Thirty Haemonchus contortus male worms were collected from farmed red deer yearlings in order to determine whether routine administration of albendazole for a long-term period (17 years) could select anthelmintic resistance. PCR-RFLP method based on single-nucleotide polymorphism of codon 200 in isotype 1 ß-tubulin gene (Phe200Tyr) was applied. The results showed a significant frequency of either the resistant allele (85 %) or the homozygous resistant genotype (70 %). By chi-square test, Hardy-Weinberg equilibrium of the population was accepted (p = 0.334, power of test 0.01). True prevalence of the resistant genotype (RR) was estimated to be 46.5-87.2 % (confidence interval 95 %) calculated by Sterne's exact method. These results confirmed that long-term use of benzimidazoles could change the relative allele frequency of genes associated with drug resistance and may cause a large-scale spread of the resistant allele. To our knowledge, this study supported benzimidazole resistance in Haemonchus contortus in red deer for the first time.
Keywords: Albendazole; Haemonchus contortus; Red deer; Resistance.