DAO prepress abstract  -  DOI: https://doi.org/10.3354/dao03215

Virulence marker candidates in N-protein of viral hemorrhagic septicemia virus (VHSV): virulence variability within VHSV Ib clones

Takafumi Ito*, Jun Kurita, Koh-ichiro Mori, Helle Frank Skall, Niels Lorenzen, Niccolò Vendramin, Nikolaj Gedsted Andersen, Katja Einer-Jensen, Niels Jørgen Olesen

*Email: takafumi@fra.affrc.go.jp

ABSTRACT: The discovery of differences in the virulence of marine and freshwater viral hemorrhagic septicemia virus (VHSV) have increased the need for supplementing existing fast and low-cost genotyping systems based on monoclonal antibodies (MAbs) for typing of virulence. Particularly 2 genotype Ib field isolates from VHS outbreaks in sea-reared rainbow trout Oncorhynchus mykiss in Sweden, SE-SVA-14 and SE-SVA-1033, yielded contradictory reactions. Upon cloning by limited dilution, both isolates appeared to be heterogeneous in terms of reactivity with nucleo (N) protein-specific MAbs as well their gene sequences. Infection trials in rainbow trout further revealed differences in virulence of these virus clones derived from the same primary isolate. Based on a comparative analysis of the entire genome of the clones tested, we suggest that the differences in virulence are tentatively linked to substitutions of amino acids (aa) in the N protein region covered by aa 43 to 46 and amino acid position 168, or a combination of the two. The fact that such minor naturally occurring genetic differences affect the virulence implies that even low-virulent VHSV isolates in the marine environment should be considered as a potential threat for the trout farming industry. The described MAbs can represent useful tools for initial assessment of risk of disease outbreaks in farmed trout by marine VHSV isolates.