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Bergen, Norway

Karlsen M.,University of Bergen | Villoing S.,Intervet Norbio | Ottem K.F.,University of Bergen | Nylund A.,University of Bergen
BMC Research Notes | Year: 2010

Background. Salmonid alphavirus (SAV) is a widespread pathogen in European aquaculture of salmonid fish. Distinct viral subtypes have been suggested based on sequence comparisons and some of these have different geographical distributions. In Norway, only SAV subtype 3 have so far been identified. Little is known about viral mechanisms important for pathogenesis and transmission. Tools for detailed exploration of SAV genomes are therefore needed. Results. Infectious cDNA clones in which a genome of subtype 3 SAV is under the control of a CMV promoter were constructed. The clones were designed to express proteins that are putatively identical to those previously reported for the SAVH20/03 strain. A polyclonal antiserum was raised against a part of the E2 glycoprotein in order to detect expression of the subgenomic open reading frame (ORF) encoding structural viral proteins. Transfection of the cDNA clone revealed the expression of the E2 protein by IFAT, and in serial passages of the supernatant the presence of infectious recombinant virus was confirmed through RT-PCR, IFAT and the development of a cytopathic effect similar to that seen during infection with wild type SAV. Confirmation that the recovered virus originated from the infectious plasmid was done by sequence identification of an introduced genetic tag. The recombinant virus was infectious also when an additional ORF encoding an EGFP reporter gene under the control of a second subgenomic alphavirus promoter was added. Finally, we used the system to study the effect of selected point mutations on infectivity in Chinook salmon embryo cells. While introduced mutations in nsP2197, nsP3263and nsP3 323severely reduced infectivity, a serine to proline mutation in E2206appeared to enhance the virus titer production. Conclusion. We have constructed infectious clones for SAV based on a subtype 3 genome. The clones may serve as a platform for further functional studies. © 2010 Karlsen et al; licensee BioMed Central Ltd. Source


Metz S.W.,Wageningen University | Feenstra F.,Wageningen University | Villoing S.,Intervet Norbio | van Hulten M.C.,Intervet International BV | And 4 more authors.
PLoS ONE | Year: 2011

Pancreas disease (PD) and sleeping disease (SD) are important viral scourges in aquaculture of Atlantic salmon and rainbow trout. The etiological agent of PD and SD is salmonid alphavirus (SAV), an unusual member of the Togaviridae (genus Alphavirus). SAV replicates at lower temperatures in fish. Outbreaks of SAV are associated with large economic losses of ~17 to 50 million $/year. Current control strategies rely on vaccination with inactivated virus formulations that are cumbersome to obtain and have intrinsic safety risks. In this research we were able to obtain non-infectious virus-like particles (VLPs) of SAV via expression of recombinant baculoviruses encoding SAV capsid protein and two major immunodominant viral glycoproteins, E1 and E2 in Spodoptera frugiperda Sf9 insect cells. However, this was only achieved when a temperature shift from 27°C to lower temperatures was applied. At 27°C, precursor E2 (PE2) was misfolded and not processed by host furin into mature E2. Hence, E2 was detected neither on the surface of infected cells nor as VLPs in the culture fluid. However, when temperatures during protein expression were lowered, PE2 was processed into mature E2 in a temperature-dependent manner and VLPs were abundantly produced. So, temperature shift-down during synthesis is a prerequisite for correct SAV glycoprotein processing and recombinant VLP production. © 2011 Metz et al. Source


Strandskog G.,University of Tromso | Villoing S.,Intervet Norbio | Iliev D.B.,University of Tromso | Thim H.L.,University of Tromso | And 2 more authors.
Developmental and Comparative Immunology | Year: 2011

Both CpG oligodeoxynucleotides and double-stranded RNA (poly I:C) have documented effects as treatments against several viral diseases in fish. However, as stand-alone treatments their effects have been modest. We have tested here whether CpG and poly I:C, alone or in combination induce protection against Salmonid Alphavirus (SAV), the causative agent of pancreas disease in Atlantic salmon. Our results revealed a significant reduction of viraemia 2 weeks after ip injection of the combined treatment and 1 week after challenge with SAV subtype 3, followed by reduced SAV induced heart pathology 3 weeks later. The SAV titers in blood samples from the combination group were lower as compared to single treatments with either CpG or poly I:C. Surprisingly, reduced SAV levels could also be found in fish as long as 7 weeks after receiving the combination treatment. The expression of IFNγ and to a lesser extent IFNa and Mx was up-regulated in head kidney and spleen 5 days after the fish had been treated with CpG and poly I:C. Furthermore, the complement factor C4 was depleted in serum 8 weeks post treatment, suggesting complement activation leading to C4 consumption. We hypothesize that the CpG/poly I:C-induced protection against SAV3 is mediated by mechanisms involving type I and type II IFN induced antiviral activity and complement mediated protective responses. © 2011 Elsevier Ltd. Source


Graham D.A.,Agri Food and Biosciences Institute of Northern Ireland | Frost P.,Intervet Norbio | Mclaughlin K.,Agri Food and Biosciences Institute of Northern Ireland | Rowley H.M.,Agri Food and Biosciences Institute of Northern Ireland | And 3 more authors.
Journal of Fish Diseases | Year: 2011

A comparative challenge study of six marine isolates representing subtypes 1-6 of salmonid alphavirus (salmon pancreas disease virus, Genus Alphavirus, Family Togaviridae) was conducted in Atlantic salmon in a fresh water cohabitation trial. Histopathological lesions typical of pancreas disease were observed with all subtypes, and virus was re-isolated from serum of cohabitant fish in each case. Using a virus neutralization (VN) test neutralizing salmonid alphavirus (SAV) subtype 1 strain F93-125, VN antibodies were detected in all challenge groups, consistent with serological cross-reactivity between these subtypes. Using real-time RT-PCR, SAV RNA was detected in heart tissue from 2 to 3weeks post-challenge (wpc) in all cohabitant groups excluding controls. The results obtained suggested differences in the dynamics of infection between strains of SAV and potentially between subtypes. Results for SAV subtypes 1 and 3 suggested essentially synchronous infection of cohabitant fish. These two study groups also had the highest virus load in heart tissue as measured by quantitative RT-PCR and also had the most extensive histopathological changes. In contrast, results for SAV subtypes 2 and 6 strains were consistent with asynchronous infection in the cohabitant fish and were characterized by slow spread, low virus loads and mild histopathological changes. The SAV subtype 4 and 5 strains occupied an intermediate position in this regard. Despite the use of concentration procedures, it was not possible to detect SAV RNA in water samples from selected study tanks. However, testing of faeces from the SAV subtypes 1, 3 and 6 challenge groups found positive signals in each beginning at 1-3wpc and remaining detectable for a further 2-3weeks. Parallel testing of mucus samples found these became positive at 2-3wpc and remained positive for a further 1-3weeks. These results demonstrate for the first time that shedding and transmission of virus may occur by both these routes and suggest that dispersal in these matrices should be included in any disease transmission models. © 2011 Blackwell Publishing Ltd. Source


Thim H.L.,University of Tromso | Iliev D.B.,University of Tromso | Christie K.E.,Intervet Norbio | Villoing S.,Intervet Norbio | And 3 more authors.
Vaccine | Year: 2012

CpG oligonucleotides and polyinosinic:polycytidylic acid (poly I:C) are toll-like receptor (TLR) agonists that mimic the immunostimulatory properties of bacterial DNA and double-stranded viral RNA respectively, and which have exhibited potential to serve as vaccine adjuvants in previous experiments. Here, a combination of CpGs and poly I:C together with water- or oil-formulated Salmonid Alphavirus (SAV) antigen preparations has been used for a vaccine in Atlantic salmon and tested for protection in SAV challenge trial. The results demonstrate that vaccination with a high dose of the SAV antigen induced protection against challenge with SAV which correlated with production of neutralizing antibodies (NAbs). As the high antigen dose alone induced full protection, no beneficial effect from the addition of CpG and poly I:C could be observed. Nevertheless, these TLR ligands significantly enhanced the levels of NAbs in serum of vaccinated fish. Interestingly, gene expression analysis demonstrated that while addition of oil suppressed the CpG/poly I:C-induced expression of IFN-γ, the upregulation of IFNa1 was substantially enhanced. A low dose of the SAV antigen combined with oil did not induce any detectable levels of NAbs either with or without TLR ligands present, however the addition of CpG and poly I:C to the low SAV antigen dose formulation significantly enhanced the protection against SAV suggesting that CpG/poly I:C may have enhanced a cytotoxic response - a process which is dependent on the up-regulation of type I IFN. These results highlight the immunostimulatory properties of the tested TLR ligands and will serve as a ground for further, more detailed studies aimed to investigate their capacity to serve as adjuvants in vaccine formulations for Atlantic salmon. © 2012 Elsevier Ltd. Source

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