BACKGROUND: Resistance to benzimidazole (BZ) compounds is common in gastrointestinal nematodes such as Teladorsagiacircumcincta and Haemonchuscontortus in sheep and goats worldwide. Although BZs resistance has been reported from Iran so far there is no much information based on molecular epidemiology in sheep. OBJECTIVES: Given the importance of anthelmintic resistance and shortage of information about status of prevalent abomasal nematode, aim of this study was to investigate single nucleotide polymorphisms (SNPs) in sheep of northern Iran. METHODS: From June to September 2016, abomsa of 139 sheep of both sexes and different ages in Amol slaughterhouse were examined for isolation of nematodes. Totally, 45 male T.circumcincta and 5 male H. contortus that were confirmed by both microscopical and nested-PCRRFLP methods were included in this study. Susceptibility or resistance of each single nematodes worm to benzimidazoles was performed using allele-specific PCR. RESULTS: Frequency of genotypes in T. circumcincta was 33.33% heterozygote BZ and 66.67% BZ homozygote sensitive. In examined H. contortus 40% were heterozygote BZ and 60% BZ homozygote sensitive. No homozygote resistant worm was found. CONCLUSIONS: Resistance against BZs in T. circumcincta and H. contortus of sheep has occurred at a low prevalence in the north of Iran. However, mutated genes might get dominant under drug selection in future. Hence, periodic investigations for early detection of mutated alleles in nematode populations using accurate and sensitive molecular methods are recommended.
