Evaluation of the immunoprotective effects of two Infectious Spleen and Kidney Necrosis Virus (ISKNV) oral vaccines on largemouth bass.

Abstract

The high pathogenicity and mortality rate of infectious spleen and kidney necrosis virus (ISKNV) have significantly threatened the development of largemouth bass aquaculture in China. Oral vaccines are urgently needed in the aquaculture industry. This study successfully constructed recombinant strains EBY100/pYD1-ISKNV and WB600/pEB03-CotC-ISKNV that can express ISKNV MCP using surface display platforms of Saccharomyces cerevisiae and Bacillus subtilis. Oral immunization of largemouth bass was conducted to evaluate the protective efficacy of both oral vaccines. Following oral immunization, the relative expression levels of IFN-γ, TNF-α, IL-1, CD8α, MHC-Ⅰ, IgM, and IgT in the spleen and head kidney tissues of largemouth bass and serum-specific antibody levels in the E-I and W-I groups were significantly higher compared to the PBS group. Following ISKNV challenge, the survival rate of the E-I group and W-I group were 53.3 % and 50.0 %, respectively, with the relative percent survival (RPS) of 30.0 % and 25.0 %. Viral load detection revealed significantly lower viral loads in the E-I and W-I groups compared to the PBS group. Histopathological examination of tissue sections revealed that no obvious lesions were observed in the liver, spleen, and head kidney of largemouth bass immunized with either oral vaccine compared to the PBS group that exhibited severe lesions in the liver, spleen, and head kidney. In summary, oral administration of EBY100/pYD1-ISKNV and WB600/pEB03-CotC-ISKNV activated both innate and adaptive immune responses in largemouth bass, demonstrating efficacy in preventing ISKNV infection. The two oral vaccines developed in this study provide novel strategies for controlling ISKNV.