DAO prepress abstract  -  doi: 10.3354/dao01911

ABSTRACT: A survey to determine the potential distribution of viral haemorrhagic septicaemia virus (VHSV) in marine cage-based salmonid farms in Scotland was undertaken. A rapid, accurate and sensitive real-time RT-PCR (qRT-PCR) assay was developed, targeting a conserved region of the nucleoprotein (N) gene of the virus. The qRT-PCR assay was shown to be more sensitive than the conventional VHSV RT-PCR. A validation protocol included several different virus isolates as the target, and confirmed that the assay could detect all European VHSV Genotypes I-III. Both endogenous and exogenous controls were designed to control for integrity of template and distinguish between true VHSV positives and contamination with the positive control material. In total, the universal European VHSV qRT-PCR assay with exogenous positive control was applied to screen 2040 individual Atlantic salmon (Salmo salar) and 150 individual rainbow trout (Oncorhynchus mykiss). No evidence of the presence of VHSV in association with either salmonid species in Scottish marine farms was detected. However, both marine Atlantic salmon and rainbow trout are still considered possible carriers of VHSV and a potential threat to freshwater farming. Therefore a need for future surveillance of these species in marine environment will remain.