Detection of benzimidazole resistance by PCR-RFLP in Haemonchus contortus recovered from sheep Case report

The authors dissected a ewe died of haemonchosis on the 26th day after an albendazole treatment. The large number of Haemonchus contortus recovered from the abomasum suggested the possibility of benzimidazole resistance, which was confirmed by PCR-RFLP based on single-nucleotide polimorphism of codon 200 in isotype 1 beta-tubulin gene (Phe200Tyr). The proportion of resistant homozygotes (RR), heterozygotes (RS) and susceptible homozygotes (SS) were 66.78%, 33.33% and 0%, respectively (n = 15). By Haldane's exact test Hardy-Weinberg equilibrum of the population was accepted (p= 1.0). The true prevalence of resistant genotype (RR), which was calculated by Sterne's exact method, proved to be 39.68-85.83% (confidence interval: 95%). These results confirmed that long-term usage of benzimidazoles can change the relative allele frequency of genes associated with drug resistance; hereby it can cause large-scale spread of resistant allele. To our knowledge, this study proved the resistance to benzimidazole in Haemonchus contortus in Hungary for the first time.