Understanding and combating heartworm preventive resistance

During an interview with dvm360, Lindsay Starkey, DVM, PhD, DACVM (Parasitology), shared some insights into the current state of heartworm preventive resistance in veterinary medicine, what to be asking clients if a 'good client' has a heartworm-positive dog, and more.

Below is a partial transcript

Lindsay Starkey, DVM, PhD, DACVM (Parasitology): I wish I had a really good handle on what was going on, I wish anybody had a really good handle on what was going on, honestly. What we know is it happens, and we can't necessarily predict where, although we do tend to see more cases of it in that geographic region where heartworm is most endemic, right? But it is getting transported around. It is showing up in places like Canada and the West Coast, like nontraditional heartworm places, and so I think we just need to be cognizant that these preventives that we have are really, really good, and they work [mostly] all of the time, especially when we're talking about run of the mill heartworm, but if we have a mosquito carrying a resistant isolate, which we can't predict or really know, then these preventives have all been shown to fail to a certain extent, some more than others. There's still one molecule that stands out as being the strongest, if you will, at fighting against resistant harm.

Using integrated strategies, vector control, reducing mosquito populations, using products that can keep mosquitoes from biting, or lifestyle management that can keep mosquitoes from interacting with our dogs—all of that really helps reduce that overall risk, whether or not it's resistant heartworm or susceptible heartworm, but it is out there, and we do need to have it in the back of our minds, especially when we have a patient come into our clinic where a heartworm-positive diagnosis is surprising. They've been on prevention, and this is a good client, this is a healthy pet, and they're positive. What's going on here?

And the first thing is to just fact-check that test, right? Maybe it's a false positive, but if you get your confirmatory test back, now, I'm asking questions of... were we truly compliant or not? And really getting down to some very pointed questions, like, did we ever miss a dose, or could the animal have spit it out right? Like, we need to know these things. And if all of that still seems like everything was done correctly, then we question the efficacy of the drug. And I think that's fair, once we've gone through that kind of algorithm, because we do know these drugs can fail.