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Diseases of Aquatic Organisms

    DAO prepress abstract   -  DOI: https://doi.org/10.3354/dao03454

    Presence of viral haemorrhagic septicaemia virus (VHSV) in the environment of virus-contaminated fish farms and processing plants

    Pia Vennerström*, Leena Maunula, Elina Välimäki, Anna-Maija Virtala

    *Corresponding author:

    ABSTRACT: After the first outbreak of viral haemorrhagic septicaemia (VHS) in Finnish brackish water rainbow trout (Oncorhynchus mykiss) farms, infection spread rapidly between the farms. The infrastructure of fish farming did not take into account spreading of infectious fish diseases. To show the presence of VHSV in the environment, we tested seawater, sediment and wild blue mussels (Mytilus edulis) from VHSV-infected fish farms, and liquid waste from one processing plant handling infected rainbow trout. Additionally, blue mussels were bath challenged with VHSV (exposed to cultivated virus or naturally infected rainbow trout). To detect VHSV, virus isolation in cell culture and a real-time reverse transcriptase polymerase chain reaction (qRT-PCR) methods were used. The virus or viral RNA was detected in sea water and in liquid waste from processing plants during wintertime when water temperature is close to 0°C and sunlight is sparse. VHSV did not appear to replicate in blue mussels in our study. Therefore, blue mussels were not considered relevant carriers of VHSV. However, traces of viral RNA were detected up to 29 days post challenge in mussels. Contact with water from processing plants handling VHSV infected fish populations increases the risk of the disease spreading to susceptible fish populations especially during cold and dark times of the year.