H9N2 avian influenza viruses (AIVs) can cross species barriers and expand from birds tomammals and humans. It usually leads to economic loss for breeding farms and poses a serious threat to human health.This study investigated the molecular characteristics of H9N2 AIV isolated from a racing pigeon and its pathogenesis in BALB/c mice and pigeons. Phylogenetic analysis indicated that the H9N2 virus belonged to the Ck/BJ/94-like lineage, and acquired multiple specific amino acid substitutions that might contribute to viral transmission from birds to mammals and humans. A pathogenesis study showed that both mice and pigeons infected with H9N2 virus showed clinical signs and mortality. The H9N2 viruses efficiently replicated in mice and pigeons. In our study, high levels of viral shedding were detected in pigeons, but the infection was not transmitted to co-housed pigeons. Histopathological examination revealed the presence of inflammatory responses in the infected mice and pigeons. Immunohistochemical analysis showed the presence of H9N2 virus in multiple organs of the infected mice and pigeons. Moreover, the infected mice and pigeons demonstrated significant cytokine/chemokine production. Our results showed that the H9N2 virus can infect mice and pigeons, and can not be transmitted between pigeons through direct contact.

H9N2禽流感病毒（AIV）可以越过物种壁垒，并从鸟类，哺乳动物和人类传播。它通常会给种鸡场造成经济损失，并对人类健康构成严重威胁。本研究调查了从赛鸽中分离出的H9N2 AIV的分子特征及其在BALB / c小鼠和鸽子中的发病机理。系统发育分析表明，H9N2病毒属于Ck / BJ / 94样谱系，并获得了多个特定氨基酸取代，这些取代可能有助于从禽类向哺乳动物和人类的病毒传播。发病机理研究表明，感染H9N2病毒的小鼠和鸽子均表现出临床体征和死亡率。H9N2病毒在小鼠和鸽子中有效复制。在我们的研究中，在鸽子中发现了高水平的病毒脱落，但是这种感染并没有传播给同居鸽。组织病理学检查显示在感染的小鼠和鸽子中存在炎症反应。免疫组织化学分析显示，感染的小鼠和鸽子的多个器官中均存在H9N2病毒。此外，被感染的小鼠和鸽子表现出明显的细胞因子/趋化因子产生。我们的结果表明，H9N2病毒可以感染小鼠和鸽子，并且不能通过直接接触在鸽子之间传播。被感染的小鼠和鸽子表现出明显的细胞因子/趋化因子产生。我们的结果表明，H9N2病毒可以感染小鼠和鸽子，并且不能通过直接接触在鸽子之间传播。被感染的小鼠和鸽子表现出明显的细胞因子/趋化因子产生。我们的结果表明，H9N2病毒可以感染小鼠和鸽子，并且不能通过直接接触在鸽子之间传播。