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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)

A recent paper in the Journal of Clinical Pharmacy and Therapeutics entitled “A doggy tale: Risk of zoonotic infection with Bordetella bronchiseptica for cystic fibrosis (CF) patients from live licensed bacterial veterinary vaccines for dogs and cats” (Moore et al. 2021) discusses (as the title suggests) human health risks from commonly-used B. bronchiseptica vaccines for pets.

Bordetella bronchiseptica is just one of a few different bugs that causes “kennel cough” in dogs (more accurately called canine infectious respiratory disease complex (CIDRC)). A variety of vaccines against B. bronchiseptica are available, including both oral and intranasal formulations that contain “modified live” bacteria, and injectable formulations that contain killed bacteria. Modified live vaccines (MLVs) contain attenuated (weakened) forms of the bacterium or virus in question that are not supposed to be able to cause disease, but induce a more natural immune response. So MLVs aren’t completely innocuous, and therefore generally aren’t used in immunocompromised individuals, because of the chance that even a modified/weakened bug could cause disease in such a person.

Bordetella bronchiseptica causes disease in a number of different animal species, but seems to be a rare cause of disease in people (unlike it’s cousin, Bordetella pertussis which causes whooping cough). However, infection with B. brochiseptica can occur in people, and those with diseases like cystic fibrosis (CF) are presumably at higher risk.

The authors of the paper state that patients with CF “should avoid exposure to live veterinary bacterial vaccines and seek animal vaccination utilising non- live vaccines.”

  • I agree with point #1. High-risk individuals should avoid direct exposure to live vaccines, which can occur during vaccination of the animal, as the vaccine is squirted into the dog’s mouth or nose (and sometimes splattered elsewhere). Ideally, high-risk owners should not be in the room when such a vaccine is given. That’s a very practical, very easy and probably the most effective preventive measure.
  • I’d argue against point #2. Injectable killed vaccines for B. brochiseptica are inferior to MLVs, and that has relevance to the exposure and health of a high-risk owner too.

Here is my thought process when is comes to this situation:

  • No vaccination or less effective vaccination increases the risk of disease in the pet.
  • Bordetella bronchiseptica can cause disease in high-risk people, so we don’t want the pet to be infected.
  • Disease probably also increases the risk of exposure of people to this bacterium and others (from coughing/sneezing pets).
  • Disease also increases the risk that the pet may need to be treated with antibiotics, leading to an increased risk of antibiotic resistance in other bacteria carried by the pet, and some of those bugs can also be transmitted to people.

Millions of doses of these MLVs have been given to dogs with little to no clear evidence of risk to people. The main reference to which the authors point is a report about a mild infection in a boy who was squirted directly in the eye with a vaccine. That’s a lot different in terms of exposure than having contact with a recently vaccinated dog.

The issue of residual modified live bacteria from the vaccine being present in the dog’s nose or mouth for a while after vaccination is usually raised. That’s fair, to some extent, but it ignores the big picture. Yes, there is a very minimally risk that the modified live bug might be present in the dog’s nose/mouth, but there are lots of other (and more dangerous) bacteria in the nose/mouth of every dog. The risk is basically no different from a dog that was recently vaccinated and one that has not been vaccinated, because it’s the more common bacteria found in both dogs that I’m most worried about.

The statement that vaccination “requir[es] a period of CF patient exclusion from the shedding dog,” is not supported by anything I’ve ever seen and doesn’t make sense to me given the above thought process.

Like most things, we need to consider the cost-benefit in each situation.

What’s the human health risk of using MLVs for B. brochiseptica in dogs?

  • Exceptionally low.

What’s the benefit of using MLVs for B. brochiseptica in dogs?

  • Improved animal health, and I could argue reduced human health risks from decreased exposure to sick animals (because we have to think beyond just the risk from the vaccine).

There’s also a statement in the paper that “CF pharmacists, hospital pharmacists and community pharmacists are important custodians of vaccine-related advice to people with CF, who are frequently consulted for such advice. “

  • Very true. However, I’d add the need for a One Health approach. Veterinary input is needed for a proper risk assessment, and to put the issues into context for the individual pet/pet owner. It would be nice to see papers like this written in collaboration with veterinary experts, and for pharmacists and veterinarians to engage more with each other in situations like this. Connections between pharmacists (and many other human healthcare professionals) and veterinarians tend to be pretty poor.

“Kennel cough” (now more conventionally termed “canine infectious respiratory disease complex’)  is a fairly common problem in dogs that can be caused by an array of bacteria and viruses. We commonly see it in outbreaks, often linked to kennels, but sometimes we see higher levels of disease in the broader community. What we’re more concerned about is new problems , new patterns or more severe disease.

We may be seeing an increase in respiratory disease activity in dogs in a few parts on Ontario at the moment. It’s always hard to say for sure because it’s based on information from different sources, and whether it’s a true increase, an increase in reporting of the normal amount of disease, or just a misperception is hard to say.

We don’t want to over-react, but we also don’t want to miss the start of something important, so we’re paying attention to the information that’s coming in and trying to make sense of it.

An important limitation to the available data is the amount of diagnostic testing that gets done. Only a small percentage of dogs with “kennel cough” get tested to try to determine which viruses and bacteria are actually involved.

Should all dogs with “kennel cough” be tested?

  • No.  Since a lot of pathogens can cause the clinical signs we see with this syndrome and we can’t test for them all, the test results rarely impacts how we treat an individual dog. It’s nice information to have but it’s usually hard to justify the cost for an average household pet. This recommendation is also part of the 2017 ISCAID  treatment guidelines for respiratory disease in dogs and cats.

When is testing more rewarding?

  • Testing is more useful when something is unusual about the scenario or the patient. From the patient standpoint, testing can be more useful when it involves a kennel or shelter, since the result could affect the infection control response. It also can help differentiate “vaccine breakthrough” from the presence of a bug we can’t vaccinate against.
  • By “unusual scenario” I mean something different in the incidence, distribution or severity of disease. If we think we’re seeing more disease, testing is useful to see if disease is mainly caused by one bug, whether we have a mix of causes, or whether the cause can’t be identified (suggesting something different/new might be present).

When do I really want to test dogs with respiratory disease?

  • When I’m concerned about a foreign disease like canine flu, I definitely want to get testing done. Figuring out when to worry about that comes down to two big factors: high attack rates and links to imported dogs, especially from Asia. When most dogs in a group get sick, I worry about something new like flu and want to test them, so that we find out as early as possible if flu is present and we can take measures to contain it, like we successfully did last year. A high attack rate was what led to identification of the biggest flu cluster we had when canine flu hit Ontario in 2018.

So, what about now in Ontario?

  • I’d like more information but don’t have any money for testing, so I’m relying on information that comes in from various sources. It’s always a fine balance between raising awareness and causing paranoia, so it’s important to put things in perspective. We’re on the lookout for respiratory disease in dogs and want to learn more, but we’re far from panicking about the situation.
  • The average dog owner doesn’t need to do anything more than good routine care and using common sense. However, we’d like to figure out if something new or interesting is going on.

More to come (hopefully).

Kennel cough, also (and more properly) referred to as canine infectious respiratory disease complex (CIRDC), has been in the news lately. This condition is a syndrome, not a specific disease, being potentially caused by a range of bacteria, viruses and Mycoplasma, including canine parainfluenza virus, canine influenza virus, canine respiratory herpesvirus, canine adenovirus, distemper virus, Bordetella bronchiseptica and Streptococcus zooepidemicus. Regardless of the cause, it’s still a highly infectious disease characterized by a hacking cough. Serious illness, including deaths, can occur but is uncommon.

Here are a couple of kennel cough issues have hit the press lately:

  • Mandatory kennel cough vaccination is now required for dogs competing in the Iditarod Trail Sled Dog Race. It’s easy to see how this disease is a concern in these sled dogs, given the stress and rigours of competing and the mixing of many dogs from different areas. Kennel cough vaccination doesn’t prevent all cases, since it only protects against Bordetella bronchiseptica +/- parainfluenza virus, but it’s a useful infection control tool in high risk populations. The requirement has been implemented in part due to cases of kennel cough that were encountered in the 2011 race, along with the publicity that was generated (including the attention of PETA).
  • In Rocklin, California, a dog park was closed for two days because of a kennel cough outbreak. It seems the closure was in response to the diagnosis of kennel cough in two dogs, and it’s an unusual move given the apparently low number of cases. The issue isn’t the park environment itself being biohazardous – rather, the park provides an opportunity for dog-dog transmission. Given that, it’s a questionable control measures since it’s unlikely that people will keep their dogs at home. Rather, they’ll probably just go to another park, where the same risks will be present. It’s a bit like the debate around school closures with pandemic influenza. On the surface, it seems like a good idea, since kids won’t pass around flu at school. However, in reality, what happens is kids congregate at the mall and other places if schools are closed, so it just moves the site of transmission somewhere else and probably doesn’t have any net benefit. Here, a better response would probably be an educational campaign to get people to keep sick dogs at home, have people keep their dog away from other dogs at the park and encourage vaccination of high risk dogs (which would include those that go to a park and interact with other dogs).
  • A kennel cough outbreak was reported in Bozeman, Montana, with veterinarians asking owners to be on the lookout for disease. Local veterinarians reported a spike in the number of cases, with one clinic reporting  around 20 cases in the past month, which is a pretty remarkable number for your average vet clinic.
  • And locally… nothing specific, but I keep getting reports of clusters of respiratory disease in dogs. We often don’t get a chance to investigate small clusters to figure out the cause, since information often gets to me after the fact, but it’s a recurrent problem in Ontario. Most of the reports are rather poorly defined clusters of sick dogs, with occasional severe outbreaks involving fatalities (including one I’m dealing with at the moment).

An article from NBCMontana.com describes a kennel cough outbreak in dogs in Bozeman, Montana. It’s a pretty basic article that outlines a rather typical presentation of kennel cough (now largely referred to as canine infectious respiratory disease complex – a respiratory infection that can be caused by a range of viruses, bacteria and Mycoplasma).

As part of the story, they state that if you have a sick dog, the "best course of action is to call your local veterinarian and get medication." I realize it’s a quick statement, perhaps tossed in without much consideration, but there are some important issues to consider.

Should someone call a veterinarian and get medication, or should a veterinarian actually see the dog?

  • Sometimes dogs just need to be given time and rest. Viruses are often the cause of this condition, and it just takes time for the infection to resolve (just like person with a cold virus). If that’s the case, a little over-the-phone veterinary advice might be fine. If drugs are needed, then the dog needs to go to a veterinarian. Affected dogs might need something to control cough, which need to be given by prescription, and occasionally antibiotics are needed, but in either case a veterinarian needs to see the dog first. If the dog is sick enough that it needs additional treatment above and beyond this, then of course it needs to be seen by a veterinarian.

Are there any problems with a dog like this going to the veterinarian?

  • Here’s where the ball often gets dropped. The last thing we want to see is someone walking through the from door with a hacking, biohazardous dog who goes nose-to-nose with other dogs in the waiting room, breathes on half of the surfaces in the room, sits there for ten minutes while waiting for the appointment, and gets handled by every staff member before they realize the dog might be infectious. A situation like that can turn a veterinary clinic into a source of infection for many other dogs, and help an outbreak spread.

A very basic but well coordinated approach can greatly reduce the risk of dogs infecting other dogs in the clinic. These would include:

  • Not taking a biohazardous dog into the waiting room. The owner can call from the car upon arrival or come in without the dog to let the clinic know they’re there.
  • The dog can be admitted directly into isolation or an exam room, thereby avoiding contact with other animals in the waiting room or elsewhere in the clinic.
  • Veterinarians and techs that are going to work with the dog can know in advance and come in prepared, wearing appropriate protective outerwear (e.g. gloves and a labcoat or gown that they use for only that appointment) to prevent contamination of their clothing or body.

Very easy to do. Probably very effective too, but often not done.

It’s very common for kennels to require dogs be vaccinated against "kennel cough" before they are allowed in. There are two main reasons for this:

  1. Reducing the risk that a dog will bring kennel cough into the facility and spread it to other dogs.
  2. Reducing the likelihood that a dog will acquire kennel cough if someone else brought it in.

Overall, it’s a sound policy, but it’s far from 100% effective and it needs to be part of an overall kennel infection control program to work. Relying solely on vaccination to prevent kennel cough is a weak approach that can ultimately fail, particularly if other infection control practices are poor or if vaccination protocols are illogical.

Why isn’t it 100% effective?

1) Kennel cough is a syndrome, not a specific disease. It can be caused by many different viruses and bacteria, often in combination. Kennel cough vaccines are typically targeted against Bordetella bronchiseptica +/- canine parainfluenza, two important causes of kennel cough, but not the only causes.

2) No vaccine is 100% effective. Vaccines help reduce the risk of illness, but they don’t completely eliminate it. Some vaccines are better than others, and some animals respond better to vaccines than others.

3) Timing is another issue. One of the weak points of many kennel protocols is the requirement that the dog be vaccinated "before entry," or within a certain number of weeks or months. The problem with this is vaccines are not immediately effective. What often happens is people decide to board their animal at the last minute or realize the night before that they need their dog vaccinated, so the vaccine gets given a day (or less) before kenneling. The intranasal kennel cough vaccine (squirted up the nose) takes a few (3-5) days to be effective, and the injectable vaccine takes even longer (a week or more). Vaccination very soon before boarding, particularly for a dog that has never been vaccinated against kennel cough before, is unlikely to result in protection from infection by the time of boarding.

Requiring vaccination before boarding makes sense, but it’s important to remember that:

  • It’s not 100% effective.
  • It doesn’t negate the need for a good infection control program.
  • It needs to be given at an appropriate time to be effective.

I had a call from a colleague in Ottawa (Ontario) the other day, asking if I’d seen an increase in kennel cough in dogs lately. Kennel cough is a respiratory infection of dogs that can be caused by a variety of different viruses and bacteria, or combinations thereof, but is often associated with the bacterium Bordetella bronchiseptica. Apparently, this colleague’s clinic has seen a large number of cases compared to normal, and he was wondering if the trend was more widespread and/or if there’s something new out there to be concerned about.

Informal reports like this are often the key to identifying new problems. There are only a few reportable diseases of companion animals (such as rabies), and existing federal and provincial public health and animal health agencies tend to have little mandate regarding non-reportable infectious diseases of companion animals. That means that there is no centralized reporting or investigation for all these other diseases (in other words: we’re on our own).

Most often, reports of higher disease rates or suspected outbreaks don’t end up leading to anything. Things tend to revert back to baseline fairly quickly without any explanation of what happened. Sometimes, however, reports like this are the first in a series that can flag the emergence of a new disease or a change in existing disease patterns.

Is anything actually going on with kennel cough in Ottawa? It’s hard to say. A report like this could be due to:

  • A focal outbreak caused by exposure at a single kennel, park or event.
  • A local outbreak of "run-of-the-mill" kennel cough that is being spread from multiple sources, but which involves the normal kennel cough bacteria and viruses.
  • Increased reporting of the normal baseline rate of disease, with increased awareness leading to the appearance of an outbreak.
  • A new disease (either a brand new disease or, more likely, the first instance of an existing disease in the area).

Whenever I hear reports like this in Ontario, I think about canine influenza. This virus is present in dogs in many regions of North America, but we have yet to identify it in Ontario (at least from the last data I have. We also couldn’t find any evidence of canine influenza virus in a surveillance study we did a while ago). It is certainly possible that this virus could make it to Ontario, and I would not be surprised at all if canine flu caused a readily detectable cluster of respiratory disease cases when it arrived.

Should dog owners in Ottawa be worried? No.

Should dog owners and veterinarians in Ottawa pay attention? Sure. It’s always good to be aware of things that are happening locally. Dog owners need to be aware of the risk of exposure to a variety of infectious diseases. Veterinarians should consider testing for canine influenza (and dog owners need to be willing to pay for the testing) if they see changes in respiratory disease patterns in their area.

How can dog owners reduce the risk of exposure of their dogs to respiratory diseases? Common sense. The more dogs that a dog meets, the closer they get to them and the less vaccination in the population, the greater the risk. Kenneling and other situations where many dogs get together increase the risk, and preemptive kennel cough vaccination should be considered in such cases. This vaccine doesn’t protect against all causes of respiratory infection, but it can protect against some of the most likely causes. People should keep their dogs away from other dogs that look sick (especially dogs that are coughing), and if they have a sick dog, they should keep their dog away from other dogs for a few weeks.

(click image for source)

A large whooping cough (pertussis) outbreak has been ongoing in people California in 2010. This bacterial infection, caused by Bordetella pertussis, is a highly transmissible disease that can result in serious problems (including death) in young infants. At last report, there were over 6000 cases of whooping cough, making this the largest outbreak in 60 years. Over 200 infants have been hospitalized, and there have been at least 10 deaths. Nine of the 10 deaths were in infants less than two months of age.  Infants in this age group have little to no immunity to the disease because they haven’t been vaccinated, and they are more prone to severe complications.

Bordetella pertussis is a human bacterium. It does not infect animals and animals are not direct sources of infection. (Actually, experimental infection of neonatal puppies with large doses of B. pertussis can result in shedding of the bacterium by a small percentage of dogs, but that’s not particularly relevant to the normal household situation). Therefore, people don’t need to worry about infecting their pets and pets passing the infection on to other people. However, it’s not impossible that pets could play an indirect role in transmission. A pet’s haircoat could possibly become contaminated with the pertussis bacterium from someone coughing around it, or touching it with contaminated hands. The bacterium could survive on the haircoat for a while (probably days), and someone could potentially get the bacterium on their hands by petting it, and subsequently become infected.

What are the odds of this happening? Who knows. It’s not something that anyone has investigated, as far as I know.

Could dogs and cats be important sources of pertussis in households? Probably not. I assume that if there is a person with whooping cough in a household, that person is more likely to be the source of infection for other people than a pet. 

Could pets spread pertussis outside the home? That might be a more realistic concern. People with pertussis might keep themselves away from others and stay at home, but if they contaminate their dog’s coat and the dog meets people on a walk or at the park (or at a veterinary clinic, or anywhere else), I have to wonder whether there could be the potential for spread of the disease.

What should we do about this? Common sense should prevail, and itt’s important for pertussis as well as other diseases. If someone in the household has an infectious disease that is transmissible and for which a pet could potentially be a vector, some basic precautions should be taken. Good attention to hygiene might help reduce contamination of the pet’s haircoat. This includes regular handwashing (especially after coughing and before petting an animal), avoiding coughing close to the pet and not letting the pet sleep close to the person’s head. Keeping the pet away from people outside the house, or at least limiting it’s contact with high-risk people might also be useful. In particular, keeping pets that might have been contaminated away from infants would be wise.

Overall, the risks are very low. We don’t need to fear dogs and cats as potential pertussis vectors. However, in the absence of proof that there’s no risk, and with a highly transmissible and potentially serious disease, use of some simple infection control measures makes sense. https://youtube.com/watch?v=KZV4IAHbC48%3Ffs%3D1%26hl%3Den_US

Kennel cough is a highly infectious respiratory disease in dogs. The disease got its name because infection and outbreaks often occur in kennels, where many dogs from various backgrounds are mixed together.  Some of the dogs in kennels may be carrying infectious diseases, and other dogs may be very susceptible these diseases – putting them all together in what can be a stressful environment for any dog creates a recipe for infection.

Kennel cough itself is more of a syndrome than a specific disease. It can be caused by a few different bacteria and viruses (and combinations thereof) that produce the same type of clinical signs. These pathogens include Bordetella bronchiseptica, Mycoplasma, canine parainfluenza virus, canine adenovirus-2, canine distemper virus and canine herpesvirus. Of these, only Bordetella bronchiseptica is a potential concern in terms of transmission to humans.  Bordetella bronchiseptica can cause respiratory infections in people, but this is probalby quite rare and largely confined to high-risk individuals, like those with a weakened immune system, who have had their spleen removed, who already have underlying respiratory disease of another kind, and pregnant women. The evidence of transmission of B. bronchiseptica from pets to people is relatively weak and circumstantial – it is not clear whether the human Bordetella infections in these cases were truly due to contact with a pet.

In households with individuals with a weakened immune system (e.g. HIV/AIDS, transplant or cancer patients), some measures that can be taken to help reduce the risk of transmission of Bordetella from pets include:

  • Avoid boarding dogs at kennels or veterinary clinics. If boarding cannot be avoided, ensure that dogs have been properly vaccinated against Bordetella bronchiseptica, and that the kennel or clinic requires all other dogs boarding there to be vaccinated as well.
  • Avoid obtaining a dog directly from from an animal shelter.
  • Wash your hands regularly after handling any dog, particularly if you’ve touched the dog’s  nose or mouth.
  • Don’t allow dogs to lick your face or hands.

The Bordetella vaccine for dogs is a modified live vaccine, meaning that a live but less virulent (pathogenic) form of the bacterium is administered to "prime" the immune system against regular Bordetella. Concern has been raised by some people that exposure to the vaccine strain could actually cause disease in high-risk individuals, whose immune systems might be unable to fight off even this "weaker" version of the bacteria.  It is unclear whether exposure to the vaccine strain actually poses any risk.  Nonetheless, it is reasonable to pay extra attention to avoiding contact with the dog’s face for a day or two after vaccination. Also, it is probably wise for immunocompromised owners to not hold the dog when it is being vaccinated, in order to reduce the risk of exposure to the vaccine. 

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Canada recently lost its measles-free status, in large part because of a slip in our overall vaccination rate. A lot of that has been driven by vaccine hesitancy. The resurgence of measles in people shows what can happen when we aren’t using one of our best control methods (vaccination) optimally.

Vaccine hesitancy is an issue in veterinary medicine too, and it’s probably increasing. There are known overlaps between vaccine hesitancy in humans and animals; people who are wary of or opposed to human vaccination often have similar approaches to vaccination of animals. It’s a complex issue, though, with many causes, and unfortunately pretty limited data.

  • One study of people in the US (Motta et al. 2023) showed that 53% of respondents reported at least one component of hesitancy, i.e. expressing concern that veterinary vaccines may be unsafe (37%), ineffective (22%), or unnecessary (30%). We don’t have comparative data for Canada; my guess is it’s less prominent here, but still a significant issue.

Vaccines are highly effective disease control tools, in both human healthcare and veterinary medicine. They aren’t perfect, but they are critically important. They can range from useful aids to critical tools to essentially the only line of protection, depending on the vaccine and the disease. Without vaccines, pet life expectancy would be shorter: we’d lose a lot of young animals to preventable diseases. Veterinary care costs would also be higher. We’d probably have fewer people with pets because of these challenges, especially in urban areas where a lot of pets and pet contacts would mean a lot of disease transmission.

Why are people vaccine hesitant?

It’s critical to understand the reasons behind vaccine hesitancy to try to mitigate the problem.

  • Some people have completely understandable and valid concerns.
  • Some people fundamentally do not believe vaccines are safe or effective, and they will not trust anyone or anything that says otherwise.
  • Some people may not really know why they are hesitant – they’re simply unsure.
  • Internal conflicts can be part of the problem too, such as a person who is really worried about the cost of vaccines, but doesn’t want to admit it (openly or to themselves), and might therefore convince themselves that it’s safer not to vaccinate, to avoid feeling like they are compromising their pet’s health by not vaccinating.

Various other complex scenarios occur too. The bottom line is it’s complicated, and often unclear. That makes addressing vaccine hesitancy challenging.  

  • If someone has trust issues, we can educate them all we want about vaccine efficacy and safety. It won’t matter.
  • If they’re terrified that their dog is going to die from the vaccine because of something they read online, that’s a completely different scenario that requires a different approach.
  • If cost is driving concerns, that’s harder to address.

There’s a lot more to discuss about reasons for vaccine hesitancy, but I’ll hold off on that for now. My focus today is on the implications of vaccine hesitancy.

Potential impacts of moderate decreases in vaccine coverage

Less vaccination means more disease at the individual level. It can also increase the risk of outbreaks, increase the risk of well-controlled diseases becoming uncontrolled, and allow for re-introduction of diseases that were previously successfully contained.

For humans, we want really high measles vaccination rates (>95%) to prevent spread, as well as to protect individuals from disease. That way if someone happens to have measles, the risk of spread is low because so many people are already protected. We need a really high percentage of vaccinated people in the population for this to work for a highly transmissible virus like measles, but we were previously able to do that in Canada – until recently. As vaccine rates slip, when there is an introduction of measles virus into a population, there is a higher risk of sustained transmission among unprotected people, sometimes with devastating results.

It’s a bit different for dogs and cats. We don’t have the same level of baseline vaccine coverage for most of the diseases against which we vaccinate pets, and for some diseases, we also have feral and wildlife reservoirs.

Individual animal risk is straightforward, but population risks in pets are harder to understand. Those risks can’t be ignored, but they also shouldn’t be overstated, since we need to be transparent and clear in our communication with pet owners in order to maintain trust. Let’s use vaccination of dogs as an example:

Distemper

Canine distemper virus (a relative of measles virus) is one of our big concerns in dogs. Disease can be really severe, but vaccines are highly effective. However, we’re nowhere close to eradication because we still have a fairly large pool of unvaccinated dogs, and canine distemper virus is also endemic in wildlife in many areas (especially in raccoons). Reduced vaccination in dogs won’t lead to re-emergence of the disease, since it’s already endemic. Reduced vaccination will mean more disease in general.

So, the risks of less vaccination are mainly to the unvaccinated dogs. However, there is a spillover risk. Just like in humans, where we focus on vaccinating as many people as possible to protect those who can’t be vaccinated, the same principle applies in dogs, since some dogs cannot be vaccinated or cannot respond well to a vaccine. An unvaccinated dog that gets distemper poses a risk to those dogs. The more unvaccinated dogs, the greater the risk to puppies especially, and for a potentially devastating outbreak.

Parvovirus

Issues with parvo are pretty similar to those with distemper. It’s a potentially life-threatening disease in unvaccinated dogs. There’s low level but continual circulation of parvo in the dog population because there are enough unvaccinated dogs (domestic and stray) to maintain it. The risks of decreased vaccination are mainly to the unvaccinated animals. However, as with distemper, when there are more infected dogs, there’s more risk of transmission to other dogs, including puppies that are still to young to be vaccinated.

Leptospirosis

This is an important vaccine in many areas. Leptospirosis is a bacterial disease caused by the spread of Leptospira from wildlife reservoirs (e.g. raccoons, rats). We can’t eliminate lepto from wildlife, so reduced vaccination doesn’t change the overall risk of exposure, but it increases the risk to the unvaccinated dog.

However, there are some secondary risks here too. Dog-to-dog and dog-to-human transmission of lepto seem to be rare, but can happen. If a dog is unvaccinated, it’s at risk of severe disease, and that risk extends (at a low but non-zero level) to its canine and human contacts.

Rabies

There are a lot of interesting aspects to rabies when it comes to dogs. In North America, we don’t have the strain of rabies virus (canine variant) that circulates in dog populations in other countries. Dogs can still get rabies from wildlife reservoirs, such as bats, raccoons and skunks, but we don’t expect strains from those species to result in ongoing transmission of rabies within the dog population. However, canine variant rabies is highly prevalent in some parts of the world, where it causes most of the ~60,000 global human rabies deaths annually. We are at some risk of importing dogs carrying canine rabies. Despite the controls we have in place to prevent it, at least two rabid dogs have been imported into Ontario since 2021, and there’s ever-present risk of it happening again.

If a dog is not vaccinated against rabies, the main risk is to itself. If it tangles with a bat and is exposed to the virus, it’s more likely to develop rabies (which is essentially always fatal). There are other risks, though. When a dog has rabies, there is a short but important window of time when it can transmit the virus through its saliva to any human, domestic mammal or wild mammal contact. There can also be substantial healthcare costs for investigation of human exposures and treatment of exposed individuals. Unvaccinated dogs and cats that are potentially exposed to the virus can be at risk of developing rabies for months, necessitating long confinement periods to prevent exposure of even more people and animals (and sometimes pet are even euthanized because of the risk if they can’t be safely and effectively confined).

The broader population risk from decreased rabies vaccination is much lower. We have eradicated canine rabies in Canada and really don’t want it back. For that to happen, we’d have to import a dog with rabies, it would have to infect other dogs or wild canids, and they would have to keep infecting enough new dogs/canids to keep the disease cycle going. That’s not realistic in a controlled pet dog population, but is a concern with feral dogs (which we don’t have many of in most regions) and wild canids (which are very common in some areas).

The odds of canine rabies virus coming into the country, making it into wild canids and establishing itself anew are really, really low, but they are not zero. While the risk of an unvaccinated pet dog contributing to re-establishment of canine rabies in Canada are likewise exceptionally low, the implications were it to happen, both in terms of health (human and animal) and the costs for control are substantial. So it should not be ignored. Still, the main risks from a dog that is not vaccinated for rabies are to the unvaccinated dog itself and its close contacts.

“Kennel cough” (canine infectious respiratory disease complex, CIRDC)

When it comes to CIRDC, we mainly vaccinate dogs against Bordetella bronchiseptica and canine parainfluenza, with a smattering of vaccination against canine flu. These vaccines are meant to help reduce the risk of infection and reduce severity of illness when it occurs. They’re useful, but they’re mainly for individual health, not reducing transmission or containing the disease. These vaccines are also not as widely used as others, so overall vaccine coverage is pretty low. A moderate reduction in vaccination would not do too much to impact the broader epidemiology of this complex. It would mean that more dogs would get sick, or get sicker than they would have with vaccination.

Do I worry about vaccine hesitancy?

Yes. I hate to see animals dying of vaccine preventable diseases. We can’t prevent all disease, but by optimizing vaccination, we can maximize the benefits to vaccinated animals, and to some degree, other animals and people around them.

How do we address vaccine hesitancy?

That’s way more complex that I can cover in a few paragraphs, but I’ll highlight a few key aspects for addressing vaccine hesitancy (hard core anti-vaxxers and people who spread misinformation are a separate topic):

Communicate communicate communicate

  • We have to listen to why people are hesitant.
  • We have to acknowledge their concerns, even if we disagree.
  • Sometimes we can educate.
  • Sometimes we can work to provide more confidence in veterinary care or vaccines.
  • Sometimes we can allay fears.
  • Sometimes we can just have a good conversation, agree to disagree, and still work to care for the animal.
  • …and unfortunately sometimes it falls apart, or views are so polarized that there’s no moving forward. We just hope those are the minority of cases.

We don’t have the exact same issues in veterinary medicine as human medicine, and approaches to vaccine hesitancy aren’t necessarily going to be identical, but vaccine hesitancy among animal owners is definitely a concern. We need to develop a better understanding of how common it is (and more importantly, the reasons for it), look at ways to address it (including how it’s done in human medicine), have open and honest discussions, and try to optimize vaccination. There’s no one-size-fits-all approach to vaccination and there’s no one-size-fits-all approach to a vaccine-hesitant owner.