High prevalence of the E198A polymorphism in isotype-1 β-tubulin gene of Haemonchus contortus populations in organized goat farms in Kerala, South India

Abstract

The study was done to determine the benzimidazole resistance-associated polymorphisms in seven organized goat farms in northern, central and southern regions of Kerala in south India. Results of Fecal Egg Count Reduction Test (FECRT) indicated benzimidazole resistance in all the farms with per cent reduction in fecal egg counts ranging from 16 to 94 per cent. A total of 250 Haemonchus contortus larvae were genotyped at codons 167, 198 and 200 of isotype 1 β-tubulin gene by PCR-RFLP. A 451 bp region of isotype 1 β-tubulin gene amplified by semi-nested PCR was subsequently digested with restriction enzymes Eco1051 (SnaBI), HpyCH4V and HpyCH4III for identification of SNPs at codons 167, 198 and 200, respectively. The results of genotyping revealed E198A polymorphism (GAA to GCA, glutamate to alanine at codon 198) with an overall frequency of 0.516 while no polymorphism was detected at codons 167 and 200. The high prevalence of E198A polymorphism and the absence of F200Y polymorphism in H. contortus populations in organized goat farms in Kerala might be attributed to the prolonged and intensive use of benzimidazoles resulting in high selection pressure for benzimidazole resistance mutations.