Hirame rhabdovirus (HIRRV) as the cause of a natural disease outbreak in cultured black seabream (Acanthopagrus schlegeli) in Korea

In 2015, a high mortality rate of about 40 % was observed in black seabream (Acanthopagrus schlegeli) on a farm on the southern coast of Korea. Most of the diseased fish showed a hemorrhage of the mouth, pale liver, petechial hemorrhaging in the internal fat, and an enlarged spleen. Other than Alella sp., no parasites or bacteria were isolated from the diseased fish, and all of the tissue filtrates produced cytopathic effects (CPEs) in FHM and CHSE-214 cells. A polymerase chain reaction analysis revealed that the cell culture supernatants with CPE expressed specific 730-bp fragments for the hirame rhabdovirus (HIRRV) phosphoprotein gene. The nucleotide sequences showed a minimum of 95.8 % identity to five other known isolates of HIRRV, including CA-9703 and 8401-H from olive flounder (Paralichthys olivaceus) in Korea and Japan. An experimental challenge was conducted in which the virus was delivered by injection, and the cumulative mortalities of black seabream challenged with this new HIRRV isolate at 10^4.8 TCID₅₀/fish and 10^3.8 TCID₅₀/fish were 100 % and 20 %, respectively. This fulfilled Koch’s postulates and confirmed that HIRRV was the cause of disease and mortality for both the natural and experimental infection of black seabream.