Genetic and antigenic characterization of bluetongue virus serotype-1 isolated from goat in India

Abstract

Bluetongue virus (BTV) affects domestic and wild ruminants and is transmitted by Culicoides spp. In the present study, genetic and antigenic characterization of the BTV-1 serotype (MKD20/08/Ind isolate) isolated from goat was carried out to understand the phylogenetic relationship and molecular epidemiology of bluetongue. Full genome sequencing of BTV-1 isolate was carried out using next-generation sequencing (NGS). The sequence data was analyzed and the phylogenetic relationship of the goat isolate with other BTV-1 was established. Phylogenetic analysis grouped the MKD-20/08/Ind isolate within BTV serotype 1, with a high level of nucleotide sequence identity (>99%) to the previous BTV-1, confirming its serotype. The phylogenetic tree constructed from the outer capsid protein genes, seg-2 and seg-6, segregated MKD-20/08/Ind with other Indian BTV-1 isolates reported earlier. All BTV genome segments were found to be evolving under strong purifying (negative) selection. The mean substitution rate of different segments of BTV-1 isolates varied from 1.663×10-2 (seg-8) to 3.949×10-3 (seg-1) substitutions per site per year. The time to the most recent common ancestor (tMRCA) indicates all the genome segments of BTV-1 might have an older ancestor. The phenotypic antigenic relationship (r) of the MKD20/08/Ind isolate with other BTV-1 isolate-specific hyperimmune serum (HIS) determined by serum neutralization test (SNT) was 0.44 to 0.80. The neutralization behaviours of the MKD20/08/Ind with other BTV-1 isolate-specific HIS suggest probable minor subtype antigenic variation. Full-genome sequencing and phylogenetic analysis of BTV-1/MKD-20/08/Ind isolate indicate ancestral relationships amongst the Indian and Mediterranean BTV-1 isolates.