An oral nervous necrosis virus vaccine that induces protective immunity in larvae of grouper (Epinephelus coioides)

Nervous necrosis virus (NNV) is a major viral pathogen that infects grouper and other fish at their larval stage. This infection often causes mortality rates higher than 99% and leads to total losses in the hatchery; hence, it is important to develop a preventive vaccine. However, the onset of this disease at the larval stage, with fish small and sensitive to handling makes the vaccination by injection or immersion impossible.In this report, we describe an oral NNV vaccine composed of Artemia-encapsulated recombinant E. coli expressing the NNV capsid protein gene. The NNV VP-containing Artemia were used to vaccinate grouper larvae. Immuno-histochemical analysis showed antigen to be delivered to, and absorbed in, the hindgut of grouper, and that it induced anti-NNV VP specific antibodies 7 days after vaccination, as assayed by ELISA. The vaccinated larvae showed a certain degree of protection after challenge with NNV achieving a Relative Percentage Survival of 64.2% and 69.5%. Oral NNV vaccine could effectively immunize grouper larvae. This method could be expanded to the development of other oral vaccines and for use in other fish species.