Optimization and application of a DNA-launched infectious clone of equine arteritis virus

Development of an improved dual-promoter-based reverse genetics system for emerging Senecavirus A

Senecavirus A (SVA), a recently emerging picornavirus, poses a great threat to the swine industry because it causes swine idiopathic vesicular disease and epidemic transient neonatal losses. Thus far, the progress in SVA viral pathogenesis studies and vaccine development remains sluggish, and an available and convenient reverse genetics system would undoubtedly promote relevant research. Herein, we established an improved universal dual-promoter reverse genetics system with an SVA-specific hammerhead ribozyme and hepatitis delta virus ribozyme at both terminals of the viral genome; this system could be applied to rescue all SVA strains by both eukaryotic and prokaryotic RNA polymerase systems. The genome of the clone-derived Chinese field strain CH/HeN-2018 was assembled into the universal vector pcDNA-rSVAuni through the Gibson assembly technique. Moreover, two silent mutations, G6848C and C7163 G, were separately engineered into the full-length cDNA clone with one step site-directed mutagenesis to create a KpnI restriction enzyme site, which served as a unique genetic marker. The viruses, designated rCH/HeN-2018-T7, rCH/HeN-2018-CMV, rCH/HeN-2018-6484 m and rCH/HeN-2018-7163 m, were successfully rescued through both CMV- and T7-dependent pathways, and their biological properties were further evaluated. The results showed that all four viruses grew rapidly in PK-15 cells and exhibited viral titers and growth kinetics similar to those of parental wtCH/HeN-2018. The established reverse genetics system is easily operated and can be applied to rescue all SVA strains in a short time, which will be helpful for studying SVA biology, including viral pathogenesis, antiviral therapies and vaccine development.

Development of an antigen-capture ELISA for the quantitation of equine arteritis virus in culture supernatant

Quantitation of virions is one of the important indexes in virological studies. To establish a sensitive and rapid quantitative detection method for equine arteritis virus (EAV), an antigen-capture enzyme-linked immunosorbent assay (AC-ELISA) was developed by using two EAV nucleoprotein monoclonal antibodies (mAbs), 2B9 and 2B3, prepared in this study. After condition optimization, mAb 2B9 was used as the capture antibody, and HRP-labeled 2B3 was chosen as the detecting antibody. The AC-ELISA had a good standard curve when viral particles of the Bucyrus EAV strain were used as a reference standard. The detection limit for the Bucyrus EAV strain was 36 PFU, and the method had a good linear relationship between 72-2297 PFU. The AC-ELISA could specifically detect the Bucyrus EAV strain and had no cross-reaction with other equine viruses. The sensitivity of the AC-ELISA was much higher than that of a western blotting assay but lower than that of a real-time PCR method. However, as a quantitative antigen detection method, the sensitivity of the AC-ELISA was approximately 300 times than the western blotting assay. Furthermore, the AC-ELISA assay could be successfully used in quantification of viral content in an in vitro infection assay, such as a one-step growth curve of EAV, as well as in a transfection assay, such as virus rescue from an infectious cDNA clone of EAV. These results show that the AC-ELISA established in this study is a good alternative for antigen detection of EAV, being a simple, convenient and quantitative detection method for EAV antigens.