Tehran University of Medical Sciences Iranian Journal of Parasitology 1735-7020 20 3 2025 09 01 Evaluation of Benzimidazole Resistance in Equine Cyathostomins in the Kermanshah Province of Iran Using Coprological Analysis and Allele-Specific PCR 389 399 EN Rezvan Jamshidpour Department of Clinical Science, Faculty of Veterinary Medicine, Razi University, Kermanshah, Iran Reza Nabavi Department of Pathobiology, Faculty of Veterinary Medicine, Bu-Ali Sina University, 6517658978, Hamedan, Iran Hossein Moadab Department of Clinical Science, Faculty of Veterinary Medicine, Razi University, Kermanshah, Iran Farid Rezaei Department of Pathobiology, Faculty of Veterinary Medicine, Razi University, Kermanshah, Iran Abdolali Chale Chale Department of Pathobiology, Faculty of Veterinary Medicine, Razi University, Kermanshah, Iran Neil Sargison Royal (Dick) School of Veterinary Studies and RoslinInstitute, Easter Bush Veterinary Centre, University of Edin-burgh, Midlothian EH25 9RG, UK 2025 04 11 2025 07 26 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. https://ijpa.tums.ac.ir/index.php/ijpa/article/view/4571 https://ijpa.tums.ac.ir/index.php/ijpa/article/download/4571/1445