canine flu is much rarer than seasonal flu is in people, so there’s less potential benefit simply because there’s less disease to prevent. There’s also less baseline protection against canine flu in dogs because it’s rare and therefore vaccination is uncommon. So from a disease transmission standpoint for dogs, a new flu strain against which they don’t have immunity isn’t that different from the current H3N2 canine flu strain, since most dogs don’t have immunity to that either.

However, there could potentially be a difference in terms of disease severity. Fatal H5N1 infections have occurred in many mammals and at least one dog, and we don’t want an H3N2/H5N1 recombinant virus that spreads nicely dog-to-dog and is more likely to cause severe disease.  The odds of that happening are extremely low, but not zero.

Also bear in mind that canine flu vaccines aim to reduce the severity of disease more than prevent infection altogether. That still might be useful, as a mildly affected dog with some degree of immunity might have a lower H3N2 viral burden, but it’s hard to say how much that would really help protect against recombination of flu viruses, even if we had more widespread vaccination in the dog population. Probably not too much.

Public health benefits would be less of a reason to promote vaccination of dogs against canine flu stains. Canine H3N2 flu poses little risk of infection of people, so a hybrid of canine H3N2 and H5N1 wouldn’t be expected to be more transmissible to people (even though it would potentially add some mammalian adaptations to an H5N1-related virus, which is definitely not the direction we want the virus to go). For dogs to be a flu “mixing vessel” of public health concern, a human flu strain would need to be involved. While dogs can occasionally be infected with human flu strains, the odds of a dog having H3N2, human seasonal flu and H5N1 at the same time are pretty low. Even then, whether or not the dog was vaccinated against H3N2 wouldn’t really affect the risk, since we’d be primarily concerned about the human flu and the H5N1 flu mixing in the dog, not whether or not H3N2 joins the party.

Should we change how we approach canine flu vaccination?

I’d mostly stick with our current approach, which is based on assessment of the risk of exposure of the dog to canine flu, and the risk of serious consequences should the dog get flu (e.g. elderly, brachycephalic, underlying heart or respiratory disease). Since there are some plausible dog health concerns about H3N2/H5N1 recombinants, I’d drop my threshold for vaccination in dogs that also have a higher risk of exposure to wild birds (or dairy farms in the US). Dogs that have a reasonable risk of exposure to both types of flu virus (canine and avian) would be higher on my list to vaccinate, but that’s a very small subset (currently), and the benefits of vaccination beyond H3N2 protection are probably very limited.

test

Warning: Long post. Lots to unpack here.

As H5N1 avian influenza continues to spillover into domestic animals and people, the question of when to test animals (especially cats) keeps coming up. Testing isn’t just a matter of swabbing a bunch of animals and sending the samples to the lab (which unfortunately is not uncommonly done, and it often leads to problems). There are lots of things to consider before we start testing, which I’ll bin into 4 major questions: what is the goal, who will be tested, what test will be used, and what will be done with the results?

What is the goal of testing?

This should always be question #1. We need to know why we’re testing to figure out how to do it and what to do with the results. Specifically are we testing:

  • to understand more about how common the disease is, what it looks like clinically, risk factors, virus variants and transmission risks? Those are surveillance goals.
  • OR to inform how we’ll care for and manage individual animals? That’s clinical testing.

These goals can overlap, but they are not the same. If we think first about what we want to achieve, we run the risk of wasting time and money, and not answering the right questions.

Who will be tested?

In the case of H5N1 testing in companion animals, do we test all cats and dogs? All the cats? All cats and dogs with certain signs of illness? All cats and dogs with certain risk factors? Any pet that looks abnormal?

What we learn will vary a lot based on who we test. It will also impact efficiency and costs. More testing can provide more information but also costs more (time and money). For rare diseases (and I still consider spillovers of H5N1 influenza into pets to be rare overall at this point), you can do a lot of testing and get no positive results. That’s still informative in some ways, but broad testing can be pretty low yield in this type of scenario.

What test will be used?

For H5N1 influenza, PCR is our standard go-to test for a number of reasons, but there are also some “rapid” point-of-care tests that get talked up periodically (more on that below).  Different tests perform differently, so we need to pick the right test for the right population based on the goal of the testing.

What will be done with the test results?

This is the biggest question.

  • If we’re doing surveillance testing, is the design of the testing scheme robust enough to actually allow us to infer anything relevant beyond the animals sampled? Poor study design leads to poor (or no) conclusions.
  • If we’re doing clinical testing, what will be the response be, and will it differ if the test is positive or negative?

Too often, people do a test, and only think about what to do after they get the result. That can be problematic. What will we do with pets that test positive for H5N1 influenza?

Will we euthanize positive pets?

I hope not, but it’s a knee jerk response we handle sometimes. I can’t see any value in euthanizing infected pets. We can typically isolate them effectively, and then they’ll either get better and eliminate the virus, or die. Either way, the infection is contained, and there’s no concern about long term shedding of the virus. Yes, there’s some short-term risk from the pet while it’s infected, so we need to do it right, but there’s risk in most of what we do, and it can be managed.

Will we treat positive pets?

If we have an effective treatment for a given disease, early clinical testing can be really useful. For H5N1 influenza, it’s less useful since we don’t have a treatment we’d typically use in a pet, and by the time we get test results back, it might be too late for it to have any effect anyway. We can potentially use antivirals (e.g. oseltamivir) in dogs and cats, but that would be reserved for rare situations where the animal has early and severely progressive disease, or where it’s at high risk for severe disease (e.g. an immunocompromised animal on chemotherapy). Most often, we’re just going to give them supportive care, whether they have influenza or not.

Will we isolate positive pets?

This would be useful to help prevent spread of the virus. However, if we think there’s a reasonable chance that a pet has influenza (of any kind), we should isolate them anyway. Since tests are not 100% sensitive and we don’t get results back right away, we have to err on the side of isolating sick animals from the start. If the case is high risk for flu (i.e. compatible clinical signs and realistic risk of exposure), I would want to test it, but even if it tests negative I would still consider it a flu suspect and manage it accordingly to be on the safe side.

Will we do nothing different for positive vs negative pets?

That’s probably the case most of the time. So then why would we want to add complexity and cost by testing pets?

  • There are some limited surveillance benefits (discussed below).
  • If the animal is in the clinic, it’s easier to do the testing and the cost/benefit is more reasonable.
  • If the animal is at home, we need to consider whether or not the stress to the animal (i.e. taking it to the clinic, sample collection), the risk to the owner transporting it to the clinic, the risk to clinic personnel handling the pet, and the cost of sampling and testing are worthwhile, if instead the pet could just stay quiet at home (and hopefully recover)?

What I would like to see/do in terms of H5N1 influenza testing in pets

Surveillance testing

  1. Testing of cats/dogs with clinical signs suggestive of H5N1 influenza infection.
    • Right now, the focus is on pets with severe neurological and/or respiratory disease. Testing these animals lets us know how common the infection is in these cases, lets us investigate risk factors and transmission risks, and lets us do viral sequencing.
    • Currently the most widespread testing for H5N1 flu in pets is probably secondary testing of rabies suspects, whereby cats that are being tested for rabies (which often have neurological disease) get tested for flu if the rabies test is negative. This is a convenient and useful surveillance method that can contribute useful infomation, especially if other organized surveillance is lacking, but the sample is limited.
  2. Testing of dogs/cats with more common respiratory or flu-like illness signs.
    • We need this to understand the scope of disease caused by H5N1 influenza in pets. Are severe cases all that occur or are they all that we’re currently diagnosing? We need to know if there’s a fraction of cases that only have milder disease, particularly to help us assess and mitigate transmission risks.
    • We can’t test every sneezing cat, but we can do targeted surveillance by focusing on animals with a realistic risk of exposure to the virus. So, I’d like to test sick cats and dogs in areas where H5N1 flu is active (i.e. in wild birds) and where there’s a reasonable risk of exposure (e.g. outdoor access). This balances throwing a wide net to get a better broad understanding, and being efficient with our time and money.

Clinical testing

This is a tougher call. Most often, H5N1 flu testing would not impact patient care. It could help inform us about risk to the clinic or household, so it’s good information to have, but we can’t dismiss risk based on a negative test, so it doesn’t have a huge impact on what we do regardless.

The less surveillance testing there is, the more valuable opportunistic clinical test is for quasi-surveillance purposes, but that’s usually going to be at the owner’s cost. Spending a couple of hundred dollars to test a severely ill animal with little expectation that the test will change the response or the outcome is hard to justify. If money is tight, I’d rather have owners spend that on treatment.  Some people will pay for the testing because they want to know, or because they are worried about exposure of family members, but relying on owners to cover testing isn’t a great approach. It’s still worth discussing in any case since there can be some limited benefits.

What about rapid in-clinic tests for H5N1 influenza in pets?

It’s been suggested that veterinarians should start stocking rapid in-clinic H5N1 tests and use them liberally when presented with sick dogs and cats. I’m a bit wary of this because we don’t know how good those tests are. If we test a lot of low-risk animals and the test isn’t 100% specific, most of our positives are likely to be false positives. That’s alright if we’re just using it as a screening test and we follow-up with a proper test ASAP, but sometimes people rely too much on the screening test, and that can lead to over-reactions and other problems. On the other hand, if the test isn’t very sensitive, we run a good chance of missing the small number of true positives. If the test is no better than a coin toss, it won’t help.

Collecting good samples can be a challenge (especially trying to swab cats) so that drops the functional sensitivity of any test (i.e. we get more false negatives because of poor samples.

To be useful, we would need:

  •  a rapid test with high sensitivity (reliably detects all the infected animals) AND high specificity (gives us very few false positives)
  • AND good samples
  • AND the capacity to follow up positive tests with PCR testing
  • AND a communication plan for animals that are confirmed positive

But we’re not necessarily there yet. I’d consider rapid testing appealing, but probably not ready for prime time.

What will I do with my own pets?

I have two cats. Milo’s an indoor cat and Alice was a completely feral cat who’s gradually become very affectionate and just recently made the jump to being largely indoor. But we’re still not sure she uses a litterbox, and she’ll be at least partially outdoor for a while, I assume. She’s therefore at greatest risk of exposure to influenza from contact with wildlife. If she had a sudden onset of neurological or other severe disease, I’d test her, primarily because I’d really want to know, given my infectious disease mindset.

  • If she was negative, I’d still assume she might have flu, but that we missed it with the test.
  • If she was positive, then I’d have an early warning of potential exposure in the house. If anyone (human) started to get sick, flu would be on the radar and odds are high that we’d get tested ASAP and would probably be offered antivirals.

Barriers to surveillance

Money $$$

There’s VERY little funding available for companion animal infectious disease research. We try to scrape by with leftovers and token amounts, and we still manage to get good things done, but more support is needed. We can’t test if we don’t have the funding, and we rarely have funding.

Access to animals

You’d think it’d be easy, but field studies are actually very challenging. Veterinary clinics are really busy. When clinics are asked to remember that we have a study, to determine if their patient fits the inclusion criteria, and to contact us about sample collection, that takes time that just might not be available on a busy day. It took us a long time to get a good sample size for our SARS-CoV-2 research project and that was a lot higher profile.

  • Lack of money compounds the issue, since we usually can’t pay clinics for the time required to communicate with us and any extra effort to collect samples (including getting consent forms completed, collecting samples, collecting other data and shipping samples. or helping us arrange to collect samples). We try to do as much as we can to take the burden off the veterinary clinic team. With local cases we can often do almost everything, but the farther away they are, the more we rely on clinics to help out.

There’s no single approach to surveillance. We need combined approaches both because we have different questions to answers and for practical purposes. We want as much well-designed formal surveillance as possible, but since that’s not always going to be available, we rely on opportunistic information from clinical testing. We’re learning more as more work gets done, but we have a long way to go before we have a reasonable understanding of the dynamics of H5N1 influenza in companion animals and the potential for transmission to and from cats and dogs.

When we talk about vaccines of dogs*, we tend to split them into “core” and “non-core” vaccines.

(*The same applies to cats. I use dogs by default for posts like this, which sometimes gets me an earful, but I’m not actually ignoring cats.)

Core vaccines are those that every animal should get (e.g. rabies vaccine in areas where rabies exists, canine parvovirus in areas where dogs exist). Non-core vaccines are those that aren’t required by every dog, or that are less convincingly needed in every case.

Non-core vaccines are also often referred to as “lifestyle vaccines,” because the nature of the dog’s (or cat’s) lifestyle can put the animal at more or less risk of exposure to a disease, which affects the relative need for vaccination. Respiratory diseases are a great example. All dogs are at some degree of risk, but the risk is much higher in dogs whose lifestyles create more dog-dog contact (e.g. going to daycare, boarding, off-leash dog parks). That’s a good way to think about how to prioritize vaccination for an individual dog, but it misses a big part of the disease prevention equation.

When I’m assessing the need for vaccination in a pet, I think about two main things:

  1. Risk of exposure. The lifestyle aspect covers this.
  2. Risk of serious disease. This often gets ignored.

Some dogs are at higher risk of severe disease or death from respiratory infections. I’d put senior dogs, brachycephalics (i.e. flat-faced breeds), pregnant dogs, dogs with pre-existing heart or lung disease and dogs with compromised immune systems on that list. I’m more motivated to protect them because the implications of infection are higher, even if their risk of exposure may be fairly low.

Take my two dogs as an example (again):

Ozzie is 1.5 years old and healthy. If he gets a respiratory infection, most likely he’ll have transient disease and, while it will be annoying (for him and us) and I’d like to prevent it, odds are quite low he’ll suffer any serious consequences.

In contrast, Merlin is an 11 year old dog with chronic lymphoid leukemia who’s been getting chemotherapy for about 2 years. He’s doing really well, but he has a significant chronic disease and he’s old. If he gets a respiratory infection he’s at much greater risk of dying than Ozzie.

If we look at lifestyle of these two dogs, they’re similar, since they do everything together. The exception is in the summer when we go to a cottage for 2 weeks. Since 2 weeks with Ozzie at a cottage isn’t much of a vacation for us or Merlin, he went to a local day care for part of the time. (An exhausted Ozzie is a good Ozzie, and he often came home close to comatose, which was perfect.) So Ozzie has a major additional lifestyle risk factor, therefore he’ll get a respiratory vaccine again this summer (both because of the risk and because the day care requires it).

Merlin doesn’t have that same direct exposure risk, but he has some added risk through being exposed to Ozzie. Should he get a respiratory vaccine? If we just look at his lifestyle, we’d say no, he’s pretty low risk for exposure. However, his higher risk for severe disease increases my motivation to vaccinate him, and he’ll likely get a respiratory vaccine this summer at the same time Ozzie does.

Lifestyle is definitely important to consider, but we need to make sure we don’t just focus on the dog’s lifestyle and consider the dog (or cat) as a whole.

As awareness of canine infectious respiratory disease complex (CIRDC, formerly known as “kennel cough”) has spiked recently, there are more discussions happening about respiratory vaccines in dogs. A large number of different bacteria and viruses play a role in CIRDC. We can vaccinate against a few of them including parainfluenza virus (the most commonly diagnosed contributor to CIRDC), the bacterium Bordetella bronchiseptica (typically number 2 or 3 on the list of diagnosed contributors), canine adenovirus (pretty uncommon) and canine influenza (very sporadic).

We also have different ways to vaccinate dogs, specifically use of injectable versus mucosal (oral or intranasal) vaccines.

  • Injectable vaccines tend to induce a better systemic antibody responses. Mucosal vaccines provide a better local immune response at the mucosal surface. For respiratory infections, the local immune response is probably the most effective. There’s reasonable evidence that mucosal vaccines are superior to injectable vaccines for Bordetella. We don’t have good data for parainfluenza, but I’d assume the same applies. (We only have injectable influenza vaccines for dogs.)
  • Mucosal vaccines are modified live organisms – versions of Bordetella and parainfluenza that are still alive (i.e. functional) but have been attenuated so that while they can elicit an immune response, there is negligible risk of causing disease in the animal. We never say a modified live vaccine (MLV) is 100% guaranteed not to cause disease, but the risk is really low, and the protection is really good, so overall they’re beneficial for vaccination in “normal” animals. However, we tend to avoid MLVs in immunocompromised animals because low virulence organisms might be more likely to cause disease in an individual with a compromised immune system.

That’s the dog side. But, we have to remember that each dog is attached to one or more people too. When we vaccinate a dog with a mucosal vaccine, it sheds the modified bacterium/virus for a while, and might have a large load of the vaccine strain in their nose or mouth right after the initial administration.

That means people can be exposed to the vaccine strains as well. Generally, that’s not a big deal, and it’s really only a potential issue for Bordetella (because canine parainfluenza and canine adenovirus of any form don’t infect people). I get asked about this a lot, by both veterinarians and pet owners, and I write a similar post to this one every few years, but each time we have a bit more data.

Why is there concern about human exposure to Bordetella in canine vaccines?

  • Bordetella bronchiseptica can cause infections in people. They are rare, but they occur. So, if the “normal” Bordetella bronchiseptica can cause disease in people, we have to think about whether the vaccine strains can cause disease too.
  • The answer is “yes,” with a big “but” (actually, a series of “buts”).

Yes, there have been a couple of reports of human infections with canine vaccine-strain Bordetella, some of which are more convincing that others.

A recent report (Kraai et al. 2023) described vaccine-strain Bordetella bronchiseptica infection in a 43-year-old woman who was taking immunosuppressive medication.

  • She developed bronchitis with malaise and a mild fever two weeks after her dog had received an intranasal vaccine.
  • Bordetella bronchiseptica was isolated from her sputum. When it’s gene sequence was assessed, it was consistent with the vaccine strain.
  • She had mild disease and responded to antimicrobial treatment.

Clearly there is some risk with human exposure, that’s certain. Some groups have said to avoid MLVs in animals living with immunocompromised people. But let’s thing about that critically for a moment. All vaccination decisions require consideration of the costs (risks) versus benefits:

  • The risk to humans from canine vaccines is really low. Millions of doses of mucosal vaccines are given to dogs every year, yet human infections are still extremely rare.
  • Disease that has been reported in people who do get sick is mild.
  • Mucosal vaccination is superior to parenteral vaccination, and prevention of disease in dogs can also reduce the risk of exposure to the “wild type” (non-attenuated) strains of Bordetella in humans.

Broad “don’t use modified live vaccines in animals owned by high risk people” statements overlook a few big-picture issues:

  • The big one is the vaccine strain is much less likely to cause disease than the circulating (non-attenuated, disease causing) strains. A person is much more likely to be infected with the Bordetella from a naturally infected dog than from a vaccinated dog, so I’d rather prevent the dog from getting infected by vaccinating with the most effective method available.
  • Natural Bordetella infection (unlike vaccination) also tends to make the dog cough, which increases human exposure to any number of bugs in the dog’s respiratory tract.
  • If that dog needs treatment with antimicrobials, we run the risk of the person being exposed to antimicrobial resistant bacteria, some of which can pose additional risks to people.
  • Antimicrobials also increase the risk of the dog developing diarrhea, which can greatly increase human exposure to disease-causing bacteria in feces (especially if the dog poops on the floor).

Some more food for thought:

If I have a dog that was recently vaccinated with a mucosal vaccine, and I was asked to rank the top 5 zoonotic pathogens that are in the dog, vaccine-strain Bordetella wouldn’t even crack that list. There’s a mix of potentially disease-causing bacteria in every dog, all the time. Getting tunnel vision about one in particular, especially one that’s really quite low risk, is not helpful.

What about killed, injectable Bordetella vaccines?

Injectable killed Bordetella vaccines (which contain no live organisms, as the name suggested) do work, they just don’t work as well. If there’s significant concern from the owner, or some other unusual circumstance that makes use of a mucosal vaccine undesirable, then by all means, use an injectable vaccine. I’d consider that to be a rare situation.

Also bear in mind that killed “kennel cough” vaccines are just for Bordetella. They don’t include anything for parainfluenza virus, the most common cause of CIRDC. Parainfluenza is part of common combination “core” vaccines (e.g. DA2PP), but those vaccines don’t do a great job of protecting against paraflu. So, while an injectable Bordetella vaccine removes the risk of exposure to vaccine-strain Bordetella, it offers less protection against Bordetella and none against paraflu, so we have greater risk of disease in the dog overall, and the implications described above that come with it.

Let’s be clear: There’s never a zero risk situation when it comes to exposure to infectious bugs (from vaccination or pet ownership in general). We have to consider the risks and benefits in every situation.

But, almost always, for high risk households, I support vaccination whenever the dog’s lifestyle and risk factors indicate that Bordetella vaccination is warranted. I’d stick with mucosal vaccines for respiratory diseases whenever possible, since they provide much better protection and we can easily mitigate the very low risk from the vaccine. Those mitigation measures include:

  • Keeping the owner outside of the exam room when the dog is vaccinated.
  • Wiping the dog’s nose/mouth after vaccination to remove any major external contamination.
  • Recommending that the owner avoid direct contact with the dog’s oral and nasal secretions. That’s particularly important for the first 24 hours after vaccination, but it’s something I’d recommend for a high risk owner to always avoid.
  • Being diligent about routine hygiene practices (e.g. handwashing), especially after contact with the dog’s face (again, something that’s actually always important for a high risk owner).

Photo credit: Dr. Kate Armstrong (from Weese & Evason, Infectious Diseases of the Dog and Cat, A Color Handbook)