Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, 550 University Ave, Charlottetown, P,E,I,, C1A 4P3, Canada.
Virol J. 2013 Nov 23;10:344. doi: 10.1186/1743-422X-10-344.
Infectious salmon anaemia (ISA) is a serious disease of marine-farmed Atlantic salmon (Salmo salar) caused by ISA virus (ISAV), which belongs to the genus Isavirus, family Orthomyxoviridae. ISA is caused by virulent ISAV strains with deletions in a highly polymorphic region (HPR) of the hemagglutinin-esterase (HE) protein (designated virulent ISAV-HPR∆). This study shows the historic dynamics of ISAV-HPR∆ and ISAV-HPR0 in Chile, the genetic relationship among ISAV-HPR0 reported worldwide and between ISAV-HPR0 and ISAV-HPR∆ in Chile, and reports the 2013 ISA outbreak in Chile. The first ISA outbreak in Chile occurred from mid-June 2007 to 2010 and involved the virulent ISAV-HPR7b, which was then replaced by a low pathogenic ISAV-HPR0 variant. We analyzed this variant in 66 laboratory-confirmed ISAV-HPR0 cases in Chile in comparison to virulent ISAV-HPR∆ that caused two new ISA outbreaks in April 2013. Multiple alignment and phylogenetic analysis of HE sequences from all ISAV-HPR0 viruses allowed us to identify three genomic clusters, which correlated with three residue patterns of ISAV-HPR0 (360PST362, 360PAN362 and 360PAT362) in HPR. The virus responsible for the 2013 ISAV-HPR∆ cases in Chile belonged to ISAV-HPR3 and ISAV-HPR14, and in phylogenetic analyses, both clustered with the ISAV-HPR0 found in Chile. The ISAV-HPR14 had the ISAV-HPR0 residue pattern 360PAT362, which is the only type of ISAV-HPR0 variant found in Chile. This suggested to us that the 2013 ISAV-HPR∆ re-emerged from ISAV-HPR0 that is enzootic in Chilean salmon aquaculture and were not new introductions of virulent ISAV-HPR∆ to Chile. The clinical presentations and diagnostic evidence of the 2013 ISA cases indicated a mixed infection of ISAV with the ectoparasite Caligus rogercresseyi and the bacterium Piscirickettsia salmonis, which underscores the need for active ISAV surveillance in areas where ISAV-HPR0 is enzootic, to ensure early detection and control of new ISA outbreaks, as it is considered a risk factor. This is the first report of ISA linked directly to the presence of ISAV-HPR0, and provides strong evidence supporting the contention that ISAV-HPR0 shows a strong relationship to virulent ISAV-HPR∆ viruses and the possibility that it could mutate to virulent ISAV-HPR∆.
传染性鲑鱼贫血症（ISA）是一种严重的海水养殖大西洋鲑鱼（Salmo salar）疾病，由 ISA 病毒（ISAV）引起，属于正粘病毒科的 Isavirus 属。ISA 是由在血凝素酯酶（HE）蛋白高度多态性区域（HPR）中缺失的强毒 ISAV 株引起的（命名为强毒 ISAV-HPR∆）。本研究显示了智利 ISAV-HPR∆和 ISAV-HPR0 的历史动态、全球报告的 ISAV-HPR0 之间的遗传关系以及智利的 ISAV-HPR0 和 ISAV-HPR∆ 之间的关系，并报告了智利 2013 年的 ISA 暴发。智利的第一次 ISA 暴发发生在 2007 年 6 月中旬至 2010 年，涉及强毒 ISAV-HPR7b，随后被一种低致病性 ISAV-HPR0 变体取代。我们分析了智利 66 例实验室确诊的 ISAV-HPR0 病例中的这种变体，与 2013 年 4 月引起两次新的 ISA 暴发的强毒 ISAV-HPR∆进行了比较。对所有 ISAV-HPR0 病毒的 HE 序列进行多重比对和系统发育分析，使我们能够识别出三个基因组簇，这与 HPR 中 ISAV-HPR0 的三个残基模式（360PST362、360PAN362 和 360PAT362）相关。导致 2013 年智利 ISAV-HPR∆病例的病毒属于 ISAV-HPR3 和 ISAV-HPR14，在系统发育分析中，两者均与智利发现的 ISAV-HPR0 聚类。ISAV-HPR14 具有 ISAV-HPR0 残基模式 360PAT362，这是智利发现的唯一类型的 ISAV-HPR0 变体。这表明，2013 年 ISAV-HPR∆ 的重新出现是源自智利鲑鱼养殖中地方性存在的 ISAV-HPR0，而不是智利新引入的强毒 ISAV-HPR∆。2013 年 ISA 病例的临床症状和诊断证据表明，ISA 与外寄生虫 Caligus rogercresseyi 和细菌 Piscirickettsia salmonis 的混合感染，这突显出需要在 ISAV-HPR0 地方性存在的地区进行积极的 ISAV 监测，以确保早期发现和控制新的 ISA 暴发，因为它被认为是一个危险因素。这是首次直接将 ISA 与 ISAV-HPR0 的存在联系起来的报告，并提供了强有力的证据支持以下观点：ISAV-HPR0 与强毒 ISAV-HPR∆ 病毒密切相关，并且它有可能发生变异成为强毒 ISAV-HPR∆。
