Development of oral vaccine using calcium phosphate nanoparticles conjugated with outer membrane protein of Aeromonas hydrophila in Oreochromis niloticus (Tilapia).

The development of an effective vaccine for Oreochromis niloticus (Tilapia) against Aeromonas hydrophila, a major pathogen in aquaculture, is crucial for enhancing disease resistance and sustainability in fish farming. This study investigates the use of calcium phosphate (CaP) nanoparticles conjugated with the outer membrane protein (OMP) of A. hydrophila as a novel vaccine delivery system, referred to as CaP-OMP. Specific IgM response and Opsonophagocytic killing activity (OPKA) demonstrated improved Aeromonas clearance in vaccinated fish. Furthermore, immune gene expression analysis was performed using quantitative PCR (qPCR) to monitor the expression levels of key immune genes. The results showed a significant upregulation of these immune markers in the CaP-OMP vaccinated groups compared to that of OMP vaccinated groups, suggesting enhanced activation of both the innate and adaptive immune responses. The protective efficacy of the vaccine was demonstrated by a relative percentage survival (RPS) of 85.7 %, indicating significantly lower mortality in the CaP-OMP vaccinated group compared to controls following a challenge study with virulent A. hydrophila. Overall, This oral vaccine approach offers a non-invasive alternative for fish immunization and underscores the potential of calcium phosphate nanoparticles conjugated with outer membrane proteins as a promising vaccine platform for aquaculture. The enhanced immune response, combined with targeted antigen delivery, positions this strategy as a viable tool for controlling A. hydrophila infections in Tilapia, contributing to improved disease management in aquaculture.