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Spring viremia of carp virus (SVCV) has a broad fish host spectrum and is responsible for a disease that generally affects juvenile fishes with a mortality rate of up to 90%. In the absence of treatments or vaccines against SVCV, the search for prophylactic or therapeutic solutions is thus relevant, particularly to identify solutions compatible with mass vaccination. In addition to being a threat to aquaculture and ecosystems, SVCV is a unique pathogen to study virus-host interactions in the zebrafish model. Establishing the first reverse genetics system for SVCV and the design of recombinant SVCV (rSVCV) expressing fluorescent or bioluminescent proteins adds a new dimension for the study of these interactions using innovative imaging techniques. The infection by bath immersion of zebrafish larvae with rSVCV expressing mCherry allows us to define the first SVCV replication sites and the host innate immune responses using different transgenic lines of zebrafish. The fins were found as the main initial sites of infection in both zebrafish and carp, its natural host. Hence, new insights into the physiopathology of SVCV infection have been described. We report that neutrophils are recruited at the sites of infection and persist up to the death of the animal leading to an uncontrolled inflammation correlated with the expression of the pro-inflammatory cytokine IL1β. Tissue damage was observed at the site of initial replication, a likely consequence of virus-induced injury or the pro-inflammatory response. Interestingly, SVCV infection by bath immersion triggers a persistent pro-inflammatory response rather than activation of the antiviral IFN signaling pathway as observed following intravenous injection, highlighting the importance of the route of infection on the progression of pathogenicity. Thus, this model of zebrafish larva infection by rSVCV offers new perspectives to study in detail virus-host interactions and to discover new prophylactic or therapeutic solutions. Author summary: In addition to being a threat to many valuable aquaculture species, spring viremia of carp virus (SVCV) is a model pathogen used to study host immune responses for the zebrafish community. Here, we bring another dimension to these studies thanks to the generation of traceable recombinant viruses by reverse genetics enabling for the first time in vivo imaging of SVCV infection. Upon zebrafish inoculation with a recombinant SVCV expressing mCherry, we established a robust and highly reproducible model of infection based on the natural route of infection. This powerful model allows us to define the first SVCV replication sites, viral spreading, target organs as well as host responses using different transgenic lines of zebrafish. We found that the fins were the main initial sites of infection and not the gills as commonly reported. This was confirmed in carp, the natural host of SVCV. New insights into the physiopathology of SVCV infection have been described. Thus, the development of this standardized model of viral infection in zebrafish larvae opens new perspectives to better understand SVCV infection and to discover antiviral drugs and/or immunomodulating compounds assessed by in vivo high content screening while ensuring 3R compliance on animal experimentation. [ABSTRACT FROM AUTHOR]

West Nile Virus (WNV) is a zoonotic mosquito-transmitted flavivirus that can infect and cause disease in mammals including humans. Our study aimed at developing a WNV vectored vaccine based on a fish Novirhabdovirus, the Viral Hemorrhagic Septicemia virus (VHSV). VHSV replicates at temperatures lower than 20°C and is naturally inactivated at higher temperatures. A reverse genetics system has recently been developed in our laboratory for VHSV allowing the addition of genes in the viral genome and the recovery of the respective recombinant viruses (rVHSV). In this study, we have generated rVHSV vectors bearing the complete WNV envelope gene (EWNV) (rVHSV-EWNV) or fragments encoding E subdomains (either domain III alone or domain III fused to domain II) (rVHSV-DIIIWNV and rVHSV-DII-DIIIWNV, respectively) in the VHSV genome between the N and P cistrons. With the objective to enhance the targeting of the EWNV protein or EWNV-derived domains to the surface of VHSV virions, Novirhadovirus G-derived signal peptide and transmembrane domain (SPG and TMG) were fused to EWNV at its amino and carboxy termini, respectively. By Western-blot analysis, electron microscopy observations or inoculation experiments in mice, we demonstrated that both the EWNV and the DIIIWNV could be expressed at the viral surface of rVHSV upon addition of SPG. Every constructs expressing EWNV fused to SPG protected 40 to 50% of BALB/cJ mice against WNV lethal challenge and specifically rVHSV-SPGEWNV induced a neutralizing antibody response that correlated with protection. Surprisingly, rVHSV expressing EWNV-derived domain III or II and III were unable to protect mice against WNV challenge, although these domains were highly incorporated in the virion and expressed at the viral surface. In this study we demonstrated that a heterologous glycoprotein and non membrane-anchored protein, can be efficiently expressed at the surface of rVHSV making this approach attractive to develop new vaccines against various pathogens. [ABSTRACT FROM AUTHOR]

A recombinant sleeping disease virus (rSDV) was previously shown to be totally attenuated and provide long-term protection in trout (C. Moriette, M. Leberre, A. Lamoureux, T. L. Lai, M. Brémont, J. Virol. 80:4088-4098, 2006). Sequence comparison of the rSDV to wild-type genomes exhibited a number of nucleotide changes. In the current study, we demonstrate that the virulent phenotype of SDV was essentially associated with two amino acid changes, V8A and Ml 36T, in the E2 glycoprotein, with the V8A change mostly being involved in the acquisition of the virulent phenotype. [ABSTRACT FROM AUTHOR]

We report here the first full-length sequence of the eight ssRNA genome segments of the infectious salmon anemia virus (ISAV, Glesvaer/2/90 isolate), a salmonid orthomyxovirus-like. Comparison of ISAV genome sequence with those of others orthomyxovirus reveals low identity values, and a remarkable feature is the extremely long 5' end UTR of ISAV segments, which all contain an additional conserved motif of unknown function. In addition to the genome nucleotide sequence determination, specific mAbs have been produced through mice immunization with sucrose-purified ISAV. Four mAbs directed against the haemagglutinin-esterase glycoprotein, the nucleoprotein and free or actin-associated forms of the matrix protein have been characterized by (i) indirect fluorescent antibody test; (ii) virus neutralization; (iii) radioimmunoprecipitation and (iv) Western blot assays. These mAbs will potentially be useful for the development of new diagnostic tests, and the nucleotide sequences will help to establish a reverse genetics system for ISAV.