Montanide IMS 1312 VG adjuvant enhances the efficacy of immersion vaccine of inactivated viral hemorrhagic septicemia virus (VHSV) in olive flounder, Paralichthys olivaceus

Vaccination by immersion is suitable for mass vaccination of small size fish. However, no viral vaccine has been developed for immersion applications, because of low efficacy. In this study, we evaluated the efficacy and safety of immersion vaccine against viral hemorrhagic septicemia (VHS) containing Montanide IMS 1312 VG adjuvant in olive flounder (Paralichthys olivaceus). Healthy fish were vaccinated by an immersion method with a heat-inactivated FP-VHS2010-1 strain of VHS virus (VHSV) in combination with Montanide IMS 1312 VG for 5 min at 20 ± 2 °C. The control group was vaccinated with sterile PBS. No toxicity of immersion vaccine with Montanide IMS 1312 VG adjuvant was observed by hematological and histopathological analysis. Immersion vaccine with adjuvant enhanced gene expression of immune-associated genes, i.e., genes encoding interleukin (IL)-1β, IL-6, IL-8, and Toll-like receptor (TLR) 3. Relative percent survival (RPS) of fish was measured on weeks 4 and 8 post vaccination. In fish vaccinated with adjuvant, RPS was significantly higher than that of fish vaccinated without adjuvant. The results of the present study provide evidence that the VHSV immersion vaccine with Montanide IMS 1312 VG induces protective immunity in olive flounder against VHS.