流感病毒灭活疫苗研究进展

流感病毒的不断变异是造成流感经常流行的主要原因．研究表明人流感病毒的来源与禽流感病毒的存在密切相关．最近出现的禽流感病毒跨种属感染人的事件,预示引起下一次爆发的流感病毒流行可能直接来源于禽流感病毒．因人类对新出现的病毒缺乏免疫力,开发有效疫苗仍然是预防流感流行的关键．对流感灭活疫苗包括灭活疫苗有效成分的改良,H5N1、H9N2型人．禽流感疫苗研究和应用反向遗传技术制备流感灭活疫苗等方面的研究进展进行了探讨．     

人禽流感H7N9、H5N1、H10N8临床特征

人禽流感(human-avian influenza)是一种由禽流感病毒中某些亚型感染人所引起的急性呼吸道传染病,目前能够感染人的禽流感病毒主要有H5、H7、H9和H10亚型。人感染禽流感病毒A(H5N1)、A(H7N9)、A(H10N8)与重症季节性流感临床表现相似,主要表现为重症肺炎,病死率高。人禽流感与重症季节性流感和重症新甲型H1N1流感患者有相同的危险因素,如高龄、合并基础疾病等,但人禽流感临床表现更重。     

序言

<正>"流感"一词,对于我们从来都不是很陌生。季节性流感、大流感、禽流感等词汇经常会成为新闻头条,人类与流感已经成为并存的"朋友"。继2009-H1N1流感大流行之后,2013年春天发生的H7N9禽流感感染人事件再次提醒人们,流感病毒可能给人类带来危害与灾难,同时也为流感相关科学研究提出了重要的科学命题:H7N9禽流感病毒的病原学特征如何,临床表现如何,如何实现跨种传播;同为高致病性禽流感病毒的H5N1的流行特征如何;另外,能为H7N9和H5N1禽流感病毒提     

禽流感病毒与人流感的关系

禽流感病毒 (AIV)是甲 (A)型流感病毒 ,常引起禽类全身性感染或主要限于呼吸器官传染病 ,带来巨大的经济损失并严重威胁人类健康。对AIV的基因组、所编码的蛋白质及其功能、AIV毒力变异的分子基础、禽流感疫苗以及AIV与人流感的关系等进行概述。     

野禽禽流感病毒监测概述

野禽(主要是雁形目和鸻形目)被认为是禽流感病毒的天然宿主。北美和欧洲自二十世纪七十年代后陆续开展野禽禽流感病毒的监测。研究发现从野鸭和滨鸟及鸥类能分离到所有HA和NA亚型的禽流感病毒,而且野禽中禽流感病毒与家禽和人感染禽流感病毒的疫情密切相关。因而野禽禽流感病毒对家禽养殖业和人类健康构成了极大的威胁。本文将从禽流感病毒在野禽、家禽和人群中的传播、全球野禽禽流感病毒监测的主要结果以及监测方法、采样类型和检测方法进行归纳总结,以期能帮助我们更好地了解野禽禽流感病毒的生态分布和流行规律,从而使我们更为有效地预防和控制禽流感,应对未来可能出现的流感大流行。     

H7亚型禽流感病毒与禽类和人类的关系

2013年在中国首次发生了H7N9亚型流感病毒感染人事件,已经证实H7N9型禽流感是一种新型禽流感,是全球首次发现感染人类的新亚型流感病毒,以往这种病毒只在野生鸟类存在和传播。H7N9型禽流感病毒属于H7亚型中的一种,全球感染人的H7亚型病毒主要分为两大支系,即北美支系和欧亚支系,感染人的流感亚型也主要集中在H7N7,H7N3,H7N2等亚型上。为了清晰的了解H7亚型病毒的来龙去脉,本文重点讨论了A亚型流感病毒的宿主分布、H7亚型病毒感染禽类和人类的历史、H7亚型病毒的生物学特性以及未来研究展望。     

人用禽流感疫苗研究渐入佳境

由高致病性禽流感病毒导致的人流行性感冒(简称流感)发病和死亡迄今仍严重危害人类健康和公共卫生安全.据世界卫生组织(WHO)报道,自2003年12月～2006年7月,全球共报告131例死于禽流感;我国已累计报告人感染高致病性禽流感病例19例,死亡12例,报告病例的省份11个.对于人禽流感,目前尚无有效的特异性预防手段,而高致病性禽流感病毒一旦突破人群免疫屏障,演变为人-人间可传播的高致病性流感病毒,将造成大量的感染和死亡病例.进行有效的疫苗接种是迅速建立人群免疫屏障,阻断流感大流行的蔓延,减少和降低其危害的有效手段.为此,世界各国迅速开展了禽流感疫苗的研制,特别是人用禽流感预防性疫苗的研制.     

21世纪的首次大流行：2009甲型（H1N1）流感

2009年4月初,在墨西哥和美国出现一种新型甲型（H1N1）流感病毒。该病毒通过人-人传播迅速在全球范围蔓延。该病毒拥有来自人流感病毒、禽流感病毒和猪流感病毒的基因片段,其HA基因与引发1918年大流行的流感病毒株的HA基因同源性很高。该病毒倾向于感染儿童、青少年、孕妇,以及具有心肺疾病的人。据观察,它在人群中的传播能力高于季节性流感。部分感染患者具有在季节性流感中罕见的呕吐和腹泻症状。先前的流感病毒大流行和2009年爆发的甲型H1N1流感病毒大流行表明,由于流感病毒变异速度快、容易发生基因重排,新产生的变异毒株很可能造成新的大流行,威胁人类健康。由于禽流感病毒和人流感病毒都能感染猪,猪被认为是通过基因重排生成新的大流行病毒的＂混合容器＂。     

H7亚型禽流感病毒概述

自2002年以来,全球报道的人感染H7亚型禽流感病毒病例超过100人,波及荷兰、意大利、加拿大、美国以及英国等国家。人感染H7亚型禽流感病毒的临床表现由结膜炎至轻微的上呼吸道疾病,甚至是肺炎。2013年3月31日,中国报道了上海市和安徽省两地共3例H7N9亚型禽流感病毒(AIVs)感染死亡病例。由于从家禽中分离到的H7亚型流感病毒不断增加,而且H7亚型AIVs感染人所导致的严重的临床症状,因此该亚型流感病毒对人类健康造成严重威胁,所以我们必须提高对H7亚型AIVs的认识,并要加强人群和动物中流感病毒的持续监测以及疫苗和药物的研究,以应对可能由于H7亚型AIVs引起的流感大流行。     

新型H7N9禽流感病毒的病原学研究进展

2013年初在中国长三角地区首次发现一种新的H7N9禽流感病毒可导致人的感染和死亡。该病毒是由H7、N9以及H9N2禽流感病毒重配而成,病毒传播到其他地区之后仍与当地的H9N2病毒不断重配,产生不同的基因型。H7N9禽流感病毒特殊的双受体结合特性是其突破种属屏障感染人的重要机制,也是该病毒比H5N1禽流感病毒更容易感染人的原因,这种受体特性的分子基础主要与病毒HA蛋白的Q226L和G186V突变有关。H7N9病毒对禽类不致病,但人感染后的病死率超过30%。人群没有免疫力、病毒感染所导致的免疫病理以及病毒在肺部组织的高效复制是导致人感染H7N9病毒后高病死率的重要原因。雪貂动物模型研究也表明该病毒能够在雪貂中有效复制和接触传播。因此,H7N9禽流感病毒导致流感大流行的风险不容忽视,对动物和人群中H7N9禽流感病毒的监测不容松懈。     

Influenza type A in humans,mammals and birds: determinants of virus virulence,host-range and interspecies transmission

The virulence of a virus is determined by its ability to adversely affect the host cell, host organism or population of host organisms. Influenza A viruses have been responsible for four pandemics of severe human respiratory disease this century. Avian species harbour a large reservoir of influenza virus strains, which can contribute genes to potential new pandemic human strains. The fundamental importance of understanding the role of each of these genes in determining virulence in birds and humans was dramatically emphasised by the recent direct transmission of avian influenza A viruses to humans, causing fatal infection but not community spread. An understanding of the factors involved in transmission between avian and mammalian species should assist in the development of better surveillance strategies for early recognition of influenza A virus strains having human pandemic potential, and possibly in the design of anti-viral strategies.     

Emergence of avian H1N1 influenza viruses in pigs in China.

Avian influenza A viruses from Asia are recognized as the source of genes that reassorted with human viral genes to generate the Asian/57 (H2N2) and Hong Kong/68 (H3N2) pandemic strains earlier in this century. Here we report the genetic analysis of avian influenza A H1N1 viruses recently isolated from pigs in southern China, a host suspected to generate new pandemic strains through gene reassortment events. Each of the eight gene segments was of avian origin. Phylogenetic analysis indicates that these genes form an Asian sublineage of the Eurasian avian lineage, suggesting that these viruses are an independent introduction into pigs in Asia. The presence of avian influenza viruses in pigs in China places them in an optimal position for transmission to humans and may serve as an early warning of the emergence of the next human influenza virus pandemic.     

Avian influenza H5N1: an update on molecular pathogenesis

Avian influenza A virus constitutes a large threat to human health. Recent outbreaks of highly pathogenic avian influenza H5N1 virus in poultry and in humans have raised concerns that an influenza pandemic will occur in the near future. Transmission from avian species to humans remains sporadic, but the mortality associated with human infection is very high (about 62%). To date, there are no effective therapeutic drugs or a prophylactic vaccines available, which means that there is still a long way to go before we can eradicate or cure avian influenza. This review focuses on the molecular pathogenesis of avian influenza H5N1 virus infection. An understanding of the viral pathogenesis may facilitate the development of novel treatments or effective eradication of this fatal disease.     

Influenza—an emerging and re-emerging disease

Influenza A viruses continue to emerge from the aquatic avian reservoir and cause pandemics. There are periodic exchanges of influenza virus genes or whole viruses between avians and other species giving rise to pandemics of diseases in humans, lower animals and birds. It is hypothesized that pigs are an intermediate host and that China is an epicenter for the evolution of human pandemic strains. However, the transmission of avian influenza viruses to pigs in Europe in 1979 and detection of reassortants with human influenza genes in pigs raises the question of whether the next pandemic of influenza will emerge in Europe!     

Persistent host markers in pandemic and H5N1 influenza viruses

Avian influenza viruses have adapted to human hosts, causing pandemics in humans. The key host-specific amino acid mutations required for an avian influenza virus to function in humans are unknown. Through multiple-sequence alignment and statistical testing of each aligned amino acid, we identified markers that discriminate human influenza viruses from avian influenza viruses. We applied strict thresholds to select only markers which are highly preserved in human influenza virus isolates over time. We found that a subset of these persistent host markers exist in all human pandemic influenza virus sequences from 1918, 1957, and 1968, while others are acquired as the virus becomes a seasonal influenza virus. We also show that human H5N1 influenza viruses are significantly more likely to contain the amino acid predominant in human strains for a few persistent host markers than avian H5N1 influenza viruses. This sporadic enrichment of amino acids present in human-hosted viruses may indicate that some H5N1 viruses have made modest adaptations to their new hosts in the recent past. The markers reported here should be useful in monitoring potential pandemic influenza viruses.     

Isolation and mutation trend analysis of influenza A virus subtype H9N2 in Egypt

ABSTRACT: BACKGROUND: Avian influenza virus H9N2 is a panzootic pathogen that affects poultry causing mild to moderate respiratory distress but has been associated with high morbidity and considerable mortality. Interspecies transmission of H9N2 from avian species to mammalian hosts does occur. The virus possesses human virus-like receptor specificity and it can infect humans producing flu-like illness. METHODS: Recently, mild influenza like symptoms were detected in H5N1 vaccinated flocks. Influenza A subtype H9N2 was isolated from the infected flock. The virus evolution was investigated by sequencing the viral genes to screen the possible virus recombination. The viral amino acid sequences from the isolated H9N2 strains were compared to other related sequences from the flu data base that were used to assess the robustness of the mutation trend. Changes in the species-associated amino acid residues or those that enabled virulence to mammals were allocated. RESULTS: Phylogenetic analyses of haemagglutinin and neuraminidase genes showed that the recently isolated Egyptian strain belonged to the H9N2 sub-lineage that prevails in Israel. The six internal segments of the isolated virus were found to be derived from the same sub-lineage with no new evidence of reassortment. The results demonstrated conserved genetic and biological constitution of H9N2 viruses in the Middle East. The recently isolated H9N2 virus from chicken in Egypt possessed amino acids that could enable the virus to replicate in mammals and caused severe disease in domestic chickens. CONCLUSION: The study highlights the importance of continuous monitoring of the mutations evolved in avian influenza viruses and its impact on virulence to avian species in addition to its importance in the emergence of new strains with the capacity to be a pandemic candidate.     

The evolutionary emergence of pandemic influenza

Pandemic influenza remains a serious public health threat and the processes involved in the evolutionary emergence of pandemic influenza strains remain incompletely understood. Here, we develop a stochastic model for the evolutionary emergence of pandemic influenza, and use it to address three main questions. (i) What is the minimum annual number of avian influenza virus infections required in humans to explain the historical rate of pandemic emergence? (ii) Are such avian influenza infections in humans more likely to give rise to pandemic strains if they are driven by repeated cross-species introductions, or by low-level transmission of avian influenza viruses between humans? (iii) What are the most effective interventions for reducing the probability that an influenza strain with pandemic potential will evolve? Our results suggest that if evolutionary emergence of past pandemics has occurred primarily through viral reassortment in humans, then thousands of avian influenza virus infections in humans must have occurred each year for the past 250 years. Analyses also show that if there is epidemiologically significant variation among avian influenza virus genotypes, then avian virus outbreaks stemming from repeated cross-species transmission events result in a greater likelihood of a pandemic strain evolving than those caused by low-level transmission between humans. Finally, public health interventions aimed at reducing the duration of avian virus infections in humans give the greatest reduction in the probability that a pandemic strain will evolve.     

Emergence of the Virulence-Associated PB2 E627K Substitution in a Fatal Human Case of Highly Pathogenic Avian Influenza Virus A(H7N7) Infection as Determined by Illumina Ultra-Deep Sequencing

Avian influenza viruses are capable of crossing the species barrier and infecting humans. Although evidence of human-to-human transmission of avian influenza viruses to date is limited, evolution of variants toward more-efficient human-to-human transmission could result in a new influenza virus pandemic. In both the avian influenza A(H5N1) and the recently emerging avian influenza A(H7N9) viruses, the polymerase basic 2 protein (PB2) E627K mutation appears to be of key importance for human adaptation. During a large influenza A(H7N7) virus outbreak in the Netherlands in 2003, the A(H7N7) virus isolated from a fatal human case contained the PB2 E627K mutation as well as a hemagglutinin (HA) K416R mutation. In this study, we aimed to investigate whether these mutations occurred in the avian or the human host by Illumina Ultra-Deep sequencing of three previously uninvestigated clinical samples obtained from the fatal case. In addition, we investigated three chicken samples, two of which were obtained from the source farm. Results showed that the PB2 E627K mutation was not present in any of the chicken samples tested. Surprisingly, the avian samples were characterized by the presence of influenza virus defective RNA segments, suggestive for the synthesis of defective interfering viruses during infection in poultry. In the human samples, the PB2 E627K mutation was identified with increasing frequency during infection. Our results strongly suggest that human adaptation marker PB2 E627K has emerged during virus infection of a single human host, emphasizing the importance of reducing human exposure to avian influenza viruses to reduce the likelihood of viral adaptation to humans.     

Evidence of an absence: the genetic origins of the 1918 pandemic influenza virus

Annual outbreaks of influenza A infection are an ongoing public health threat and novel influenza strains can periodically emerge to which humans have little immunity, resulting in devastating pandemics. The 1918 pandemic killed at least 40 million people worldwide and pandemics in 1957 and 1968 caused hundreds of thousands of deaths. The influenza A virus is capable of enormous genetic variation, both by continuous, gradual mutation and by reassortment of genome segments between viruses. Both the 1957 and 1968 pandemic strains are thought to have originated as reassortants in which one or both human-adapted viral surface proteins were replaced by proteins from avian influenza strains. Analyses of the genes of the 1918 pandemic virus, however, indicate that this strain might have had a different origin. The haemagglutinin and nucleoprotein genome segments in particular are unlikely to have come directly from an avian source that is similar to those that are currently being sequenced. Determining whether a pandemic influenza virus can emerge by different mechanisms will affect the scope and focus of surveillance and prevention efforts.     

Replication and Immunogenicity of Swine,Equine, and Avian H3 Subtype Influenza Viruses in Mice and Ferrets

Since it is difficult to predict which influenza virus subtype will cause an influenza pandemic, it is important to prepare influenza virus vaccines against different subtypes and evaluate the safety and immunogenicity of candidate vaccines in preclinical and clinical studies prior to a pandemic. In addition to infecting humans, H3 influenza viruses commonly infect pigs, horses, and avian species. We selected 11 swine, equine, and avian H3 influenza viruses and evaluated their kinetics of replication and ability to induce a broadly cross-reactive antibody response in mice and ferrets. The swine and equine viruses replicated well in the upper respiratory tract of mice. With the exception of one avian virus that replicated poorly in the lower respiratory tract, all of the viruses replicated in mouse lungs. In ferrets, all of the viruses replicated well in the upper respiratory tract, but the equine viruses replicated poorly in the lungs. Extrapulmonary spread was not observed in either mice or ferrets. No single virus elicited antibodies that cross-reacted with viruses from all three animal sources. Avian and equine H3 viruses elicited broadly cross-reactive antibodies against heterologous viruses isolated from the same or other species, but the swine viruses did not. We selected an equine and an avian H3 influenza virus for further development as vaccines.