Abstract

Bluetongue virus (BTV) is the ‘type’ species of the genus Orbivirus within the family Reoviridae. The BTV genome is composed of ten linear segments of double-stranded RNA (dsRNA), each of which codes for at least one of ten distinct viral proteins. Phylogenetic analysis based on VP2, VP3, VP5, VP7 and NS3 gene has been advocated by different researchers around the world. However, very little information about the phylogenetic analysis based on the NS1 gene of BTV-16 isolates is available. In this study, a partial sequence of segment 5 (Seg 5) from the BTV-16 Hisar isolate was sequenced. Sequence analysis of the Seg 5 of the BTV-16 Hisar isolate revealed highest nucleotide sequence identity of 98.9% (BTV-21), -96.4% (BTV-9) with sequences of NS1 genes of Indian isolates and 97.8% (BTV-3),-93.4%(BTV-1) isolates from other countries. The lowest sequence identity detected was 91.2% between sequences of NS1 gene of JQ924824 of BTV 16 Indian isolate and JX861502 BTV-1 of France. The study also assessed the comparative identity from the deduced amino acid sequences and found maximum homology (100% identity) with Indian isolates and 95.2 to 98.8% identity with Western isolates with only three amino acid difference. Phylogenetic analysis of the NS1 gene of the BTV-16 Hisar isolate with others around the world has revealed two major clusters which includes the Indian (Eastern) linage and Western linage separately. The BTV-16 Hisar isolate was found to be closely related with the BTV-9 and 21 Indian isolates based on its NS1 gene. Phylogenetic analysis of segment 5 is highly conserved among the different serotypes however, NS1 of BTV-3 of USA clustered with the Eastern lineage indicating introduction of Western BTV strains and a possible reassortment between Eastern and Western field strains in India.

Key words: Bluetongue virus, genome, NS1, Orbivirus, phylogeneticanalysis, segment-5, serotype.