Nylund A, Devold M, Plarre H, Isdal E, Aarseth M
Department of Fisheries, University of Bergen, 5020 Bergen, Norway.
Dis Aquat Organ. 2003 Aug 15;56(1):11-24. doi: 10.3354/dao056011.
The present study describes the use of molecular methods in studying infectious salmon anaemia virus (ISAV), an important pathogen of farmed salmon in Norway, Scotland, the Faeroe Islands, Canada, USA and Chile. The nucleotide sequences of the haemagglutinin gene (HA) from 70 ISAV isolates have been analysed for phylogenetic relationship and the average mutation rate of nucleotide substitutions calculated. The isolates constitute 2 major groups, 1 European and 1 North American group. The isolate from Chile is closely related to the North American isolates. The European isolates can be further divided into 3 separate groups reflecting geographical distribution, time of collection, and transmission connected with farming activity. Based on existing information about infectious salmon anaemia (ISA) and new information emerging from the present study, it is hypothesised that: (1) ISAV is maintained in wild populations of trout and salmon in Europe; (2) it is transmitted between wild hosts mainly during their freshwater spawning phase in rivers; (3) wild salmonids, mainly trout, possibly carry benign wild-type ISAV isolates; (4) a change (mutation) in virulence probably results from deletions of amino acid segments from the highly polymorphic region (HPR) of benign wild-type isolates; (5) ISA emerges in farmed Atlantic salmon when mutated isolates are transmitted from wild salmonids or, following mutation of benign isolates, in farmed salmon after transmission from wild salmonids; (6) farming activity is an important factor in transmission of ISAV between farming sites in addition to transmission of ISAV from wild salmonids to farmed salmon; (7) transmission of ISAV from farmed to wild salmonids probably occurs less frequently than transmission from wild to farmed fish due to lower frequency of susceptible wild individuals; (8) the frequency of new outbreaks of ISA in farmed salmon probably reflects natural variation in the prevalence of ISAV in wild populations of salmonids.
本研究描述了分子方法在研究传染性鲑鱼贫血病毒（ISAV）中的应用，ISAV是挪威、苏格兰、法罗群岛、加拿大、美国和智利养殖鲑鱼的一种重要病原体。已对70株ISAV分离株的血凝素基因（HA）核苷酸序列进行了系统发育关系分析，并计算了核苷酸替换的平均突变率。这些分离株构成2个主要组，1个欧洲组和1个北美组。来自智利的分离株与北美分离株密切相关。欧洲分离株可进一步分为3个独立的组，反映了地理分布、采集时间以及与养殖活动相关的传播情况。基于现有的关于传染性鲑鱼贫血（ISA）的信息以及本研究中出现的新信息，提出以下假设：（1）ISAV在欧洲的野生鳟鱼和鲑鱼种群中持续存在；（2）它主要在野生宿主于河流中的淡水产卵期在野生宿主之间传播；（3）野生鲑科鱼类，主要是鳟鱼，可能携带良性野生型ISAV分离株；（4）毒力的变化（突变）可能是由于良性野生型分离株高度多态性区域（HPR）的氨基酸片段缺失所致；（5）当突变的分离株从野生鲑科鱼类传播而来，或者良性分离株发生突变后从野生鲑科鱼类传播至养殖鲑鱼后，ISA在养殖的大西洋鲑鱼中出现；（6）养殖活动是ISAV在养殖场之间传播的一个重要因素，此外还有ISAV从野生鲑科鱼类传播至养殖鲑鱼；（7）由于易感野生个体的频率较低，ISAV从养殖鲑鱼传播至野生鲑科鱼类的频率可能低于从野生鱼类传播至养殖鱼类的频率；（8）养殖鲑鱼中ISA新暴发的频率可能反映了野生鲑科鱼类种群中ISAV流行率的自然变化。
