Improved safety for molecular diagnosis of classical rabies viruses by use of a TaqMan real-time reverse transcription-PCR "double check" strategy.

To improve the diagnosis of classical rabies virus with molecular methods, a validated, ready-to-use, real-time reverse transcription-PCR (RT-PCR) assay was developed. In a first step, primers and 6-carboxyfluorescien-labeled TaqMan probes specific for rabies virus were selected from the consensus sequence of the nucleoprotein gene of 203 different rabies virus sequences derived from GenBank. The selected primer-probe combination was highly specific and sensitive. During validation using a sample set of rabies virus strains from the virus archives of the Friedrich-Loeffler-Institut (FLI; Germany), the Veterinary Laboratories Agency (VLA; United Kingdom), and the DTU National Veterinary Institute (Lindholm, Denmark), covering the global diversity of rabies virus lineages, it was shown that both the newly developed assay and a previously described one had some detection failures. This was overcome by a combined assay that detected all samples as positive. In addition, the introduction of labeled positive controls (LPC) increased the diagnostic safety of the single as well as the combined assay. Based on the newly developed, alternative assay for the detection of rabies virus and the application of LPCs, an improved diagnostic sensitivity and reliability can be ascertained for postmortem and intra vitam real-time RT-PCR analyses in rabies reference laboratories.