[Establishment and preliminary evaluation of recombinase aided isothermal amplification (RAA) assay for specific nucleic acid detection of Clonorchis sinensis]

New rapid detection by using a constant temperature method for avian leukosis viruses

The avian leukemia virus causes avian leukemia (AL), a severe immunosuppressive disease in chickens (ALV). Since the 1990s, the diversity of ALV subpopulations caused by ALV genome variation and recombination, and the complexity of the infection and transmission, with currently no effective commercial vaccine and therapeutic for ALV, has resulted in severe economic losses to the chicken business in various parts of the world. Therefore, as a key means of prevention and control, an effective, rapid, and accurate detection method is imperative. A new real-time reverse transcription recombinase-aided amplification (RT-RAA) assay for ALV with rapid, highly specific, low-cost, and simple operational characteristics have been developed in this study. Based on the amplification of 114 base pairs from the ALV P12 gene, real-time RT-RAA primers and a probe were designed for this study. The lowest detection line was 10 copies of ALV RNA molecules per response, which could be carried out at 39°C in as fastest as 5 min and completed in 30 min, with no cross-reactivity with Marek's disease virus, avian reticuloendothelial virus, Newcastle disease virus, infectious bronchitis virus, infectious bursal disease virus, infectious laryngotracheitis virus, and avian influenza virus. Furthermore, the kappa value of 0.91 (>0.81) was compared with reverse transcription–polymerase chain reaction (RT-PCR) for 44 clinical samples, and the coefficients of variation were within 5.18% of the repeated assays with three low-level concentration gradients. These results indicate that using a real-time RT-RAA assay to detect ALV could be a valuable method.

Development and Application of RAA Nucleic Acid Test Strip Assay and Double RAA Gel Electrophoresis Detection Methods for ASFV and CSFV

African swine fever (ASF) is an acute, severe and hemorrhagic infectious disease caused by African swine fever virus (ASFV) infecting domestic pigs and wild boars. Since the outbreak of the disease in China in 2018, it has brought a great impact on China’s pig industry. Classical swine fever (CSF) is an acute contact infectious disease of pigs caused by classical swine fever virus (CSFV) infection. Clinically, acute CSF usually shows persistent high fever, anorexia, extensive congestion and bleeding of the skin and mucosa, which are similar to ASF. It is of great significance to prevent, control and accurately detect ASF and CSF in pig farms. In this study, Recombinase aided amplification (RAA) technology combined with a nucleic acid test strip (RAA-strip) was established for simple and specific detection of ASFV/CSFV. The sensitivity and preliminary clinical application results showed that the RAA test strip established in this study could detect recombinant plasmids containing ASFV/CSFV gene fragments as low as 103 copies/µL. The minimum detection limits of virus DNA/cDNA were 10 and 12 pg respectively, and there was no cross-reaction with other porcine viruses. The specificity of the method was good. We used 37–42 clinical samples to evaluate the performance of our established method, and the positive concordance rates with conventional PCR were 94.1 and 57.1%, respectively. In addition, ASFV and CSFV double RAA agarose gel electrophoresis detection methods were established. The results showed that the method had good specificity. The detection limit of this method is 106 copies for ASFV p72 gene recombinant plasmid and 105 copies for CSFV NS5B Gene recombinant plasmid. The use of this method for clinical material detection was consistent with the PCR method. In summary, the developed method of RAA-strip assay for ASFV and CSFV realized the visual detection of pathogens, and the developed method of dual RAA agarose gel electrophoresis assay for ASFV and CSFV realized the simultaneous detection of two pathogens in one reaction, with good specificity, high sensitivity and rapid reaction rate, which was expected to be clinically feasible for the differential diagnosis of ASF and CSF provided technical support.