Oral immunization of olive flounder (Paralichthys olivaceus) with recombinant live viral hemorrhagic septicemia virus (VHSV) induces protection against VHSV infection

作者：Kim Min Sun; Kim Dong Soo; Kim Ki Hong^*

来源：Fish & Shellfish Immunology, 2011, 31(2): 212-216.

DOI：10.1016/j.fsi.2011.05.003

• Recombinant VHSV
• rVHSV-Delta
• NV-EGFP
• Live vaccine
• Oral vaccine

A recombinant viral hemorrhagic septicemia virus (rVHSV-Delta NV-EGFP) that has enhanced green fluorescent protein (EGFP) gene instead of NV gene was previously generated using reverse genetics technology. In this study, potential of the rVHSV-Delta NV-EGFP to be used as a live oral vaccine candidate was assessed. The presence of the recombinant virus in internal organs of orally administered olive flounder (Paralichthys olivacetts) was analyzed by semi-quantitative RT-PCR. Although the recombinant VHSV-specific band was detected only when the number of PCR cycle was increased to 35, the band was detected from internal organs, such as kidney, spleen, and liver of fish that were reared at either 15 degrees C or 20 degrees C till even 20 days, suggesting that a few orally administered rVHSV-Delta NV-EGFP might be transported to internal organs, and might keep weak replication ability in the organs. VHSV-neutralizing activity was induced by oral immunization of olive flounder with the NV gene knock-out recombinant VHSV not only in skin and intestinal mucus but also in serum, suggesting that mucosal and systemic adaptive immune responses were elicited by oral immunization. In challenge experiment, groups of fish immunized with 10(4), 10(5), and 2 x 10(5) PFU of rVHSV-Delta NV-EGFP/fish showed 25%, 50%, and 70% of relative percent survival (RPS), respectively. The RPSs were elevated to 60%, 75%, and 90% by a boost immunization in fish boost immunized with 10(4), 10(5), and 2 x 10(5) PFU of rVHSV-Delta NV-EGFP, respectively. The cumulative mortality of fish in the control groups was 100%. Conclusionly, the present results demonstrate that the NV gene knock-out recombinant VHSV administered orally to olive flounder can induce dose- and boosting-dependent VHSV-neutralizing antibody in mucus and serum, and can provide a high protection in olive flounder against a virulent VHSV challenge.