Characterization of an Indian bluetongue virus isolate by RT-PCR and restriction enzyme analysis of the VP-7 gene sequence.

The reverse transcription-polymerase chain reaction (RT-PCR) was standardized to amplify the VP-7 gene sequences of an Indian isolate of bluetongue virus serotype 23. Using two different sets of primers, a sequence of 1156 bp comprising the complete coding sequence of the VP-7 gene and its 770 bp internal sequence were amplified. The sensitivity of RT-PCR, using these two sets of primers individually was 40 pg and 4 pg, with the external and internal primers, respectively, whereas the nested PCR was 100-fold more sensitive than the single PCR with the external primers. Further, by restriction enzyme digestion of the 1156 bp amplicon, using CfoI, PstI and TaqI enzymes, the Indian isolate was found to be genetically different from isolates from the United States and Australia. RT-PCR and restriction enzyme digestion were applied to detect virus directly in blood samples taken from sheep suspected of bluetongue virus infection.