Dual protection against grouper Rana-Iridovirus (GIV-R) and nervous necrosis virus (NNV) by novel GIV-R-Δ51-NNV-CP chimeric vaccine candidates.

Grouper Rana-iridovirus (GIV-R) and nervous necrosis virus (NNV) are two distinct yet very important causative agents in several fish species. However, as of now, no effective treatment has been developed to simultaneously prevent these two pathogens. In this study, we developed GIV-R-NNV chimeric vaccine candidates by using GIV-R to chimerically express the full length and P domain of the coat protein of NNV, and designated as GIV-R-Δ51-NNV-CP-FL, GIV-R-Δ51-NNV-CP-P, respectively. Firstly, the orf51 deletion recombinant GIV-R (GIV-R-Δ51) was constructed and characterized. The results showed that GIV-R-Δ51 was a partially attenuated mutant. Based on the recombinant site of orf51, GIV-R-Δ51-NNV-CP-FL and GIV-R-Δ51-NNV-CP-P were constructed and robust data demonstrated that both chimeric mutants were well constructed and also showed partially attenuated. Finally, the water-in-oil (W/O) formulation of the inactivated GIV-R-Δ51-NNV-CP-FL and GIV-R-Δ51-NNV-CP-P vaccines were prepared and immune-protection effects were tested. As results, both chimeric vaccines conferred approximately 60 % (N = 40) and 90 % (N = 50) relative protections against GIV-R in grouper and Asian sea bass, respectively. The significant elevations of anti-NNV specific antibodies were determined, and the in vitro neutralizing effects were also measured. All these results showed that the both chimeric vaccines work effectively to prevent GIV-R and NNV. Taken together, two chimeric vaccine candidates against GIV-R and NNV were firstly constructed and characterized, which showed potent efficacies in preventing two dangerous viral diseases in cultured fish.