Oral immunization of fish against iridovirus infection using recombinant antigen produced from rice callus

Fish iridoviruses cause systemic diseases with high morbidity and mortality in various species of wild and farm-raised fish, resulting in severe economic losses, and no large-scale protective vaccine program or therapy is currently available. In this study, we expressed a recombinant major capsid protein (rMCP) of rock bream iridovirus in transgenic rice callus. The rMCP in lyophilized rice callus powder was added to feed to induce intestinal mucosal immunity for protection against and/or to reduce the severity of the iridovirus infection. We found that fish (Rock bream) immunized orally with rMCP underwent successful induction of antibodies (P < 0.05) and were protected (P < 0.001) against viral challenge. These results suggest that oral administration of rMCP as an antigen is a useful method to implement a vaccine program against iridovirus and other marine viral diseases.