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.