A profiling of faecal parasites in horses in Mauritius and resistance to Fenbendazole at one horse-riding stable

Mauritius hosts a population of approximately 900 equids, but no investigations have delved into issues such as the prevalence of equine helminths, anthelmintic usage, and resistance emergence.

This study aimed to devise a qualitative and quantitative profile of common helminthic intestinal parasites in equines at eight out of twenty-eight stables (272 horses, 29 % of local population) and to determine whether helminthic intestinal parasites in equines at one stable have developed resistance to Fenbendazole by quantitatively assessing pre-treatment faecal egg counts, post-treatment faecal egg counts and percentage faecal egg count reduction (%FECR).

Targeted parasites included Parascaris equorum, strongyles (Cyathostomum spp. and Strongylus spp.), Fasciola hepatica, Dictyocaulus arnfieldi, Trichostrongylus axei, and Strongyloides westeri, identified based on their morphological characteristics and relative size.

Results indicated a prevalence for P. equorum in 31 % and strongyles in 22 % of horses sampled. No other helminth eggs were detected in any of the samples studied. Quantitative analysis, employing the McMaster Technique for faecal egg count (FEC), revealed that 99 % and 98 % of horses sampled exhibited FEC < 200 eggs per gram (epg) for P. equorum and strongyles respectively, categorizing them as low shedders by AAEP standards. Two percent of horses were classified as moderate strongyle egg shedders (between 200 and 500 epg), and 0 % were high strongyle egg shedders (more than 500 epg). For P. equorum, 0.4 % of horses were categorized as moderate egg shedders and 0.4 % were high egg shedders. No significant correlations were discerned between FEC and stable parameters such as location and size.

At one stable, fenbendazole (FBZ) was administered orally at a dosage of 5 mg/kg via stomach tube to 24 equids. Pre-treatment FEC values were compared to post-treatment FECs taken 14 days after anthelmintic administration, with the %FECR computed. Mean %FECR and adjusted mean %FECR for P. equorum were 91 % and 92 % respectively, which suggested drug efficacy. For strongyle, mean %FECR and adjusted mean %FECR were 59 % and 98 % respectively, which also seemingly supported the hypothesis of lack of resistance. Bayesian analysis however, revealed only a 63 % probability (i.e. <95 %) that true reduction exceeds 90 %. The findings suggested the presence or imminent presence of resistance to fenbendazole at this stable and emphasized the imperative for judicious anthelmintic administration coupled with a surveillance-oriented approach to mitigate resistance emergence in other stables. Furthermore, the pressing need to adopt alternative integrated control measures is emphasized, reflecting the urgency in addressing this burgeoning challenge in equine health management.