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

M. Raja-Halli, T.K. Vehmas, E. Rimaila-Parnanen, S. Sainmaa, Helle Frank Skall, Niels Jørgen Olesen, H. Tapiovaara

    Research output: Contribution to journalJournal articleResearchpeer-review

    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.
    Original languageEnglish
    JournalDiseases of Aquatic Organisms
    Volume72
    Issue number3
    Pages (from-to)201-211
    ISSN0177-5103
    DOIs
    Publication statusPublished - 2006

    Keywords

    • viral haemorrhagic septicaemia virus
    • VHSV
    • epidemiology
    • rainbow trout

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