AbstractBluetongue (BT) is an economically important viral disease for sheep and goat causing high morbidity and mortality. In the present study, eight Bluetongue virus (BTV) isolates of goat origin from Utter Pradesh (UP) and four BTV isolates of sheep origin from Andhra Pradesh (AP) adapted in BHK-21 cell line were used. After appearance of 75% of cytopathic effect in BHK-21 cells the virus along with cells were pelleted down and nucleic acid (dsRNA) was extracted using Tri Reagent. All the isolates were confirmed as BTV based on characteristic cytopathic effect in BHK-21 cell culture, RNA-PAGE study (3:3:3:1 pattern) and 366bp amplicon size with group specific ns1 gene based RT-PCR. All the isolates were confirmed as BTV 1 based on segment 2 based serotype specific RT-PCR showing specific amplicon of 605bp size. The nucleotide sequencing of vp2 gene followed by BLAST search also confirmed the isolates as BTV1. The phylogenetic study revealed the eastern topotype origin of these isolates. The phylogenetic analysis also revealed that BTV1 isolates from north India form more closely related sub cluster with other Indian isolates of BTV1. However, BTV1 from south India form separate sub cluster with BTV1 from Greece with in same eastern cluster. The presence of a common culicoides vector species C. oxystoma has been reported in all these states and could be the possible cause for spread of virus in these parts of the India.
Keywords: Bluetongue virus serotptype-1, cytopathic effect, Phylogenetic analysis, vp2 gene