Viral diseases of fish as a factor of epizootic risk in freshwater aquaculture of the north-western region of the Russian Federation: features of pathogenesis and threats to coregonid and char species

For the northwestern regions of Russia, where industrial fish farming is focused on cold-water salmon, whitefish (Coregonus spp.), and char (Salvelinus spp.) species, four viral nosologies form a stable pool of constant epizootic pressure: viral hemorrhagic septicemia (VHSV genotype II, dominant in the Baltic basin), infectious hematopoietic necrosis (IHN), infectious pancreatic necrosis (IPN), and salmon pancreatic disease caused by alphavirus (SAV). The aim of this study was to analyze the degree of virological threat to fish farms in a specific region and such key aspects as the molecular mechanisms by which viruses evade the antiviral immunity of fish, epidemiological routes of pathogen introduction into farms through the international circulation of seed and caviar, data on the susceptibility of whitefish and char species to viruses, which in some cases exceed the susceptibility of the main model species, rainbow trout (Oncorhynchus mykiss). An analysis of the whole genome sequences of VHSV (NC_000855.1), IHNV (GQ413939.1), IPNV (AJ622822.1), and SAV (AY604235.1) from the NCBI GenBank and RefSeq databases was conducted. Urgent needs for virological monitoring of fish farms in the Northwest, based on molecular genetic detection methods, were formulated. We concluded that the key practical measures capable of significantly reducing the virological risk to the industry include: the introduction of multiplex RT-PCR screening of imported material for VHSV, IHNV, IPNV, and SAV; the organization of regular monitoring of fish on farms based on these methods; the creation of a Russian database of reference sequences and circulating isolates; and the development of specialized protocols for whitefish and char as separate monitoring targets.

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