Pathogenicity characterization, immune response mechanisms, and antiviral strategies analysis underlying a LMBV strain in largemouth bass ( Micropterus salmoides )

Largemouth bass virus (LMBV) always causes a high mortality rate and results in severe economic losses among cultivated largemouth bass. However, the pathogenic mechanism of LMBV is still unclear and there is still no specific antiviral treatment so far. The present study isolated and identified a highly pathogenic LMBV strain from diseased largemouth bass. The challenge experiments revealed that the infected juvenile fish suffered high mortality and severe histopathological changes in multiple tissues. Moreover, typical traits of the family Iridoviridae and apoptosis signals were observed using transmission electron microscopy (TEM) and fluorescence microscope, respectively. Transcriptomic analysis revealed that classical immune -related pathways and DNA replication -related pathways were enriched following LMBV infections, including immune response, phagosome, autophagy, DNA replication, and DNA metabolic process. Furthermore, we found that apoptosis increased LMBV replication, while, rapamycin-induced autophagy restricted viral replication by repressing apoptosis signal and improved the survival rate of largemouth bass. Taken together, these findings provide new insights into LMBV pathogenesis and antiviral strategies targeting autophagy-restricted virus replication in teleosts.