I was at the airport the other day and, as per usual, there were lots of traveling dogs there too. As I was watching one dog getting lots of random attention while in line to board, I could only smile given how happy the dog and the people looked – a key reason why we have pets and work hard to keep them healthy!

However, the infectious disease side of my brain never completely shuts off, so “this would be a nightmare for contact tracing” also trickled into my thoughts.

The vast majority of random dog-human encounters are totally benign, but a miniscule fraction are not, and those can be a real pain. Tracing human contacts even within a specific neighbourhood is tough. We can flood local social and conventional media with “if you might have touched this dog, give us a call” notices, and if most people are still around town that can be reasonably effective. When we’re dealing with exposure of people who hopped on planes to various cities and countries around the world… that’s a whole other ball game.

A recent paper in Zoonoses and Public Health (Williams et al. 2024) describes a slightly easier-to-contain situation involving international travel: exposure of passengers on an airplane to the uncommonly discussed but concerning bacterium, Brucella canis.

Brucella canis is a bacterium that flies under the radar a bit. It’s more common that most people recognize, as we found out a few years ago when we did a surveillance study of B. canis in dogs in breeding kennels in Ontario, and we found quite a bit of it. In dogs, it can cause a range of disease, with reproductive problems being the biggest issue. Human infections are uncommon, but can be serious and hard to treat. The greatest risk of infection is when people are in contact with infected dogs that are giving birth or aborting stillborn puppies.

Here are the highlights from the paper (Williams et al. 2024):

• A pregnant 10-month-old French bulldog (Dog A) flying in the cabin of a commercial airliner started to abort three fetuses during a flight from Poland to Chicago.
• A second 12-month-old dog (Dog B) from the same facility was on the same plane, flying in cargo.

It’s stated that the two dogs were to be imported by a breeder, but importing a pregnant dog is sometimes a way to bypass rules against importing puppies (which are very valuable in terms of sales), so I have to wonder if this was really a breeder purchasing new, high quality breeding stock versus a puppy mill situation. The fact that they were French bulldogs, a common and lucrative puppy mill breed, heightens my concerns.

• Dog A’s distress was reported by the pilot 1 hour before the plane landed (I’m impressed with that) and on arrival the dog was evaluated at US CDC’s Chicago Port Health Station.
• An infectious cause of abortion was on the list of possible causes, so testing was performed and Port Health Officers interviewed the crew and passengers that sat by the dog, paying particular attention to whether there were any who were pregnant, or children.
• Potentially contaminated areas of the plane were disinfected (but that’s tough to do effectively with the types of surfaces found on a plane…) and presumably the plane took off with a few hundred more passengers not long after.
• Both dogs were sent to a veterinary clinic, where Dog A aborted a fourth fetus. Both dogs were otherwise stable, though underweight. Dog B was also pregnant (more “puppy mill” alarm bells going off).
• Samples were collected from both dogs for testing. Dog A was positive for B. canis and was euthanized at the request of the importer. (I suspect that’s because one of the key components of treating this infection is spaying the dog, and spayed dogs don’t generate profitable puppies.) Testing for B. canis can unfortunately be complicated by a few factors (veterinarians can access fact sheet on B. canis from the Ontario Animal Health Network).
• Dog B was negative for B. canis, but if she was only recently exposed (e.g. from the other dog), we’d have to wait at least a month and retest to have confidence that she wasn’t infected too. So, rather than isolate the dog and retest it, the importer decided to ship the dog back to Poland (making it two long trips for a young pregnant dog… not great from the dog’s standpoint). The dog was then presumably lost to follow-up. (Unfortunately it’s quite plausible the dog ended up back on another plane to the US, Canada or elsewhere the next day. Who knows.)
• Five people (3 crew and 2 passengers) were determined to have had high risk exposures because of direct contact with Dog A (including one crew member who apparently tried mouth-to-mouth resuscitation on one of the aborted puppies). Staff members at the veterinary clinic were also evaluated, including two who were pregnant. Exposed people were provided with information about the risks, told to monitor for symptoms of disease and to discuss post-exposure prophylaxis with their healthcare providers. It’s not clear if any got post-exposure treatment.
• The CDC estimated the cost of their investigation at over $22,800 USD. The importer was on the hook for $16,500 in veterinary expenses for both dogs. They also estimated costs to the veterinary clinic (where the dogs took up space while being isolated that could have been used to house clinical patients) at $10,000. Overall, the authors estimated the total cost of the entire incident to be close to $50,000. It would have been higher if the importer hadn’t shipped Dog B back.

Fortunately, it doesn’t sound like anyone got sick as a result of exposure to these dogs.

There’s an inherent risk associated with dog (or any animal) movement, but there are also things that increase the risk. Here, there were several red flags that this was a higher risk situation. The combination of a high risk dog in a densely packed airplane is a recipe for problems.

This scenario raises another question too: what if the dog hadn’t aborted on the plane? If it had happened the day after, it’s quite possible that no one associated with the flight would have known, no one would have investigated, and there’d be more ongoing exposure risk to these dogs in the community. While it was a bad luck situation for the people on the plane, perhaps it was a good luck situation more broadly.

Regardless, this type of incident won’t be entirely prevented by the new US CDC canine importation rules (which mainly target rabies risk), but increasing the number of hoops and health measures for imported dogs will probably have some impact, as it’s a disincentive to ship dogs to the US. Unfortunately for us north of the border, shipping those same dogs to Canada is much easier and, as we saw when the US increased dog import restrictions a few years ago, that meant more dogs of questionable health status coming to Canada instead.

The paper’s conclusion raises some good points: “In conclusion, a multifaceted approach is needed to appropriately reduce public health risks posed by B. canis in imported dogs that are sexually intact. Efforts that could reduce the public health risks include: strengthening import surveillance; development of better screening and diagnostic tests for B. canis; increased brucellosis screening and quarantine by importers, breeders and organizations involved in the sale or adoption of dogs; and increased awareness by owners of the importance of procuring dogs from responsible sources. Airlines may also consider adopting policies that promote readiness to respond to ill animals and to prevent the transport of pregnant dogs to reduce the risks posed by B. canis.“