Effectively protecting Asian seabass Lates calcarifer from ISKNV-I, ISKNV-II, RSIV-II and SDDV by an inactivated ISKNV-I and SDDV bivalent vaccine

The members of genus Megalocytivirus are classified into ISKNV species and SDDV species. Both are important causative agents to cultured Asian seabass Lates calcarifer in wide Southeast Asia. However, no cross-protection effect exists between two viral species. Here, a formalin-killed bivalent vaccine containing ISKNV-I and SDDV was developed and the vaccine effectiveness in Asian seabass against three sub-genotype isolates in ISKNV species and one SDDV was evaluated under laboratory condition. The result showed the survivals of the immunized-Asian seabass juveniles were 86.67% (26/30), 93.3% (28/30), 93.3% (28/30) and 96.7% (29/30) upon ISKNV-I, ISKNV-II, RSIV-II and SDDV challenge, respectively. By contrast, the corresponding cumulative mortalities of four non-immunized control groups reached to 93.3% (28/30), 96.7% (29/30), 100% (30/30) and 23.3% (7/30), respectively. Correspondingly, the calculated relative percentage survivals (RPS) against four types of megalocytiviruses are 85.7%, 93.1%, 93.3% and 85.7%, respectively. The clinical symptoms of diseased Asian seabass infection with ISKNV/RSIV and SDDV were characterized by lethargy, darkened bodies, liver blood loss, and pallor of gills. Histopathological analysis showed that numerous abnormal enlargement cells were observed both in ISKNV/RSIV-and SDDV-infected fish, which was further demonstrated by specific monoclonal antibodies-based immunofluorescence assay examination. Collectively, we are the first to develop a highly effective bivalent inactivated vaccine against both ISKNV/RSIV and SDDV in Asian seabass vaccination model. Furthermore, the featured enlargement cell was firstly clearly presented and confirmed in SDDV-infected Asian seabass. Our findings provide important data for preventing and controlling various megalocytiviruses in Asian seabass.

Automated summary

A bivalent inactivated vaccine against ISKNV/RSIV and SDDV was developed and evaluated in Asian seabass. The survival rates of immunized fish were between 86.67% and 96.7%. The study also provided important information on the clinical symptoms and pathological changes caused by the viruses, contributing to the prevention and control of megalocytiviruses in Asian seabass.