One of the most valuable aquaculture fish in Europe is the rainbow trout, Oncorhynchus mykiss, but the profitability of trout production is threatened by a highly lethal infectious disease, viral hemorrhagic septicemia (VHS), caused by the VHS virus (VHSV). For the past few decades, the subgenogroup Ia of VHSV has been the main cause of VHS outbreaks in European freshwater-farmed rainbow trout. Little is currently known, however, about the phylogenetic radiation of this Ia lineage into subordinate Ia clades and their subsequent geographical spread routes. We investigated this topic using the largest Ia-isolate dataset ever compiled, comprising 651 complete G gene sequences: 209 GenBank Ia isolates and 442 Ia isolates from this study. The sequences come from 11 European countries and cover the period 1971–2015. Based on this dataset, we documented the extensive spread of the Ia population and the strong mixing of Ia isolates, assumed to be the result of the Europe-wide trout trade. For example, the Ia lineage underwent a radiation into nine Ia clades, most of which are difficult to allocate to a specific geographic distribution. Furthermore, we found indications for two rapid, large-scale population growth events, and identified three polytomies among the Ia clades, both of which possibly indicate a rapid radiation. However, only about 4% of Ia haplotypes (out of 398) occur in more than one European country. This apparently conflicting finding regarding the Europe-wide spread and mixing of Ia isolates can be explained by the high mutation rate of VHSV. Accordingly, the mean period of occurrence of a single Ia haplotype was less than a full year, and we found a substitution rate of up to 7.813 × 10−4 nucleotides per site per year. Finally, we documented significant differences between Germany and Denmark regarding their VHS epidemiology, apparently due to those countries’ individual handling of VHS.
Institute of Infectology (IMED) of the Friedrich-Loeffler-Institut (FLI), Federal Research Institute for Animal Health, Insel Riems, Germany;Section for Virology, National Veterinary Institute, DTU, Frederiksberg, Denmark;Fish Health, Department of Animal Science, Aarhus University, Tjele, Denmark;Ploufragan-Plouzané Laboratory (ANSES), Viral Fish Pathology Unit, Université Européenne de Bretagne, Technopôle Brest-Iroise, Plouzané, France;Centre for Fish and Wildlife Health (FIWI), Vetsuisse-Faculty, University of Bern, Bern, Switzerland;Central Veterinary Institute of Wageningen UR, NRL for Fish and Shellfish Diseases, Lelystad, the Netherlands;Central Veterinary Institute of Wageningen UR, NRL for Fish and Shellfish Diseases, Lelystad, the Netherlands;Institute of Infectology (IMED) of the Friedrich-Loeffler-Institut (FLI), Federal Research Institute for Animal Health, Insel Riems, Germany;Istituto Zooprofilattico Sperimentaledelle Venezie, OIE Reference Laboratory for Viral Encephalopathy and Retinopathy, Legnaro, Italy;Centre for Fish and Wildlife Health (FIWI), Vetsuisse-Faculty, University of Bern, Bern, Switzerland;Section for Virology, National Veterinary Institute, DTU, Frederiksberg, Denmark;Institute of Infectology (IMED) of the Friedrich-Loeffler-Institut (FLI), Federal Research Institute for Animal Health, Insel Riems, Germany
Recommended Citation:
Michael Cieslak,Susie S. Mikkelsen,Helle F. Skall,et al. Phylogeny of the Viral Hemorrhagic Septicemia Virus in European Aquaculture[J]. PLOS ONE,2016-01-01,11(10)