Development and application of quantitative detection method for nervous necrosis virus(NNV) isolated from sevenband grouper Hyporthodus septemfasciatus

Objective:To develop the rapid and efficient quantitative detection tool for nervous necrosis virus isolated from sevenband grouper Hyporhodus septemfasciatus.Methods:The viral genes of the NNV(SGYeosu08) isolated from sevenband grouper were phylogenetically analyzed.In addition,novel quantitative PCR primers based on the genomic sequence of SGYeosu08 isolate were designed and compared it with the conventional bio-assay method(TCID_(50)) using in vitro and in vivo samples.Results:The phylogenetic analysis of viral genes demonstrated the relationship of SGYeosu08 with members of red-spotted grouper nervous necrosis virus(RGNNV).The qNNV_Rl primer set(R1_F and R1_R) and the qNNV_R2 primer set(R2_F and R2_R) revealed 93%primer efficiency(regression:y=-0.2861 x + 9.9401,R^2= 0.9976)and the revealed 108%primer efficiency(regression:y=-0.3172 x + 10.0611,R^2= 0.9982),respectively.Its comparison with viral infectivity calculated by TCID_(50) method showed similar kinetic pattern at in vitro and NNV challenged fish(in vivo) samples.Conclusions:Result show that this method is rapid and efficient to diagnose NNV infection compare to traditional bioassay method(TCID_(50)).

Diagnosis of nervous necrosis virus in orange-spotted grouper,Epinephelus coioides, by a rapid and convenient RT-PCR method

Viral nervous necrosis （VNN） causes high mortality in marine fish, especially in the grouper, worldwide and in China. Since there is no effective vaccine or drug to deal with VNN, early detection and prevention is important to block its outbreak. In this study, a reverse transcription-polymerase chain reaction （RT-PCR） was developed for the rapid, convenient, and sensitive detection of the VNN pathogen, nervous necro- sis virus （NNV）, in the grouper. The whole process was completed within 3.5 h from the RNA extraction to PCR product visualization. The detection limit of this method was 200 copies of NNV RNA standard, which corresponded to 200 copies of virus particles. This RT-PCR method was specific to the NNV detection with no cross-reactivity to other fish viral disease pathogens, such as infectious pancreatic necrosis virus （IPNV）, infectious hematopoietic necrosis virus （IHNV）, spring viraemia of carp virus （SVCV）, epizootic haematopoietic necrosis virus （EHNV）, and large yellow croaker iridovirus （LYC1V）. With this method, the orange-spotted grouper （Epinephelus coioides） fry from hatcheries with or without incidence of the VN- N epidemic in Fujian Province were detected. The results showed that all or 93% of the fry from the two hatcheries with incidence of the epidemic were diagnosed as positive, while 40% or 25% of fry from the t- wo hatcheries without the VNN epidemic were also detected as NNV positive, indicating that this RT-PCR method can be used for rapid, sensitive detection of NNV infection and applied in the VNN epidemic alert.

Detection of coat protein gene of nervous necrosis virus using loopmediated isothermal amplification

Objective:To establish a novel and highly specific loop-mediated isothermal amplification(LAMP) assay for the identification of nervous necrosis virus(NNV) infection.Methods:A set of synthesized primers was used to match the sequences of a specific region of the nnr gene from the National Center for Biotechnology Information database,not originating from NNV-infected fish,the efficiency and specificity of LAMP were measured dependent on the concentration of DNA polymerase and the reaction temperature and time.In addition,to determine species-specific LAMP primers,cross reactivity testing was applied to the reaction between NVV and other virus families including viral hemorrhagic septicemia virus and marine birnavirus.Results:The optimized LAMP reaction carried out at 64 ℃ for 60 min,and above 4 U Bst DNA polymerase.The sensitivity of LAMP for the detection of nnv was thus about 10 times greater than the sensitivity of polymerase chain reaction.The LAMP assay primers were specific for the detection NNV infection in Epinephelus septemfasciatus.Conclusions:The development of LAMP primers based on genetic information from a public database,not virus-infected samples,may provide a very simple and convenient method to identify viral infection in aquatic organisms.

Protective immunity of orange-spotted grouper(Epinephelus coioids) against a nervous necrosis virus isolated from China,and determination of the complete sequences of the virus

On the basis of the sequence and analysis of genome from the orange-spotted nervous necrosis virus（ OGNNV）, China strain, a pair of special primers were designed according to the nucleotide sequences of RNA2 from OGNNV. The major capsid protein （ MCP）gene of OGNNV was cloned by means of reverse-transcriptase polymerase chain reaction （RT-PCR） and ligated into the pET32a expression plasmid. The MCP gene of OGNNV was 1 017 bases, encoded a protein of 338 amino acid with a molecular mass of 37.1 kDa. Recombinant protein with a molecular mass of 57.4 kDa was expressed in E. coli BL21 （DE3）. Vaccine was prepared from the recombinant protein expressed in recombinant cells. The juvenile orange-spotted groupers （8 cm in average length） were immunized by intraperitoneal injection. Group A was challenged with infected tissue filtrates 25 d post-vaccination. The mortality in the vaccined group （ A1,30% ） was a little higher than the unvaccined group （ B2, 27.8% ）. Group B was challenged after three vaccine injections. The mortality in the vaccined group （B1, 16.7% ） was lower than the unvaccined group （132, 27.8% ）, And the relative percentage survival （RPS） value of vaccined group, compared with the unvaccined group, was 40%. The anti-recombinant protein sera with a 1 ： 100 dilution were mixed with double volume of infected tissue filtrates and incubated at 4 ℃ for 12 h and then intramuscularly injected into the juvenile orange-spotted grouper. Treatment of infected tissue filtrates with anti-recombinant protein serum resulted in a significantly lower mortality of fish （ Group C1, mortality of 18.18% ）, compared with the fish （ Group C2, mortality of 40% ） which received infected tissue filtrates treated with control serum. Results implied the potential use of the capsid protein in immunization against OGNNV.

Establishment of Real-time Fluorescent RT-LAMP Detection Method for Grouper Nervous Necrosis Virus

Nervous necrosis virus （NNV） is the causative agent of fulminant infectious diseases in marine fishes such as grouper. Specific primers were designed based on the conserved sequence of capsid protein （CP） gene of red-spotted grouper nervous necrosis virus （NNV）. By optimizing the reaction conditions, a rapid and simple reverse transcription loop-mediated isothermal amplification （RT-LAMP） method was established for NNV detection. After adding SYTO-9 fluorescent dye in the reaction system, the amplification curve was monitored in real time using a fluorescence detector, and the result was obviously easy to assess. Moreover, the specificity and sensitivity of the established method was analyzed. The results showed that the established RT-LAMP method has good specificity with a detection limit of 1.3 pg/μl. The detection sensitivity of the established RT-LAMP method is 100 times that of the conventional RT-PCR method, and the detection duration is only 40 min. The established RT-LAMP method is suitable for quarantine and rapid detection of grouper nervous necrosis virus.

Cell Surface Display of Red-Grouper Nervous Necrosis Virus Capsid Protein on <i>Pichia pastoris</i>

Nervous necrosis virus (NNV), the etiological agent of viral nervous necrosis, has a high mortality rate of 100% in hatchery-reared larvae and juveniles. At present, there are still no effective vaccines available for NNV. Pichia pastoris surface display of viral capsid proteins was generated in hopes of developing an oral vaccine against red-grouper-nervous-necrosis virus (RGNNV) in fish. Fingerlings or juveniles that showed clinical signs of NNV infection were proved by RT-PCR for the appearance of expected length of 198 bpcDNA and further analysis by DNA sequencing. The DNA fragment containing AGα1 linked to RG-NNVRNA2, 2100 bp in length, was inserted into pPIC9K vector. Linearlized plasmids were electroporated into P. pastoris GS115 (mut+His?) and yeast isolates that had Muts?His+ and resistance phenotype at 4 mg/mL geniticin were selected to determine the integration of the target gene by PCR reaction. The extracted cell walls from the yeasts cultured in buffered-methanol-complex medium (BMMY) through an induction of 0.5% methanol for 6 days, were investigated for the fusion proteins by western blot. A protein band of 73 kDa predicted to be the fusion protein and a non-specific one of 56 kDa were detected. Staining of the fusion proteins expressing cells with corresponding antibodies revealed their presence of NNVRNA2, but varied the intensity of detected signals from cell to cell by confocal laser scanning fluorescence microscopy. The predicted fusion proteins tertiary structure also confirmed exposed conformation of the fusion protein on the cell wall. In this study, the capsid proteins from the red-spotted grouper nervous necrosis virus were successfully expressed on the cell surface of P. pastoris but still low levels of fusion protein expression. Further studies are required to optimize fully surface protein expression prior to evaluate the possible use of the constructed recombinant yeast as an oral vaccine against RG-NNV infection.

Betanodavirus: Mitochondrial disruption and necrotic cell death

Betanodaviruses cause viral nervous necrosis, an infectious neuropathological condition in fish that is characterized by necrosis of the central nervous system, including the brain and retina. This disease can cause mass mortality in larval and juvenile populations of several teleost species and is of global economic importance. The mechanism of brain and retina damage during betanodavirus infection is poorly understood. In this review, we will focus recent results that highlight betanodavirus infection-induced molecular death mechanisms in vitro. Betanodavirus can induce host cellular death and post-apoptotic necrosis in fish cells. Betanodavirus-induced necrotic cell death is also correlated with loss of mitochondrial membrane potential in fish cells, as this necrotic cell death is blocked by the mitochondrial membrane permeability transition pore inhibitor bongkrekic acid and the expression of the antiapoptotic Bcl-2 family member zf Bcl-x L. Moreover, this mitochondria-mediated necrotic cell death may require a caspase-independent pathway. A possible cellular death pathway involving mitochondrial function and the modulator zf Bcl-xs is discussed which may provide new insights into the necrotic pathogenesis of betanodavirus.

Inhibition of Fish Nodavirus by Gymnemagenol Extracted from Gymnema sylvestre

Viral nervous necrosis(VNN)has emerged to become a major problem in the culture of larval and juvenile marine fish worldwide.Bioactive phytochemicals isolated from commonly available medicinal plants are often screened for their efficacy in controlling fish viral diseases.Occurrence of newer viral strains and resistance to existing antiviral drugs are problems currently as-sociated with treatment of VNN,which necessitates looking for alternate sources for effective antiviral drugs.The aim of the present study was to screen antiviral potential of gymnemagenol(C30H50O4)previously extracted from leaves of Gymnema sylvestre.The fish nodavirus,grouper nervous necrosis virus(GNNV)in infected Sahul Indian Grouper Eye(SIGE)cell lines were used to study the antiviral activity of gymnemagenol under in vitro conditions.The susceptibility of the virus to gymnemagenol was confirmed by measuring the viral titre(TCID50 mL?1)in virus-infected SIGE cells every 24 h.Gymnemagenol at 20 μg mL?1 inhibited the prolifera-tion of GNNV to 53% at the end of the 6th d by inhibiting the proliferation of GNNV-infected SIGE cells.The viable SIGE cells were reduced to 47% as determined by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT)assay.The viral titre(TCID50 mL?1)was also reduced to log 2.8 at the end of the 7th d in gymnemagenol-treated SIGE cells after inoculated with GNNV when compared to untreated control SIGE cell viral titre(log 4.1).Based on our results it can be concluded that gymnemagenol could be used as an antiviral agent against GNNV infection.

鱼类神经坏死病毒研究进展

神经坏死病毒(nervous necrosis virus, NNV)是病毒性神经坏死病(viral nervous necrosis, VNN)的病原,可感染120余种海水鱼,感染后导致鱼类脑部与视网膜空泡化,发病死亡率最高可达100%.综述了神经坏死病毒的基因组、编码的蛋白、病毒的受体、诱导的免疫反应以及病毒的检测与防治研究,并对该疾病未来的防治手段和研究方向进行了探讨,以期对科学防治神经坏死病提供理论依据,推进石斑鱼、海鲈鱼等海水鱼养殖业的发展.

赤点石斑鱼神经坏死病毒外壳蛋白全基因克隆与序列分析

Viral nervous necrosis (VNN) is a worldwide disease among teleost fish. In the mainland of China, VNN was first identified in 2 species of hatchery-reared groupers, Epinephelus akaara and E. coioides. In the present study, samples were collected from larvae of E. akaara with signs of VNN in Dayawan bay which is located in southern China. The complete viral coat protein gene was amplified using extracted total RNA as template. The reverse transcription polymerase chain reaction (RT-PCR) amplification was performed using primers containing a heterologous restriction site for NotI. PCR products were cloned into pcDNA3 vector and sequenced. The results indicated that the coat protein gene of Dayawan isolate (RG-CN) was 1056 bases in length and contained a single open reading frame (ORF) of 1017 bases encoding a protein of 338 amino acids. The sequence similarities between the coat protein gene of RG-CN and other 8 isolates of NNV from Dayawan, Taiwan, Japan, Singapore and France were 79.1%-99.5% at the nucleotide level and 83.7%-100% at the amino acid level, respectively.The homology between RG-CN and the other 5 isolates from groupers was high and relatively lower between RG-CN and guppy nervous necrosis virus (GNNV), sea bass nervous necrosis virus (DIEV), but more divergences existed between RG-CN and striped jack nevous necrosis virus (SJNNV). Compared with SJNNV, RG-CN and the other 7 isolates all lacked 6 nucleotides and 2 amino acids in the same positions. Based on the result of molecular phylogenetic analysis, Dayawan isolate belongs to red-spotted grouper nervous necrosis virus (RGNNV) genotype.

七带石斑鱼神经坏死病毒的RT-LAMP检测方法

报道了一种可以快速、灵敏地检测七带石斑鱼神经坏死病毒(NNV)的逆转录环介导等温扩增方法(RT-LAMP)。该方法参考赤点石斑鱼NNV病毒的主衣壳蛋白(MCP)基因的保守序列,设计1对引物克隆出七带石斑鱼NNV的基因序列,利用Primer Explorer V4软件设计了3对针对所克隆NNV基因序列的特异性引物,建立了RT-LAMP的反应体系,并分别对反应系统的引物浓度、反应温度和时间进行了优化,形成了七带石斑鱼NNV病毒RT-LAMP检测技术。实践应用结果表明,在63℃的最佳反应温度下,采用RT-LAMP检测技术经过45 min就能完成一次检测,准确率达到100%。本研究建立的RT-LAMP检测NNV技术设备要求简单,为七带石斑鱼等石斑鱼无NNV受精卵和仔稚鱼的生产现场检测和筛选提供了一种方便、灵敏的检测方法。

Establishment and Characterization of a Fin Cell Line Derived from the Atlantic Salmon Salmo salar and Its Application to Fish Virology Study

Atlantic salmon(Salmo salar)is an important economic fish that is seriously threatened by various viruses.A cell line designated as ASF derived from the caudal fin tissue of Atlantic salmon was established and characterized in this study.ASF cells grew well in Dulbecco’s modified Eagle’s medium(DMEM)containing 20%fetal bovine serum at 20℃.DNA sequencing and comparative analysis of the cytochrome B gene verified that the ASF cell line originated from Atlantic salmon.Chromosome analysis indicated that the modal chromosome number of ASF cells was 58.Viral susceptibility test showed that ASF cells were susceptive to two important fish viruses,viral hemorrhagic septicemia virus(VHSV)and red-spotted grouper nervous necrosis virus(RGNNV).Viral replication in ASF cells was further confirmed by qRT-PCR and transmission electron microscopy.Moreover,VHSV and RGNNV infections could induce the cellular responses in ASF cells,as indicated by the differential expression of cellular antiviral response-related genes,interferon-1 and Mx-1.In conclusion,the newly established ASF cell line can be applied as an in vitro tool in fish virology and immunity studies.