Humoral immune response in Asian seabass vaccinated with inactivated and recombinant viral nervous necrosis vaccine

Abstract

Viral nervous necrosis is a serious viral disease of marine and brackishwater finfish hatcheries. The red-spotted grouper nervous necrosis virus (RGNNV) is the most prevalent genotype among fishes in tropical and temperate regions. RGNNV was propagated in SSN-1 cell line and inactivated using BEI. The capsid protein of RGNNV was cloned and expressed in Escherichia coli and purified. Inactivated and recombinant VNN vaccines were produced by emulsifying the antigen with commercial adjuvant and administered to Asian seabass, Lates calcarifer, fingerlings and broodstock intraperitoneally. The immune response was assessed at regular intervals by indirect ELISA. The maternal antibodies in one-day post-hatch larvae obtained from the vaccinated and control broodstock were assessed by indirect ELISA. The larvae were subjected to challenge with virulent RGNNV and the relative per cent survival (RPS) was estimated. The efficacy of the vaccine was also assessed under field conditions. The recombinant vaccine produced significantly higher specific antibody levels than the inactivated vaccine in fingerlings and broodstock and the immune response was dose-dependent. Recombinant vaccine at 50 and 100 μg/fish produced significantly higher antibody levels and immune response could be observed as early as one-week post vaccination. Vaccinated broodstock produced larvae with maternal antibodies and had higher RPS when challenged at 18 days post-hatch. The vaccine produced a significant immune response even under field conditions. The vaccine can be used to vaccinate broodstock to reduce loss due to VNN in early larval stages.