Identification of infectious spleen and kidney necrosis virus from farmed barramundi Lates calcarifer in Thailand and study of its pathogenicity

Infectious spleen and kidney necrosis disease (ISKND) is one of major viral diseases in marine fish species. Here, we isolated infectious spleen and kidney necrosis virus (ISKNV) from diseased barramundi in Thailand and evaluated its pathogenicity with intramuscular challenge in naïve barramundi. ISKNV infection in grunt fin (GF) cells was observed within 14 days post inoculation (dpi) by immunofluorescence assay using a monoclonal antibody against red seabream iridovirus (M10). Phylogenetic analysis of the major capsid protein amino acid sequences revealed that two ISKNV isolates belong to genotype I ISKNV. In the challenge test, 35% mortality was observed in fish intramuscularly injected with 10-0.55 TCID50/fish, whereas higher mortalities, 44% and 77%, were observed after injection with 100.55 and 101.55 TCID50/fish, respectively. These results demonstrate dose dependent virulence of ISKNV in barramundi. This study is the first report of ISKNV in farmed barramundi in Thailand. A high susceptibility of barramundi to the infection may suggest an immediate need for control of the emerging disease in barramundi culture including effective vaccine.