Avian influenza virus exhibits rapid evolutionary dynamics

Influenza A viruses from wild aquatic birds, their natural reservoir species, are thought to have reached a form of stasis, characterized by low rates of evolutionary change. We tested this hypothesis by estimating rates of nucleotide substitution in a diverse array of avian influenza viruses (AIV) and allowing for rate variation among lineages. The rates observed were extremely high, at >10(-3) substitutions per site, per year, with little difference among wild and domestic host species or viral subtypes and were similar to those seen in mammalian influenza A viruses. Influenza A virus therefore exhibits rapid evolutionary dynamics across its host range, consistent with a high background mutation rate and rapid replication. Using the same approach, we also estimated that the common ancestors of the hemagglutinin and neuraminidase sequences of AIV arose within the last 3,000 years, with most intrasubtype diversity emerging within the last 100 years and suggestive of a continual selective turnover.     

Avian influenza virus, a very sticky situation

The appearance of the highly pathogenic avian influenza virus H5N1 highlighted the potential impact of influenza virus on humanity. The emergence of this high profile virus stimulated much research towards a better understanding of the key determinants for successful human-to-human transmission and as such has provided new directions for therapeutic intervention strategies. For example, a phylogenetic-based grouping of influenza virus sialidases into either Group 1 or 2 has been proposed. This has provided new opportunity for the development of Group 1-specific anti-influenza drugs. Furthermore, a number of next generation sialidase inhibitors as anti-influenza drugs have also been developed.     

Avian influenza virus infection dynamics in shorebird hosts

To gain insight into avian influenza virus (AIV) transmission, exposure, and maintenance patterns in shorebirds at Delaware Bay during spring migration, we examined temporal AIV prevalence trends in four Charadriiformes species with the use of serial cross-sectional data from 2000 through 2008 and generalized linear and additive models. Prevalence of AIV in Ruddy Turnstones (Arenaria interpres morinella) increased after arrival, peaked in mid-late May, and decreased prior to departure. Antibody prevalence also increased over this period; together, these results suggested local infection and recovery prior to departure. Red Knots (Calidris canutus rufa), Sanderlings (Calidris alba), and Laughing Gulls (Leucophaeus atricilla) were rarely infected, but dynamic changes in antibody prevalence differed among species. In Red Knots, declining antibody prevalence over the stopover period suggested AIV exposure prior to arrival at Delaware Bay with limited infection at this site. Antibody prevalence was consistently high in Laughing Gulls and low in Sanderlings. Both viral prevalence and antibody prevalence in Sanderlings varied directly with those in turnstones, suggesting virus spillover to Sanderlings. Results indicate that, although hundreds of thousands of birds concentrate at Delaware Bay during spring, dynamics of AIV infection differ among species, perhaps due to differences in susceptibility, potential for contact with AIV at this site, or prior exposure. Additionally, Ruddy Turnstones possibly act as a local AIV amplifying host rather than a reservoir.     

利用基因芯片技术区分禽流感病毒主要亚型

[目的]研制可同时区分AIV的H5、H7、H9血凝素亚型及N1、N2神经氨酸酶亚型的基因诊断芯片.[方法]分别克隆了禽流感病毒的M基因,H5、H7、H9亚型HA基因,N1、N2亚型NA基因以及看家基因GAPDH的重组质粒.以重组质粒为模板,用PCR方法扩增制备探针,纯化后点于氨基修饰的片基上,制备基因芯片.在PCR过程中对待检样品进行标记,然后与芯片杂交,洗涤,扫描并进行结果分析.[结果]结果显示检测探针可特异性的与相应的标记样品进行杂交,呈现较强的杂交信号,且无交叉杂交.同时用RT-PCR、鸡胚接种和基因芯片方法对H1-H15亚型AIV参考毒株、30份人工感染样品、21份现地疑似样品进行检测,结果发现,对人工感染样品芯片检测方法与鸡胚接种和RT-PCR的符合率分别为100%和96%,现地样品符合率为100%.[结论]研究表明该方法可用于同步鉴别部分主要流行的禽流感亚型,是一种有效的新方法.     

Avian influenza a virus in wild birds in highly urbanized areas

Avian influenza virus (AIV) surveillance studies in wild birds are usually conducted in rural areas and nature reserves. Less is known of avian influenza virus prevalence in wild birds located in densely populated urban areas, while these birds are more likely to be in close contact with humans. Influenza virus prevalence was investigated in 6059 wild birds sampled in cities in the Netherlands between 2006 and 2009, and compared with parallel AIV surveillance data from low urbanized areas in the Netherlands. Viral prevalence varied with the level of urbanization, with highest prevalence in low urbanized areas. Within cities virus was detected in 0.5% of birds, while seroprevalence exceeded 50%. Ring recoveries of urban wild birds sampled for virus detection demonstrated that most birds were sighted within the same city, while few were sighted in other cities or migrated up to 2659 km away from the sample location in the Netherlands. Here we show that urban birds were infected with AIVs and that urban birds were not separated completely from populations of long-distance migrants. The latter suggests that wild birds in cities may play a role in the introduction of AIVs into cities. Thus, urban bird populations should not be excluded as a human-animal interface for influenza viruses.     

禽流感与粘膜免疫

抗流感病毒感染需要同时诱发系统免疫和粘膜局部免疫．自然感染诱发的粘膜免疫有更好的交叉免疫保护效果。应用不同禽流感病毒（AIV）疫苗和佐剂,经过粘膜免疫,可以取得交叉保护免疫作用。粘膜免疫和粘膜免疫疫苗的研制在禽流感防治上有着非常重要的意义。就近年来使用不同类型AIV疫苗和不同佐剂的粘膜免疫情况作一简要综述。     

利用苏云金芽胞杆菌细胞表面展示系统表达禽流感病毒NP蛋白

首次利用苏云金芽胞杆菌(Bacillus thuringiensis,Bt)S-层蛋白CTC表面展示系统研究在Bt细胞表面展示禽流感病毒NP蛋白的可行性和最佳方案,为研制能常温长期保藏和运输的禽用口服疫苗奠定基础。用全长np基因或部分np基因(npp)代替S-层蛋白ctc基因的3′-端或中部,构建了4个重组质粒pSNP(含ctc-np)、pCSA-SNP(csa-ctc-np)、pCTC-NPP(ctc-npp)和pCSNPP(csa-ctc-npp)。将重组质粒分别电转化入Bt受体菌株BMB171中,获得了5个重组菌株BN、BCN、C-S、BCCN和CN。用5个重组菌株的营养细胞做玻片凝集试验,结果显示5个重组菌株均成功地在细胞表面展示了NP蛋白。用5个重组菌株的营养细胞免疫小鼠,ELISA测定血清抗体效价,结果显示5个重组菌株均具有免疫原性,其中重组菌株CN的免疫原性最高,其含融合基因csa-ctc-npp,证明该种融合基因的构建方式最佳。这为利用S-层蛋白CTC表面展示系统构建展示其它禽类病原体抗原的重组菌株以研制禽用热稳定性口服疫苗奠定了基础。     

Avian influenza virus directly infects human natural killer cells and inhibits cell activity

Natural killer (NK) cell is a key component of innate immunity and plays an important role in host defense against virus infection by directly destroying infected cells. Influenza is a respiratory disease transmitted in the early phase of virus infection. Evasion of host innate immunity including NK cells is critical for the virus to expand and establish a successful acute infection. Previously, we showed that human influenza H1N1 virus infects NK cells and induces cell apoptosis, as well as inhibits NK cell activity. In this study, we further demonstrated that avian influenza virus also directly targeted NK cells as an immunoevasion strategy. The avian virus infected human NK cells and induced cell apoptosis. In addition, avian influenza virion and HA protein inhibited NK cell cytotoxicity. This novel strategy has obvious advantages for avian influenza virus, allowing the virus sufficient time to expand and subsequent spread before the onset of the specific immune response. Our findings provide an important clue for the immunopathogenesis of avian influenza, and also suggest that direct targeting NK cells may be a common strategy used by both human and avian influenza viruses to evade NK cell immunity.

Open image in new window

     

Avian influenza viruses isolated in Japan

Currently, H5N1 influenza viruses remain a serious public health concern in Asia and now in Europe. We showed that the H5N1 viruses associated with outbreaks of HPAI in chickens in Japan were genotypically closely related to an H5N1 virus isolated from a chicken in China in 2003 (genotype V), but were different from those prevalent in southeastern Asia in 2003-2004 (i.e., genotype Z). H5N1 viruses were also isolated from duck meat imported from China during this routine surveillance in May of 2003. We characterized these H5N1 isolates and found that poultry products contaminated with influenza viruses of high pathogenic potential to mammals are a threat to public health even in countries where the virus is not enzootic and represent a possible source of influenza outbreaks in poultry.     

Avian influenza A virus susceptibility,infection, transmission,and antibody kinetics in European starlings

Avian influenza A viruses (IAVs) pose risks to public, agricultural, and wildlife health. Bridge hosts are spillover hosts that share habitat with both maintenance hosts (e.g., mallards) and target hosts (e.g., poultry). We conducted a comprehensive assessment of European starlings (Sturnus vulgaris), a common visitor to both urban and agricultural environments, to assess whether this species might act as a potential maintenance or bridge host for IAVs. First, we experimentally inoculated starlings with a wild bird IAV to investigate susceptibility and replication kinetics. Next, we evaluated whether IAV might spill over to starlings from sharing resources with a widespread IAV reservoir host. We accomplished this using a specially designed transmission cage to simulate natural environmental transmission by exposing starlings to water shared with IAV-infected mallards (Anas platyrhynchos). We then conducted a contact study to assess intraspecies transmission between starlings. In the initial experimental infection study, all inoculated starlings shed viral RNA and seroconverted. All starlings in the transmission study became infected and shed RNA at similar levels. All but one of these birds seroconverted, but detectable antibodies were relatively transient, falling to negative levels in a majority of birds by 59 days post contact. None of the contact starlings in the intraspecies transmission experiment became infected. In summary, we demonstrated that starlings may have the potential to act as IAV bridge hosts if they share water with IAV-infected waterfowl. However, starlings are unlikely to act as maintenance hosts due to limited, if any, intraspecies transmission. In addition, starlings have a relatively brief antibody response which should be considered when interpreting serology from field samples. Further study is needed to evaluate the potential for transmission from starlings to poultry, a possibility enhanced by starling’s behavioral trait of forming very large flocks which can descend on poultry facilities when natural resources are scarce.     

Avian influenza spread and seabird movements between colonies

Seabirds have recently been experiencing high rates of mortality across wide scales due to highly pathogenic avian influenza (HPAI). During breeding, seabird populations are highly spatially structured, while over their lifetimes they spend much time at sea. This makes them unique systems in which to document how movement and interspecies interactions affect eco-epidemiological dynamics.     

Avian influenza A virus H5N1 causes autophagy-mediated cell death through suppression of mTOR signaling

Of the few avian influenza viruses that have crossed the species barrier to infect humans,the highly pathogenic influenza A (H5N1) strain has claimed the lives of more than half of the infected patients.With largely unknown mechanism of lung injury by H5N1 infection,acute respiratory distress syndrome (ARDS) is the major cause of death among the victims.Here we present the fact that H5N1 caused autophagic cell death through suppression of mTOR signaling.Inhibition of autophagy,either by depletion of autophagy gene Beclinl or by autophagy inhibitor 3-methyladenine (3-MA),significantly reduced H5N1 mediated cell death.We suggest that autophagic cell death may contribute to the development of ARDS in H5N1 influenza patients and inhibition of autophagy could therefore become a novel strategy for the treatment of H5N1 infection.     

Avian influenza: an osteopathic component to treatment

Avian influenza is an infection caused by the H5N1 virus. The infection is highly contagious among birds, and only a few known cases of human avian influenza have been documented. However, healthcare experts around the world are concerned that mutation or genetic exchange with more commonly transmitted human influenza viruses could result in a pandemic of avian influenza. Their concern remains in spite of the fact that the first United States vaccine against the H5N1 virus was recently approved. Under these circumstances the fear is that a pandemic of avian influenza could result in the kind of mortality that was seen with the Spanish influenza pandemic of 1918–1919, where the number of deaths was estimated to be as high as 40 million people. Retrospective data gathered by the American Osteopathic Association shortly after the 1918–1919 influenza pandemic have suggested that osteopathic physicians (DOs), using their distinctive osteopathic manipulative treatment (OMT) methods, observed significantly lower morbidity and mortality among their patients as compared to those treated by allopathic physicians (MDs) with standard medical care available at the time. In light of the limited prevention and treatment options available, it seems logical that a preparedness plan for the treatment of avian influenza should include these OMT procedures, provided by DOs and other healthcare workers capable of being trained to perform these therapeutic interventions. The purpose of this paper is to discuss the characteristics of avian influenza, describe the success of DOs during the 1918–1919 Spanish influenza pandemic, describe the evidence base for the inclusion of OMT as part of the preparedness plan for the treatment of avian influenza, and describe some of the specific OMT procedures that could be utilized as part of the treatment protocol for avian influenza patients.     

Avian influenza (H5N1) virus of clade 2.3.2 in domestic poultry in India

South Asia has experienced regular outbreaks of H5N1 avian influenza virus since its first detection in India and Pakistan in February, 2006. Till 2009, the outbreaks in this region were due to clade 2.2 H5N1 virus. In 2010, Nepal reported the first outbreak of clade 2.3.2 virus in South Asia. In February 2011, two outbreaks of H5N1 virus were reported in the State of Tripura in India. The antigenic and genetic analyses of seven H5N1 viruses isolated during these outbreaks were carried out. Antigenic analysis confirmed 64 to 256-fold reduction in cross reactivity compared with clade 2.2 viruses. The intravenous pathogenicity index of the isolates ranged from 2.80-2.95 indicating high pathogenicity to chickens. Sequencing of all the eight gene-segments of seven H5N1 viruses isolated in these outbreaks was carried out. The predicted amino acid sequence analysis revealed high pathogenicity to chickens and susceptibility to the antivirals, amantadine and oseltamivir. Phylogenetic analyses indicated that these viruses belong to clade 2.3.2.1 and were distinct to the clade 2.3.2.1 viruses isolated in Nepal. Identification of new clade 2.3.2 H5N1 viruses in South Asia is reminiscent of the introduction of clade 2.2 viruses in this region in 2006/7. It is now important to monitor whether the clade 2.3.2.1 is replacing clade 2.2 in this region or co-circulating with it. Continued co-circulation of various subclades of the H5N1 virus which are more adapted to land based poultry in a highly populated region such as South Asia increases the risk of evolution of pandemic H5N1 strains.     

乳胶凝集试验检测H5亚型禽流感病毒血凝素抗体的研究

利用原核表达并经过纯化的H5亚型禽流感病毒的血凝素蛋白做为抗原,经碳二亚胺（EDAC）将表达产物和羧基化的乳胶共价偶联,并对偶联乳胶的蛋白量和偶联时间进行合理选择,建立H5亚型禽流感病毒血凝素蛋白乳胶凝集试验的方法。临床检测H5亚型禽流感病毒实验免疫鸡血清126份,同血凝抑制试验相比,其敏感性为87.03％,特异性为88.8％,两者的符合率为87.30%。结果证明建立的方法可用于H5亚型禽流感抗体水平监测和流行病学调查。