Isolation and characterization of the Japanese flounder (Paralichthys olivaceus) lymphocystis disease virus

Japanese flounder lymphocystis disease virus (JF-LCDV) was isolated from lymphocystis cells from Japanese flounder (also known as olive flounder and hirame) Paralichthys olivaceus using a natural embryo (HINAE.) cell line. Of the 39 fish cell lines tested, only the HINAE cell line exhibited a cytopathic effect. The JF-LCDV reached a titer of 1050 tissue culture infectious dose with 50% endpoint per milliliter. By electron microscopy, the virus particles were determined to be icosahedral in shape and approximately 250 nm in diameter, Virus propagated in cell culture was sensitive to low pH, diethyl ether, and ultraviolet irradiation. Infectivity was reduced by pretreatment of the virus with rabbit anti-JF-LCDV serum and Japanese flounder sera that were obtained from fish convalescing from lymphocystis disease. By polymerase chain reaction, the same single band of DNA encoding a portion of the major capsid protein was amplified from virus propagated in vitro and virus obtained directly from lymphocystis cells. Although the cell-culture-replicated virus was not pathogenic to Japanese flounder by intramuscular injection, these fish appeared resistant to reinfection.