Abstract
Background: Grass carp (Ctenopharyngodon idella) hemorrhagic disease (GCHD) is a devastating disease that leads to substantial economic losses in the freshwater aquaculture industry. Results: In this study, we investigated an outbreak of GCHD in large-scale grass carp and identified GCRV-II infection. Notably, hematoxylin and eosin (H&E) staining showed severe histopathological changes in the spleen, head kidney, gill, and gut. Furthermore, we sequenced the entire genome of the viral isolate, and multiple sequence alignment and phylogenetic tree analysis indicated that it represents a novel strain of GCRV-II, provisionally named GCRV-YX246. Finally, artificial infection experiments confirmed the strong virulence, high mortality, and severe pathological damage caused by GCRV-YX246, as demonstrated through artificial infection. Conclusions: A novel reovirus from large-scale grass carp cultured in China was identified. The discovery of this novel GCRV-II strain enhances our understanding of GCRV-II biology and provides valuable insights for developing more effective prevention strategies for GCHD.