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The interactive applications of immunization route, vaccine type and delivery vectors are emerging as a key area of research within the field of mass immunization in fishery production. In an effort to improve DNA vaccine's immune efficiency in large‐scale immunization, a promising bacterial ghost‐loaded DNA vaccine was constructed based on Escherichia coli DH5α. In common carp was investigated the immune response to immersion immunization via related indicator analysis, and the challenge test of spring viraemia of carp virus (SVCV) was carried out. The result indicated that BG‐loaded DNA vaccine induced higher serum antibody level than naked pEG‐G. Simultaneously, the immunophysiological indicators and genes change at the more advanced levels in the BG/pEG‐G immune group. At the treatment concentration of 20 mg/L of the BG/pEG‐G group, IgM and IgZ expressions in vivo were markedly increased by 21.62 times and 6.91 times, respectively, and the relative percentage survival reached the peak of 59.57%. This study paves the way for future aquatic animal vaccine research, which aimed to develop the highly effective immersion vaccine system by delivery vectors, with the ultimate aim to prevent and restrict SVCV in actual production. [ABSTRACT FROM AUTHOR]

Immersion vaccination of single‐walled carbon nanotubes loaded with mannose‐modified glycoprotein (SWCNTs‐MG) vaccine has been proved to be effective in preventing spring viraemia of carp virus (SVCV). Immunization procedure has immense consequence on the immune effect of the immersion vaccine. However, immunization procedure optimization for SWCNTs‐MG vaccine against SVCV has not been reported. In this study, accordingly, a full‐factor experiment was designed to optimize the immunization procedure of SWCNTs‐MG vaccine by three aspects of vaccine dose (30 mg/L, 40 mg/L and 50 mg/L), immunization density (8 fish L−1, 24 fish L−1 and 48 fish L−1) and immunization time (6, 12 and 24 hr). Furthermore, we used the immunization group (A1B2C1, 30 mg/L, 24 fish L−1 and 6 hr) in the previous study as a positive control (PC) to evaluate the immunization effect optimized conditions from the expression of immune‐related genes and relative percentage survival (RPS). At 28 days post‐vaccination (DPV), common carps were intraperitoneal injected SVCV challenged test indicated that the A1B2C2 group (30 mg/L, 24 fish L−1, 12 hr) displayed superiority of protective efficacy compare with other groups and the RPS with 77.9%, which was 15.6% higher than the PC group of RPS with 62.3%. Moreover, the expression of immune‐related genes such as IL‐10, CD4 and MHC‐II was also significantly higher than PC group. The specific experimental flow chart is shown in Figure 1. Conclusively, these results demonstrated that vaccine dose, immunization density and immunization time are 30 mg/L, 24 fish L−1 and 12 hr, which is the more appropriate immunization programme with juvenile carp for SWCNTs‐MG vaccine. This study provides a profitable reference for improving the immune efficiency of aquatic immersion vaccine. 1 FIGURE: The experiment process and timeline chart of the present research [ABSTRACT FROM AUTHOR]

Abstract: A bacterial strain with putative immunomodulatory properties was isolated from Xi’an hot springs in China. Comparison of 16S rRNA gene revealed a 97% similarity between the tested strain (designated XA-1) and Anoxybacillus kamchatkensis. Two compounds isolated from the secondary metabolites of XA-1 were identified by spectral data (infrared, nuclear magnetic resonance and mass spectrometry) as: (1) cyclo (Gly-l-Pro) and (2) cyclo (l-Ala-4-hydroxyl-l-Pro). Two cyclic dipeptides showed stimulatory properties towards a range of parameters when a dose of 20mgkg−1 body weight was intraperitoneally injected in naive common carp, Cyprinus carpio. Innate immune parameters (serum SOD, lysozyme and bactericidal activity, and phagocytic activity by peripheral blood leucocytes) along with the expression of two immune-related genes (IL-1β and iNOS) in blood were examined after 7, 14, 21, and 28 days of injection. In the absence of infection, immunomodulators should ideally not affect normal physiology and immunity of the host; possible negative outcomes of activated immune responses in the naive state are discussed. Protection by two bacterial dipeptides was assessed in an intraperitoneal injection challenge trial with live Aeromonas hydrophila. Both compounds reduced mortality, with the highest survival rate observed in the group that received compound 2 (80%) followed by the group that received compound 1 (65%) while control group scored the worse (15%). Elucidation of the involved protective mechanisms in carp requires future studies. [Copyright &y& Elsevier]

Abstract: A bacterial strain, designated DR-834 and producing immunostimulatory activities to carp (Cyprinus carpio), was isolated from Qinghai–Tibetan Plateau permafrost soil. Cultural characteristic studies suggested that this strain belongs to the genus Bacillus. The nucleotide sequence of the 16S rRNA gene of strain DR-834 exhibited close similarity (99%) with the 16S rRNA gene of Bacillus simplex. Two compounds showing potent activity were isolated from secondary metabolites of the strain through bioassay-guided isolation techniques and identified by spectral data (infrared, nuclear magnetic resonance and mass spectrometry) as: (1) 4-trans-hydroxy-l-proline and (2) cyclo-(l-Pro-Gly)2. They were found to be significantly increased the selected innate immune function parameters, serum SOD activity, serum lysozyme activity, serum bactericidal activity, superoxide anion production and phagocytic activity by isolated blood leucocytes. The effects of two compounds on immune-related genes expression were further investigated. The outcomes of real-time quantitative polymerase chain reaction (RQ-PCR) proved that the transcribing level of interleukin 1β (IL-1β) and inducible nitric oxide synthase (iNOS) mRNA in the blood have been augmented by 4-trans-hydroxy-l-proline and cyclo-(l-Pro-Gly)2. Compounds 1 and 2 administration the challenge with live Aeromonas hydrophila decreased the percentage mortality in the experimental groups with the consequence increase in relative percent survival (RPS) values. Compound 2 produced the highest protection with the RPS values of 87.50, 77.78, 55.56 and 55.56 after 1, 2, 3 and 4 weeks, respectively. The study indicates that the isolated compounds could be positively influence the immune response and protect the heath status of carp against A. hydrophila infection. [Copyright &y& Elsevier]

Spring viremia of carp virus (SVCV) causes devastating disease in aquaculture, resulting in significant economic impact. To develop an effective means against SVCV infection, a Lactococcus lactis (L.lactis) based subunit vaccine (pNZ-UGA) was developed based on surface displaying of SVCV glycoprotein using anchoring motif of the cA (C terminus of the peptidoglyvsn-binding) domains of AcmA, a major autolysin from L.lactis. The surface expression of SVCV glycoprotein was verified by indirect immunofluorescence assay. The efficacy of the constructed vaccine was further evaluated in common carp. The results showed that the higher levels of specific IgM could be detected in fish vaccinated with pNZ-UGA, compared with that in PBS and L.lactis groups. Immune-related genes including TNF-α , IL-6b , IL-1β , Cxcr 1 , Cxca , IFNg2b , I-IFN , and IgM expression in pNZ-UGA group were strongly up-regulated, revealing that robust innate immune response was induced. Notably, the lowest cumulative mortality (13.46%) was observed in fish vaccinated with pNZ-UGA vaccine after SVCV challenge, whereas the cumulative mortality were 100.00% and 92.31% in PBS and L.lactis groups, respectively. This study suggests the potential use of the recombinant L.lactis with surface displaying antigen proteins as effective vaccines against SVCV and other fish virus infection. • SVCV glycoprotein was displayed on the surface of Lactobacillus lactis. • Immunization by injection with pNZ-UGA strongly induced immune response in common carp. • Immunization with pNZ-UGA enhance disease resistance against SVCV. [ABSTRACT FROM AUTHOR]

Glycoprotein (G) is the most common gene used in SVCV vaccine constructions. To identify the major immunogenicity determinant region of SVCV G gene, herein we truncated G gene to 4 parts (G-1 , G-2 , G-3 and G-4). Bioinformatics and the enzyme linked immunosorbent assay (ELISA) were used to identify the antigenicity of these 4 truncated G proteins. Immunological assays (serum antibody production, enzyme activity, immune genes expression and challenge test) were carried out to further identify the immunogenicity of the screened G protein in common carp. Moreover, to further verify the immune response of the screened G protein-based subunit vaccine, its protective effects on common carp against SVCV infection using single-walled carbon nanotubes (SWCNTs) as a carrier were evaluated. Results showed that G-3 protein could induce higher antibody titer than other truncated G proteins. Furthermore, carps vaccinated with G-3 and G (positive control) showed significant enhancement of immune response (serum antibody production, enzyme activity and immune related genes expression) when compared with control groups. Meanwhile, as a promising vaccine carrier, SWCNTs could significantly enhance the immune effect of naked subunit vaccine (G-3 and G). Notably, after SVCV challenge, there was no significant difference in immune protection between G-3 and G, nor between SWCNTs-G-3 and SWCNTs-G. These results so far suggest G-3 might be the potential antigen epitope of SVCV. This study lays a foundation for developing vaccine and immunodiagnostic techniques. • SVCV antigenic sites might lies in G-3 (751–1143 bp). • The truncated G protein (G-3) could induce similar immune response to G protein. • Common carp vaccinated with SWCNTs-G-3 confers strong immunity against SVCV. [ABSTRACT FROM AUTHOR]

Spring viremia of carp virus (SVCV) has caused mass mortality in cyprinids, with case fatality rates of young fish up to 90%, resulting in enormous economic losses in the aquaculture industry. Immersion vaccination is considered as the most effective method for juvenile fish to combating disease, due to its convenience for mass vaccination and stress-free administration. However, immune responses following immersion vaccination are generally less robust and of shorter duration as those induced through intraperitoneal injection. Herein, to enhance the efficient of immersion vaccine, functionalized single-walled carbon nanotubes (SWCNTs) as carrier were used to manufacture immersion DNA vaccine system (SWCNTs-pEGFP-M) with chemical modification. Results showed that SWCNTs-pEGFP-M could enter into fish body via immersion administration and express antigen proteins in fish kidney and spleen. Moreover, stronger and longer duration immune responses (including serum antibody production and immune genes expression) can be induced in fish vaccinated with SWCNTs-pEGFP-M in comparison with those vaccinated with pEGFP-M alone. Notably, SWCNTs can increase the immune protective effect of naked DNA vaccine by ca. 23.8%. Altogether, this study demonstrates that SWCNTs as a promising DNA vaccine carrier might be used to vaccinate large-scale juvenile fish by bath administration approach, which can provide an outlook for future vaccination strategies against SVCV. • SWCNTs-pEGFP-M encoding the SVCV matrix protein were constructed. • SWCNTs as a promising vehicle can enhance immune effect of DNA vaccine. • Common carps immersed with SWCNTs-pEGFP-M confers duration immunity against SVCV. • SWCNTs based immersion vaccine have prospects for application to aquatic vaccine. [ABSTRACT FROM AUTHOR]

• Anisomycin caused profound inhibition of SVCV replication in EPC cells. • Anisomycin blocked morphological cell damage caused by SVCV replication. • Anisomycin suppressed SVCV replication in vivo , resulting in a prolonged survival of infected zebrafish. Spring viraemia of carp (SVC) caused by spring viraemia of carp virus (SVCV) is an acute and highly lethal viral disease of cyprinid fish. However, effective therapy for SVC is still scarce until now. Here we evaluated the inhibition of anisomycin (Ani), a metabolite produced by Streptomyces griseolus , on the replication of SVCV in vitro and in vivo. Our results demonstrated that Ani could suppress SVCV replication with the maximum inhibitory rate > 95% in epithelioma papulosum cyprini (EPC) cells. And the half maximal inhibitory concentrations (IC 50) of Ani on SVCV glycoprotein (G), nucleoprotein (N) and phosphoprotein mRNA expressions were 21.79, 13.13 and 12.24 nM, respectively. Besides, Ani decreased SVCV-induced cytopathic effects and nucleus damages. As expected, Ani also showed a strong anti-SVCV activity in vivo , as indicated by inhibiting viral gene expression and increasing the survival rate of zebrafish. Intraperitoneal injection of Ani increased the survival rate of zebrafish by 30% and markedly inhibited the expressions of G and N mRNA by > 60% in kidney and spleen at day 1 and day 4 post-infection. Results so far suggest that Ani as a powerful agent against SVCV can be applied to the control of SVC in aquaculture. [ABSTRACT FROM AUTHOR]

Abstract Although vaccine is a prophylaxis measure for the contagious and fatal disease caused by spring viremia of carp virus (SVCV), until now, no commercial vaccine is available for worldwide use. To find more effective and safe means for the control of SVCV infection, here, an Escherichia coli DH5α bacterial ghost (DH5α-BG, non-living bacterial) based DNA vaccine delivery system (BG/pEG-G) was constructed. Carp were injected intramuscularly by different treatments (PBS, pEGFP, BG, pEG-G and BG/pEG-G), and the immunoprotective effect induced by these treatments were analyzed. We found a stronger and longer duration immune response (serum antibody production and immune-related genes expression) can be induced in fish vaccinated with BG/pEG-G in comparison with those vaccinated with pEG-G alone. Additionally, a good immune protective effect (relative percentage survival >81.48%) was observed in fish vaccinated with BG/pEG-G vaccine at the dose of 0.2 μg DNA/g of fish. Overall, this study for the first time demonstrates the ability of DH5α-BG as DNA vaccine carrier against SVCV infection in carps, suggesting a practical multivalent strategy for the control of aquatic disease. Highlights • E.coli DH5α ghost was used as carrier to prepare a novel DNA vaccine in common carp. • Immunization with BG/pEG-G induced stronger immune response than naked pEG-G. • Immunization with BG/pEG-G enhanced disease resistance against SVCV in fish. • Bacterial ghost based DNA vaccine have prospects for application to aquatic vaccine. [ABSTRACT FROM AUTHOR]

Abstract Spring viraemia of carp virus (SVCV) is a viral fish pathogen causing high mortality in several carp species and other cultivated fish. However, robust anti-SVCV drugs currently are extremely scarce. For the purpose of seeking out anti-SVCV drugs, here a total of 35 arctigenin derivatives were designed, synthesized and evaluated for their anti-viral activities. By comparing the inhibitory concentration at half-maximal activity (IC 50) of the 15 screened candidate drugs (max inhibitory response surpassing 90%) in epithelioma papulosum cyprini (EPC) cells infected with SVCV, 2Q and 6 A were chosen for additional validation studies, with an IC 50 of 0.077 μg/mL and 0.095 μg/mL, respectively. Further experiments revealed that 2Q and 6 A could significantly decrease SVCV-induced apoptosis and have a protective effect on cell morphology at 48 and 72 h post-infection. Moreover, the reactive oxygen species (ROS) induced upon SVCV infection could be obviously inhibited by 2Q and 6 A, while SVCV-infected cells were clearly observed. On account of these findings, 2Q and 6 A could have a promising application for the treatment of infection of SVCV and provide a considerable reference for novel antivirals in aquaculture. Graphical abstract Image 1 Highlights • A total of 35 arctigenin derivatives were synthesized and evaluated for their anti-SVCV activities. • 2Q and 6 A displayed a robust inhibitory effect on SVCV proliferation in EPC cells. • Structure-activity relationship showed the importance of the length of the R3 substituted group. [ABSTRACT FROM AUTHOR]

Spring viraemia of carp virus (SVCV), a highly pathogenic rhabdovirus, could cause spring viraemia of carp (SVC) with up to 90% lethality. Like other rhabdoviruses, the entry of SVCV into susceptible cells was mediated by a single envelope glycoprotein G. Specific inhibitors targeting the glycoprotein were the most effective means to alleviate the epidemic. The programs including SWISS-MODEL, I-TASSER, Phyre2 and AlphaFold2 were used to build a three-dimensional structural model of glycoprotein. The structural comparison between SVCV-G and homology protein VSV-G revealed that the SVCV glycoprotein ectodomain (residues 19 to 466) folded into four distinct domains. Based on the potential small molecule binding sites on glycoprotein surfaces, virtual screening of the anti-SVCV drug libraries was performed using Autodock software and 4'-(8-(4-Methylimidazole)-octyloxy)-arctigenin (MOA) with a high binding affinity was identified. The solubility enhancer tags including trigger factor and maltose binding protein were fused with the ectodomain of glycoprotein, and the target protein with a purity of about 90% was successfully obtained. The interaction confirmation tests revealed that the fluorescence intensity of a characteristic peak induced by the endogenous chromophores in glycoprotein was decreased with the addition of MOA, indicating changes in the microenvironment of glycoprotein. Moreover, the interaction could cause a slight conformational change in glycoprotein, as shown by the content of β-turn, β-folding, and random coil of protein all increased with the decrease of α-helix content after the addition of MOA compound. These results demonstrated that MOA could act as a novel drug against fish rhabdovirus via direct targeting of glycoprotein. • The ectodomain of SVCV glycoprotein folded into four distinct domains. • A soluble form of the ectodomain of glycoprotein was obtained. • MOA was proved to be the first inhibitor of fish rhabdovirus glycoprotein. • The interaction changed the microenvironment and conformation of glycoprotein. [ABSTRACT FROM AUTHOR]

Highlights • SWCNTs can be used as carriers for subunit vaccine. • SWCNTs-subunit vaccine can enhance the immunological activity against SVCV infection. • SWCNTs based subunit vaccine have prospects for application to aquatic vaccine. Abstract As a successful prevention strategy for controlling the highly contagious and pathogenic disease of spring viremia of carp (SVC), DNA vaccines reported in recent years could trigger protective responses against SVC with the means of injection. However, there remains many concerns and uncertainties related to DNA vaccination as well as injection is labor intensive, costly and not suitable to vaccinate large numbers of fish. Therefore, more efficient and safe prophylactic measures should be urgently investigated. In this research, single-walled carbon nanotubes (SWCNTs) as the candidate SWCNTs-pET32a- G subunit vaccine carrier were administrated via bath (1, 5, 10, 20, 40 mg L−1) or injection (1, 4, 8, 12, 20 μg) in common carp juvenile, and the different immune treatments to induce immunoprotective effect were analyzed. The results showed that SWCNTs-pET32a- G could enter fish body after immersion for 10 h, furthermore, compared to control groups, antibody levels, the non-specific immune parameters (complement activity, superoxide dismutase activity and alkaline phosphatase activity), and immune-related genes (especially the TNF-α and IFNg2b) in vaccinated groups were significantly enhanced in fish immunized with SWCNTs-subunit vaccine. In addition, as a promising carrier, SWCNTs can increase the immune protective effect of naked subunit vaccine by ca. 16% in bath immunization group and by ca. 23% in injection group. This study suggests that SWCNTs-vaccine may represent a potentially efficient immersion vaccine against viral pathogens of fish in the future. [ABSTRACT FROM AUTHOR]

Different viruses could induced ROS generation to alter intracellular redox state in the host cells, and unbalanced redox state was suggested to have various effects on viral replication. In this study, we investigated the influence of reactive oxygen species (ROS) on replication of spring viraemia of carp virus (SVCV) in fish cells. After SVCV infection, there existed a time-dependent increase in ROS generation. The present results revealed that antioxidant N-acetyl- l -cysteine (NAC) resulted in a lower ROS levels and increased SVCV replication in EPC cell. In contrast, a GSH synthesis inhibitor buthionine sulfoximine (BSO) induced ROS generation and decreased SVCV replication. In addition, activation of NF-κB suppressed SVCV replication by using two inhibitors of cytokine-induced IκBα phosphorylation. More importantly, enhancement of the activity of NF-κB was found in BSO treatment, which indicated that dropped SVCV replication likely occurred via ROS activation of NF-κB. Overall, our results revealed that the SVCV infection and replication could generate ROS and be affected by the redox state, where this progression was associated with the alteration in NF-κB pathway induced by oxidative stress. [ABSTRACT FROM AUTHOR]

Abstract: The study isolated three strains of intestinal autochthonous bacteria Aeromonas veronii BA-1, Vibrio lentus BA-2, and Flavobacterium sasangense BA-3 from the intestinal tract of the common carp (Cyprinus carpio). To reveal the effects of these three strains of bacteria on the innate immunity of carp, the lysozyme, complement C3, total serum protein, albumin and globulin levels, respiratory burst activity, phagocytic activity by blood leucocytes and the expression of IL-1b, lysozyme-C, and TNF-α were examined after feeding with seven different diets for up to 28 days. Also the survival of carp against Aeromonas hydrophila was challenged for 14 days. The carp were fed seven different diets: one control, three diets supplemented with 1 × 108 cell g−1 of carp intestinal bacteria BA-1 (Group D-I), BA-2 (Group D-II) and BA-3 (Group D-III), and three diets supplemented with extracellular products FA-1 (Group E-I), FA-2 (Group E-II) and FA-3 (Group E-III) which were corresponding to the strains BA-1, BA-2, and BA-3, respectively, up to 28 days. For groups D-I, D-III, E-I and E-III, the innate immune parameters of carp were significantly increased, the expression of three immune-related genes in blood was significantly up-regulated examined during 7, 14, and 21 days of feeding, and the survival rate was improved. The study indicates that the two isolated intestinal autochthonous bacteria A. veronii BA-1 and F. sasangense BA-3 could positively influence immune response and enhance disease resistance of carp against A. hydrophila infection. [Copyright &y& Elsevier]

Glycoprotein mediated the entry of rhabdoviruses into the host cell and was the target of neutralizing antibodies. It was a prime tool for the study of the evolution and pathogenesis of viruses. Here, four different expression systems including cell-free synthesis system, Escherichia coli , Pichia pastoris and the baculovirus infected Spodoptera frugiperda were used to explore the recombinant expression of spring viraemia of carp virus glycoprotein. The results indicated that the recombinant glycoprotein could be detected in E. coli cell-free system after in vitro incubation for 16 h at 25 °C. E. coli was found to be the optimal expression system for the production of the largest amount of recombinant glycoprotein. Although robust yields were considerable in E. coli , the formation of insoluble aggregates and the removal of solubilizing labels were challenging for the expression and purification of glycoprotein. For this reason, the higher eukaryotic expression systems, yeast GS115 and insect Sf9 cells were used for the production of glycoprotein. The purity of the recombinant protein obtained from yeast culture was over 90% after purification by Ni-NTA. In insect cells, the target protein was expressed mainly in the intracellular environment, but secretory glycoprotein was also detected by western blotting. These findings provided a basis for further investigations into the structure and function of SVCV glycoprotein. • The full length glycoprotein was synthesized in E. coli cell-free system. • A soluble form of the ectodomain of glycoprotein was expressed in E. coli C41 strain. • Glycoprotein was found in the secreted fraction expressed by P. pastoris. • Glycoprotein was mainly localized intracellularly in baculovirus-infected Sf9 cells. [ABSTRACT FROM AUTHOR]

Spring viraemia of carp virus (SVCV), an important aquatic rhabdoviruses, causing devastating mortality in various carp species and other cultivated fish. In our previous studies, 4′-(8-Imidazole-octyloxy)-arctigenin (6A) with an eight carbon atoms of linker showed the higher activity against SVCV in EPC cells, based on the structure-activity relationship of 35 arctigenin derivatives. In this study, the antiviral activity and mechanism of 6A was further investigated both in vivo and in vitro. An analysis of survival curve of zebrafish indicated that 6A-treated group increased the survival rate by 23.4% and 20.0% following with 100 and 103 TCID 50 doses of SVCV, respectively. Besides, 6A inhibited the gene expression of SVCV nucleoprotein and glycoprotein in brain, spleen, and liver at 4 and 7 d post-infection (dpi) by over 90% and 60%, respectively. Consistent with above results, there were no apparent signs of infection and inflammation in the brain, spleen and liver of the 6A-treated fish. However, we unexpectedly found an inability on 6A-treated zebrafish and EPC cells to mount a strong IFNф1 response to SVCV, which indicated that 6A inhibited SVCV replication not via the activation of IFNф1-related genes. Moreover, pre-treatment, co-treatment, and post-treatment of 6A with SVCV, 6A was observed to possess an intense antiviral response in the early stage of viral infection. Altogether, 6A was expected to be a therapeutic agent for the treatment of SVCV in aquaculture. • 6A treatment could raise the survival rate of zebrafish infected with SVCV. • 6A inhibited SVCV replication not by the upregulation of fish IFNф1 production. • 6A had an intense antiviral response in the early stage of SVCV infection. [ABSTRACT FROM AUTHOR]

Spring viraemia of carp virus (SVCV), a highly pathogenic fish rhabdovirus, caused an acute hemorrhagic and highly contagious disease in cyprinids. In this study, a new strain of SVCV was isolated from diseased zebrafish in Yangling, Shaanxi Province, China, and named SVCV-CG01. Tissue filtrates of diseased fish were detected by Nest PCR using the specific 714 bp and 606 bp fragments from the glycoprotein gene of SVCV. The genes encoding for the N, P, M and G protein were amplified, and the fragments were inserted into pMD-19T vectors to determine the genome of SVCV. Based on phylogenetic analysis of G protein gene, the isolated virus was classified into the Ia genogroup. The titer of the new strain at 48 h and 72 h was approximately 108 and 109 times higher than that of the 0504 strain, respectively. The virus could produce typical cytopathic effects (CPE) and induce apoptosis in EPC cells at 48 and 72 h post infection (hpi). Healthy zebrafish were injected with different doses of SVCV and mass mortality of fish was detected after 4 d infection, with a cumulative death rate of 100% from 107 TCID 50 group at 7 d post infection (dpi). Using cultured mammalian 293T cells, an average transfection efficiency of the four structural proteins was 49.1% and 69.6% at 24 and 48 h post transfection (hpt), respectively. This study could be served as a reference for the research on the molecular epidemiology, evolution and pathogenicity of fish viruses. • A novel highly virulent SVCV was isolated and identified from diseased zebrafish. • The high pathogenicity of SVCV (CG-01) was observed in vitro and in vivo. • The structural proteins of CG-01 strain could be highly expressed in 293T cells. [ABSTRACT FROM AUTHOR]