title: European freshwater VHSV genotype Ia isolates divide into two distinct subpopulations.
abstract: Viral haemorrhagic septicaemia (VHS), caused by the novirhabdovirus VHSV, often leads to significant economic losses to European rainbow trout production. The virus isolates are divided into 4 distinct genotypes with additional subgroups including sublineage Ia, isolates of which are the main source of outbreaks in European rainbow trout farming. A significant portion of Danish rainbow trout farms have been considered endemically infected with VHSV since the first disease outbreak was observed in the 1950s. However, following a series of sanitary programs starting in 1965, VHSV has not been detected in Denmark since January 2009. Full-length G-genes of all Danish VHSV isolates that were submitted for diagnostic analyses in the period 2004-2009 were sequenced and analysed. All 58 Danish isolates from rainbow trout grouped with sublineage Ia isolates. Furthermore, VHSV isolates from infected Danish freshwater catchments appear to have evolved into a distinct clade within sublineage Ia, herein designated clade Ia-1, whereas trout isolates originating from other continental European countries cluster in another distinct clade, designated clade Ia-2. In addition, phylogenetic analyses indicate that VHSV Ia-1 strains have caused a few outbreaks in Germany and the UK. It is likely that viruses have been transmitted from infected site(s) out of the Danish environment, although a direct transmission pathway has not been identified. Furthermore, VHSV Ia-2 isolates seem to have been transmitted to Denmark at least once. Interestingly, one viral isolate possibly persisted in a Danish watershed for nearly 4 yr without detection whereas other subclades of VHSV isolates appear to have been eliminated, probably because of implemented eradication procedures.
authors.affiliation: National Veterinary Institute, Technical University of Denmark, 8200 Aarhus N, Denmark. ska@teknologisk.dk
authors.forename: S
authors.initials: S
authors.lastname: Kahns
authors.forename: H F
authors.initials: HF
authors.lastname: Skall
authors.forename: R S
authors.initials: RS
authors.lastname: Kaas
authors.forename: H
authors.initials: H
authors.lastname: Korsholm
authors.forename: B
authors.initials: B
authors.lastname: Bang Jensen
authors.forename: S P
authors.initials: SP
authors.lastname: Jonstrup
authors.forename: M J
authors.initials: MJ
authors.lastname: Dodge
authors.forename: K
authors.initials: K
authors.lastname: Einer-Jensen
authors.forename: D
authors.initials: D
authors.lastname: Stone
authors.forename: N J
authors.initials: NJ
authors.lastname: Olesen
mesh_terms: D000818:Animals; D003718:Denmark / Q000453:epidemiology; D005838:Genotype; D031941:Hemorrhagic Septicemia, Viral / Q000453:epidemiology / Q000821:virology*; D029141:Novirhabdovirus / Q000145:classification* / Q000235:genetics*; D017686:Oncorhynchus mykiss; D010802:Phylogeny; D012367:RNA, Viral / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary; D013997:Time Factors
chemical_list: D012367:RNA, Viral