Anthelmintic resistance (AR) poses a growing threat to existing equine parasite control methods. Quarterly data summaries from fecal worm egg count testing (FWECT) performed by laboratories in the United Kingdom have appeared in Equine Quarterly Disease Surveillance Reports (EQDSR) since 2007 but have not previously been assessed. This laboratory survey and analysis of laboratory summary data aimed to assess strongyle FWECT methods and thresholds used by laboratories in the U.K. and investigate factors associated with quarterly laboratory FWECT positivity rates between 2007-2023.
Researchers surveyed laboratories in Q3 of 2018 and again in Q4 of 2023. They analyzed proportions of FWECTs reported positive (PTP) each quarter by individual laboratories between 2007-2023 using multiple mixed-effects linear regression, evaluating laboratory-level random-effects and fixed-effects variables for ordered categories of FWECT-thresholds, year-quarters, and consecutive year groups.
Ten laboratories responded in 2018, and 13 laboratories responded in 2023. Samples were commonly reported positive at > 0 to < 100 eggs per gram (epg) and ≥ 200 epg. Regression modeling of 1,190 EQDSR submissions confirmed significantly decreased PTP for thresholds ≥ 100 to < 300 epg (level-2: −12.0%, p = 0.03), ≥ 300 epg (level-3: −18.0%, p = 0.03), and when thresholds were not specified (level-4: −12.2%, p = 0.0), relative to level-1 baseline (> 0 to < 100 epg). No significant seasonal variation in PTP between year-quarters was evident. Overall, controlling for between-laboratory variation and FWECT thresholds, there remained evidence for a significant gradient in increasing PTP over the study period relative to baseline (2007-2009). PTP increased by 6.9% in 2010-2011 (p < 0.001), 10.1% in 2012-2013 (p < 0.001), 14.1% in 2014-2015 (p < 0.001), 16.0% in 2016-2017 (p < 0.001), 15.6% in 2018-2019 (p < 0.001), 17.1% in 2020-2021 (p < 0.001), and 18.9% in 2022-2023 (p < 0.001).
Bottom Line
Controlling for laboratories and FWECT thresholds, there was strong residual evidence from FWECT summary data for increasing egg counts in horses in the U.K. between 2007-2023.
https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.14478
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