Generation of a recombinant classical swine fever virus stably expressing the firefly luciferase gene for quantitative antiviral assay.

Classical swine fever (CSF), caused by classical swine fever virus (CSFV), is a highly contagious swine disease leading to significant economic losses worldwide. Vaccines are widely used to control the disease, and no CSFV-specific antivirals are currently available. To facilitate anti-CSFV molecule discovery, we developed a reporter virus CSFV-N(pro)Fluc stably expressing the firefly luciferase (Fluc) gene in the N(pro) gene. The reporter virus enabled more sensitive and convenient detection of the N(pro) protein expression and the viral replication by luciferase reporter assay than by traditional methods. The CSFV N(pro) protein was detectable as early as 4.5h post-infection. As a proof-of-concept for its utility in rapid antiviral screening, this reporter virus was used to quantify anti-CSFV neutralizing antibodies of 50 swine sera and to assess 12 small interfering RNAs targeting different regions of the CSFV genome. The results were comparable to those obtained by traditional methods. Taken together, the reporter virus CSFV-N(pro)Fluc represents a useful tool for rapid and quantitative screening and evaluation of antivirals against CSFV.