Gamma-Ray Inactivation of Betanodavirus: Antigen Preservation and Vaccine Potential

Viral nervous necrosis (VNN), caused by Betanodavirus , poses a significant challenge to Mediterranean aquaculture, especially for European sea bass ( Dicentrarchus labrax ). Conventional chemical inactivation methods often compromise viral immunogenicity or introduce cytotoxic effects, highlighting the need for safer and more effective alternatives for virus inactivation. This study explores gamma irradiation as an alternative approach to inactivate reassortant Betanodavirus (RGNNV/SJNNV) while preserving its antigenic properties for vaccine development. Virus samples were exposed to gamma radiation doses ranging from 5 to 60 kGy. The D₁₀ value (7.55 kGy), the inactivation dose (55.35 kGy), and the gamma radiation dose (70.45 kGy) ensuring a Sterility Assurance Level (SAL) of the Tunisian Betanodavirus were established based on viral infectivity reduction. In vitro immunological assays, including enzyme-linked immunosorbent assay (ELISA) demonstrated that the structural proteins of the virus retained antigenicity post-irradiation, as evidenced by consistent IgM antibody recognition titers. Transmission electron microscopy confirmed that irradiation did not alter the viral shape or structural integrity. The addition of trehalose as a radioprotectant prior to irradiation did not enhance the immunogenic response, as measured by ELISA. Notably, the highest immune response characterized by 92% IgM-positive individuals, was observed in fish vaccinated with irradiated virus in absence of trehalose. These results highlight gamma irradiation as a promising, non-chemical method for the development of safe and immunogenic inactivated vaccines against Betanodavirus in aquaculture.