Evaluation of a Low-Temperature Immersion Immunization Strategy for the Infectious Spleen and Kidney Necrosis Virus Gene-Deleted Attenuated Vaccine.

Background: Infectious spleen and kidney necrosis virus (ISKNV) poses a significant threat to aquaculture sustainability, particularly affecting mandarin fish () and causing significant economic losses.

Methods: To address this challenge, this study developed an ISKNV Δ vaccine strain, where the gene was knocked out. Infection assays conducted at 28 °C showed that the knocking out the gene decreased the virulence of ISKNV and reduced lethality against mandarin fish by 26.7% compared to wild-type ISKNV. To further diminish residual virulence, the effect of low-temperature (22 °C) immersion immunization was evaluated.

Results: The results indicate that low temperature significantly diminished the virulence of the Δ vaccine strain, elevating the survival rate of mandarin fish to 90%. Furthermore, the vaccine strain effectively triggered the expression of crucial immune-related genes, such as , , , , , and , while inducing the production of specific neutralizing antibodies. Low-temperature immersion with Δ achieved a high relative percentage of survival of 92.6% ( = 30) in mandarin fish, suggesting the potential of Δ as a promising immersion vaccine candidate.

Conclusions: These findings contribute to advancing fish immersion vaccine development and demonstrate the importance and broad applicability of temperature optimization strategies in vaccine development. Our work carries profound implications for both the theoretical understanding and practical application in aquaculture disease control.