Efficacy Comparison of LINEAR ARRAY EPITOPE SUBUNIT VACCINE and NERVOUS NECROSIS VIRUS-Like particle vaccine iN Giant grouper

Viral nervous necrosis caused by nervous necrosis virus (NNV) is a serious disease results in high economic losses in Taiwan. Several NNV vaccines including recombinant NNV coat protein (CP) and NNV-like particle (VLP) have been developed, and vaccines using VLP are considered more effective than using single recombinant protein. Here we want to develop a subunit vaccine that antigen composed of CP epitope repeats using a linear array epitope (LAE) technique and compare the protective efficacy and safety of the LAE vaccine and VLP vaccine for the vaccine administration in giant grouper larvae.  In this study, we predicted NNV CP epitope based on the NNV-like particle crystal structure and constructed multiple copies of CP epitope by LAE technique for developing the subunit vaccine, namely NNVCP-S5E. The VLP vaccine named NNV-VLP was tested here for comparison of protective efficacy. Vaccine safety was evaluated and all fish survived with no pathological changes, indicating that no harmful effects of NNVCP-S5E and NNV-VLP vaccination. The antibody titers in the vaccinated fish increased within 4 weeks after vaccines administration. After fish were challenged by NNV, the significant low mortalities were observed in the vaccinated groups injected with NNVCP-S5E or NNV-VLP vaccines with or without adjuvant compare to the control groups injected with PBS combined with or without adjuvant ISA763. The fish injected with NNVCP-S5E combined with adjuvant had higher survival rate than the NNV-VLP vaccinated groups. Additionally, the NNV-neutralizing antibody titers in serum collected from NNVCP-S5E or NNV-VLP vaccinated grouper larvae were raised within 8 weeks post vaccines administration.

In summary, utilization of the LAE subunit vaccine shows more effective with using VLP vaccine for reducing mortality caused by NNV infection in giant grouper.