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Research Document 2020/064

Characterization of viral haemorrhagic septicaemia virus (VHSV) to inform pathogen transfer risk assessments in British Columbia

By Garver, K.A. and Hawley, L.M.


Viral haemorrhagic septicaemia virus (VHSV) is a rhabdovirus and the causative agent of the disease viral haemorrhagic septicaemia which can occur in a wide range of wild and farmed fish species in both marine and freshwater environments. Phylogenetically, VHSV groups into four major genotypes (I, II, III, IV) and ten subtypes (Ia-If and IVa-IVd). In British Columbia, VHSV-IVa is endemic in the marine environment where it causes significant mortality events in Pacific Herring and Pacific Sardines. Less commonly, the virus has been detected in cultured and wild salmon; however, not all salmon species are susceptible to VHSV. Specifically, Sockeye Salmon appear refractory compared to other species such as Atlantic Salmon. Government surveillance programs of farmed Atlantic Salmon in the Discovery Islands area of British Columbia from 2002-2018 detected VHSV in four of the seventeen years tested while there has been no confirmed detection of VHSV among independent surveys collectively testing over 5000 wild Sockeye Salmon. Furthermore, laboratory studies exposing Pacific Herring, Atlantic Salmon, and Sockeye Salmon to VHSV, corroborate a gradient of susceptibility such that Pacific Herring were the most susceptible experiencing upwards of 100% mortality after exposure to extremely low levels of virus. Atlantic Salmon demonstrated low to moderate susceptibility as they remained free of VHSV infection after being exposed to waterborne virus for a short duration; however, became infected when exposed for a longer duration via cohabitation with VHS diseased Pacific Herring. Conversely, Sockeye Salmon, regardless of whether exposed to VHSV through waterborne or cohabitational exposure, for short or long periods, proved refractory to VHSV infection. Consequently, without evidence of either natural or non-invasive experimental VHSV infections, Sockeye Salmon are not considered susceptible to VHSV based on the World Organization for Animal Health (OIE) criteria for listing species as susceptible to infection with a specific pathogen.

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