evaluation of benzimidazole resistance in haemonchus contortus us-ing comparative pcr-rflp methods

background: in order to deworm the ruminants especially of sheep in iran, consumption of benzimi­dazoles has more than 2 decades history and today farmers are using imidazothiazoles, macrocyclic lactones and mostly benzimidazole compounds (bzs) to treat infected farm animals. it has been demonstrated that the most common molecular mechanism leading to bzsresistance in haemonchus contortus is a single mutation at amino acid 200 (phenylalanine to tyrosine) of the isotype 1 of beta tubulin gene. according to the report of such mutations in iranian telador­sagia circumcincta isolates with restriction site created pcr-rflp, we decided to evaluate the frequency of such mutations in h. contortus in three different geographical areas of iran. methodes: a total of 102 collected adult male h. contortus were evaluated with pcr-rflp (us­ing psp1406i as restriction enzyme). by means of a second step to compare function of different methods and to increase sensitivity of detection mechanism, a third of samples were examined by another pcr-rflp method (using taai as restriction enzyme) and finally beta tubulin gene of two samples was sequenced. results: all of samples were detected as bzss homozygote. finally, beta tubulin gene sequenc­ing of two samples showed no point mutation at codon 200. conclusion: it seems that bzresistance of h. contortus in iran is not a serious problem as antici­pated before.