Related Experiment Video
Updated: May 25, 2026
13:42
Clinical Examination Protocol to Detect Atypical and Classical Scrapie in Sheep
Published on: January 19, 2014
A computer simulation study to evaluate resistance development with a derquantel-abamectin combination on UK sheep
J Learmount1, M A Taylor, D J Bartram
1The Food and Environment Research Agency, Sand Hutton, York, YO41 1LZ, United Kingdom. jane.learmount@fera.gsi.gov.uk
Veterinary Parasitology
|January 27, 2012
Summary
The combination of derquantel (DQL) and abamectin (ABA) significantly delays anthelmintic resistance in sheep parasites. Following Sustainable Control of Parasites in Sheep (SCOPS) guidelines, particularly with high refugia, further extends the efficacy of these drugs.
Area of Science:
- Veterinary Parasitology
- Anthelmintic Resistance
- Sheep Health Management
Background:
- Anthelmintic drug resistance in sheep parasites poses a significant threat to animal health and the agricultural economy.
- The Sustainable Control of Parasites in Sheep (SCOPS) guidelines promote strategies to mitigate resistance development.
- Novel anthelmintic formulations require evaluation to ensure their long-term efficacy and integration into resistance management plans.
Purpose of the Study:
- To evaluate the potential for resistance development to derquantel (DQL) and abamectin (ABA) using a computer model.
- To compare the impact of different farm management scenarios (low vs. high refugia) on resistance development.
- To inform recommendations for the sustainable use of a novel oral formulation of derquantel-abamectin.
Main Methods:
- A computer simulation model was developed using UK field data to represent low (non-SCOPS) and high (SCOPS) refugia scenarios.
- Simulations evaluated resistance allele frequencies and field efficacy under various treatment strategies involving DQL, abamectin (ABA), and their combination.
- Initial resistance allele frequencies for DQL (0.0001) and ML (0.165 or 0.8) were set based on UK prevalence.
Main Results:
- Derquantel (DQL) resistance reached a detectable level by year 5 (sequential) or year 10 (annual rotation) under non-SCOPS management, versus year 16 and year 31 under SCOPS management.
- Abamectin (ABA) resistance showed faster development, reaching detectable levels by year 1 (sequential) or year 2 (annual rotation) under non-SCOPS, versus year 4 and year 8 under SCOPS.
- The combination formulation of DQL-ABA showed no detectable reduction in field efficacy after 40 years with SCOPS management, but resistance was detected by year 6-32 under non-SCOPS management, depending on initial ML resistance.
Conclusions:
- Formulating derquantel (DQL) in combination with abamectin (ABA) significantly delays the development of resistance to both active ingredients.
- Adherence to SCOPS guidelines, promoting adequate refugia, substantially extends the effective lifespan of DQL-ABA formulations.
- The findings support the use of DQL-ABA as a sustainable anthelmintic strategy for sheep parasite control when integrated with appropriate resistance management practices.
