[Equine strongyles II. Occurrence of anthelmintic resistance in Switzerland].

The study investigates the occurrence of anthelmintic resistance in strongyles, a type of parasitic worm, in horses across 90 farms in Switzerland. Findings suggest that resistance to benzimidazole (BZ)-based treatments is present in nearly half the farms, while treatments using pyrantel and ivermectin remain largely effective — highlighting the need for strategies to prevent further resistance development.

Understanding Anthelmintic Resistance

• Anthelmintic resistance refers to the ability of parasites, in this case strongyles, to survive medications that are supposed to kill them or prevent their growth.
• This research paper investigates the prevalence of this resistance in equine strongyles – a type of parasitic worm that infests horses, affecting their health.
• Resistance poses a significant challenge to effective parasite control and can severely affect the health of infected animals, including horses.

Methodology and Findings

• The investigation was conducted on 440 horses across 90 farms in Switzerland and utilized techniques such as egg hatch assay and faecal egg count reduction to determine resistance levels.
• Benzimidazole (BZ) resistance was indicated in almost half of the farms (40 out of 82).
• Pyrantel treatment remained highly effective on most farms, with one exception where its efficacy dropped to 80%.
• Ivermectin, a commonly used anthelmintic, remained highly effective with efficiency rates between 98 and 100%.
• Post-treatment faecal cultures were primarily composed of larvae from the Cyathostominae family, indicating the prevalence of this strongyle subset.

Anthelmintic Usage and Resistance

• The study found that horses were treated on average 3.5 times per year, and BZ was used in the seasonal treatment schedule on 75% of the farms.
• A significant correlation was established between the use of BZ and the occurrence of BZ-resistance, substantiating previous research that overuse of a particular anthelmintic can lead to increased resistance.

Recommendations

• Data suggests that BZ-resistance is already a significant issue in the control of equine strongyles in Switzerland, and the effectiveness of other anthelmintics could also be compromised if similar usage patterns continue.
• Therefore, the researchers recommend control measures that minimize the risk of resistance development against still-effective anthelmintics, for the protection of horse health and the long-term efficacy of these vital treatments.