Reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay for the visual detection of European and North American porcine reproductive and respiratory syndrome viruses

A reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay for visual detection of European (EU) and North American (NA) porcine reproductive and respiratory syndrome viruses (PRRSVs) were established and evaluated with reference PRRSV strains and clinical samples. The assay was performed in two reaction tubes containing each set of primers specific for EU or NA-PRRSV at 58 °C for 40 min, and the results could be visually detected by the naked eye, using hydroxynaphthol blue dye. The detection limit of the assay was 1 or 0.1 TCID₅₀/0.1 mL for EU or NA PRRSV, respectively, which was comparable to that of the previously described real-time RT-PCR (qRT-PCR). The detection rate of the assay on 130 field samples was 72.3%, relatively higher than that of qRT-PCR (70.8%), and there was high overall percentage agreement between the two assays. The high specificity, sensitivity, and reliability of the RT-LAMP assay described in this study renders it useful for the rapid and differential diagnosis of EU and NA PRRSVs, even in under-equipped laboratories.