Ito Takafumi, Kurita Jun, Mori Koh-Ichiro, Skall Helle Frank, Lorenzen Niels, Vendramin Niccolò, Gedsted Andersen Nikolaj, Einer-Jensen Katja, Olesen Niels Jørgen
Tamaki Laboratory, Research Center for Fish Diseases, National Research Institute of Aquaculture, Fisheries Research Agency, 224-1 Hiruda, Tamaki, Mie 519-0423, Japan.
Dis Aquat Organ. 2018 Mar 22;128(1):51-62. doi: 10.3354/dao03215.
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.
从许多海洋和淡水鱼类中分离出的四种主要基因型的病毒性出血性败血症病毒（VHSV），其毒力有所不同。虽然已经开发出基于单克隆抗体（MAb）的快速低成本基因分型系统用于VHSV毒力分型，但仍需要补充相关知识。特别是，从瑞典海水养殖虹鳟Oncorhynchus mykiss的病毒性出血性败血症（VHS）疫情中分离出的2株野外毒株SE-SVA-14和SE-SVA-1033（均为Ib基因型）产生了相互矛盾的反应。在本研究中，通过有限稀释克隆后，这两株毒株在与核蛋白（N）特异性MAb的反应性及其基因序列方面似乎都是异质的。虹鳟感染试验进一步揭示了源自同一原始分离株的这些病毒克隆在毒力上的差异。基于对所测试克隆的全基因组的比较分析，我们认为毒力差异初步与第43 - 46位氨基酸和第168位氨基酸所覆盖的N蛋白区域中的氨基酸（aa）替换有关，或者与两者的组合有关。这种微小的自然发生的基因差异影响毒力这一事实意味着，即使是海洋环境中低毒力的VHSV分离株也应被视为对鳟鱼养殖业的潜在威胁。所描述的MAb可作为对养殖鳟鱼中由海洋VHSV分离株引起的疾病爆发进行初步风险评估的有用工具。
