Genetic polymorphism of p- Tubulin isotype 1 gene conferring benzimidazole resistance in Haemonchus contortus in sheep of Andhra Pradesh

A study was undertaken to determine the polymorphism at codon 200 of P-tubulin isotype 1 gene associated with benzimidazole (BZ) resistance, by PCR-RFLP (Polymerase chain reaction linked restriction fragment length polymorphism) in Haemonchus contortus from sheep across eight districts of Andhra Pradesh. RFLP using Taa I revealed three distinct patterns named as ‘rr’ (homozygous resistant), ‘rS’ (heterozygous susceptible) and ‘SS’ (homozygous susceptible). The overall genotype frequencies for SS, rS and rr were 0.26, 0.44 and 0.30, respectively. The allelic frequencies of ‘r’ and ‘S’ were 0.52 and 0.48, respectively. The prevalence of benzimidazole resistance allele (r) was significantly (P<0.001) higher than susceptible allele in the study area indicating inconsistency with Hardy-Weinberg equilibrium (HWE). The expected heterozygosity (He) and observed heterozygosity (Ho) estimates were 0.50 and 0.44, respectively. The effective population size (Ne), polymorphic information content (PIC) and fixation index (F_IS) were 1.99, 0.37 and 0.13, respectively. The analysis revealed significant heterozygote deficiency. The study revealed that BZ resistance could be a future threat in the area as high frequency of heterozygous worms occur in different districts of Andhra Pradesh.