For small ruminant farmers worldwide, the barber’s pole worm (Haemonchus contortus) is a relentless threat. This blood-feeding nematode causes anaemia, weight loss, and even death in sheep and goats, costing the livestock industry millions annually. For decades, control relied on two mainstays: anthelmintic drugs and vaccines like Barbervax (with cumbersome dosing protocols). But by 2025, a crisis loomed: multiple drug resistance had become widespread, leaving farmers with fewer options to protect their herds.
The application of RNA interference (RNAi), a tool that silences specific genes, to identify essential genes and target candidates for improved control of H. contortus has been proposed for a decade (please see detailed information in our recent paper in Veterinary Research 2025, 56:194). Our team at Zhejiang University had spent over a decade asking a critical question: Can we target the worm’s own biology to stop its infection—without relying on dwindling drug supplies? This question led us to RNAi and three key genes that keep H. contortus alive. Our recent paper shares how this work moved from lab benches to sheep pens—and what it means for the future of parasite control.
The Starting Point: Why Target H. contortus’s “Weak Spots”?
To beat a parasite, you first need to understand its life cycle. H. contortus has two phases: a free-living stage (eggs, L1–L3 larvae) in soil, and a parasitic stage (L4 larvae, adults) in the host’s abomasum (stomach). The critical jump happens when sheep ingest infective L3 larvae: these “dormant” worms activate, shed their protective sheath, moult into L4s, and start feeding on blood. If we could block this jump, we could stop infection before it starts.
Past research had identified genes linked to nematode development, but few had been tested in live animals—a gap we wanted to fill. We focused on three biological processes the worm can’t live without:
Larval activation: The switch from dormant L3 to infective L4.
Moulting: Shedding the cuticle (outer layer) to grow into the next stage.
Haem utilisation: Using iron from the host’s blood to survive (since H. contortus can’t make its own haem).
The Hunt for Target Genes: From Databases to Microscopes
We started by mining genomic and transcriptomic data—public datasets from WormBase ParaSite and our own past work—to find genes tied to these processes.
First, we zeroed in on daf-9/cyp-22a1, a gene known to regulate larval development in free-living nematodes like C. elegans. In H. contortus, we found this gene went into overdrive when activated L3 larvae were exposed to sheep serum (mimicking the host’s stomach environment). When we blocked its protein with a chemical inhibitor (dafadine A), the larvae curled up and stopped developing—proof it was essential for the L3-to-L4 transition.
Next, we turned to bli-5, a gene linked to moulting. In C. elegans, bli-5 mutations cause “blister” defects in the cuticle, but no one had studied it in parasitic worms. We discovered bli-5 was highly active in H. contortus’s L3 stage—and that its sequence was only found in nematodes, not in sheep. That was a game-changer: targeting it would avoid harming the host. When we silenced bli-5 in L3 larvae, they developed abnormal bodies (shrinking, swelling) and couldn’t moult properly.
Finally, we looked for genes tied to blood-feeding or haem utilisation. The worm uses a transporter called HRG-1 to take up haem from blood, but HRG-1 is also present in sheep—making it a risky target. Then we found HCON_00083600: a novel gene linked to HRG-1’s function, with no homologs in mammals. It was highly active in blood-feeding L4s and adults, and its protein was concentrated in the worm’s intestine—exactly where haem is absorbed.
The Big Test: From In Vitro Success to Sheep Trials
Lab experiments (measuring larval motility, survival, and gene expression) were promising, but we needed to prove these genes mattered in live hosts. This is where RNAi became our tool of choice.
We used two RNAi methods to silence each gene:
Feeding: For free-living L1–L3 larvae, we fed them E. coli engineered to produce double-stranded RNA (dsRNA) targeting our genes.
Soaking: For infective L3s (xL3s, after sheath removal), we soaked them in small interfering RNA (siRNA) mixed with a delivery reagent to ensure uptake.
Then came the moment of truth: we infected groups of helminth-free Hu sheep with RNAi-treated larvae, alongside control groups (untreated larvae or larvae with non-targeting RNA).
We monitored the sheep for 35 days, measuring:
Faecal egg count (EPG): A marker of adult worm reproduction.
Worm burden: The number of adult worms in the abomasum after necropsy.
The results exceeded our expectations:
When daf-9/cyp-22a1 was silenced: By day 28, sheep had no detectable eggs in their faeces. At necropsy, we found zero adult worms—the silenced larvae never established infection.
When bli-5 was silenced: EPG dropped by ~40% compared to controls, and adult worm numbers fell from ~1,400 to ~800 per sheep. Surviving worms were shorter (a “dumpy” phenotype), meaning they were less able to reproduce.
When HCON_00083600 was silenced: Like daf-9/cyp-22a1, there were no eggs or adult worms in the sheep—proof this novel gene is critical for the worm’s blood-feeding survival.
The Roadblocks: What We Learned (and Still Need to Fix)
This work wasn’t without challenges. RNAi in parasitic nematodes is notoriously tricky: gene silencing efficiency varies, and delivering dsRNA/siRNA to all worm stages (not just larvae) is hard. For example, while we achieved strong silencing in L3s, bli-5 expression bounced back slightly in adult worms—suggesting we need longer-lasting RNAi tools.
We also had to address safety: Could silencing cyp genes (which are part of a large enzyme family) harm the sheep? Because we targeted genes unique to nematodes (like bli-5 and HCON_00083600) or genes with distinct sequences in worms vs. hosts (like daf-9/cyp-22a1), the sheep showed no adverse effects—no weight loss, no changes in bloodwork.
Another lesson: Context matters. In the lab, silencing genes stopped larvae in their tracks, but in live sheep, the immune system also plays a role. We saw that RNAi-treated larvae were less able to evade the sheep’s defences—hinting that combining RNAi with immune boosters could be even more effective.
What’s Next? A New Era for Parasite Control
For us, this paper is just the start. The three genes we identified are now validated targets for H. contortus control, and RNAi has proven it can work in real-world conditions (not just petri dishes). Here’s what we’re working on next:
Better delivery systems: We’re exploring lentivirus-based RNAi to silence genes inside the host, so we don’t have to treat larvae before infection.
Combination therapies: Pairing RNAi with low-dose anthelmintics could reverse drug resistance—a critical need for farmers.
Broadening to other nematodes: Genes like daf-9/cyp-22a1 are conserved in other parasitic worms (e.g., Nippostrongylus brasiliensis), so this work could help control multiple parasites.
A Note of Gratitude
This work wouldn’t have been possible without the farmers who shared their challenges, the students and lab technicians who counted thousands of larvae, and the funding bodies that supported risky, long-term research (including the National Natural Science Foundation of China nos. 32473050, 32202829, and 32172877). Most importantly, it’s a reminder that solving agricultural problems requires bridging basic science and real-world application.
For the research community: We hope this paper inspires more work on RNAi for parasite control—especially in understudied species. For farmers: The end of drug resistance isn’t here yet, but we’re one step closer to tools that protect your herds and the planet.
— Guangxu Ma, and the entire research team
Read the full paper here: https://doi.org/10.1186/s13567-025-01633-6