Isolation and identification of a novel highly pathogenic marine RSIV genotype strain from Siniperca chuatsi
In this study, a virus strain was isolated from diseased Siniperca chuatsi collected from a fish farm in Jiangsu Province, China. This virus could proliferate efficiently in mandarin fish embryo cells (MFF) and significantly induce the expression of multiple host immune-related genes. Genome sequencing revealed that its complete genome is 112,278 bp in length with a GC content of 53.17%, containing 124 open reading frames (ORFs). Phylogenetic analysis showed that this strain clustered within the RSIV genotype clade and was designated as RSIV-2024. Sequence similarity analysis indicated that it shared 97.00%-99.70% nucleotide similarity with RSIV genotype strains. Recombination analysis demonstrated that it possesses a chimeric genomic structure with two highly credible recombination events. Artificial infection experiments showed that RSIV-2024 is highly pathogenic to Siniperca chuatsi, resulting in a cumulative mortality rate of 100%. Quantitative real-time PCR (qPCR), histopathological examination, and transmission electron microscopic observation revealed that the spleen was the main target organ, with the highest viral load, severe tissue damage in the infected spleen, and a large number of icosahedral viral particles with a diameter of 120 nm +- 5 nm could be observed. This study identified a novel highly pathogenic RSIV genotype strain infecting Siniperca chuatsi, suggesting a trend of marine pathogens spreading to freshwater environments, which provides important references for the monitoring and prevention of diseases in Siniperca chuatsi aquaculture.