Validation of a loop-mediated isothermal amplification assay for visualised detection of wild-type classical swine fever virus

Loop-mediated isothermal amplification (LAMP) is a nucleic acid amplification method applied and adapted to the detection of a number of pathogens. A LAMP assay was developed for the specific detection of wild-type classical swine fever virus (CSFV). Based on an alignment of genomic sequences of pestiviruses available in GenBank, four primers were selected targeting six positions in the NS5B gene region of the viral genome. The assay was performed in a simple water bath at a constant temperature of 62 °C, and after adding SYBR Green I, the results were visualised by the naked eye. This assay allowed easy applicability in a laboratory that is equipped simply, or even on site, close to the outbreaks and under field conditions. For confirmation, the results could also be visualised under UV light or by separation of the amplified products on 2% agarose gels. The detection limit of the assay was 2.5 medium tissue culture infectious dose (TCID50). The assay was validated with 116 clinical samples from vaccinated swineherds and 53 blood samples from experimental infections, and the results were comparable to a real-time RT-PCR assay. In summary, the LAMP assay provides a simple, rapid, and sensitive tool for the detection of wild-type CSFV under field conditions.