Genotyping of benzimidazole susceptible and resistant alleles in different populations of Haemonchus contortus from Himalayan and sub-Himalayan regions of North-West India.

An allele-specific PCR was standardized to diagnose the mutation (Phe to Try) at residue 200 of the isotype 1 beta tubulin gene responsible for benzimidazole resistance in Haemonchus contortus adult and infective larvae. Adult and infective larvae of Haemonchus contortus were collected from sheep under different managemental practices (intensive and extensive) in temperate Himalayan regions (Mukteshwar and Kedarkhatta), sub-himalayan region (Pantnagar) of Uttarakhand state and subtropical region of Uttar Pradesh (Bareilly) in north-west India. Genotyping of adult H. contortus, collected from abomasi of slaughtered sheep reared under extensive management, by AS-PCR revealed that the frequency of resistant (r) alleles was significantly higher (P < 0.001) at Pantnagar (0.57) as compared to Bareilly (0.25) and Mukteshwar (0.08). Also, genotyping of infective larvae of the parasite from intensively managed sheep farms indicated that the frequency of resistant (r) alleles was significantly higher (P < 0.001) at Pantnagar (0.85) as compared to Kedarkattha (0.70) and Bareilly (0.62). The results revealed that managemental practices followed in the areas under study have a direct bearing on the spread of benzimidazole resistant alleles.