I very commonly get emails from vets like this:

My client was diagnosed with [insert various diseases here] and their physician said they probably got it from their [insert various pets here] and as a result they want the animal [tested / treated / rehomed].

  • Sometimes the disease in question isn’t even potentially zoonotic.
  • Sometimes the concern is about a zoonotic pathogen, but the pet is an unlikely source.
  • Sometimes human-to-pet transmission is actually more likely than pet-to-human.

Very rarely does testing the pet make sense, and even more rarely does “treating” a healthy pet make sense.

That’s not to say pet-to-human infections don’t happen. They obviously do and they are important considerations. However, all too often we run into issues because someone was quick to jump to blaming the animal, and then trying to force owners (or veterinarians) to use illogical or even harmful treatments.

Why not just test the animal for the disease in question?

I don’t like to do tests that don’t make sense, because it’s a waste of time, a waste of money, and it diverts attention from the real issues. Sometimes it’s harmless, but it often leads to bad decisions.

Before I test a healthy animal (which I very rarely do apart from surveillance studies), I ask myself “What will I do with a positive or negative result?” If the answer is “I don’t know.” or if the answer is the same for both positive and negative, there’s no value in testing.

If the animal tests positive, what does that mean?

That’s hard to say.  A positive test result often leads to more questions than answers.

If an animal tests positive for the same organism as its owner, we often can’t make any conclusions about whether the pet infected the owner.  It could in fact mean any of the following:

  • The owner got it from the pet
  • The pet got it from the owner
  • They both got it from the same source
  • They have unrelated strains of the same organism

Even if the pet was the source of the person’s infection, what does testing tell us?

It’s always nice to round out the story, and confirming the source of infection helps  provide some awareness, but it doesn’t always (and I’d argue usually doesn’t) change anything.

If a person if infected by a bacterium that’s normally in/on an animal, testing the animal is useless.  Let’s say a person has a wound, and their cat licked it, and they get a Pasteurella infection. If someone tested the cat and tells me they found Pasteurella, that’s not a eureka moment, it’s a “you just spent $200 to confirm that the cat is actually a cat” moment.  Finding a bacterium that is normally found in an animal isn’t noteworthy. It’s also not actionable. I’m not going to give a cat antibiotics to eliminate Pasteurella from its mouth because:

  • It won’t work
  • It’s improper use of antibiotics
  • It’s associated with risk of adverse effects in the cat
  • The cat could bite or expose the owner to its saliva again while being medicated, which might set up another Pasteurella infection
  • It might select for resistant bacteria in the cat that pose a greater risk to the cat (or the owner) than Pasteurella

After treatment, I’m certainly not going to say “go ahead and let your cat lick your wounds” or “don’t worry about the cat biting you.” I’m going to say to avoid contact of saliva with broken skin, try to prevent bites and do good first aid if bitten. I’d say the exact same thing for any cat… tested or not, treated or not.

There are rare situations where testing the animal might make sense. However, 99% of the time it doesn’t, and I spend a fair bit of time trying to defuse situations after someone has tested an animal for something with no plan on how to interpret the results, or when a veterinarian just tested an animal based on pressure from an owner after a request from a physician.

It’s great to see physicians thinking about pet-associated infections. However, we still have a long way to go to start having good conversations (not directives) about risk and risk mitigation when it comes to zoonoses and pets.

I’ll write more about the specific bacterium (Helicobacter heilmannii) from today’s email that prompted this post soon. It’s an interesting bug that’s worth separate discussion.