Isolation of bluetongue virus serotype 1 from Culicoides vector captured in livestock farms and sequence analysis of the viral genome segment-2.

Bluetongue virus serotype-1 (BTV-1) was isolated from Culicoides oxystoma vectors captured on livestock farms in two places of Gujarat, India. The viruses were isolated on BHK-21 cells, which produced characteristic BTV-related cytopathic effects between 24 and 48 h post-infection. Virus antigen was demonstrated in infected cells at different passage by a BTV-specific sandwich ELISA. Further, polyacrylamide gel electrophoresis and silver staining of viral genomic RNA revealed ten double-stranded RNA segments characteristic of BTV. Serotype of the isolates was identified by virus neutralization and PCR coupled with sequencing. The isolates were designated as SKN-7 and SKN-8 and their genome segment-2 (VP2) were sequenced. Phylogenetic analyses revealed very close relationship between them although they are not identical. SKN-8 showed closer relationship with a recently isolated BTV-1 from goat. Bluetongue virus was earlier isolated from Culicoides in adjacent state more than 20 years ago, although the serotype of the virus was not determined.