Is it resistance or reinfection?

During her lecture at the 2025 American Veterinary Medical Association (AVMA) Convention in Washington, DC, Jeba Jesudoss Chelladurai, BVSc, MS, PhD, DACVM (Parasitology; Immunology), broke down the current understanding out there in regard to resistance in heartworms, hookworms, and tapeworms in canine patients. In an interview following her lecture with dvm360, she explained that it can be difficult to determine if it is resistance or reinfection, but provided some ways veterinary professionals can try and differentiate the 2 options.

Below is a full transcript, edited lightly for clarity

Jeba Jesudoss Chelladurai, BVSc, MS, PhD, DACVM (Parasitology; Immunology): My name is Jeba Jesudoss Chelladura [and]I'm a veterinarian by training. I am a specialist in veterinary parasitology and board certified in veterinary parasitology and Immunology. I'm an assistant professor at Auburn University College of Veterinary Medicine

Yeah, so reinfection versus resistance is a hard diagnosis to make. Sometimes there are, in some cases, we have a PCR that can confirm resistance, like with hookworms, we have a PCR that can confirm fenbendazole resistance with this reinfection, then, if you use those same tests, then you won't have a resistance marker, for example.

But essentially, reinfection means you have a mixed population, whether it could be susceptible populations of worms or resistant populations of the worm, but you have it, you know, just as a new infection, almost, whereas with resistance, you have the same drug, same worms, that you have been trying to kill for a while, and so they cannot be killed, right? So that's resistance versus then reinfection a whole new population.