Epidemiology, evolution, and biological characteristics of H6 avian influenza viruses in China

H6 avian influenza virus (AIV) is one of the most prevalent AIV subtypes in birds globally. To investigate the current situation and characteristics of H6 AIVs circulating in China, we analysed the epidemiology, genetic evolution and pathogenic features of this subtype. During 2000-2021, H6 subtype AIVs spread widely through Southern China and presented high host diversity. On analysing 171 H6 viruses isolated during 2009-2021, dynamic reassortments were observed among H6 and other co-circulating AIV subtypes, and these generated a total of 16 different genotypes. A few H6N6 strains possessed L226 and S228 mutations of hemagglutinin (H3 numbering), which may enhance the affinity of H6 viruses to human receptors. H6N6 viruses also exhibited divergent pathogenicity and growth profiles <i>in vivo</i> and <i>in vitro</i>. Some of the H6N6 viruses could infect mice without mammalian adaptation, and even caused death in this species. Therefore, our study demonstrated that the H6 AIVs posed a potential threat to human health and highlighted the urgent need for continued surveillance and evaluation of the H6 influenza viruses circulating in the field.

H6亚型禽流感病毒（Avian Influenza Virus, AIV）是全球范围内禽类中流行最为广泛的禽流感病毒亚型之一。为探究我国流行的H6亚型禽流感病毒的流行现状与特征，本研究对该亚型病毒的流行病学、遗传演化及致病特性展开了分析。2000年至2021年间，H6亚型禽流感病毒在中国南方地区广泛传播，且宿主多样性较高。通过对2009年至2021年分离得到的171株H6亚型病毒进行分析，研究团队发现H6亚型与其他共同流行的禽流感病毒亚型之间发生了动态重配，最终产生了共计16种不同的基因型。部分H6N6毒株的血凝素（采用H3编号规则）携带L226和S228位点突变，该突变可能增强H6亚型病毒对人类受体的结合亲和力。H6N6毒株在体内（in vivo）和体外（in vitro）均表现出差异化的致病特性与增殖特性。部分H6N6毒株无需经过哺乳动物适应性改造即可感染小鼠，甚至可导致该动物死亡。综上，本研究证实H6亚型禽流感病毒对人类健康存在潜在威胁，并强调亟需对野外环境中流行的H6亚型流感病毒持续开展监测与评估工作。