The Efficacy of Inactivated Virus Vaccine against Viral Nervous Necrosis (VNN)

The efficacy of inactivated betanodavirus as a vaccine against viral nervous necrosis (VNN) was evaluated using juvenile sevenband grouper Epinephelus septemfasciatus. Fish were intraperitoneally injected once with formalin-inactivated redspotted grouper nervous necrosis virus (RGNNV). Virus-neutralizing antibodies were detected in the vaccinated fish from Day 10 to the end of the experimental period (Day 160), showing 1 : 2, 000 or higher mean antibody titers from Day 21 to Day 77. The vaccinated and unvaccinated control fish were challenged by intramuscular injection with the homologous virus at 14, 35 and 74 days post-vaccination. The vaccinated fish showed significantly lower mortalities at any challenges than the control fish, with the RPS (relative percent survival) values 67 or higher. A field trial, in which fish were exposed to natural infection in net pens, also resulted in higher survival rates in the vaccinated fish (RPS = 85) during the experimental period of 9 weeks. This high induction of neutralizing antibodies and protection indicates the potential of the inactivated virus vaccine against VNN.