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.