The recombinant subunit vaccine encapsulated by alginate-chitosan microsphere enhances the immune effect against Micropterus salmoides rhabdovirus

Vaccine Molecule Design Based on Phage Display and Computational Modeling against Rhabdovirus

Rhabdoviruses with rich species lead a variety of high lethality and rapid transmission diseases to plants and animals around the globe. Vaccination is one of the most effective approaches to prevent and control virus disease. However, the key antigenic epitopes of glycoprotein being used for vaccine development are unclear. In this study, fish-derived Abs are employed for a Micropterus salmoides rhabdovirus (MSRV) vaccine design by phage display and bioinformatics analysis. We constructed an anti-MSRV phage Ab library to screen Abs for glycoprotein segment 2 (G2) (G129-266). Four M13-phage-displayed Abs (Ab-5, Ab-7, Ab-8 and Ab-30) exhibited strong specificity to target Ag, and Ab-7 had the highest affinity with MSRV. Ab-7 (300 μg/ml) significantly increased grass carp ovary cell viability to 83.40% and significantly decreased the titer of MSRV. Molecular docking results showed that the key region of Ag-Ab interaction was located in 10ESQEFTTLTSH20 of G2. G2Ser11 and G2Gln12 were replaced with alanine, respectively, and molecular docking results showed that the Ag-Ab was nonbinding (ΔG > 0). Then, the peptide vaccine KLH-G210-20 was immunized to M. salmoides via i.p. injection. ELISA result showed that the serum Ab potency level increased significantly (p < 0.01). More importantly, the challenge test demonstrated that the peptide vaccine elicited robust protection against MSRV invasion, and the relative percentage survival reached 62.07%. Overall, this study proposed an approach for screening key epitope by combining phage display technology and bioinformatics tools to provide a reliable theoretical reference for the prevention and control of viral diseases.

Experimental evidence of effective disinfectant to control the transmission of Micropterus salmoides rhabdovirus

Micropterus salmoides rhabdovirus (MSRV) is a significant pathogen that causes high morbidity and mortality in largemouth bass, leading to enormous economic losses for largemouth bass aquaculture in China. The aim of this study was to investigate the efficacy of four disinfectants (potassium permanganate, glutaraldehyde, trichloroisocyanuric acid and povidone iodine) on MSRV, to control the infection and transmission of MSRV in largemouth bass aquaculture. The disinfectants were tested at different concentrations (5, 25, 50, 100 and 500 mg/L) prepared with distilled water for 30 min contact time, and the viral nucleic acid was quantified using qPCR and the infectivity was tested by challenge experiment. Potassium permanganate at 5-500 mg/L, glutaraldehyde at 500 mg/L, trichloroisocyanuric acid at 50-500 mg/L and povidone iodine at 500 mg/L concentration could effectively decrease the virus nucleic acid, and the survival rate of largemouth bass juveniles after challenge experiment increased significantly from 3.7% ± 6.41% to 33.33 ± 11.11% - 100%. Moreover, the minimum effective time of 5 mg/L potassium permanganate was further studied at 2, 5, 10 and 20 min contact time. The viral nucleic acid decreased significantly at 5-20 min exposure time, and the survival rate increased significantly from 7.41% ± 6.41% to 77.78 ± 11.11% - 100%. The median lethal concentration (LC50 ) values of potassium permanganate were 10.64, 6.92 and 3.7 mg/L at 24, 48 and 96 h, respectively. Potassium permanganate could be used for the control of MSRV in the cultivation process; the recommended concentration is 5 mg/L and application time should be less than 24 h. The results could be applied to provide a method to control the infection and transmission of MSRV in water, and improve the health status of largemouth bass.

Oral vaccination with recombinant Saccharomyces cerevisiae expressing Micropterus salmoides rhabdovirus G protein elicits protective immunity in largemouth bass

Micropterus salmoides rhabdovirus (MSRV) is one of the main pathogens of largemouth bass, leading to serious economic losses. The G protein, as the only envelope protein present on the surface of MSRV virion, contains immune-related antigenic determinants, thereby becoming the primary target for the design of MSRV vaccines. Here, we displayed the G protein on the surface of yeast cells (named EBY100/pYD1-G) and conducted a preliminary assessment of the protective efficacy of the recombinant yeast vaccine. Upon oral vaccination, a robust immune response was observed in systemic and mucosal tissue. Remarkably, following the MSRV challenge, the relative percent survival of EBY100/pYD1-G treated largemouth bass significantly increased to 66.7 %. In addition, oral administration inhibited viral replication and alleviated the pathological symptoms of MSRV-infected largemouth bass. These results suggest that EBY100/pYD1-G could be used as a potential oral vaccine against MSRV infection.