A simple colorimetric detection of porcine epidemic diarrhea virus by reverse transcription loop-mediated isothermal amplification assay using hydroxynaphthol blue metal indicator

•LAMP assay using HNB was developed for the rapid and visual detection of PEDV.•The LAMP assay is simple, rapid, highly specific and highly sensitive.•The assay will be a valuable tool for the rapid diagnosis of PEDV. A simple reverse transcription loop–mediated isothermal amplification combined with visual detection method (vRT–LAMP) assay was developed for rapid and specific detection of porcine epidemic diarrhea virus (PEDV) in this study, which overcomes the shortcomings of previously described RT–LAMP assays that require additional detection steps or pose a risk of cross-contamination. The assay results can be directly detected by the naked eye using hydroxynaphthol blue after incubating for 40 min at 62 °C. The assay specifically amplified PEDV RNA and no other viral nucleic acids. The limit of detection of the assay was less than 50 RNA copies per reaction, which was 100 times more sensitive than conventional reverse transcription polymerase chain reaction (RT-PCR) and comparable to real-time RT-PCR (RRT-PCR). In the clinical evaluation, the PEDV detection rate of vRT–LAMP was higher than that of RRT-PCR, showing 99 % concordance, with a kappa value (95 % confidence interval) of 0.97 (0.93–1.01). Considering the advantages of high sensitivity and specificity, simple and direct visual monitoring of the results, no possibility for cross–contamination, and being able to be used as low-cost equipment, the developed vRT–LAMP assay will be a valuable tool for detecting PEDV from clinical samples, even in resource-limited laboratories.