CAS Key Laboratory of Special Pathogens and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, Hubei, 430071, China.
Hubei Wildlife Rescue, Research and Development Center, Wuhan, Hubei, 430074, China.
Emerg Microbes Infect. 2018 Apr 11;7(1):62. doi: 10.1038/s41426-018-0064-7.
After the emergence of H7N9 avian influenza viruses (AIV) in early 2013 in China, active surveillance of AIVs in migratory birds was undertaken, and two H7N7 strains were subsequently recovered from the fresh droppings of migratory birds; the strains were from different hosts and sampling sites. Phylogenetic and sequence similarity network analyses indicated that several genes of the two H7N7 viruses were closely related to those in AIVs circulating in domestic poultry, although different gene segments were implicated in the two isolates. This strongly suggested that genes from viruses infecting migratory birds have been introduced into poultry-infecting strains. A Bayesian phylogenetic reconstruction of all eight segments implied that multiple reassortments have occurred in the evolution of these viruses, particularly during late 2011 and early 2014. Antigenic analysis using a hemagglutination inhibition test showed that the two H7N7 viruses were moderately cross-reactive with H7N9-specific anti-serum. The ability of the two H7N7 viruses to remain infectious under various pH and temperature conditions was evaluated, and the viruses persisted the longest at near-neutral pH and in cold temperatures. Animal infection experiments showed that the viruses were avirulent to mice and could not be recovered from any organs. Our results indicate that low pathogenic, divergent H7N7 viruses circulate within the East Asian-Australasian flyway. Virus dispersal between migratory birds and domestic poultry may increase the risk of the emergence of novel unprecedented strains.
自 2013 年初中国出现 H7N9 禽流感病毒（AIV）以来，对候鸟中的 AIV 进行了主动监测，随后从候鸟的新鲜粪便中分离出两株 H7N7 株；这两株病毒株来自不同的宿主和采样地点。系统进化和序列相似性网络分析表明，两株 H7N7 病毒的几个基因与在家禽中流行的 AIV 非常相似，尽管两个分离株涉及不同的基因片段。这强烈表明，感染候鸟的病毒基因已被引入到感染家禽的病毒株中。对所有 8 个片段的贝叶斯系统进化重建表明，这些病毒在进化过程中发生了多次重配，特别是在 2011 年底和 2014 年初。血凝抑制试验的抗原分析表明，两株 H7N7 病毒与 H7N9 特异性抗血清中度交叉反应。评估了两株 H7N7 病毒在不同 pH 值和温度条件下的感染能力，结果表明，病毒在接近中性 pH 值和低温下存活时间最长。动物感染实验表明，这些病毒对小鼠无致病性，不能从任何器官中恢复。我们的研究结果表明，低致病性、分化的 H7N7 病毒在东亚-澳大拉西亚飞行路线上传播。候鸟和家禽之间的病毒传播可能会增加出现新型前所未有的病毒株的风险。
