Reverse transcription loop-mediated isothermal amplification assays for rapid identification of eastern and western strains of bluetongue virus in India

•Seg-1 based RT-LAMP assays for eastern and western Bluetongue virus (BTV) strains circulating in India have been developed.•The assays detected BTV RNA with high specificity and efficiency.•The analytical sensitivity of the RT-LAMP assays is equal to real-time RT-PCR.•The RT-LAMP assays can detect BTV RNA within 60-90 min.•RT-LAMPs are rapid, easy and can be adapted as a pen-side test for field use.

Bluetongue virus (BTV) infects all ruminants, including cattle, goats and camelids, causing bluetongue disease (BT) that is often severe in naïve deer and sheep. Reverse-transcription-loop-mediated-isothermal-amplification (RT-LAMP) assays were developed to detect eastern or western topotype of BTV strains circulating in India. Each assay uses four primers recognizing six distinct sequences of BTV genome-segment 1 (Seg-1).The eastern (e)RT-LAMP and western (w)RT-LAMP assay detected BTV RNA in all positive isolates that were tested (n = 52, including Indian BTV−1, −2, −3, −5, −9, −10, −16, −21 −23, and −24 strains) with high specificity and efficiency. The analytical sensitivity of the RT-LAMP assays is comparable to real-time RT-PCR, but higher than conventional RT-PCR. The accelerated eRT-LAMP and wRT-LAMP assays generated detectable levels of amplified DNA, down to 0.216 fg of BTV RNA template or 108 fg of BTV RNA template within 60-90 min respectively. The assays gave negative results with RNA from foot-and-mouth-disease virus (FMDV), peste des petits ruminants virus (PPRV), or DNA from Capripox viruses and Orf virus (n = 10), all of which can cause clinical signs similar to BT. Both RT-LAMP assays did not show any cross-reaction among themselves. The assays are rapid, easy to perform, could be adapted as a 'penside' test making them suitable for 'front-line' diagnosis, helping to identify and contain field outbreaks of BTV.