WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2024 63 (CONTINUED ON PAGE 64) Results and discussion The results of this study indicated that monovalent and bivalent inactivated vaccines elicit specific immune antibody responses in systemic and mucosal systems. Following vaccination, all treatment groups displayed similar serum and mucosal antibody response patterns with moderately increasing levels from day 0 to day 21. The peak IgM titer in both the serum and mucosal systems was predominantly observed after boosting on day 21 and was significantly higher than those in the control group (see Figures 2 and 3). Interestingly, while the monovalent inactivated vaccines exhibited a significantly higher specific antibody titer in both serum and mucus compared to the bivalent vaccine (likely due to antigen competition from the two bacteria), the high RPS values observed in the laboratory challenge for the bivalent vaccine (ranging from 70% to 85%) were not significantly different from those of the tested monovalent vaccines (ranging from 70% to 75%) (see Figure 4). This suggests that vaccine efficacy may not solely rely on IgM levels but also on other factors of the adaptive immune system. The rapid increase in specific IgM levels following the booster with the second inactivated vaccine indicated the induction of memory cells in the immunized fish, although the antibody levels in the serum were higher than in the mucus. It is important to note that producing monovalent vaccines might not be feasible, especially when dealing with multiple bacterial strains. Bivalent vaccines offer significant advantages Technology (AIT) in Thailand, attempted to develop and evaluate monovalent and bivalent vaccines against Sa and Si infections in Asian seabass, assessing systemic and mucosal antibody responses and protective efficacy in laboratory challenges. This approach holds promise to prevent streptococcosis in farmed Asian seabass. Study setup Fish were randomly assigned to four groups, each containing 150 individuals in freshwater. Before vaccination, fish were anesthetized using 20 ppm of clove oil. Subsequently, each fish received an intraperitoneal (IP) injection of 0.1 mL of prepared vaccines using a 23-G needle. A booster with the corresponding water-based vaccine was administered on day 21 post-primary immunization through injection in the same manner. Vaccinated fish were kept until 63 days before undergoing challenge tests. Mucus and serum samples were collected from six fish per group on days 0, 7, 14, 21, 28, 35, 42, 49, 56, and 63 post-vaccinations to assess antibody responses. Two months after vaccination, Asian seabass were challenged with Sa and Si in two replications by IP injection to evaluate the efficacy of the vaccines, followed by calculation of relative percent survival (RPS). Laboratory analyses of the samples were conducted at Centex Shrimp (BIO-TEC/Mahidol University), Thailand. FIGURE 2. Systemic antibody responses in Asian seabass post-vaccination with monovalent inactivated vaccines (A) and bivalent vaccines (B), determined by ELISA, at 1:256 dilutions, with measurements taken at OD 450 nm. Significant differences (P < 0.05) within the same days are denoted by capital letters, while significant differences between days are indicated by lowercase letters. FIGURE 3. Mucosal antibody responses in Asian seabass post-vaccination with monovalent inactivated vaccines (C) and bivalent vaccines (D), determined by ELISA, at 1:8 dilutions, with measurements taken at OD 450 nm. Significant differences (P < 0.05) within the same days are denoted by capital letters, while significant differences between days are indicated by lowercase letters.
RkJQdWJsaXNoZXIy MjExNDY=