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Understanding the ecology, epidemiology and evolution of the 2017 outbreak of highly-pathogenic H5N8 avian influenza virus in a wild mute swans

了解2017年野生疣鼻天鹅爆发高致病性H5N8禽流感病毒的生态学、流行病学和进化

基本信息

批准号：
NE/R002126/1
负责人：
Oliver Pybus
金额：
$ 6.68万
依托单位：
University of Oxford
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2017
资助国家：
英国
起止时间：
2017 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FR002126%2F1
关键词：
Understanding ecology epidemiology evolution 2017

项目摘要

Highly pathogenic avian influenza (HPAI) viruses cause substantial economic losses to the poultry industry, and pose a significant threat to animal and human health. HPAI first came to prominence in the late 1990s with the emergence from Asia of the H5N1 lineage, which resulted in the culling of 100s of millions of birds and more than 500 human deaths. HPAI resurfaced as a global threat in 2013, with the emergence in China of a novel strain belonging to subtype H5N8. The speed of global H5N8 spread since 2014 has surprised scientists. The strain spread rapidly through Asia, North America, Europe, and most recently, Africa. The spread to North America is unprecedented, at an estimated cost of ~$3.3 billion to businesses there. A report published last October concluded that H5N8 global spread was driven primarily by long-distance bird migration.Reports of H5N8 outbreaks in both wild and farmed birds across Europe increased in autumn 2016, spreading westwards until they reached the UK in late December. Cases in wild birds have been reported in Wales, Scotland and England. The largest outbreak to date is ongoing within a large population (~750) of wild mute swans in Abbotsbury, on the Dorset coast in southern England. Although only 9 swans (so far) have laboratory confirmed H5N8 infections, more than 175 untested swans have died since the start of the outbreak, vastly in excess of normal mortality. The first H5N8 infection was detected in a dead swan found at the Swannery on 23rd December 2016. Although mortality appears to have decreased from the apparent peak in the second week of January 2017, an above-normal number of dead birds are still being recovered and the outbreak is still considered to be current and ongoing by the authorities (2nd February 2017). This outbreak, whilst devastating for the bird population, could tell us much about how HPAI spreads in wild birds. The long-lived swans have been subjected to long-term ecological study by ornithologists at the University of Oxford and are individually ringed; for most birds we know age, sex, parentage and other variables. Crucially, exactly the same population suffered an outbreak of H5N1 HPAI in early 2008. However, in 2008 only 10 swans died, almost all of which were <3 years old. Our research after the 2008 outbreak showed that older birds were more likely to have antibody responses that might help give immunological protection against avian influenza. Specifically almost all birds >3 years old harbour influenza antibodies and older birds have antibodies to a broader range of different influenza strains. Thus we hypothesise that previous exposure to common, mild forms of influenza may have protected these wild birds against H5N1 infection.The current outbreak offers the potential to directly compare H5N1 and H5N8 HPAI epidemiology in the same population of wild birds, an opportunity that we think is unique worldwide. High bird mortality during H5N8 outbreaks have been reported elsewhere in Europe, and by comparing the ecology and epidemiology of the H5N8 and H5N1 outbreaks at Abbotsbury we may be able to find out the cause of this. We aim to find out how, and from where, the H5N8 virus entered the population, how long it was present locally before it was detected, and how the virus spread through the population. To do this we will sequence the genomes of the viruses recovered from affected birds, and analyse these genomes using established statistical methods. We will look at the antibodies that birds in the population carry, to see if some birds, particularly the older ones, are protected against severe disease as a result of previous exposure to harmless strains of avian influenza. This will help us understand if immunity to flu in humans and long-lived birds is similar or different, and extend our understanding of how this virus spreads in wild birds.

高致病性禽流感（HPAI）病毒给家禽业造成重大经济损失，并对动物和人类健康构成重大威胁。 HPAI 在 20 世纪 90 年代末首次受到关注，当时 H5N1 谱系在亚洲出现，导致数百只禽类被扑杀，500 多人死亡。 2013 年，随着中国出现一种属于 H5N8 亚型的新型病毒株，高致病性禽流感重新成为全球威胁。 2014年以来H5N8在全球的传播速度令科学家感到惊讶。该菌株在亚洲、北美、欧洲以及最近的非洲迅速传播。病毒向北美的蔓延是史无前例的，估计给当地企业造成约 33 亿美元的损失。去年10月发布的一份报告得出的结论是，H5N8全球传播主要是由长途鸟类迁徙驱动的。2016年秋季，欧洲各地野生和养殖鸟类中H5N8疫情爆发的报告有所增加，并向西蔓延，直到12月底到达英国。威尔士、苏格兰和英格兰均报告了野生鸟类病例。迄今为止最大规模的疫情正在英格兰南部多塞特海岸阿伯茨伯里的大量（约 750 只）野生疣鼻天鹅中爆发。尽管（到目前为止）只有 9 只天鹅经实验室确诊感染 H5N8，但自疫情爆发以来已有超过 175 只未经检测的天鹅死亡，远远超过正常死亡率。 2016 年 12 月 23 日，在 Swannery 发现的一只死天鹅中发现了首例 H5N8 感染。尽管死亡率似乎较 2017 年 1 月第二周的明显峰值有所下降，但仍在恢复中的死鸟数量高于正常水平，当局仍认为疫情仍在持续（2017 年 2 月 2 日）。这次疫情虽然对鸟类种群造成了毁灭性打击，但可以告诉我们很多有关高致病性禽流感如何在野生鸟类中传播的信息。这些长寿天鹅经过牛津大学鸟类学家的长期生态研究，并被单独圈上；对于大多数鸟类，我们知道年龄、性别、亲子关系和其他变量。至关重要的是，完全相同的种群在 2008 年初爆发了 H5N1 HPAI。然而，2008 年只有 10 只天鹅死亡，几乎所有天鹅都在 3 岁以下。我们在 2008 年疫情爆发后的研究表明，年龄较大的鸟类更有可能产生抗体反应，这可能有助于提供针对禽流感的免疫保护。具体而言，几乎所有 3 岁以上的鸟类都含有流感抗体，而年龄较大的鸟类则具有针对更广泛的不同流感病毒株的抗体。因此，我们假设之前接触过常见、温和形式的流感可能保护这些野鸟免受 H5N1 感染。当前的疫情爆发提供了直接比较同一野鸟种群中 H5N1 和 H5N8 HPAI 流行病学的潜力，我们认为这是全球独一无二的机会。欧洲其他地方也报告了 H5N8 疫情期间鸟类死亡率较高的情况，通过比较阿伯茨伯里 H5N8 和 H5N1 疫情的生态学和流行病学，我们也许能够找出其原因。我们的目标是查明 H5N8 病毒如何、从何处进入人群，在被发现之前在当地存在了多长时间，以及病毒如何在人群中传播。为此，我们将对从受影响鸟类中回收的病毒的基因组进行测序，并使用既定的统计方法分析这些基因组。我们将检查种群中鸟类携带的抗体，看看某些鸟类，尤其是年长的鸟类，是否因之前接触过无害的禽流感毒株而免受严重疾病的影响。这将帮助我们了解人类和长寿鸟类对流感的免疫力是否相似或不同，并加深我们对这种病毒如何在野生鸟类中传播的理解。