Why a follow-up is essential after deworming

Image Credit: © otsphoto - stock.adobe.com

At this year’s WVC Annual Conference, Jeba Jesudoss Chelladurai, BVSc, MS, PhD, DACVM (Parasitology; Immunology), delivered a session titled "Tackling Tough Topics: Resistance in Canine Parasitology."¹ Among the many insights she shared, one key takeaway was just how important it is to schedule follow-ups after deworming to ensure pets remain parasite-free. “I am very surprised at how often, when I teach students, they're still in the [mindset of] ‘diagnose, treat, goodbye.” Chelladurai impressed upon the attendees that a single round of deworming is not enough due to the risk of reinfection and the emergence of drug resistance.

The rapid parasite life cycle and the challenge of drug resistance

Chelladurai reminded the audience that some species of hookworms (eg, Ancylostoma caninum) and tapeworms (eg, Dipylidium caninum) may complete their life cycle in dogs in as little as 2 to 4 weeks. This rapid cycle means that even if the initial deworming treatment appears successful, there is a high risk of reinfection almost immediately from the environment, she said.

Not only is reinfection a concern, but anthelmintic-resistant parasites have also been growing in prevalence, according to Chelladurai. “Anthelmintic resistance is a genetic trait. It is a heritable trait that goes from one generation of worms to their…offspring,” she said. In other words, anthelmintic resistance develops through genetic changes that can alter drug target sites, enhance parasite metabolism to break down the drug, or increase the parasite’s ability to expel the drug. These heritable adaptations allow resistant worms to survive treatment and pass resistance traits to future generations, making follow-up diagnostics essential.²

For tapeworms, Chelladurai noted that the standard FDA-approved dose—which once reliably cleared infections—may fail. She discussed options such as adjusting praziquantel dosage or considering alternative treatments like nitroscanate in cases of suspected resistance. However, she emphasized that any changes to treatment protocols should be based on clinical judgment, resistance testing, and current veterinary guidelines to ensure efficacy and safety.

In the case of hookworms, she mentioned that resistance was first observed in greyhounds and has since been reported in other breeds. She also talked about genetic markers—specifically F167Y and Q134H—that indicate resistance in certain drug classes, although she did not pinpoint a product name beyond noting trends in the benzimidazole drug class.

Follow-up diagnostics

Given these challenges, Chelladurai advised practitioners to schedule follow-up diagnostics and to not rely on a single deworming treatment alone. She explained that after conducting a fecal egg count reduction test, a reduction of greater than or equal to 95% is considered successful. However, reductions between 75% and 89% suggest potential resistance or the need for protocol adjustments.³

If the reduction meets or exceeds 95%, it suggests that the deworming was successful, and any new parasites likely stem from reinfection (which tends to be less pronounced). However, if the reduction falls into a “gray zone” between 75% and 89%, this is a strong indicator that drug resistance may be at play. Values in this range imply that the parasites are not being effectively cleared by the treatment, she said.

If resistance is suspected, the next step would be to change the treatment protocol. This might involve switching to a different drug class or increasing the dose of the current medication among the options she discussed above. If a simple change in treatment doesn’t resolve the issue, she recommends consulting with a parasitologist for further guidance.

Takeaway

Chelladurai’s session at the 2025 WVC Annual Conference serves as an important reminder: Although deworming remains a critical part of pet care, confirming treatment success through follow-up diagnostics is essential in today’s landscape of evolving parasite resistance and rapid reinfection.

References

1. Chelladurai JJ. Tackling tough topics: resistance in canine parasitology. Presented at: 2025 WVC Annual Conference; March 2-5, 2025; Las Vegas, NV.
2. Fissiha W, Kinde MZ. Anthelmintic resistance and its mechanism: a review. Infect Drug Resist. 2021;14:5403-5410. doi:10.2147/IDR.S332378
3. Miller MW. Diagnosing resistance in canine hookworms. Clinician’s Brief. August 2022. Accessed March 2, 2025. https://www.cliniciansbrief.com/article/hookworm-dogs-drug-resistance-diagnosis