Genomic characterization and host immune responses to Decapod iridescent virus 1 (DIV1) in Macrobrachium rosenbergii

Decapod iridescent virus 1 (DIV1) is an emerging virus associated with high morbidity and mortality in crustaceans. In this study, we obtained a novel, highly pathogenic strain of DIV1, named DIV1-ZH, and performed whole-genome sequencing. The full length of the DIV1-ZH genome is 166,964 bp, with a GC content of 34.56 %. A total of 176 open reading frames (ORFs) were identified. Based on the phylogenetic analysis of the predicted major capsid protein (MCP), DIV1-ZH has a high homology with CQIV and SHIV. The 50 % lethal dose (LD₅₀) of the DIV1-ZH strain for M. rosenbergii at 72 h post-infection was estimated to be 1.30 × 10⁸ copies/mL, accompanied by characteristic clinical signs such as a white triangle at the rostrum base and gut emptiness. Viral load measurements showed rapid viral replication in hepatopancreas, gills, and intestine from 0 to 72 hpi. Histopathology revealed eosinophilic inclusions, nuclear pyknosis, parenchymal necrosis, and immune cell infiltration in the hepatopancreas. Electron microscopy confirmed the presence of icosahedral viral particles in the cytoplasm of hepatopancreatic and intestinal cells. In addition, qRT-PCR revealed significant upregulation of immune-related genes (TPI, RSAD2, Caspase3, Crustin, ALF2, ALF5) in infected tissues, indicating a robust host immune response. These results provide new insights into the molecular pathogenesis and host interactions of DIV1-ZH, and lay the groundwork for future prevention and control strategies in crustacean aquaculture.