Development of a fluorescent-intercalating-dye-based reverse transcription loop-mediated isothermal amplification assay for rapid detection of seasonal Japanese B encephalitis outbreaks in pigs

The standardization and validation of a one-step, single-tube, accelerated fluorescent-intercalating-dye-based reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay targeting the NS3 gene of Japanese B encephalitis virus (JEV) is described for rapid, simple, and high-throughput detection of JEV. The amplification can be completed in 35 min under isothermal conditions at 63°C by employing a set of six primers targeting the NS3 gene of JEV. The RT-LAMP assay described demonstrated high sensitivity for detecting JEV, with a detection limit in swine samples of 8.13 PFU/ml. The specificity of the selected primer sets was established by cross-reactivity studies with pathogens that exhibit similar clinical signs and testing of samples from healthy animals. The clinical applicability of the RT-LAMP assay was validated using either spiked samples or samples from seasonal outbreaks. The comparative evaluation of the RT-LAMP assay revealed 79.59 % concordance with conventional RT-PCR targeting the E gene of JEV. The RT-LAMP assay reported here is a valuable tool for rapid real-time and high-throughput seasonal infection surveillance and quarantine after outbreak through blood sampling by using ordinary real-time PCR thermocyclers without purchasing an expensive Loopamp real-time turbidimeter.