Segment-2 sequencing and cross-neutralization studies confirm existence of a neutralization resistant VP2 phenotypic variant of bluetongue virus serotype 1 in India

- VP2 gene of an Indian BTV-1 isolate (WGV104/08/Ind) was sequenced.
- Critical amino acid substitutions on B-cell and neutralizing epitope on VP2.
- Substitution generated neutralization resistant VP2 phenotypic variant.
- Cross-neutralization revealed major subtype antigenic divergence.

Segment-2 (seg-2) of a bluetongue virus seropype-1 (BTV-1) isolate WGV104/08/Ind of Indian origin was sequenced and its neutralization behavior was studied to understand the antigenic similarity and relationship with other BTV-1 isolates. Multiple alignments of the coding region of seg-2 of WGV104/08/Ind revealed 97.6-99.0% and 97.2-98.4% similarity with other Indian BTV-1 isolates at nucleotide and deduced amino acid sequence level respectively. Several conservative and non-conservative substitutions were observed on the deduced VP2 amino acid sequence of WGV104/08/Ind. Non-conservative substitution of Lys119Glu on the B-cell epitope and Arg330Gly on the neutralizing epitope of VP2 of this isolate was observed. Using isolate-specific heterologous hyperimmune serum (HIS) the phenotypic antigenic relationship (r) was determined between WGV104/08/Ind and other Indian BTV-1 isolates which ranged from 0.092 to 0.208. The relationship score ranged from 0.203 to 0.295 when neutralization behavior of other Indian BTV-1 isolates was studied with the HIS of WGV104/08/Ind. Antigenic similarity (R) between WGV104/08/Ind and other Indian BTV-1 isolates was estimated from a reciprocal cross-neutralization study and ranged from 14.70% to 24.80% indicating existence of major subtype antigenic divergence and neutralization resistant behavior of WGV104/08/Ind.