Anthelmintic resistance in the equine roundworm
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Short summary
The roundworm, Parascaris univalens, is the horse's largest intestinal parasite and very common in foals and young horses. In this research project, we are investigating a possible mutation in the parasite that may be behind the resistance – and horses are being recruited for the study!
Foal with roundworm sought for research project!
Roundworms in horses have developed resistance to deworming agents, which means that treatment is sometimes no longer effective. If we are left without effective deworming agents, this can pose a serious threat to the health of foals.
In this research project, we are investigating a possible mutation in the parasite that may be behind the resistance.
Would you like to participate? Answer YES to the following questions:
- Do you have around 10 foals born between April and August 2025, and recurring foals on the farm?
- Have the foals not been treated with Axilur since November 2025?
- Do you have the opportunity to take individual fecal samples from the foals?
If so, please get in touch!
Contact: Veterinary student Astrid Minten admn0002@stud.slu.se.
As a participant, you will recieve:
- Referral form and envelope with prepaid postage
- Free parasite analysis
Thank you in advance! More information about the research project can be found below.
More information about the specific research project
The roundworm, Parascaris equorum, is the main intestinal parasite of horses. Fluke infection is very common in foals and young horses, after which horses develop immunity to the worm, and in horses over 4 years of age, fluke infection is very uncommon.
Roundworm eggs are highly resistant and can remain infective on pasture for many years. The foals ingest the eggs on the pasture and the eggs then hatch in the gut. Symptoms of roundworm infection include reduced appetite and general condition, nasal discharge, coughing, shaggy coat and poor growth. If the foal has a very high parasite burden, it can lead to small intestinal obstruction/ constipation resulting in severe colic and possible death.
Resistance to deworming agents reported
In general, foals are dewormed against roundworm several times during their first year of life. In the past, all available deworming agents have been effective against roundworm, but about 15 years ago there were international reports of resistance to ivermectin (Ivomec® and others). In 2005, the first cases of resistance to ivermectin were detected on Swedish farms. Currently, benzimidazole (Axilur®) or pyrantel (Banminth® and others) are used for deworming against roundworms, but resistance to these drugs has also been detected internationally.
Resistance means that the parasite survives a dose of drug that would normally be lethal. It is clear that excessive use of deworming agents has led to increased drug resistance in parasites, posing a major threat to both animal and human health. In order to reduce this alarming development of resistance, the Danish Medicines Agency decided in 2007 that deworming agents for horses and other animals must be prescribed by a veterinarian.
Aim and objective
This project will give us a picture of the resistance situation in the horse roundworm today, and may influence future recommendations on deworming and parasite control. Hopefully, we will also gain new knowledge about how resistance develops in the roundworm. We also hope to find markers to identify incipient resistance, and that the project will help advance research in the field of drug resistance in parasites.