Viral haermorrhagic septicaemia virus (VHSV) in wild and farmed fish in Norway

Screening The sampling of wild fish started in 2009 and finished in November 2011. 2700 fish from 43 different fish species have been sampled. Fish like cod and herring are couth by trawling, while sea trout, wrasse etc. are couth by fishing or traps. M ost of the samples are tested in cell culture, and some are tested by real time rt-PCR. Presentations of the screening were given at the Havbrukskonferanse 2010, FriskFisk2011, EAFP conference 2013 and several international meetings listed in the publica tion list. Viral haemorrhagic septicemia virus (VHSV) has been detected in several herring both in Finnmark and on the west coast. This is the first detection of VHS-virus that far north and the preliminary results have been published at www.forskning .no/artikler/2011/september/297742. Testing of herring during the spawning season of 2010 showed a high prevalence of VHS-virus especially in the gills. These results were presented at the EAFP-conference in Split 2011 and www.forskning.no/artikler/2 011/november/303755. Results are published in MEPS (Johansen et al 2013) Lately VHSV has also been detected in silver cod and the sequences show that this is also a genotype Ib. Some additional PCR testing, sequencing etc. is needed on the large scree ning paper and this will be analyzed this fall. A selection of the material sampled in this project has also been tested for Piscine Myocarditis virus (PMCV) and Piscine reovirus (PRV) with positive results (Bockerman et al. 2011, Wiik-Nielsen et al. 2012). This shows the potensiale for further use of this material and we have a new NFR-project for testing the same material also for Salmonid alphavirus (SAV) and Infectious salmonid anemia virus (ISAV) (NFR-project 224931). Challenge trails We ha ve succeeded in challenging cod with the VHS-virus isolate from Storfjorden. The first challenge trail were done by i.p. injection, and resulted in high mortality rates. A cohabitant challenge showed no mortality and low susceptibility. Histopathology and immunohistochemistry show virus detection in many organs of the i.p. inj. fish, and the paper is submitted to Diseases of Aquatic animals (DAO). The EU project NADIR has provided financing of a challenge trail on herring in Århus Denmark. The VHS-vir us isolated from herring in Norway killed 46% of the herring. Histopathology and immunohistochemistry confirms that the herring died from VHS. Further analyzing of the material will be done in the VHSV-wild-farmed-project and published in 2013. Results so far are published on www.forskning.no/artikler/2012/august/332054 and presented at the EAFP-conference in Tampere Finland. VHS-virus testing Most screening programs for VHS-virus are done by sampling several organs from 5 fish and testing the pooled organs in cell culture. We have sampled both pooled organs from 5 fish and separate organs in RNAlater from individual fish. This has provided us with a unique opportunity to compare these two sampling routines. The results show clearly that RT-PCR on si ngle organs provides a much higher prevalence of detection than pooled organs on cell culture. Gills were only sampled on RNAlater and tested by RT-PCR. The gills show a much higher prevalence of VHS-virus than the internal organs (heart, kidney, spleen, brain). Whether this represents a real gill inflammation or exogenously bound virus needs to be further investigated. Epidemiology A risk-based surveillance system has been established and the model has been presented on several international meetin gs. Results were presented at the EAFP-conference in Split and a report has been made to the food safety authorities. A research paper is in preparation. LITERATURE CITED Bockerman I, Wiik-Nielsen CR, Sindre H, Johansen R, Tengs T (2011) Prevalen ce of piscine myocarditis virus (PMCV) in marine fish species. Journal of fish diseases 34:955-957 Johansen et al. 2013 "High prevalence og viral haemorrhagic septicaemia virus (VHSV) in Norwegian spring-spawning herring" Marine Ecology Progress Serie s 478: 223-230 Wiik-Nielsen CR, Lovoll M, Sandlund N, Faller R, Wiik-Nielsen J, Bang Jensen B (2012) First detection of piscine reovirus (PRV) in marine fish species. Dis Aquat Organ 97:255-258

An overview of reduction in the project due to reduction in the budget is provided in the revised project description attached. Viral Haemorrhagic septicaemia virus (VHSV), the causative agent of viral haemorrhagic septicaemia (VHS), is widespread among several fresh water and marine fish species, both farmed and wild. The virulence of different VHSV strains to different fish species varies, and rainbow trout Oncorhynchus mykiss is regarded as one of the most susceptible species. The presence of VHSV in wild fish has been considered as a threat to the salmonid farming industry. The recent outbreak of VHS in sea farmed rainbow trout in Western Norway (Storfjorden) was caused by VHSV of a genotype that has hitherto only been detected in wild marine speci es and has never earlier been associated with outbreak of VHS in farmed salmonids. The proposal suggests an approach to this objective by screening saltwater populations of wild fish species, including salmonids, for VHSV with subsequent genetic characte rization of detected virus. Experimental pathogenicity studies performed on susceptible species and development of a risk-based surveillance system will contribute to the understanding of possible transmission of VHSV from wild to farmed fish and vice ver sa.