Titled Reasons to be fearful? Rising proportions of positive faecal worm egg counts among UK horses (2007–2023), the study analysed quarterly surveillance data summaries of FWEC test results that were submitted to the Equine Quarterly Disease Surveillance report (EQDSR) by 36 UK laboratories. Of these, 18 laboratories provided additional details through a survey on the testing methods adopted. There was considerable variation between laboratories in both the FWEC test methods used and the FWEC positivity thresholds applied to designate a test result as positive for either surveillance reporting or for treatment purposes. Analysis revealed an increase in the proportion of positive FWECs over time, even after accounting for the time of year that testing was conducted, the FWEC positivity threshold used for reporting a sample as positive and the laboratory undertaking the testing.
These findings raise questions about targeted treatment strategies, where anthelmintics are administered if FWECs exceed a certain threshold. If this threshold remains low, the increasing proportion of positive FWECs that we identified would lead to increased use of wormers, potentially accelerating the development of anthelmintic resistance. This highlights the need to better understand the factors driving rising FWEC positivity rates and if they are a cause for concern. For example, is this trend leading to increased numbers of horses exceeding the treatment threshold and therefore being recommended for treatment? The continuation of coordinated efforts to enhance parasite control strategies across the UK equine industry is essential. The recently available guidelines from the British Equine Veterinary Association (BEVA) and CANTER provide essential resources for vets, pharmacists, registered animal medicines advisors (RAMAs) and suitably qualified persons (SQPs) who prescribe equine anthelmintics to optimise parasite control.
The EQDSR has been collecting laboratory testing data for 20 years and this study demonstrates the benefits and insights that can be gleaned from an extensive surveillance dataset. There are, however, some inherent limitations in such data which must be considered when interpreting surveillance outputs. For example, there was no ability to capture important background data such as the age of sampled horses and their prior anthelmintic treatment history and worm risk from a summary laboratory surveillance dataset like this. Additionally, results are only provided as positive or negative, without quantifiable data on the exact eggs per gram count for each FWEC test result. EIDS will consider ways to enhance and standardise surveillance data collection methods to overcome these current challenges.
Lead author Fleur Whitlock, MRCVS, discusses the importance of these findings: “This paper highlights the remarkable achievements of two decades of sustained surveillance efforts, showcasing how data contributions and analysis can deepen our understanding and drive progress. It emphasises the critical importance of advancing the monitoring and interpretation of surveillance data to better address industry challenges, such as the growing concerns around anthelmintic resistance.”
For a detailed understanding of the study and its implications, the full article is available to read through open access licensing in the Equine Veterinary Journal.
