Anthelmintic Resistance

Host

Welcome to this podcast on Anthelmintic Resistance – A Global Perspective. I’m joined today by Professor Jane Hodgkinson from Liverpool University, Professor Kris Hughes from Charles Sturt University in Australia, and Dr David Rendle of EMT Consultancy. All three guests bring extensive experience in tackling anthelmintic resistance. Today, we’ll explore how this global issue is being addressed and what steps can be taken to safeguard future efficacy.
So, welcome Jane, Kris, David – how are we all today?

Jane

Very well, thanks.

Host

Great! Let’s dive in. What is the extent of resistance in the UK and Australia? How big a problem is this? Jane, let’s start with you.

Jane

We don’t know definitively, but we do know there’s resistance to benzimidazoles (BZs) and pyrantel. Macrocyclic lactones are harder to track due to a lack of surveillance. However, when we do look, we often find reduced efficacy—and in some cases, confirmed resistance. For example, in a recent study across four studs, we found clear resistance in one and reduced efficacy in the others.

Host

And this was in cyathostomins?

Jane

Yes, primarily cyathostomins. Ascarid resistance is another concern, but Kris may be better placed to speak on that.

David

To add to that, in the UK we now have evidence of resistance to all major classes of anthelmintics in both cyathostomins and ascarids. It’s likely widespread, particularly in intensively managed studs. Jane’s recent work strongly supports this.

Jane

Exactly. We’ve been tracking this over the last decade. Our most recent findings show shortened egg reappearance periods and, in one of four randomly selected studs, clear resistance. We’re now entering a phase where we can no longer assume these drugs will work.

Host

Kris, how does this compare in Australia?

Kris

It’s very similar. We’ve documented resistance to BZs and pyrantel in cyathostomins, and we’re seeing increasing macrocyclic lactone resistance. In a recent study, we found multiple studs showing resistance to both drug classes. Like the UK, multidrug resistance is emerging.

Host

What happens if this continues unchecked? What are we facing?

Jane

The risk is a rise in diseases associated with cyathostomins, like larval cyathostominosis. We’re already hearing reports from studs about clinical cases they wouldn’t have seen in the past. Parasite control is becoming suboptimal, and there’s a real danger of resistant parasite populations accumulating in pastures.

David

And don’t forget—these yearlings are sold and moved between studs. They carry resistant parasites with them, spreading the issue globally. It’s reminiscent of what happened in the sheep industry, where management practices had to change drastically.

Jane

Unlike the sheep industry, we don’t have alternative drug classes for horses. That’s why behavioural change is absolutely critical.

Host

Can resistance be reversed?

Kris

Theoretically, yes—but in practice, there’s little evidence. If you remove selection pressure, susceptibility might return over time, but this isn’t guaranteed.

Jane

Exactly. Prevention is more important than reversal. We need to focus on sustainable, non-drug-based control strategies. Asking whether we can reverse resistance can distract us from addressing the bigger issue—changing how we manage parasites.

Host

What about education? Are current efforts effective?

David

Tamzin Furtado’s research suggests they aren’t. Most horse owners don’t voluntarily change behaviour. Blanket worming remains the default—it’s cheap and easy. Without restricting access to anthelmintics, meaningful change is unlikely.

Kris

Same issue here in Australia. Large commercial studs are especially resistant to change. We need more behavioural science to understand what truly influences horse owners.

Jane

Agreed. Horse owners often find modern parasite control strategies confusing. We need veterinary-led support plans—not just information dumps.

Host

Let’s talk about combination products. Are they helping or hindering the situation?

David

Mixed views. Some modelling suggests combinations might help delay resistance. But if parasites are resistant to both actives, combinations are ineffective and potentially misleading.

Kris

In Australia, most products are combinations. When used correctly, they can help—but without guidance, misuse is common. Evidence is still limited, especially in equines.

Jane

They also complicate resistance testing. You need single actives to properly assess drug efficacy.

Host

So, what’s the solution?

David

Veterinary-led herd health plans. Every property should have one. They should include diagnostics like faecal egg count reduction tests (FECRTs), and integrate pasture management and non-drug measures.

Jane

And prescribers—whether vets or SQPs—must have access to single-active products and up-to-date training. Health plans help contextualise treatment decisions and avoid inappropriate use.

Kris

In Australia, access to anthelmintics is virtually unregulated. That needs to change. You can’t expect good decision-making from retail outlets.

Host

What’s the one takeaway message you wish every vet knew?

David

Start with FECRTs. It’s the simplest way to demonstrate resistance and kickstart the conversation with clients.

Kris

We’re stuck with the drugs we have. Use them wisely, based on evidence and herd-level plans.

Jane

Remember, it’s the parasites that are resistant—not the horse. Resistant parasites on pasture can infect new animals. Always consider the herd and pasture ecology, not just the individual case.

Host

Thank you all. There’s certainly a lot of work to be done—but also real hope. With global collaboration and local implementation, we can move toward more sustainable parasite control. Thanks again to Kris, Jane, and David.