Avian-to-human transmission of highly pathogenic avian influenza viruses (HPAIV) and their subsequent adaptation to humans are of great concern to public health. Surveillance and early warning of AIVs with the potential to infect humans and pandemic potential is crucial. In this study, we determined whether adaptive evolution occurred in human-isolated H5 viruses. We evaluated all available genomes of H5N1 and H5N6 avian influenza A virus. Firstly, we systematically identified several new mutations in H5 AIV that might be associated with human adaptation using a combination of novel comparative phylogenetic methods and structural analysis. Some changes are the result of parallel evolution, further demonstrating their importance. In total, we identified 102 adaptive evolution sites in eight genes. Some residues had been previously identified, such as 227 in HA and 627 in PB2, while others have not been reported so far. Ten sites from four genes evolved in parallel but no obvious positive selection was detected. Our study suggests that during infection of humans, H5 viruses evolved to adapt to their new host environment and that the sites of adaptive/parallel evolution might play a role in crossing the species barrier and are the response to new selection pressure. The results provide insight to implement early detection systems for transitional stages in H5 AIV evolution before its potential adaptation for humans. Author summary line The prerequisite of surveillance and early warning of avian influenza viruses with the potential to infect humans depends on the identification of human-adaptation related mutations. In this study, we used a novel approach combining both phylogenetic and structural analysis to identify possible human-adaptation related mutations in H5 AIVs. Previous studies reported human-adaptation related mutations and some novel mutations exhibiting parallel evolution. Our result provides new insights into how AIVs adapt to humans by point mutations.

中文翻译：

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人类分离的H5禽流感病毒的适应性和并行进化。

高致病性禽流感病毒（HPAIV）的禽传人传播及其对人类的适应性是公共卫生的重要问题。具有可能感染人类和大流行潜力的AIV的监视和预警至关重要。在这项研究中，我们确定了人类分离的H5病毒中是否发生了适应性进化。我们评估了H5N1和H5N6禽流感A病毒的所有可用基因组。首先，我们结合新颖的比较系统发育方法和结构分析，系统地鉴定了可能与人类适应有关的H5 AIV中的几个新突变。一些变化是并行进化的结果，进一步证明了它们的重要性。总共，我们在八个基因中鉴定出102个适应性进化位点。先前已经发现了一些残留物，例如HA中的227和PB2中的627，而到目前为止还没有其他报告。来自四个基因的十个位点平行进化，但未检测到明显的阳性选择。我们的研究表明，在人类感染期间，H5病毒会进化以适应其新的宿主环境，而适应性/平行进化的位点可能在越过物种障碍中发挥作用，并且是对新选择压力的反应。研究结果为在H5 AIV进化为人类应用之前，为H5 AIV进化的过渡阶段实施早期检测系统提供了见识。作者摘要专栏监视和预警可能感染人类的​​禽流感病毒的先决条件取决于与人类适应相关的突变的鉴定。在这个研究中，我们使用了一种结合系统发育和结构分析的新颖方法来鉴定H5 AIV中可能与人类适应相关的突变。先前的研究报道了与人类适应有关的突变，以及一些表现出平行进化的新型突变。我们的结果为AIV如何通过点突变适应人类提供了新的见解。