Lyngstad Trude M, Kristoffersen Anja B, Hjortaas Monika J, Devold Magnus, Aspehaug Vidar, Larssen Rolf B, Jansen Peder A
Norwegian Veterinary Institute, PO Box 750 Sentrum, 0106 Oslo, Norway.
Dis Aquat Organ. 2012 Nov 19;101(3):197-206. doi: 10.3354/dao02520.
Infectious salmon anaemia (ISA) is a severe disease in farmed Atlantic salmon Salmo salar that has caused epidemic outbreaks in most salmon-producing countries worldwide. The disease is caused by virulent ISA virus (ISAV). Low virulent variants of the virus, characterised by a full-length sequence in the highly polymorphic region of segment 6 in the virus genome, have been reported with increasing frequencies. These variants of the virus, termed HPR0, have been proposed to be ancestors of virulent ISAV. We examined this idea through studies of the phylogeographic and environmental distribution of ISAV-HPR0, as well as phylogeographic associations between virulent ISAV and ISAV-HPR0. Samples from 232 fish groups were screened for ISAV. Real-time RT-PCR was used for detection of ISAV, and the ISAV haemagglutinin esterase (HE) gene was characterised for positive samples. A Mantel test was used to test phylogeographic associations between pairs of ISAV-HPR0 HE gene sequences. A rank test was used to test associations between HE gene sequences from virulent ISAV and ISAV-HPR0. ISAV-HPR0 was detected in fish groups both in freshwater and marine environments, and in juveniles, on-grown marine salmon and broodstock salmon. Genetic and geographic distances between pairs of ISAV-HPR0 HE gene sequences were positively correlated, suggesting that the population of ISAV-HPR0 is geographically structured. Finally, we found a spatial association between fish groups with virulent ISAV (n = 21) and fish groups with ISAV-HPR0 (n = 27), supporting the hypothesis that ISAV-HPR0 may undergo a transition to virulent ISAV.
传染性鲑鱼贫血症（ISA）是养殖大西洋鲑鱼（Salmo salar）的一种严重疾病，已在全球大多数鲑鱼生产国引发了疫情爆发。该疾病由强毒性传染性鲑鱼贫血病毒（ISAV）引起。据报道，该病毒的低毒力变体在病毒基因组第6节段的高度多态性区域具有全长序列，其出现频率越来越高。这些病毒变体被称为HPR0，有人提出它们是强毒性ISAV的祖先。我们通过对ISAV-HPR0的系统地理学和环境分布以及强毒性ISAV与ISAV-HPR0之间的系统地理学关联进行研究，来检验这一观点。对来自232个鱼群的样本进行了ISAV筛查。使用实时逆转录聚合酶链反应（RT-PCR）检测ISAV，并对阳性样本的ISAV血凝素酯酶（HE）基因进行特征分析。使用Mantel检验来测试ISAV-HPR0 HE基因序列对之间的系统地理学关联。使用秩和检验来测试强毒性ISAV和ISAV-HPR0的HE基因序列之间的关联。在淡水和海洋环境中的鱼群以及幼鱼、成年海洋鲑鱼和亲鱼中均检测到了ISAV-HPR0。ISAV-HPR0 HE基因序列对之间的遗传距离和地理距离呈正相关，这表明ISAV-HPR0的种群在地理上是有结构的。最后，我们发现携带强毒性ISAV的鱼群（n = 21）和携带ISAV-HPR0的鱼群（n = 27）之间存在空间关联，这支持了ISAV-HPR0可能会转变为强毒性ISAV的假设。
