H9N2 avian influenza viruses (AIVs) can cause respiratory symptoms and decrease the egg production. Additionally, H9N2 AIVs can provide internal genes for reassortment with other subtypes. During the monitoring of live poultry markets in 2016, a total of 32 (32/179, 17.88%) H9N2 AIVs were isolated from poultry in Eastern China, and seven representative strains were selected based on the isolation time, isolation location and sequence homology for further characterization. Phylogenetic analysis of hemagglutinin and neuraminidase showed that these H9N2 AIVs clustered into the Y280 sublineage. And the phylogenetic trees of six internal genes showed that the source of these gene fragments was more abundant, suggesting that extensive reassortment has occurred in these H9N2 viruses. Molecular analysis showed that multiple specific amino acid mutations occurred that increased H9N2 AIVs’ infectivity, transmissibility, and affinity to mammals, including Q226L and Q227M in hemagglutinin, E627K in polymerase basic protein 2 (PB2), L13P in polymerase basic protein 1 (PB1), and A70V and S409N in polymerase acidic protein (PA). Pathogenicity tests in mice showed these H9N2 AIVs could replicate in lungs and exhibited slight to moderate virulence. The continuous circulation of these H9N2 viruses suggests the necessity for persistent surveillance of the H9N2 AIVs in poultry.

H9N2 禽流感病毒 (AIV) 可引起呼吸道症状并减少产蛋量。此外，H9N2 AIV 可以提供与其他亚型重配的内部基因。2016年活禽市场监测中，华东地区共分离出32株（32/179，17.88%）H9N2禽流感病毒，根据分离时间、分离部位和序列同源性筛选出7株代表株。进一步表征。血凝素和神经氨酸酶的系统发育分析表明，这些 H9N2 AIV 聚集到 Y280 亚系中。并且6个内部基因的系统发育树显示这些基因片段的来源更为丰富，表明这些H9N2病毒发生了广泛的重配。分子分析表明，发生了多个特定氨基酸突变，增加了 H9N2 AIV 的感染性、传播性和对哺乳动物的亲和力，包括血凝素中的 Q226L 和 Q227M，聚合酶碱性蛋白 2 (PB2) 中的 E627K，聚合酶碱性蛋白 1 (PB1) 中的 L13P ，以及聚合酶酸性蛋白 (PA) 中的 A70V 和 S409N。小鼠的致病性测试表明，这些 H9N2 AIV 可以在肺中复制，并表现出轻微至中等的毒力。这些 H9N2 病毒的持续传播表明有必要持续监测家禽中的 H9N2 AIV。聚合酶酸性蛋白 (PA) 中的 A70V 和 S409N。小鼠的致病性测试表明，这些 H9N2 AIV 可以在肺中复制，并表现出轻微至中等的毒力。这些 H9N2 病毒的持续传播表明有必要持续监测家禽中的 H9N2 AIV。聚合酶酸性蛋白 (PA) 中的 A70V 和 S409N。小鼠的致病性测试表明，这些 H9N2 AIV 可以在肺中复制，并表现出轻微至中等的毒力。这些 H9N2 病毒的持续传播表明有必要持续监测家禽中的 H9N2 AIV。