Antigenic characterization of a marine fish iridovirus from grouper, Epinephelus spp.

Iridoviruses, recognized as causative agents of serious systemic diseases, have been identified from more than 20 fish species. Antigenic properties of a pathogenic iridovirus isolated from grouper, Epinephelus spp., in Singapore (SGIV) were investigated using rabbit IgG against the virus. Antisera were prepared by immunization of rabbit with purified virions. The rabbit IgG was purified from antiserum using a protein A-agarose column and adsorbed onto acetone-dried grouper (GP) cells. The viral surface-exposed antigens were visualized by a combination of immunogold transmission electron-microscopy and by indirect immunofluorescence, and the viral antigenic related proteins were discriminated by Western blot. The cross immunofluorescence assay showed that the grouper virus isolate was serologically close to viruses of the genus Ranavirus of family Iridoviridae. The viral antigens were detected from virus infected-cell cultures as early as 4 h of post infection using IFAT, and could be detectable in virus-infected fish blood as early as 3 days post infection. Immuno-dot assays revealed that the rabbit anti-SGIV IgG allowed sensitive detection of SGIV viral antigens. This study will facilitate the development of diagnostic techniques and vaccines for grouper iridovirus.