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

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.