Bratland André, Nylund Are
Department of Biology, University of Bergen, Post Box 7800, N-5020 Bergen, Norway.
J Aquat Anim Health. 2009 Sep;21(3):173-8. doi: 10.1577/H08-038.1.
Disease associated with salmonid Alphavirus (SAV) infection is a significant problem for farm production of salmonids in Europe. The SAV subtype 3 (SAV3) is a Norwegian subtype present exclusively in production systems for Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss in western Norway. It has been suggested that SAV3 is transmitted through smolt transport from the main area for SAV disease in western Norway to as far as northern Norway. One explanation for this type of spread is that SAV is present at freshwater production sites for Atlantic salmon smolts. The present study confirms this, showing that SAV3 is present at smolt production sites in Norway. At two sites in northern Norway that had received eggs from broodfish companies in Hordaland County, western Norway, 2-4-g fry were positive for SAV3. Hence, it cannot be excluded that vertical transmission could have contributed to the presence of SAV3 in northern Norway. In the present study, we followed the normal production cycle for Atlantic salmon in a fish farming company in Hordaland County. Twelve of 353 broodfish in study 1 and 28 of 31 broodfish in study 2 were found to be carriers of SAV3. In the same two studies, SAV was also detected in eggs (1 of 220), eyed eggs (3 of 270), and fry (6 of 600). The SAV was not detected in parr, smolts, or postsmolts, but after a year at sea the fish developed SAV disease. Given the difficulties in tracing the virus through the production cycle until development of SAV disease in the marine farm, we cannot draw any firm conclusions about whether vertical transmission occurs in Norwegian salmon production, and we cannot exclude the possibility that the development of SAV after 1 year at sea was caused by horizontal transmission rather than vertical transmission.
与鲑鱼α病毒（SAV）感染相关的疾病是欧洲鲑鱼养殖生产中的一个重大问题。SAV亚型3（SAV3）是挪威特有的一个亚型，仅存在于挪威西部大西洋鲑（Salmo salar）和虹鳟（Oncorhynchus mykiss）的生产系统中。有人认为，SAV3是通过鱼苗运输从挪威西部SAV疾病的主要区域传播到挪威北部的。这种传播类型的一种解释是，SAV存在于大西洋鲑鱼苗的淡水生产场所。本研究证实了这一点，表明SAV3存在于挪威的鱼苗生产场所。在挪威北部的两个从挪威西部霍达兰郡的亲鱼公司接收鱼卵的场所，2 - 4克重的鱼苗检测出SAV3呈阳性。因此，不能排除垂直传播可能导致了SAV3在挪威北部的存在。在本研究中，我们跟踪了霍达兰郡一家养鱼公司大西洋鲑的正常生产周期。研究1中353尾亲鱼中有12尾、研究2中31尾亲鱼中有28尾被发现是SAV3的携带者。在同样的两项研究中，还在鱼卵（220枚中的1枚）、眼点卵（270枚中的3枚）和鱼苗（600尾中的6尾）中检测到了SAV。在幼鱼、鱼苗或后鱼苗阶段未检测到SAV，但在海水中养殖一年后鱼患上了SAV疾病。鉴于在海洋养殖场直到SAV疾病发生之前，在整个生产周期中追踪病毒存在困难，我们无法就挪威鲑鱼生产中是否发生垂直传播得出任何确凿结论，并且我们不能排除在海水中养殖一年后SAV的发生是由水平传播而非垂直传播引起的可能性。
