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Diseases of Aquatic Organisms

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DAO 72:201-211 (2006)  -  doi:10.3354/dao072201

Viral haemorrhagic septicaemia (VHS) outbreaks in Finnish rainbow trout farms

Marianne Raja-Halli1, Tuija K. Vehmas1, Eija Rimaila-Pärnänen2, Sanna Sainmaa1,4, Helle Frank Skall3, Niels Jørgen Olesen3, Hannele Tapiovaara1,*

1Finnish Food Safety Authority Evira, Department of Animal Diseases and Food Safety Research, Virology Unit, Mustialankatu 3, 00790 Helsinki, Finland
2Finnish Food Safety Authority Evira, Department of Animal Diseases and Food Safety Research, Pathology Unit, Mustialankatu 3, 00790 Helsinki, Finland
3Danish Institute for Food and Veterinary Research, Department for Poultry, Fish and Fur Animals, Section for Fish Diseases, Hangøvej 2, 8200 Århus N, Denmark
4Present address: Finlands’s Poultry Association, Keskuskatu 21, 31600 Jokioinen, Finland
*Corresponding author. Email:

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.

KEY WORDS: Viral haemorrhagic septicaemia virus · VHSV · Rainbow trout · Epidemiology

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