Antiviral effects of esculin on largemouth bass ranavirus in vivo and in vitro

Largemouth bass ranavirus (LMBRaV), a double-stranded DNA (dsDNA) virus, leads to considerable mortality and significant economic impacts in the largemouth bass ( Micropterus salmoides ) aquaculture sector. This study evaluated and screened compounds from Chinese herbs for their activity against LMBRaV. Esculin exhibited the highest rate (73 %) of inhibition on LMBRaV major capsid protein (MCP) gene expression at a concentration of 60 mg/L in a cellular environment. It also significantly reduced the cytopathic effect (CPE), protecting infected cells from LMBRaV-induced nuclear damage and hindering LMBRaV infection by modulating viral entry mechanisms. For in vivo study, esculin increased the survival rate of LMBRaV-infected largemouth bass by 60.0 % and 53.3 %, in prevention experiment and treatment experiment, respectively. Concurrently, esculin significantly reduced viral loads and induced the upregulation of antiviral-associated genes, indicating its potential for immunoregulation. In summary, esculin holds potential for both preventing and treating LMBRaV infections in the aquaculture context.