Since 2004, there have been multiple outbreaks of H5 highly pathogenic avian influenza (HPAI) viruses in Laos. Here, we isolated H5N1 HPAI viruses from poultry outbreaks in Laos during 2015-2018 and investigated their genetic characteristics and pathogenicity in chickens. Phylogenetic analysis revealed that the isolates belonged to clade 2.3.2.1c and that they differed from previous Laos viruses with respect to genetic composition. In particular, the isolates were divided into two genotypes, each of which had a different NS segments. The results of possible migration analysis suggested a high likelihood that the Laos isolates were introduced from neighbouring countries, particularly Vietnam. The recent Laos isolate, A/Duck/Laos/NL-1504599/2018, had an intravenous pathogenicity index score of 3.0 and showed a 50% chicken lethal dose of 102.5 EID50 /0.1 ml, indicating high pathogenicity. The isolated viruses exhibited no critical substitution in the markers associated with mammalian adaptation, but possess markers related to neuraminidase inhibitor resistance. These results emphasize the need for ongoing surveillance of circulating influenza virus in South-East Asia, including Laos, to better prepare for and mitigate global spread of H5 HPAI.

中文翻译：

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从老挝家禽暴发中分离出的2.3.2.1c进化枝H5N1高致病性禽流感病毒的遗传和致病特征。

自2004年以来，老挝已爆发多起H5高致病性禽流感（HPAI）病毒。在这里，我们从2015-2018年老挝的家禽暴发中分离出H5N1 HPAI病毒，并调查了它们在鸡中的遗传特征和致病性。系统发育分析表明，分离物属于进化枝2.3.2.1c，它们在遗传组成上与以前的老挝病毒不同。特别地，分离株被分为两个基因型，每个基因型具有不同的NS区段。可能的迁移分析结果表明，老挝分离株很可能是从邻国特别是越南引入的。最近的老挝分离株A / Duck / Laos / NL-1504599 / 2018的静脉内致病性指数得分为3.0，显示50％的鸡致死剂量为102。5 EID50 /0.1 ml，表明高致病性。分离出的病毒在与哺乳动物适应性相关的标志物中没有显示出关键的取代，但具有与神经氨酸酶抑制剂抗性有关的标志。这些结果强调，有必要对包括老挝在内的东南亚地区不断传播的流行性感冒病毒进行监测，以更好地准备和减轻H5 HPAI在全球的传播。