Lack of nervous necrosis virus (NNV) neutralizing antibodies in convalescent sevenband grouper Hyporthodus septemfasciatus after NNV infection

• Published in: Vaccine 2018-03, Vol.36 (14), p.1863-1870
• Main Authors: Gye, Hyun Jung, Oh, Myung-Joo, Nishizawa, Toyohiko
• Format: Article
• Language: English
• Subjects: Antibodies; Aquaculture; Chromatography; Convalescent fish; Deoxyribonucleic acid; DNA; Enzymes; Epinephelus coioides; Epinephelus septemfasciatus; Fish; Fish diseases; Gangrene; Hyporthodus septemfasciatus; Immune response; Immune system; Immunoglobulins; Infections; Infectivity; Live vaccine; Mortality; Necrosis; Nervous necrosis virus; Neutralizing; Neutralizing antibody; Oplegnathus fasciatus; Proteins; Seawater; Temperature; Vaccines; Viruses; Water temperature
• ISSN: 0264-410X; 1873-2518
• DOI: 10.1016/j.vaccine.2018.02.063

•Convalescent fish from NNV infection were protected against NNV re-challenge.•NNV-specific antibodies were detected in a few convalescent fish from NNV infection.•NNV multiplied in convalescent fish after NNV re-infection, but was strongly regulated.•No NNV-neutralizing antibody was detected in almost all convalescent fish.•NNV-neutralizing antibody was not a major protective factor in convalescent fish. Viral nervous necrosis (VNN) is caused by nervous necrosis viruses (NNVs) belonging to genus Betanodavirus (Nodaviridae). It is one of the most serious diseases in aquaculture industry worldwide. In the present study, the kinetics of NNV-infectivity and NNV-specific antibodies in convalescent sevenband grouper Hyporthodus septemfasciatus after NNV infection was determined. When fish were infected with NNV at 17.5 °C, and reared for 84 days at natural seawater temperature (increasing rate: approximately 0.1 °C/day), NNV infectivity peaked on day 14 with 107.80 TCID50/g at the highest, and declined to below the detection limit. When convalescent fish were reared at 27 °C, and re-infected with NNV at 104.3 or 106.3 TCID50/fish, no mortality was observed although NNV multiplied up to 108.80 and 107.80 TCID50/g at the highest, respectively, suggesting NNV-specific immune response. It also revealed that convalescent fish were re-infected by NNV although NNV multiplication was strongly regulated. Interestingly, NNV-specific antibodies were detectable in 20% and ≥80% of convalescent fish before and after re-infection with NNV, respectively. However, no NNV-neutralizing activity was detected before and after re-infection in almost all of the convalescent fish. Therefore, NNV-neutralizing antibodies might not be necessary for the protection of convalescent fish against NNV re-infection after previous NNV infection.