an inactivated bivalent vaccine effectively protects asian sea bass (lates calcarifer) against streptococcus iniae and vibrio harveyi infections

Co-infection with streptococcus iniae and vibrio harveyi is the major health challenge in asian sea bass (lates calcarifer) farms. vaccination is the most effective means of preventing these diseases, therefore, this study presents an efficacious bivalent vaccine against s. iniae and vibrio harveyi infections in asian sea bass. 420 juvenile sea bass (weighing 20.35 ± 0.37 g) were separated into seven equal groups in triplicates: group a: received phosphate-buffered saline as a control group, groups b and e: immunized with s. iniae vaccine via injection (s.i-inj) and immersion (s.i-im) routes, groups c and d: immunized with v. harveyi vaccine via immersion (v.h-im) and injection (v.h-inj) routes, and groups f and g: immunized with bivalent s. iniae+v. harveyi vaccine via immersion (bi-im) and injection (bi-inj) routes. the blood, serum, and gene samples were taken on 0, 30, and 60 days of the experiment and to measure specific and non-specific immune parameters, hematological and immune-related gene expression. the bacterial challenge test was used as a protective immunity measure at the end of the experiment. the results showed that the injection bivalent vaccine (s. iniae+v. harveyi) route was more effective than monovalent vaccines in enhancing the specific (antibody titer) and non-specific (lysozyme and complement activity, nitro blue tetrazolium (nbt) reduction, protein, and globulin level) immune responses. meanwhile, the vaccine efficacy and expression of il-10 and gm-cfc genes in the bivalent vaccine were significantly higher (p<0.05) than monovalent vaccines. these results indicate that the high immunogenicity and protective immunity provided by the bivalent vaccine (s. iniae+v. harveyi) strongly support its use as a general preventive measure against streptococosis and vibriosis in asian sea bass farms.