Evaluation of Benzimidazole Resistance in Equine Cyathostomins in the Kermanshah Province of Iran Using Coprological Analysis and Allele-Specific PCR

Background: Resistance to benzimidazole (BZ) by cyathostomin nematodes has become a major threat to equine health around the world. We aimed to evaluate the efficacy of BZ drugs against small strongyle nematodes in horses of western Iran using coprological and molecular examination. Methods: Faecal egg count reduction tests were performed on 398 horses kept in 16 stables in western Iran (Kermanshah Province), to detect benzimidazole resistance in small strongyle nematodes. Allele-specific PCR was used to identify the F200Y (TAC/TTC) SNP in the beta-tubulin gene codon in cyathostomin larvae. Results: There was a 96.1%-98.3% (90% CI) reduction in faecal egg counts following mebendazole treatment and a 96.6% - 98.7% (90% CI) reduction in faecal egg counts following fenbendazole treatment. The allele-specific PCR showed BZ-susceptible homozygote genotypes in all examined samples (Two pools of 10 to 50 L3 of cyathostomin nematodes from each of the 18 selected horses). Conclusion: Benzimidazole resistance in equine small strongyles has been reported globally, and the results of the present study were unexpected. The probable reasons for the slow development of BZ-resistance are climatic conditions in the country that have significant negative effects on the ability of free stages of the resistant strongyle nematode to survive and develop.