Specificity of molecular hybridization techniques for the detection of bluetongue virus serotypes in Culicoides variipennis.

Direct blot hybridization (DBH) and sandwich hybridization (SH) were evaluated for their ability to detect bluetongue virus (BTV) RNA in the biting midge Culicoides variipennis (Coquillett). Probes were derived from the L3 RNA segment of BTV, serotype 17. RNA of the five BTV serotypes occurring in the USA (BTV-2, BTV-10, BTV-11, BTV-13, and BTV-17) was extracted from pools of varying numbers of infected and uninfected biting midges and assayed by direct blot and sandwich hybridization tests. Direct blot hybridization using an RNA transcript probe or cDNA probe was a fast, efficient and sensitive technique, detecting as few as one midge infected with any BTV serotype in a pool of 50 or 100. Sandwich hybridization was able to detect the homologous serotype, BTV-17, in pools containing a single infected midge in a total of 50 or 100. However, detection of the heterologous serotypes, BTV-10, BTV-11, and BTV-13, was limited to pools containing 5 or more infected midges in a total of 50, and BTV-2 was undetectable by SH. Hybridization techniques provide an alternative to the conventional detection methods of inoculation of cell culture or embryonated chicken eggs for detection of BTV.