Viral hemorrhagic septicemia virus (VHSV) infectivity dynamics in olive flounder, Paralichthys olivaceus with injection and immersion challenge routes

Abstract Viral hemorrhagic septicemia virus infection can cause cumulative mortality as high as 90%, resulting in serious economic losses to the aquaculture industries. Mortality due to VHSV infection in olive flounder ( Paralichthys olivaceus ) appears at 8 to 15 °C. In this study, VHSV infectivity dynamics in six organs using intramuscular (IM) injection and immersion at water temperature of 10 and 13 °C were determined. Cumulative mortality of IM injection was 100 and 80% at 10 and 13 °C, respectively. The immersion group showed 50 and 10% cumulative mortality at 10 and 13 °C, respectively. The infectivity by IM injection was the highest in heart, spleen and kidney, followed brain, gill and muscle. With the immersion challenge route, the VHSV infectivity was the highest in muscle, kidney and brain, followed gill, spleen, and heart. VHSV infectivity on tested organs was swiftly increased at IM injection route than immersion challenge group. VHSV titer in the fish reared at 10 °C began to increase gradually from 3rd to 10th day by IM injection, and VHSV titer was assessed from 5th to 10th day by immersion challenge. At 13 °C, high values of VHSV infectivity were evaluated from all the tested organs in the IM injection, and tended to low infectivity ( 10  TCID 50 /mL) by immersion. Statement of relevance VHSV has been occurred in aquaculture such as olive flounder at 8–15 °C in Korea. Increasing fish rearing temperature reduced the cumulative mortality, and no mortality was observed in the fish reared at 17 °C regardless of VHSV-infected method. This study was performed to determine the different VHSV infectivity dynamics in olive flounder with two-challenge routes and VHSV infectious temperatures.