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Pathogens
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Pathogenesis, Characterization and Vaccine Development of Viral Nervous Necrosis
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Pathogenesis, Characterization and Vaccine Development of Viral Nervous Necrosis

A special issue of Pathogens (ISSN 2076-0817). This special issue belongs to the section "Viral Pathogens".

Deadline for manuscript submissions: closed (31 January 2022) | Viewed by 19106

Special Issue Editors

Dr. Anna Toffan

E-Mail Website
Guest Editor
Istituto Zooprofilattico Sperimentale delle Venezie, 35020 Legnaro, Italy
Interests: diagnosis and control of fish viruses, with special reference to viral nervous necrosis
Dr. Francesco Pascoli

E-Mail Website
Guest Editor
Istituto Zooprofilattico Sperimentale delle Venezie, 35020 Legnaro, Italy
Interests: pathogenesis of fish diseases, with special reference to viral nervous necrosis; in vivo fish experiments
Prof. Dr. Isabel Bandín

E-Mail Website
Guest Editor
Instituto de Acuicultura, Departamento de Microbiología y Parasitología, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain
Interests: fish virology; virulence mechanisms; phylogenetics; diagnostic techniques
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Viral nervous necrosis (VNN), also known as viral encephalo-retinopathy (VER), is a severe neurological disease caused by small RNA viruses belonging to the genus Betanodavirus. The extreme environmental resistance, the increasing host range and the global warming, which will probably contribute to increasing the number/severity of the outbreaks, make the threat posed by this agent to global aquaculture extremely significant. Although the body of knowledge related to VNN has increased considerably in recent years, there are several aspects of the pathogenesis and of the immunological response to natural and experimental infection that need to be further investigated. Additionally, the development of safe and efficacious vaccines is only at the very early stages, and needs to be quickly implemented. Ideally, vaccines should target larvae and broodstock stages and should be cross-protective or applicable to different fish species, in order to help the industry deal with the problem of vertical transmission and farmed–wild fish interaction.

Such knowledge will be instrumental to develop effective VNN control methods and to reduce the impact of this disease on worldwide aquaculture. For these reasons, researchers actively engaged in studies on the characterization of Betanodaviruses by molecular biology, biochemistry, and/or virology; in vivo experiments to unravel disease pathogenesis; as well as vaccine development and testing are enthusiastically encouraged to submit their works to this Special Issue.

Dr. Anna Toffan
Dr. Francesco Pascoli
Prof. Isabel Bandín
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Pathogens is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Betanodaviruses
  • viral nervous necrosis
  • viral encephalo-retinopathy
  • immunity
  • vaccine
  • aquaculture

Published Papers (7 papers)

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Research

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15 pages, 1608 KiB  
Article
Pathogenicity of Different Betanodavirus RGNNV/SJNNV Reassortant Strains in European Sea Bass
by Lorena Biasini, Paola Berto, Miriam Abbadi, Alessandra Buratin, Marica Toson, Andrea Marsella, Anna Toffan and Francesco Pascoli
Pathogens 2022, 11(4), 458; https://doi.org/10.3390/pathogens11040458 - 11 Apr 2022
Cited by 8 | Viewed by 1763
Abstract
European sea bass (Dicentrarchus labrax) is an important farmed marine species for Mediterranean aquaculture. Outbreaks of betanodavirus represent one of the main infectious threats for this species. The red-spotted grouper nervous necrosis virus genotype (RGNNV) is the most widely spread in [...] Read more.
European sea bass (Dicentrarchus labrax) is an important farmed marine species for Mediterranean aquaculture. Outbreaks of betanodavirus represent one of the main infectious threats for this species. The red-spotted grouper nervous necrosis virus genotype (RGNNV) is the most widely spread in Southern Europe, while the striped jack nervous necrosis virus genotype (SJNNV) has been rarely detected. The existence of natural reassortants between these genotypes has been demonstrated, the RGNNV/SJNNV strain being the most common. This study aimed to evaluate the pathogenicity of different RGNNV/SJNNV strains in European sea bass. A selection of nine European reassortants together with parental RGNNV and SJNNV strains were used to perform in vivo experimental challenges via intramuscular injection. Additional in vivo experimental challenges were performed by bath immersion in order to mimic the natural infection route of the virus. Overall, results on survival rates confirmed the susceptibility of European sea bass to reassortants and showed different levels of induced mortalities. Results obtained by RT-qPCR also highlighted high viral loads in asymptomatic survivors, suggesting a possible reservoir role of this species. Our findings on the comparison of complete genomic segments of all reassortants have shed light on different amino acid residues likely involved in the variable pathogenicity of RGNNV/SJNNV strains in European sea bass. Full article
(This article belongs to the Special Issue Pathogenesis, Characterization and Vaccine Development of Viral Nervous Necrosis)
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15 pages, 3934 KiB  
Article
Transmission Pathways of the VNN Introduced in Croatian Marine Aquaculture
by Snježana Zrnčić, Dragan Brnić, Valentina Panzarin, Miriam Abbadi, Ivana Lojkić, Ivana Giovanna Zupičić and Dražen Oraić
Pathogens 2022, 11(4), 418; https://doi.org/10.3390/pathogens11040418 - 30 Mar 2022
Cited by 1 | Viewed by 1878
Abstract
Due to the insufficient capacity of Croatian hatcheries, marine aquaculture depends on the importation of fry from different countries in the Mediterranean basin. Importation enables a risk of spreading pathogenic agents. Viral nervous necrosis (VNN), caused by betanodavirus is devastating for the farming [...] Read more.
Due to the insufficient capacity of Croatian hatcheries, marine aquaculture depends on the importation of fry from different countries in the Mediterranean basin. Importation enables a risk of spreading pathogenic agents. Viral nervous necrosis (VNN), caused by betanodavirus is devastating for the farming of European sea bass. We described a VNN outbreak that occurred in Croatia in 2014. After the diagnosis of VNN in sea bass fry introduced from the same hatchery to five unconnected marine farms at the Adriatic Coast, we performed surveillance within one of the affected farms. It resulted in proven horizontal spreading of the virus within the farm and to feral fish around farm cages. Real-time RT-PCR tested samples showed the dependence of the virus’ proliferation to the water temperature and the fish age. The highest mortality rates were noted during higher sea temperatures. Phylogenetic analysis of partial sequences of RNA1 and RNA2 supported the hypothesis that the virus was introduced to all studied farms from the same hatchery. Moreover, phylogenetic analysis of the whole genome sequences of infected farmed sea bass and thicklip mullet showed high similarity and it is unlikely that infection in Croatian sea bass farms has originated from wild reservoirs, as the first positive record in wild mullet was recorded after the disease outbreak. Full article
(This article belongs to the Special Issue Pathogenesis, Characterization and Vaccine Development of Viral Nervous Necrosis)
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14 pages, 2031 KiB  
Article
Differential Nervous Necrosis Virus (NNV) Replication in Five Putative Susceptible Cell Lines
by Yulema Valero, Carmen López-Vázquez, Sandra Souto, José G. Olveira, Alberto Cuesta and Isabel Bandín
Pathogens 2021, 10(12), 1565; https://doi.org/10.3390/pathogens10121565 - 30 Nov 2021
Cited by 3 | Viewed by 2083
Abstract
Viral encephalopathy and retinopathy caused by nervous necrosis virus (NNV), is one of the most threatening viral diseases affecting marine fish worldwide. In vitro propagation of NNV strains is essential for the design of effective control measures. In the present study we analysed [...] Read more.
Viral encephalopathy and retinopathy caused by nervous necrosis virus (NNV), is one of the most threatening viral diseases affecting marine fish worldwide. In vitro propagation of NNV strains is essential for the design of effective control measures. In the present study we analysed both the susceptibility and the permissiveness of five fish cell lines (E-11, GF-1, SAF-1, DLB-1, and SaB-1) to three NNV strains (one RGNNV, one SJNNV, and one reassortant RGNNV/SJNNV). E-11 and DLB-1 were demonstrated to be highly susceptible to NNV strains, with average adsorption efficiency (AE) values higher than 90%. SAF-1 also showed high susceptibility (AE 88%), whereas GF-1 can be regarded as moderately susceptible (AE around 50%). On the contrary, SaB-1 can be considered a poorly susceptible cell line (AE values below 20%). E-11 and GF-1 cell lines provided the highest production rates for RGNNV and RG/SJ (around 103) and both cell lines can be regarded as fully permissive for these viral types. However, the SJNNV production rate in GF-1 was only 17.8 and therefore this cell line should be considered semi-permissive for this genotype. In SAF-1 cells, moderate viral replication was recorded but differences in intracellular and extracellular production suggest that viral progeny was not efficiently released. In DLB-1 and SaB-1 the final viral titres obtained in E-11 were lower than those of the inoculum. However, RNA1 synthesis values seem to indicate that RGNNV replication in DLB-1 and SAF-1 could have been underestimated, probably due to a poor adaptation of the virus grown in these cell lines to E-11. Based on all these results, E-11 seems to be the most appropriate cell for in vitro culture of RGNNV, SJNNV, and reassortant strains. Full article
(This article belongs to the Special Issue Pathogenesis, Characterization and Vaccine Development of Viral Nervous Necrosis)
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26 pages, 4111 KiB  
Article
Nervous Necrosis Virus-like Particle (VLP) Vaccine Stimulates European Sea Bass Innate and Adaptive Immune Responses and Induces Long-Term Protection against Disease
by Sofie Barsøe, Kerstin Skovgaard, Dagoberto Sepúlveda, Ansgar Stratmann, Niccolò Vendramin and Niels Lorenzen
Pathogens 2021, 10(11), 1477; https://doi.org/10.3390/pathogens10111477 - 12 Nov 2021
Cited by 10 | Viewed by 2391
Abstract
The rapidly increasing Mediterranean aquaculture production of European sea bass is compromised by outbreaks of viral nervous necrosis, which can be recurrent and detrimental. In this study, we evaluated the duration of protection and immune response in sea bass given a single dose [...] Read more.
The rapidly increasing Mediterranean aquaculture production of European sea bass is compromised by outbreaks of viral nervous necrosis, which can be recurrent and detrimental. In this study, we evaluated the duration of protection and immune response in sea bass given a single dose of a virus-like particle (VLP)-based vaccine. Examinations included experimental challenge with nervous necrosis virus (NNV), serological assays for NNV-specific antibody reactivity, and immune gene expression analysis. VLP-vaccinated fish showed high and superior survival in challenge both 3 and 7.5 months (1800 and 4500 dd) post-vaccination (RPS 87 and 88, OR (surviving) = 16.5 and 31.5, respectively, p < 0.01). Although not providing sterile immunity, VLP vaccination seemed to control the viral infection, as indicated by low prevalence of virus in the VLP-vaccinated survivors. High titers of neutralizing and specific antibodies were produced in VLP-vaccinated fish and persisted for at least ~9 months post-vaccination as well as after challenge. However, failure of immune sera to protect recipient fish in a passive immunization trial suggested that other immune mechanisms were important for protection. Accordingly, gene expression analysis revealed that VLP-vaccination induced a mechanistically broad immune response including upregulation of both innate and adaptive humoral and cellular components (mx, isg12, mhc I, mhc II, igm, and igt). No clinical side effects of the VLP vaccination at either tissue or performance levels were observed. The results altogether suggested the VLP-based vaccine to be suitable for clinical testing under farming conditions. Full article
(This article belongs to the Special Issue Pathogenesis, Characterization and Vaccine Development of Viral Nervous Necrosis)
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13 pages, 1483 KiB  
Article
Direct Amperometric Sensing of Fish Nodavirus RNA Using Gold Nanoparticle/DNA-Based Bioconjugates
by Nadia Chérif, Mohamed Zouari, Fatma Amdouni, Marwa Mefteh, Ayoub Ksouri, Balkiss Bouhaouala-Zahar and Noureddine Raouafi
Pathogens 2021, 10(8), 932; https://doi.org/10.3390/pathogens10080932 - 23 Jul 2021
Cited by 9 | Viewed by 2655
Abstract
We describe the design of a simple and highly sensitive electrochemical bioanalytical method enabling the direct detection of a conserved RNA region within the capsid protein gene of a fish nodavirus, making use of nanostructured disposable electrodes. To achieve this goal, we select [...] Read more.
We describe the design of a simple and highly sensitive electrochemical bioanalytical method enabling the direct detection of a conserved RNA region within the capsid protein gene of a fish nodavirus, making use of nanostructured disposable electrodes. To achieve this goal, we select a conserved region within the nodavirus RNA2 segment to design a DNA probe that is tethered to the surface of nanostructured disposable screen-printed electrodes. In a proof-of-principle test, a synthetic RNA sequence is detected based on competitive hybridization between two oligonucleotides (biotinylated reporter DNA and target RNA) complimentary to a thiolated DNA capture probe. The method is further validated using extracted RNA samples obtained from healthy carrier Sparus aurata and clinically infected Dicentrarchus labrax fish specimens. In parallel, the sensitivity of the newly described biosensor is compared with a new real-time RT-PCR protocol. The current differences measured in the negative control and in presence of each concentration of target RNA are used to determine the dynamic range of the assay. We obtain a linear response (R2 = 0.995) over a range of RNA concentrations from 0.1 to 25 pM with a detection limit of 20 fM. The results are in good agreement with the results found by the RT-qPCR. This method provides a promising approach toward a more effective diagnosis and risk assessment of viral diseases in aquaculture. Full article
(This article belongs to the Special Issue Pathogenesis, Characterization and Vaccine Development of Viral Nervous Necrosis)
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Review

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27 pages, 395 KiB  
Review
Integrated Management Strategies for Viral Nervous Necrosis (VNN) Disease Control in Marine Fish Farming in the Mediterranean
by Francesc Padrós, Massimo Caggiano, Anna Toffan, Maria Constenla, Carlos Zarza and Sara Ciulli
Pathogens 2022, 11(3), 330; https://doi.org/10.3390/pathogens11030330 - 08 Mar 2022
Cited by 4 | Viewed by 3834
Abstract
Viral nervous necrosis (VNN) is the most important viral disease affecting farmed fish in the Mediterranean. VNN can affect multiple fish species in all production phases (broodstock, hatchery, nursery and ongrowing) and sizes, but it is especially severe in larvae and juvenile stages, [...] Read more.
Viral nervous necrosis (VNN) is the most important viral disease affecting farmed fish in the Mediterranean. VNN can affect multiple fish species in all production phases (broodstock, hatchery, nursery and ongrowing) and sizes, but it is especially severe in larvae and juvenile stages, where can it cause up to 100% mortalities. European sea bass has been and is still the most affected species, and VNN in gilthead sea bream has become an emerging problem in recent years affecting larvae and juveniles and associated to the presence of new nervous necrosis virus (NNV) reassortants. The relevance of this disease as one of the main biological hazards for Mediterranean finfish farming has been particularly addressed in two recent H2020 projects: PerformFISH and MedAID. The presence of the virus in the environment and in the farming systems poses a serious menace for the development of the Mediterranean finfish aquaculture. Several risks associated to the VNN development in farms have been identified in the different phases of the farming system. The main risks concerning VNN affecting gilthead seabream and European seabass have been identified as restocking from wild fish in broodstock facilities, the origin of eggs and juveniles, quality water supply and live food in hatcheries and nurseries, and infected juveniles and location of farms in endemic areas for on-growing sites. Due to the potential severe impact, a holistic integrated management approach is the best strategy to control VNN in marine fish farms. This approach should include continuous surveillance and early and accurate diagnosis, essential for an early intervention when an outbreak occurs, the implementation of biosecurity and disinfection procedures in the production sites and systematic vaccination with effective vaccines. Outbreak management practices, clinical aspects, diagnostic techniques, and disinfections methods are reviewed in detail in this paper. Additionally, new strategies are becoming more relevant, such as the use of genetic resistant lines and boosting the fish immune system though nutrition. Full article
(This article belongs to the Special Issue Pathogenesis, Characterization and Vaccine Development of Viral Nervous Necrosis)
30 pages, 2167 KiB  
Review
Transcriptomic Analysis of Fish Hosts Responses to Nervous Necrosis Virus
by Dimitra K. Toubanaki, Antonia Efstathiou and Evdokia Karagouni
Pathogens 2022, 11(2), 201; https://doi.org/10.3390/pathogens11020201 - 03 Feb 2022
Cited by 9 | Viewed by 3018
Abstract
Nervous necrosis virus (NNV) has been responsible for mass mortalities in the aquaculture industry worldwide, with great economic and environmental impact. The present review aims to summarize the current knowledge of gene expression responses to nervous necrosis virus infection in different fish species [...] Read more.
Nervous necrosis virus (NNV) has been responsible for mass mortalities in the aquaculture industry worldwide, with great economic and environmental impact. The present review aims to summarize the current knowledge of gene expression responses to nervous necrosis virus infection in different fish species based on transcriptomic analysis data. Four electronic databases, including PubMed, Web of Science, and SCOPUS were searched, and more than 500 publications on the subject were identified. Following the application of the appropriate testing, a total of 24 articles proved eligible for this review. NNV infection of different host species, in different developmental stages and tissues, presented in the eligible publications, are described in detail, revealing and highlighting genes and pathways that are most affected by the viral infection. Those transcriptome studies of NNV infected fish are oriented in elucidating the roles of genes/biomarkers for functions of special interest, depending on each study’s specific emphasis. This review presents a first attempt to provide an overview of universal host reaction mechanisms to viral infections, which will provide us with new perspectives to overcome NNV infection to build healthier and sustainable aquaculture systems. Full article
(This article belongs to the Special Issue Pathogenesis, Characterization and Vaccine Development of Viral Nervous Necrosis)
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