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

Classification of Multiple DNA Dyes Based on Inhibition Effects on Real-Time Loop-Mediated Isothermal Amplification (LAMP): Prospect for Point of Care Setting

LAMP has received great interest and is widely utilized in life sciences for nucleic acid analysis. To monitor a real-time LAMP assay, a fluorescence DNA dye is an indispensable component and therefore the selection of a suitable dye for real-time LAMP is a need. To aid this selection, we investigated the inhibition effects of twenty-three DNA dyes on real-time LAMP. Threshold time (T_t) values of each real-time LAMP were determined and used as an indicator of the inhibition effect. Based on the inhibition effects, the dyes were classified into four groups: (1) non-inhibition effect, (2) medium inhibition effect, (3) high inhibition effect, and (4) very high inhibition effect. The signal to noise ratio (SNR) and the limit of detection (LOD) of the dyes in groups 1, 2, and 3 were further investigated, and possible inhibition mechanisms of the DNA dyes on the real-time LAMP are suggested and discussed. Furthermore, a comparison of SYTO 9 in different LAMP reactions and different systems is presented. Of the 23 dyes tested, SYTO 9, SYTO 82, SYTO 16, SYTO 13, and Miami Yellow were the best dyes with no inhibitory effect, low LOD and high SNR in the real-time LAMP reactions. The present classification of the dyes will simplify the selection of fluorescence dye for real-time LAMP assays in point of care setting.

Detection and differentiation of Japanese encephalitis virus genotype I and genotype III by reverse transcription loop-mediated isothermal amplification combined with restriction fragment length polymorphism

Japanese encephalitis (JE), which is a mosquito-borne arboviral infection, is the leading cause of viral encephalitis in Asian countries. The causative agent of JE is Japanese encephalitis virus (JEV), in which the predominant genotype has changed from genotype III (G III) to genotype I (G I). However, a method for the rapid differentiation between JEV G I and G III remains unavailable. This study aimed to establish a rapid JEV genotyping method using reverse transcription loop-mediated isothermal amplification (RT-LAMP). An Spe I site, which was located in the target sequence (C gene) of JEV G III strains but not in JEV G I strains, was selected as the RT-LAMP target. After testing 64 specimens, results showed that RT-LAMP can detect and differentiate JEV G I and G III specifically. Thus, a novel RT-LAMP system for the rapid detection and differentiation of JEV G I and G III was developed successfully.

Rapid genome detection of Schmallenberg virus and bovine viral diarrhea virus by use of isothermal amplification methods and high-speed real-time reverse transcriptase PCR

Over the past few years, there has been an increasing demand for rapid and simple diagnostic tools that can be applied outside centralized laboratories by using transportable devices. In veterinary medicine, such mobile test systems would circumvent barriers associated with the transportation of samples and significantly reduce the time to diagnose important infectious animal diseases. Among a wide range of available technologies, high-speed real-time reverse transcriptase quantitative PCR (RT-qPCR) and the two isothermal amplification techniques loop-mediated isothermal amplification (LAMP) and recombinase polymerase amplification (RPA) represent three promising candidates for integration into mobile pen-side tests. The aim of this study was to investigate the performance of these amplification strategies and to evaluate their suitability for field application. In order to enable a valid comparison, novel pathogen-specific assays have been developed for the detection of Schmallenberg virus and bovine viral diarrhea virus. The newly developed assays were evaluated in comparison with established standard RT-qPCR using samples from experimentally or field-infected animals. Even though all assays allowed detection of the target virus in less than 30 min, major differences were revealed concerning sensitivity, specificity, robustness, testing time, and complexity of assay design. These findings indicated that the success of an assay will depend on the integrated amplification technology. Therefore, the application-specific pros and cons of each method that were identified during this study provide very valuable insights for future development and optimization of pen-side tests.

Development of a reverse transcription-loop-mediated isothermal amplification (RT-LAMP) system for rapid detection of HDV genotype 1

The object of this study was to develop a reverse transcription-loop-mediated isothermal amplification (RT-LAMP) assay for detecting hepatitis D virus (HDV) genotype 1. With an alignment analysis, a highly conserved sequence (nt 820-1020) was chosen as a suitable target to design LAMP primers. The optimal condition of RT-LAMP was a 25-μl reaction volume, which consists of the following components: 1·6 μmol l⁻¹ each of FIP and BIP, 0·2 μmol l⁻¹ each of F3 and B3, 1·5 μmol l⁻¹ dNTPs, 4 mmol l⁻¹ MgSO₄, 8 U Bst DNA polymerase, 2U M-MLV and 2 μl extracted RNA sample. The amplification reaction was carried out at 65°C for 50 min. Compared with conventional qualitative or quantitative real-time reverse transcription polymerase chain reaction, the results of RT-LAMP indicated a 1000-fold increase in sensitivity for detecting HDV. There was no cross-reaction for the RT-LAMP method between HDV 1 and HIV, HAV, HBV, HCV and HEV.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results indicate that RT-LAMP is a simple, rapid, specific, highly sensitive and cost-effective, field-based method for detecting HDV 1. The RT-LAMP assay is an acceptable alternative to diagnose the HDV genotype 1 and to investigate its epidemiology for clinical laboratories lacking specialized equipments.