Dataset Information

Managing anthelmintic resistance in cyathostomin parasites: Investigating the benefits of refugia-based strategies.

ABSTRACT: Selective anthelmintic therapy has been recommended as a sustainable strategy for cyathostomin control in horse populations for several decades. The traditional approach has been to determine strongyle fecal egg counts (FEC) for all horses, with treatment only recommended for those exceeding a predetermined threshold. The aims are to achieve a reduction of overall egg shedding, while leaving a proportion of the herd untreated, which lowers anthelmintic treatment intensity and reduces selection pressure for development of anthelmintic resistance. This study made use of the cyathostomin model to evaluate the influence of treatment strategies with between 1 and 8 yearly treatment occasions, where either 1) all horses were treated, 2) a predetermined proportion of the herd remained untreated, or 3) horses were treated if their FEC exceeded thresholds between 100 and 600 strongyle eggs per gram. Weather data representing four different climatic zones was used and three different herd age structures were compared; 1) all yearlings, 2) all mature horses 10-20 years old, and 3) a mixed age structure of 1-20 years of age. Results indicated a consistent effect of age structure, with anthelmintic resistance developing quickest in the yearling group and slowest among the mature horses. Development of anthelmintic resistance was affected by treatment intensity and selective therapy generally delayed resistance. Importantly, the results suggest that the effects of selective therapy on resistance development are likely to vary between climatic zones and herd age structures. Overall, a substantial delaying of resistance development requires that the average number of treatments administered annually across a herd of horses needs to be about two or less. However, results also indicate that an age-structured prioritisation of treatment to younger horses should still be effective. It appears that a 'one-size-fits-all' approach to the management of anthelmintic resistance in cyathostomins is unlikely to be optimal.

SUBMITTER: Leathwick DM

PROVIDER: S-EPMC6731328 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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Managing anthelmintic resistance in cyathostomin parasites: Investigating the benefits of refugia-based strategies.

Leathwick Dave M DM Sauermann Christian W CW Nielsen Martin K MK

International journal for parasitology. Drugs and drug resistance 20190828

Selective anthelmintic therapy has been recommended as a sustainable strategy for cyathostomin control in horse populations for several decades. The traditional approach has been to determine strongyle fecal egg counts (FEC) for all horses, with treatment only recommended for those exceeding a predetermined threshold. The aims are to achieve a reduction of overall egg shedding, while leaving a proportion of the herd untreated, which lowers anthelmintic treatment intensity and reduces selection p ...[more]

PMID: 31491731

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Project description:BackgroundA large survey was carried out in 2008 in Europe to evaluate the efficacy of fenbendazole (FBZ), pyrantel (PYR), ivermectin (IVM) and moxidectin (MOX), i.e. the major anthelmintic molecules used in current practice against cyathostomins affecting horses. A total of 102 yards and 1704 horses was studied in three countries: 60 yards and 988 horses from Italy, 22 and 396 from the UK, 20 and 320 from Germany. The survey consisted of Faecal Egg Count Reduction Tests (FECRTs) with a faecal egg count reduction (FECR) categorization of (I) resistance present if FECR <90% and the lower 95% confidence limit (LCL) <90%, (II) resistance suspected if FECR >/= 90% and/or LCL <90% and (III) no resistance if FECR >/= 90% and LCL >90%. The calculation of FECR data was performed employing bootstrap analysis of group arithmetic means.ResultsThe testing of FBZ on a total of 80 yards resulted in resistance present on more than 80% of the UK and German yards and on significantly fewer in Italy, i.e. in 38% (p < 0.01). PYR, IVM and MOX were tested on a total of 102 yards. For PYR resistance present was found in 25% of the yards with no significant differences between countries. For IVM resistance present was encountered in one Italian and two UK yards (3%), resistance present to MOX was not found in any yard in any country.ConclusionThe results indicate that single and/or multiple drug resistance in equine cyathostomins is present in the three countries, is widespread particularly for FBZ and/or PYR and in one UK yard multiple resistance present was detected to FBZ, PYR and IVM. Macrocylic lactones proved to be the most effective drugs, with some evidence of resistance to IVM and highest activity of MOX, despite a single case of reduced efficacy in Germany. These data call for the development and implementation, among practitioners, owners and managers, of further plans to reduce the expansion of the anthelmintic resistant populations and to use those anthelmintics that remain effective in a manner that preserves their efficacy as long as possible.

Dataset Information

Managing anthelmintic resistance in cyathostomin parasites: Investigating the benefits of refugia-based strategies.

Publications

Managing anthelmintic resistance in cyathostomin parasites: Investigating the benefits of refugia-based strategies.

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