title: Viral haemorrhagic septicaemia (VHS) outbreaks in Finnish rainbow trout farms.
abstract: In Finland, viral haemorrhagic septicaemia virus (VHSV) was diagnosed for the first time in 2000 from 4 rainbow trout farms in brackish water. Since then the infection has spread and, by the end of 2004, VHSV had been isolated from 24 farms in 3 separate locations: 2 in the Baltic Sea and 1 in the Gulf of Finland. The pathogenicity of 3 of these isolates from 2 separate locations was analysed in infection experiments with rainbow trout fry. The cumulative mortalities induced by waterborne and intraperitoneal challenge were approximately 40 and 90 %, respectively. Pair-wise comparisons of the G and NV gene regions of Finnish VHSV isolates collected between 2000 and 2004 revealed that all isolates were closely related, with 99.3 to 100% nucleotide identity, which suggests the same origin of infection. Phylogenetic analysis revealed that they were closely related to the old freshwater isolates from rainbow trout in Denmark and to one old marine isolate from cod in the Baltic Sea, and that they were located close to the presumed ancestral source. As the Finnish isolates induce lower mortality than freshwater VHSV isolates in infection experiments, they could represent an intermediate stage of marine isolates evolving towards pathogenicity in rainbow trout.
authors.affiliation: Finnish Food Safety Authority Evira, Department of Animal Diseases and Food Safety Research, Virology Unit, Mustialankatu 3, 00790 Helsinki, Finland.
authors.forename: Marianne
authors.initials: M
authors.lastname: Raja-Halli
authors.forename: Tuija K
authors.initials: TK
authors.lastname: Vehmas
authors.forename: Eija
authors.initials: E
authors.lastname: Rimaila-Pärnänen
authors.forename: Sanna
authors.initials: S
authors.lastname: Sainmaa
authors.forename: Helle Frank
authors.initials: HF
authors.lastname: Skall
authors.forename: Niels Jørgen
authors.initials: NJ
authors.lastname: Olesen
authors.forename: Hannele
authors.initials: H
authors.lastname: Tapiovaara
mesh_terms: D000818:Animals; D016009:Chi-Square Distribution; D017931:DNA Primers / Q000737:chemistry; D004196:Disease Outbreaks / Q000662:veterinary*; D005387:Finland / Q000453:epidemiology; D005398:Fisheries; D014644:Genetic Variation; D006023:Glycoproteins / Q000235:genetics; D031941:Hemorrhagic Septicemia, Viral / Q000453:epidemiology* / Q000401:mortality; D029141:Novirhabdovirus / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity; D017686:Oncorhynchus mykiss / Q000821:virology*; D010802:Phylogeny; D012367:RNA, Viral / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary; D017423:Sequence Analysis, RNA; D013997:Time Factors; D014764:Viral Proteins / Q000235:genetics
chemical_list: D017931:DNA Primers; D006023:Glycoproteins; C096112:NV protein, Rhabdovirus; D012367:RNA, Viral; D014764:Viral Proteins