Evaluation of a Low-Temperature Immersion Immunization Strategy for the Infectious Spleen and Kidney Necrosis Virus orf037l Gene-Deleted Attenuated Vaccine

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

Methods: To address this challenge, this study developed an ISKNV Δorf037l vaccine strain, where the orf037l gene was knocked out. Infection assays conducted at 28 °C showed that the knocking out the orf037l 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 Δorf037l 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 IFN-h, IL-1, IκB, Mx, TNF-α, and Viperin, while inducing the production of specific neutralizing antibodies. Low-temperature immersion with Δorf037l achieved a high relative percentage of survival of 92.6% (n = 30) in mandarin fish, suggesting the potential of Δorf037l 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.