During 1387-86, total number of 120 blood samples gathered from sheep with bluetongue-like clinical sign. The samples collected from seropositive regions .After separating serum, they were evaluated by competitive ELISA for detecting Ab against VP7 antigen. The full length of S7 gene (1156 bp) amplified by one step RT-PCR .In this method two sets specific primers, targeting 3? and 5?ends of S7 segment, were applied. For confirmation of PCR products in first amplification, nested-PCR was used. By using internal primers the most samples which displayed weak S7 band, produced a sharp and specific internal band (769 bp).By this method the sensitivity of virus detection dramatically increased .Among the blood samples, the number of BTV serogroup positive, nPCR positive, both BTV serogroup and nPCR positive and both BTV serogroup and nPCR negative cases were determined, 41(34.8%), 23(19.2%), 12(10%) and 56(46.6%) respectively. This is the first report about using RT-PCR for BTV detection in Iran. RT-PCR and nPCR molecular technique can be used as a very sensitive and reliable method for BTV detection in blood samples.
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