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Diseases of Aquatic Organisms

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DAO 128:51-62 (2018)  -  DOI: https://doi.org/10.3354/dao03215

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

Takafumi Ito1,*, Jun Kurita1, Koh-ichiro Mori2, Helle Frank Skall3, Niels Lorenzen3, Niccolò Vendramin3, Nikolaj Gedsted Andersen3, Katja Einer-Jensen3,4, Niels Jørgen Olesen3

1Tamaki Laboratory, Research Center for Fish Diseases, National Research Institute of Aquaculture, Fisheries Research Agency, 224-1 Hiruda, Tamaki, Mie 519-0423, Japan
2Research Center for Fish Diseases, National Research Institute of Aquaculture, Fisheries Research Agency, 422-1 Nakatsuhamaura, Minami-Ise, Mie 516-0193, Japan
3National Veterinary Institute, Technical University of Denmark, Kemitorvet 202, 2800 Kgs Lyngby, Denmark
4Present address: QIAGEN, Silkeborgvej 2, 8000 Aarhus C, Denmark
*Corresponding author:

ABSTRACT: Four major genotypes of viral haemorrhagic septicaemia virus (VHSV), which have been isolated from many marine and freshwater fish species, are known to differ in virulence. While fast and low-cost genotyping systems based on monoclonal antibodies (MAbs) have been developed for typing of VHSV virulence, there is a need for supplementing the knowledge. In particular, 2 field isolates from viral haemorrhagic septicaemia (VHS) outbreaks in sea-reared rainbow trout Oncorhynchus mykiss in Sweden, SE-SVA-14 and SE-SVA-1033 (both genotype Ib), have yielded contradictory reactions. In the present study, 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 the 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 43-46 and aa 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 risk assessment of disease outbreaks in farmed trout by marine VHSV isolates.


KEY WORDS: Viral haemorrhagic septicaemia virus · VHSV · Virulence · Oncorhynchus mykiss · Genotype Ib · Nucleo-protein


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Cite this article as: Ito T, Kurita J, Mori K, Skall HF and others (2018) Virulence marker candidates in N-protein of viral haemorrhagic septicaemia virus (VHSV): virulence variability within VHSV Ib clones. Dis Aquat Org 128:51-62. https://doi.org/10.3354/dao03215

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