Publications by authors named "Niccolò Vendramin"

18 Publications

  • Page 1 of 1

First description and diagnostics of disease caused by Piscirickettsia salmonis in farmed European sea bass (Dicentrarchus labrax Linnaeus) from Croatia.

J Fish Dis 2021 Mar 23. Epub 2021 Mar 23.

Croatian Veterinary Institute, Zagreb, Croatia.

During the winter of 2013 and 2016, several Croatian fish farms experienced mortalities in the fry of European sea bass, Dicentrarchus labrax. Affected fish showed abnormal swimming behaviour and reduced appetite, and death ensued several days after the onset of clinical signs of disease. Necropsy revealed pale liver, empty digestive tract, distended gall bladder, and hyperaemia and congestion of the meninges. Routine bacteriological examination tested negative, and virological examination ruled out nodavirus infection. Histological examination revealed multifocal necrosis and extensive inflammation in the brain with abundant cellular debris in the ventricles. Inflammatory cells displayed intra-cytoplasmic basophilic vacuoles leading to suspicion of Piscirickettsia salmonis infection. Fluorescent in situ hybridization using an oligonucleotide probe targeting Domain Bacterium applied to tissue sections tested positive. The pathogen was identified by 16S rRNA gene sequencing of brain material, and the sequence showed 99% similarity with P. salmonis. This result enabled the design of an oligonucleotide probe specifically targeting P. salmonis. In 2016, P. salmonis was successfully isolated on CHAB from the brain of an affected specimen and identified using 16S rRNA gene sequencing and MALDI-TOF. This study describes the first outbreak of disease caused by P. salmonis in sea bass in Croatia, while new diagnostic tools will enable further research on its epidemiology and pathogenicity.
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http://dx.doi.org/10.1111/jfd.13366DOI Listing
March 2021

Emergence and Spread of Genotype 3.

Pathogens 2020 Oct 7;9(10). Epub 2020 Oct 7.

Unit for Fish and Shellfish Diseases, National Institute of Aquatic Resources, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.

(PRV) is a relevant pathogen for salmonid aquaculture worldwide. In 2015, a new genotype of PRV (genotype 3, PRV-3) was discovered in Norway, and in 2017 PRV-3 was detected for first time in Denmark in association with complex disease cases in rainbow trout in recirculating aquaculture systems (RAS). To explore the epidemiology of PRV-3 in Denmark, a surveillance study was conducted in 2017 to 2019. Fifty-three farms, including both flow through and RAS, were screened for PRV-3. Of the farms examined, PRV-3 was detected in thirty-eight (71.7%), with the highest prevalence in grow-out farms. Notably, in Denmark disease outbreaks were only observed in RAS. Additionally, wild Atlantic salmon and brown trout populations were included in the screening, and PRV-3 was not detected in the three years where samples were obtained (2016, 2018, and 2019). Historical samples in the form of archived material at the Danish National Reference Laboratory for Fish Diseases were also tested for the presence of PRV-3, allowing us to establish that the virus has been present in Denmark at least since 1995. Sequence analyses of segment S1 and M2, as well as full genome analyses of selected isolates, did not reveal clear association between genetic makeup in these two segments and virulence in the form of disease outbreaks in the field.
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http://dx.doi.org/10.3390/pathogens9100823DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7601675PMC
October 2020

Physiological condition of Eastern Baltic cod, , infected with the parasitic nematode .

Conserv Physiol 2020 22;8(1):coaa093. Epub 2020 Sep 22.

National Institute of Aquatic Resources, Technical University of Denmark (DTU Aqua), Kemitorvet 201, Kgs. Lyngby 2800, Denmark.

Establishing relationships between parasite infection and physiological condition of the host can be difficult and therefore are often neglected when describing factors causing population declines. Using the parasite-host system between the parasitic nematode and the Eastern Baltic cod , we here shed new light on how parasite load may relate to the physiological condition of a transport host. The Eastern Baltic cod is in distress, with declining nutritional conditions, disappearance of the larger fish, high natural mortality and no signs of recovery of the population. During the latest decade, high infection levels with have been observed in fish in the central and southern parts of the Baltic Sea. We investigated the aerobic performance, nutritional condition, organ masses, and plasma and proximate body composition of wild naturally infected in relation to infection density with . Fish with high infection densities of had (i) decreased nutritional condition, (ii) depressed energy turnover as evidenced by reduced standard metabolic rate, (iii) reduction in the digestive organ masses, and alongside (iv) changes in the plasma, body and liver composition, and fish energy source. The significantly reduced albumin to globulin ratio in highly infected suggests that the fish suffer from a chronic liver disease. Furthermore, fish with high infection loads had the lowest Fulton's condition factor. Yet, it remains unknown whether our results steam from a direct effect of , or because in an already compromised nutritional state are more susceptible towards the parasite. Nevertheless, impairment of the physiological condition can lead to reduced swimming performance, compromising foraging success while augmenting the risk of predation, potentially leading to an increase in the natural mortality of the host. We hence argue that fish-parasite interactions must not be neglected when implementing and refining strategies to rebuild deteriorating populations.
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http://dx.doi.org/10.1093/conphys/coaa093DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7507771PMC
September 2020

Piscine orthoreovirus: Biology and distribution in farmed and wild fish.

J Fish Dis 2020 Nov 15;43(11):1331-1352. Epub 2020 Sep 15.

Pacific Biological Station, Fisheries and Oceans Canada, Nanaimo, BC, Canada.

Piscine orthoreovirus (PRV) is a common and widely distributed virus of salmonids. Since its discovery in 2010, the virus has been detected in wild and farmed stocks from North America, South America, Europe and East Asia in both fresh and salt water environments. Phylogenetic analysis suggests three distinct genogroups of PRV with generally discrete host tropisms and/or regional patterns. PRV-1 is found mainly in Atlantic (Salmo salar), Chinook (Oncorhynchus tshawytscha) and Coho (Oncorhynchus kisutch) Salmon of Europe and the Americas; PRV-2 has only been detected in Coho Salmon of Japan; and PRV-3 has been reported primarily in Rainbow Trout (Oncorhynchus mykiss) in Europe. All three genotypes can establish high-load systemic infections by targeting red blood cells for principal replication. Each genotype has also demonstrated potential to cause circulatory disease. At the same time, high-load PRV infections occur in non-diseased salmon and trout, indicating a complexity for defining PRV's role in disease aetiology. Here, we summarize the current body of knowledge regarding PRV following 10 years of study.
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http://dx.doi.org/10.1111/jfd.13228DOI Listing
November 2020

Characterization of ranaviruses isolated from lumpfish L. in the North Atlantic area: proposal for a new ranavirus species (European North Atlantic Ranavirus).

J Gen Virol 2020 02 20;101(2):198-207. Epub 2019 Dec 20.

Technical University of Denmark, National Institute of Aquatic Resources, Aquatic Animal Health Unit, Kgs. Lyngby, Denmark.

The commercial production of lumpfish L. is expanding with the increased demand for their use as cleaner fish, to control sea-lice numbers, at marine Atlantic salmon L. aquaculture sites throughout Northern Europe. A new ranavirus has been isolated from lumpfish at multiple locations in the North Atlantic area. First isolated in 2014 in the Faroe Islands, the virus has subsequently been found in lumpfish from Iceland in 2015 and from Scotland and Ireland in 2016. The Icelandic lumpfish ranavirus has been characterized by immunofluorescent antibody test, optimal growth conditions and transmission electron microscopy. Partial sequences of the major capsid protein gene from 12 isolates showed 99.79-100% nt identity between the lumpfish ranaviruses. Complete genome sequencing from three of the isolates and phylogenetic analysis based on the concatenated 26 iridovirus core genes suggest these lumpfish ranavirus isolates form a distinct clade with ranaviruses from cod L. and turbot L. isolated in Denmark in 1979 and 1999, respectively. These data suggest that these viruses should be grouped together as a new ranavirus species, European North Atlantic Ranavirus, which encompasses ranaviruses isolated from marine fishes in European North Atlantic waters.
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http://dx.doi.org/10.1099/jgv.0.001377DOI Listing
February 2020

Lumpfish (Cyclopterus lumpus, Linnaeus) is susceptible to viral nervous necrosis: Result of an experimental infection with different genotypes of Betanodavirus.

J Fish Dis 2019 Dec 14;42(12):1667-1676. Epub 2019 Oct 14.

National Institute of Aquatic Resources, EURL for fish and crustacean diseases, Technical University of Denmark, Lyngby, Denmark.

In recent years, the use of cleaner fish for biological control of sea lice has increased considerably. Along with this, a number of infectious diseases have emerged. The aim of this study was to investigate the susceptibility of lumpfish (Cyclopterus lumpus) to Betanodavirus since it was detected in asymptomatic wild wrasses in Norway and Sweden. Three betanodaviruses were used to challenge lumpfish: one RGNNV genotype and two BFNNV genotypes. Fish were injected and monitored for 4 weeks. Brain samples from clinically affected specimens, from weekly randomly selected fish and survivors were subjected to molecular testing, viral isolation, histopathology and immunohistochemistry. Reduced survival was observed but was attributed to tail-biting behaviour, since no nervous signs were observed throughout the study. Betanodavirus RNA was detected in all samples, additionally suggesting an active replication of the virus in the brain. Viral isolation confirmed molecular biology results and revealed a high viral titre in BFNNV-infected groups associated with typical lesions in brains and eyes of survivor fish. We concluded that lumpfish are susceptible to Betanodavirus, as proven by the high viral titre and brain lesions detected, but further studies are necessary to understand if Betanodavirus can cause clinical disease in this species.
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http://dx.doi.org/10.1111/jfd.13088DOI Listing
December 2019

Detection of Salmonid IgM Specific to the Outer Capsid Spike Protein Sigma 1 Using Lipid-Modified Antigens in a Bead-Based Antibody Detection Assay.

Front Immunol 2019 6;10:2119. Epub 2019 Sep 6.

Department of Fish Health, Norwegian Veterinary Institute, Oslo, Norway.

Bead-based multiplex immunoassays are promising tools for determination of the specific humoral immune response. In this study, we developed a multiplexed bead-based immunoassay for the detection of Atlantic salmon () antibodies against (PRV). Three different genotypes of PRV (PRV-1, PRV-2, and PRV-3) cause disease in farmed salmonids. The PRV outer capsid spike protein σ1 is predicted to be a host receptor binding protein and a target for neutralizing and protective antibodies. While recombinant σ1 performed poorly as an antigen to detect specific antibodies, N-terminal lipid modification of recombinant PRV-1 σ1 enabled sensitive detection of specific IgM in the bead-based assay. The specificity of anti-PRV-1 σ1 antibodies was confirmed by western blotting and pre-adsorption of plasma. Binding of non-specific IgM to beads coated with control antigens also increased after PRV infection, indicating a release of polyreactive antibodies. This non-specific binding was reduced by heat treatment of plasma. The same immunoassay also detected anti-PRV-3 σ1 antibodies from infected rainbow trout. In summary, a refined bead based immunoassay created by N-terminal lipid-modification of the PRV-1 σ1 antigen allowed sensitive detection of anti-PRV-1 and anti-PRV-3 antibodies from salmonids.
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http://dx.doi.org/10.3389/fimmu.2019.02119DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6743345PMC
October 2020

Presence and genetic variability of Piscine orthoreovirus genotype 1 (PRV-1) in wild salmonids in Northern Europe and North Atlantic Ocean.

J Fish Dis 2019 Aug 28;42(8):1107-1118. Epub 2019 May 28.

National Institute of Aquatic Resources, Technical University of Denmark, Lyngby, Denmark.

Piscine orthoreovirus genotype 1 (PRV-1) is widespread in farmed Atlantic salmon (Salmo salar L.) populations in northern Europe, Canada and Chile. PRV-1 occurs in wild fish in Norway and Canada; however, little information of its geographical distribution in wild populations is currently available, and the effect of PRV-1 infection in wild populations is currently unknown. In this study, we present the findings of a survey conducted on 1,130 wild salmonids sampled in Denmark, Sweden, Ireland, Faroe Islands, France, Belgium and Greenland between 2008 and 2017. PRV-1 is reported for the first time in wild salmonids in Denmark, Sweden, Faroe Island and Ireland. The annual PRV-1 prevalence ranged from 0% in France, Belgium and Greenland to 43% in Faroe Islands. In total, 66 samples tested positive for PRV-1, including Atlantic salmon broodfish returning to spawn and Atlantic salmon collected at the feeding ground north of Faroe Islands. The phylogenetic analysis of S1 sequences of the PRV-1 isolates obtained in this survey did not show systematic geographical distribution. This study sheds light on the spread and genetic diversity of the virus identified in populations of free-living fish and provides rationale for screening wild broodfish used in restocking programmes.
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http://dx.doi.org/10.1111/jfd.13025DOI Listing
August 2019

Piscine orthoreovirus subtype 3 (PRV-3) causes heart inflammation in rainbow trout (Oncorhynchus mykiss).

Vet Res 2019 Feb 18;50(1):14. Epub 2019 Feb 18.

National Institute of Aquatic Resources, Technical University of Denmark, Kongens Lyngby, Denmark.

Piscine orthoreovirus (PRV) mediated diseases have emerged throughout salmonid aquaculture. Three PRV subtypes are currently reported as causative agents of or in association with diseases in different salmonid species. PRV-1 causes heart and skeletal muscle inflammation (HSMI) in Atlantic salmon (Salmo salar) and is associated with jaundice syndrome in farmed chinook salmon (Oncorhynchus tshawytscha). PRV-2 causes erythrocytic inclusion body syndrome (EIBS) in coho salmon in Japan. PRV-3 has recently been associated with a disease in rainbow trout (Oncorhynchus mykiss) characterized by anaemia, heart and red muscle pathology; to jaundice syndrome in coho salmon (Oncorhynchus kisutch). In this study, we conducted a 10-week long experimental infection trial in rainbow trout with purified PRV-3 particles to assess the causal relationship between the virus and development of heart inflammation. The monitoring the PRV-3 load in heart and spleen by RT-qPCR shows a progressive increase of viral RNA to a peak, followed by clearance without a measurable change in haematocrit. The development of characteristic cardiac histopathological findings occurred in the late phase of the trial and was associated with increased expression of CD8+, indicating cytotoxic T cell proliferation. The findings indicate that, under these experimental conditions, PRV-3 infection in rainbow trout act similarly to PRV-1 infection in Atlantic salmon with regards to immunological responses and development of heart pathology, but not in the ability to establish a persistent infection.
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http://dx.doi.org/10.1186/s13567-019-0632-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6380033PMC
February 2019

Outbreak of viral haemorrhagic septicaemia (VHS) in lumpfish (Cyclopterus lumpus) in Iceland caused by VHS virus genotype IV.

J Fish Dis 2019 Jan 5;42(1):47-62. Epub 2018 Nov 5.

European Union Reference Laboratory for Fish Diseases, National Institute for Aquatic Resources, Technical University of Denmark, Copenhagen, Denmark.

A novel viral haemorrhagic septicaemia virus (VHSV) of genotype IV was isolated from wild lumpfish (Cyclopterus lumpus), brought to a land-based farm in Iceland, to serve as broodfish. Two groups of lumpfish juveniles, kept in tanks in the same facility, got infected. The virus isolated was identified as VHSV by ELISA and real-time RT-PCR. Phylogenetic analysis, based on the glycoprotein (G) gene sequences, may indicate a novel subgroup of VHSV genotype IV. In controlled laboratory exposure studies with this new isolate, there was 3% survival in the I.P. injection challenged group while there was 90% survival in the immersion group. VHSV was not re-isolated from fish challenged by immersion. In a cohabitation trial, lumpfish infected I.P. (shedders) were placed in tanks with naïve lumpfish as well as naïve Atlantic salmon (Salmo salar L.). 10% of the lumpfish shedders and 43%-50% of the cohabiting lumpfish survived after 4 weeks. 80%-92% of the Atlantic salmon survived, but no viral RNA was detected by real-time RT-PCR nor VHSV was isolated from Atlantic salmon. This is the first isolation of a notifiable virus in Iceland and the first report of VHSV of genotype IV in European waters.
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http://dx.doi.org/10.1111/jfd.12910DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7379627PMC
January 2019

Detection of piscine orthoreoviruses (PRV-1 and PRV-3) in Atlantic salmon and rainbow trout farmed in Germany.

Transbound Emerg Dis 2019 Jan 23;66(1):14-21. Epub 2018 Nov 23.

Fish Disease Research Unit, Institute for Parasitology, University of Veterinary Medicine, Hannover, Germany.

Piscine orthoreoviruses (PRVs) are emerging pathogens causing circulatory disorders in salmonids. PRV-1 is the etiological cause of heart and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon (Salmo salar), characterized by epicarditis, inflammation and necrosis of the myocardium, myositis and necrosis of red skeletal muscle. In 2017, two German breeding farms for Atlantic salmon and rainbow trout (Oncorhynchus mykiss) experienced disease outbreaks with mortalities of 10% and 20% respectively. The main clinical signs were exhaustion and lethargic behaviour. During examinations, PRV-1 in salmon and PRV-3 in trout were detected for the first time in Germany. Further analyses also indicated the presence of Aeromonas salmonicida in internal tissues of both species. While PRV-1 could be putatively linked with the disease in Atlantic salmon, most of the rainbow trout suffered from an infection with A. salmonicida and not with PRV-3. Interestingly, the sequence analysis suggests that the German PRV-3 isolate is more similar to a Chilean PRV-3 isolate from Coho salmon (Oncorhynchus kisutch) than to PRV-3 from rainbow trout from Norway. This indicates a wide geographic distribution of this virus or dispersal by global trade. These findings indicate that infections with PRVs should be considered when investigating disease outbreaks in salmonids.
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http://dx.doi.org/10.1111/tbed.13018DOI Listing
January 2019

Partial validation of a TaqMan real-time quantitative PCR for the detection of ranaviruses.

Dis Aquat Organ 2018 May;128(2):105-116

Department of Infectious Diseases and Pathology, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610, USA.

Ranaviruses are globally emerging pathogens negatively impacting wild and cultured fish, amphibians, and reptiles. Although conventional and diagnostic real-time PCR (qPCR) assays have been developed to detect ranaviruses, these assays often have not been tested against the known diversity of ranaviruses. Here we report the development and partial validation of a TaqMan real-time qPCR assay. The primers and TaqMan probe targeted a conserved region of the major capsid protein (MCP) gene. A series of experiments using a 10-fold dilution series of Frog virus 3 (FV3) MCP plasmid DNA revealed linearity over a range of 7 orders of magnitude (107-101), a mean correlation coefficient (R2) of >0.99, and a mean efficiency of 96%. The coefficient of variation of intra- and inter-assay variability ranged from <0.1-3.5% and from 1.1-2.3%, respectively. The analytical sensitivity was determined to be 10 plasmid copies of FV3 DNA. The qPCR assay detected a panel of 33 different ranaviral isolates originating from fish, amphibian, and reptile hosts from all continents excluding Africa and Antarctica, thereby representing the global diversity of ranaviruses. The assay did not amplify highly divergent ranaviruses, members of other iridovirus genera, or members of the alloherpesvirus genus Cyprinivirus. DNA from fish tissue homogenates previously determined to be positive or negative for the ranavirus Epizootic hematopoietic necrosis virus by virus isolation demonstrated a diagnostic sensitivity of 95% and a diagnostic specificity of 100%. The reported qPCR assay provides an improved expedient diagnostic tool and can be used to elucidate important aspects of ranaviral pathogenesis and epidemiology in clinically and sublinically affected fish, amphibians, and reptiles.
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http://dx.doi.org/10.3354/dao03214DOI Listing
May 2018

Molecular and Antigenic Characterization of Piscine orthoreovirus (PRV) from Rainbow Trout (Oncorhynchus mykiss).

Viruses 2018 04 2;10(4). Epub 2018 Apr 2.

Department of Food Safety and Infection Biology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 0454 Oslo, Norway.

(PRV-1) causes heart and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon (). Recently, a novel PRV (formerly PRV-Om, here called PRV-3), was found in rainbow trout () with HSMI-like disease. PRV is considered to be an emerging pathogen in farmed salmonids. In this study, molecular and antigenic characterization of PRV-3 was performed. Erythrocytes are the main target cells for PRV, and blood samples that were collected from experimentally challenged fish were used as source of virus. Virus particles were purified by gradient ultracentrifugation and the complete coding sequences of PRV-3 were obtained by Illumina sequencing. When compared to PRV-1, the nucleotide identity of the coding regions was 80.1%, and the amino acid identities of the predicted PRV-3 proteins varied from 96.7% (λ1) to 79.1% (σ3). Phylogenetic analysis showed that PRV-3 belongs to a separate cluster. The region encoding σ3 were sequenced from PRV-3 isolates collected from rainbow trout in Europe. These sequences clustered together, but were distant from PRV-3 that was isolated from rainbow trout in Norway. Bioinformatic analyses of PRV-3 proteins revealed that predicted secondary structures and functional domains were conserved between PRV-3 and PRV-1. Rabbit antisera raised against purified virus or various recombinant virus proteins from PRV-1 all cross-reacted with PRV-3. Our findings indicate that despite different species preferences of the PRV subtypes, several genetic, antigenic, and structural properties are conserved between PRV-1 and-3.
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http://dx.doi.org/10.3390/v10040170DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5923464PMC
April 2018

Virulence marker candidates in N-protein of viral haemorrhagic septicaemia virus (VHSV): virulence variability within VHSV Ib clones.

Dis Aquat Organ 2018 Mar;128(1):51-62

Tamaki Laboratory, Research Center for Fish Diseases, National Research Institute of Aquaculture, Fisheries Research Agency, 224-1 Hiruda, Tamaki, Mie 519-0423, Japan.

Four major genotypes of viral haemorrhagic septicaemia virus (VHSV), which have been isolated from many marine and freshwater fish species, are known to differ in virulence. While fast and low-cost genotyping systems based on monoclonal antibodies (MAbs) have been developed for typing of VHSV virulence, there is a need for supplementing the knowledge. In particular, 2 field isolates from viral haemorrhagic septicaemia (VHS) outbreaks in sea-reared rainbow trout Oncorhynchus mykiss in Sweden, SE-SVA-14 and SE-SVA-1033 (both genotype Ib), have yielded contradictory reactions. In the present study, upon cloning by limited dilution, both isolates appeared to be heterogeneous in terms of reactivity with nucleo (N)-protein-specific MAbs as well their gene sequences. Infection trials in rainbow trout further revealed differences in the virulence of these virus clones derived from the same primary isolate. Based on a comparative analysis of the entire genome of the clones tested, we suggest that the differences in virulence are tentatively linked to substitutions of amino acids (aa) in the N-protein region covered by aa 43-46 and aa position 168, or a combination of the two. The fact that such minor naturally occurring genetic differences affect the virulence implies that even low-virulent VHSV isolates in the marine environment should be considered as a potential threat for the trout farming industry. The described MAbs can represent useful tools for initial risk assessment of disease outbreaks in farmed trout by marine VHSV isolates.
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http://dx.doi.org/10.3354/dao03215DOI Listing
March 2018

Piscine orthoreovirus infection in Atlantic salmon (Salmo salar) protects against subsequent challenge with infectious hematopoietic necrosis virus (IHNV).

Vet Res 2018 03 13;49(1):30. Epub 2018 Mar 13.

National Veterinary Institute, Technical University of Denmark, Copenhagen, Denmark.

Infectious hematopoietic necrosis virus (IHNV) is endemic in farmed rainbow trout in continental Europe and in various salmonid fish species at the Pacific coast of North America. IHN has never occurred in European Atlantic salmon (Salmo salar) farms, but is considered as a major threat for the European salmon industry. Another virus, Piscine orthoreovirus (PRV), is widespread in the sea phase of Atlantic salmon, and is identified as the causative agent of heart and skeletal muscle inflammation. The aim of this study was to investigate the interactions between a primary PRV infection and a secondary IHNV infection under experimental conditions. A PRV cohabitation challenge was performed with Atlantic salmon. At peak of PRV viremia the fish were challenged by immersion with an IHNV genogroup E isolate. Clinical signs and morbidity were monitored. Target organs were sampled at selected time points to assess viral loads of both pathogens. Antiviral immune response and presence of histopathological findings were also investigated. Whereas the PRV-negative/IHNV positive group suffered significant decrease in survival caused by IHNV, the PRV infected groups did not suffer any morbidity and showed negligible levels of IHNV infection. Antiviral response genes were induced, as measured in spleen samples, from PRV infected fish prior to IHNV challenge. In conclusion, PRV-infection protects Atlantic salmon against IHNV infection and morbidity, most likely by inducing a protective innate antiviral response.
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http://dx.doi.org/10.1186/s13567-018-0524-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5850924PMC
March 2018

Infection experiments with novel Piscine orthoreovirus from rainbow trout (Oncorhynchus mykiss) in salmonids.

PLoS One 2017 5;12(7):e0180293. Epub 2017 Jul 5.

Norwegian Veterinary Institute, Oslo & Bergen, Norway.

A new disease in farmed rainbow trout (Onchorhyncus mykiss) was described in Norway in 2013. The disease mainly affected the heart and resembled heart and skeletal muscle inflammation (HSMI) in Atlantic salmon (Salmo salar L.). HSMI is associated with Piscine orthoreovirus (PRV), and a search for a similar virus in the diseased rainbow trout led to detection of a sequence with 85% similarity to PRV. This finding called for a targeted effort to assess the risk the new PRV-variant pose on farmed rainbow trout and Atlantic salmon by studying infection and disease pathogenesis, aiming to provide more diagnostic knowledge. Based on the genetic relationship to PRV, the novel virus is referred to as PRV-Oncorhynchus mykiss (PRV-Om) in contrast to PRV-Salmo salar (PRV-Ss). In experimental trials, intraperitoneally injected PRV-Om was shown to replicate in blood in both salmonid species, but more effectively in rainbow trout. In rainbow trout, the virus levels peaked in blood and heart of cohabitants 6 weeks post challenge, along with increased expression of antiviral genes (Mx and viperin) in the spleen, with 80-100% of the cohabitants infected. Heart inflammation was diagnosed in all cohabitants examined 8 weeks post challenge. In contrast, less than 50% of the Atlantic salmon cohabitants were infected between 8 and 16 weeks post challenge and the antiviral response in these fish was very low. From 12 weeks post challenge and onwards, mild focal myocarditis was demonstrated in a few virus-positive salmon. In conclusion, PRV-Om infects both salmonid species, but faster transmission, more notable antiviral response and more prominent heart pathology were observed in rainbow trout.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0180293PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5497981PMC
October 2017

A single amino acid mutation (I1012F) of the RNA polymerase of marine viral hemorrhagic septicemia virus changes in vitro virulence to rainbow trout gill epithelial cells.

J Virol 2014 Jul 9;88(13):7189-98. Epub 2014 Apr 9.

Norwegian University of Life Sciences, Oslo, Norway

Unlabelled: Viral hemorrhagic septicemia virus (VHSV) is separated into four different genotypes (I to IV) with different sublineages (K. Einer-Jensen, P. Ahrens, R. Forsberg, and N. Lorenzen, J. Gen. Virol. 85:1167-1179, 2004; K. Einer-Jensen, J. Winton, and N. Lorenzen, Vet. Microbiol. 106:167-178, 2005). European marine VHSV strains (of genotypes I to III) are, in general, nonpathogenic or have very low pathogenicity to rainbow trout after a waterborne challenge, and here we also show that genotype IVa is nonpathogenic to trout. Despite several attempts, it has not been possible to link genomic variation to in vivo virulence. In vitro virulence to gill epithelial cells (GECs) has been used as a proxy for in vivo virulence, and here we extend these studies further with the purpose of identifying residues associated with in vitro virulence. Genotype Ia (DK-3592B) and III (NO/650/07) isolates, which are pathogenic to rainbow trout (O. B. Dale, I. Orpetveit, T. M. Lyngstad, S. Kahns, H. F. Skall, N. J. Olesen, and B. H. Dannevig, Dis. Aquat. Organ. 85:93-103, 2009), were compared to two marine strains that are nonpathogenic to trout, genotypes Ib (strain 1p8 [H. F. Mortensen, O. E. Heuer, N. Lorenzen, L. Otte, and N. J. Olesen, Virus Res. 63:95-106, 1999]) and IVa (JF-09). DK-3592 and NO/650/07 were pathogenic to GECs, while marine strains 1p8 and JF-09 were nonpathogenic to GECs. Eight conserved amino acid substitutions contrasting high- and low-virulence strains were identified, and reverse genetics was used in a gain-of-virulence approach based on the JF-09 backbone. Mutations were introduced into the G, NV, and L genes, and seven different virus clones were obtained. For the first time, we show that a single amino acid mutation in conserved region IV of the L protein, I1012F, rendered the virus able to replicate and induce a cytopathic effect in trout GECs. The other six mutated variants remained nonpathogenic.

Importance: This is the first study to clearly link in vitro virulence of viral hemorrhagic septicemia virus (VHSV) with an amino acid residue in the L protein, a site located in conserved region IV of the L protein. In vitro virulence is documented by induction of cytopathic effects and viability studies of gill epithelial cells, and the observed cellular responses to infection are associated with increased viral replication levels. There are no previous studies addressing the importance of the L protein or the RNA-dependent RNA polymerase for virus virulence in vitro or in vivo. Therefore, the findings reported here should broaden the search for pathogenicity traits in novirhabdoviruses, and there is a possibility that the polymerase participates in defining the host species virulence of various VHSV strains.
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http://dx.doi.org/10.1128/JVI.00423-14DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4054441PMC
July 2014

Viral Encephalopathy and Retinopathy in groupers (Epinephelus spp.) in southern Italy: a threat for wild endangered species?

BMC Vet Res 2013 Jan 26;9:20. Epub 2013 Jan 26.

Istituto Zooprofilattico Sperimentale delle Venezie, viale dell'Università, 10-35020 Legnaro, Padova, Italy.

Background: Betanodaviruses are the causative agents of Viral Encephalopathy and Retinopathy (VER). To date, more than 50 species have proved to be susceptible and among them, those found in genus Epinephelus are highly represented. Clinical disease outbreaks are generally characterized by typical nervous signs and significant mortalities mainly associated with aquaculture activities, although some concerns for the impact of this infection in wild fish have been raised. In this study, the authors present the first documented report describing an outbreak of VER in wild species in the Mediterranean basin.

Case Presentation: In late summer--early winter 2011 (September-December), significant mortalities affecting wild Dusky grouper (Epinephelus marginatus), Golden grouper (Epinephelus costae) and European sea bass (Dicentrarchus labrax) were reported in the municipality of Santa Maria di Leuca (Northern Ionian Sea, Italy). The affected fish showed an abnormal swimming behavior and swollen abdomens. During this epizootic, five moribund fish showing clear neurological signs were captured and underwent laboratory investigations. Analytical results confirmed the diagnosis of VER in all the specimens. Genetic characterization classified all betanodavirus isolates as belonging to the RGNNV genotype, revealing a close genetic relationship with viral sequences obtained from diseased farmed fish reared in the same area in previous years.

Conclusion: The close relationship of the viral sequences between the isolates collected in wild affected fish and those isolated during clinical disease outbreaks in farmed fish in the same area in previous years suggests a persistent circulation of betanodaviruses and transmission between wild and farmed stocks. Further investigations are necessary to assess the risk of viral transmission between wild and farmed fish populations, particularly in marine protected areas where endangered species are present.
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http://dx.doi.org/10.1186/1746-6148-9-20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3566913PMC
January 2013