Reporter Flaviviruses as Tools to Demonstrate Homologous and Heterologous Superinfection Exclusion

Binjari virus (BinJV) is a lineage II or dual-host affiliated insect-specific flavivirus previously demonstrated as replication-deficient in vertebrate cells. Previous studies have shown that BinJV is tolerant to exchanging its structural proteins (prM-E) with pathogenic flaviviruses, making it a safe backbone for flavivirus vaccines. Here, we report generation by circular polymerase extension reaction of BinJV expressing zsGreen or mCherry fluorescent protein. Recovered BinJV reporter viruses grew to high titres (10(7-8) FFU/mL) in Aedes albopictus C6/36 cells assayed using immunoplaque assays (iPA). We also demonstrate that BinJV reporters could be semi-quantified live in vitro using a fluorescence microplate reader with an observed linear correlation between quantified fluorescence of BinJV reporter virus-infected C6/36 cells and iPA-quantitated virus titres. The utility of the BinJV reporter viruses was then examined in homologous and heterologous superinfection exclusion assays. We demonstrate that primary infection of C6/36 cells with BinJV(zsGreen) completely inhibits a secondary infection with homologous BinJV(mCherry) or heterologous ZIKV(mCherry) using fluorescence microscopy and virus quantitation by iPA. Finally, BinJV(zsGreen) infections were examined in vivo by microinjection of Aedes aegypti with BinJV(zsGreen). At seven days post-infection, a strong fluorescence in the vicinity of salivary glands was detected in frozen sections. This is the first report on the construction of reporter viruses for lineage II insect-specific flaviviruses and establishes a tractable system for exploring flavivirus superinfection exclusion in vitro and in vivo.

Automated summary

In this study, we generated reporter viruses of Binjari virus (BinJV) expressing fluorescent proteins, which showed high growth in insect cells and could be quantified using fluorescence detection. We found that primary infection of BinJV(zsGreen) completely inhibited secondary infection of homologous or heterologous viruses. Furthermore, strong fluorescence signals were detected in the vicinity of salivary glands in vivo. This study establishes a tractable system for exploring flavivirus superinfection exclusion in vitro and in vivo.