Development and application of a reverse transcriptase droplet digital PCR (RT-ddPCR) for sensitive and rapid detection of Japanese encephalitis virus

Japanese encephalitis (JE) is one of the most common zoonoses caused by Japanese encephalitis virus (JEV). Droplet digital PCR (ddPCR) is a novel sensitive, accurate method that enables absolute quantitation without the need for calibration curves. The aim of this study was to develop a RT-ddPCR method to detect JEV, and to compare its sensitivity with real-time TaqMan RT-PCR by analysis of clinical samples. The methods of JEV real-time RT-PCR and RT-ddPCR were established and optimal reaction conditions were confirmed. Each method was evaluated for linearity, limit of detection and specificity. A total of 103 porcine samples were analysed by both methods and the detection rate was calculated. Both methods showed a high degree of linearity and positive correlation for standards (R2 ≥ 0.999). The assays indicated that the detection limit for RT-ddPCR was approximately 2 copies/20 μL well, a 100-fold greater sensitivity than TaqMan real-time RT-PCR. The detection results for clinical samples showed that the positive detection rate of RT-ddPCR (27.2%) was higher than that of TaqMan real-time RT-PCR (16.5%). The cross-reaction was performed with other porcine pathogens, and negative amplification of the cross-reaction assay demonstrated the high specificity of this method. The novel JEV RT-ddPCR assay could be used as an efficient molecular biology tool to diagnose JEV, which would facilitate the surveillance of reproductive failure disease in swineries and would be beneficial for public health security.