Origin and diversity of novel avian influenza A H7N9 viruses causing human infection: phylogenetic, structural, and coalescent analyses

Framework for Infectious Disease Analysis: A comprehensive and integrative multi-modeling approach to disease prediction and management

The impact of infectious disease on human populations is a function of many factors including environmental conditions, vector dynamics, transmission mechanics, social and cultural behaviors, and public policy. A comprehensive framework for disease management must fully connect the complete disease lifecycle, including emergence from reservoir populations, zoonotic vector transmission, and impact on human societies. The Framework for Infectious Disease Analysis is a software environment and conceptual architecture for data integration, situational awareness, visualization, prediction, and intervention assessment. Framework for Infectious Disease Analysis automatically collects biosurveillance data using natural language processing, integrates structured and unstructured data from multiple sources, applies advanced machine learning, and uses multi-modeling for analyzing disease dynamics and testing interventions in complex, heterogeneous populations. In the illustrative case studies, natural language processing from social media, news feeds, and websites was used for information extraction, biosurveillance, and situation awareness. Classification machine learning algorithms (support vector machines, random forests, and boosting) were used for disease predictions.

AVIAN INFLUENZA A H7N9 VIRUS HAS BEEN ESTABLISHED IN CHINA

In March 2013, a novel avian-origin influenza A H7N9 virus was identified among human patients in China and a total of 124 human cases with 24 related deaths were confirmed by May 2013. From November 2013 to July 2017, H7N9 broke out four more times in China. A deterministic model is proposed to study the transmission dynamics of the avian influenza A H7N9 virus between wild and domestic birds and from birds to humans, and is applied to simulate the open data on numbers of the infected human cases and related deaths reported from March to May 2013 and from November 2013 to June 2014 by the Chinese Center for Disease Control and Prevention. The basic reproduction number [Formula: see text] is estimated and sensitivity analysis of [Formula: see text] in terms of model parameters is performed. Taking into account the fact that it broke out again from November 2014 to June 2015, from November 2015 to July 2016, and from October 2016 to July 2017, we believe that H7N9 virus has been well established in birds and will likely cause regular outbreaks in humans again in the future. Control measures for the future spread of H7N9 include (i) reducing the transmission opportunities between wild birds and domestic birds, (ii) closing or monitoring the retail live-poultry markets in the infected areas, and (iii) culling the infected domestic birds in the epidemic regions.

Genetic Characteristic and Global Transmission of Influenza A H9N2 Virus

The H9N2 virus has been demonstrated to donate its genes to other subtypes of influenza A virus, forming new reassortant virus which may infect human beings. Understanding the genetic characteristic and the global transmission patterns of the virus would guide the prevention and control of potentially emerging avian influenza A virus. In this paper, we hierarchically classified the evolution of the H9N2 virus into three main lineages based on the phylogenetic characteristics of the virus. Due to the distribution of sampling locations, we named the three lineages as Worldwide lineage, Asia-Africa lineage, and China lineage. Codon usage analysis and selective positive site analysis of the lineages further showed the lineage-specific evolution of the virus. We reconstructed the transmission routes of the virus in the three lineages through phylogeography analysis, by which several epicenters for migration of the virus were identified. The hierarchical classification of the lineages implied a possible original seeding process of the virus, starting from the Worldwide lineages to the Asian-Africa lineages and to the China lineages. In the process of H9N2 virus global transmission, the United States was the origin of the virus. China Mainland, Hong Kong SAR, Japan, and Korea were important transfer centers. Based on both the transmission route and the distribution of the hosts in each lineage, we concluded that the wild birds' migration has contributed much to the long-distance global spread of the virus, while poultry trade and people's lifestyle may have contributed to the relatively short-distance transmission in some areas of the Asia and Africa.

Molecular Markers for Interspecies Transmission of Avian Influenza Viruses in Mammalian Hosts

In the last decade, a wide range of avian influenza viruses (AIVs) have infected various mammalian hosts and continuously threaten both human and animal health. It is a result of overcoming the inter-species barrier which is mostly associated with gene reassortment and accumulation of mutations in their gene segments. Several recent studies have shed insights into the phenotypic and genetic changes that are involved in the interspecies transmission of AIVs. These studies have a major focus on transmission from avian to mammalian species due to the high zoonotic potential of the viruses. As more mammalian species have been infected with these viruses, there is higher risk of genetic evolution of these viruses that may lead to the next human pandemic which represents and raises public health concern. Thus, understanding the mechanism of interspecies transmission and molecular determinants through which the emerging AIVs can acquire the ability to transmit to humans and other mammals is an important key in evaluating the potential risk caused by AIVs among humans. Here, we summarize previous and recent studies on molecular markers that are specifically involved in the transmission of avian-derived influenza viruses to various mammalian hosts including humans, pigs, horses, dogs, and marine mammals.

Histone Deacetylase 1 Plays an Acetylation-Independent Role in Influenza A Virus Replication

Influenza A viruses (IAVs) take advantage of the host acetylation system for their own benefit. Whether the nucleoprotein (NP) of IAVs undergoes acetylation and the interaction between the NP and the class I histone deacetylases (HDACs) were largely unknown. Here, we showed that the NP protein of IAV interacted with HDAC1, which downregulated the acetylation level of NP. Using mass spectrometry, we identified lysine 103 as an acetylation site of the NP. Compared with wild-type protein, two K103 NP mutants, K103A and K103R, enhanced replication efficiency of the recombinant viruses in vitro. We further demonstrated that HDAC1 facilitated viral replication via two paths: promoting the nuclear retention of NP and inhibiting TBK1-IRF3 pathway. Our results lead to a new mechanism for regulating NP acetylation, indicating that HDAC1 may be a possible target for antiviral drugs.

Pathogen genomic surveillance elucidates the origins, transmission and evolution of emerging viral agents in China

In the past twenty years, numerous novel zoonotic viral agents with pandemic potential have emerged in China, such as the severe acute respiratory syndrome (SARS) coronavirus and, more recently, the avian-origin influenza A/H7N9 virus, which have caused outbreaks among humans with high morbidity and mortality. In addition, several emerging and re-emerging viral pathogens have also been imported into China from travelers, e.g. the Middle East respiratory syndrome (MERS) coronavirus and Zika virus (ZIKV). Herein, we review these emerging viral pathogens in China and focus on how surveillance by pathogen genomics has been employed to discover and annotate novel pathogenic agents, identify natural reservoirs, monitor the transmission events and delineate their evolution and adaption to the human host. We also highlight the application of genomic sequencing in the recent Ebola epidemics in Western Africa. In summary, genomic sequencing has become a standard research tool in the field of emerging infectious diseases which has been proven invaluable in containing these viral infections and reducing burden of disease in humans and animals. Genomic surveillance of pathogenic agents will serve as a key epidemiological and research tool in the modern era of precision infectious diseases and in the future studies of virosphere.

Genetic evolution of influenza H9N2 viruses isolated from various hosts in China from 1994 to 2013

Influenza H9N2 subtype viruses and their reassortants (such as H7N9) are posing increasing threats to birds and humans in China. During 2009–2013, multiple novel subtype viruses with H9N2 original genes emerged in China. Yet, the genetic evolution of H9N2 viruses in various host organisms in China has not been systematically investigated since 2009. In the present study, we performed large-scale sequence analysis of H9N2 viral genomes from public databases, representing the spectrum of viruses isolated from birds, mammals and humans in China from 1994 to 2013, and updated the clade classification for each segment. We identified 117 distinct genotypes in 730 H9N2 viruses. We analyzed the sequences of all eight segments in each virus and found three important time points: the years 2000, 2006 and 2010. In the periods divided by these years, genotypic diversity, geographic distribution and host range changed considerably. Genotypic diversity fluctuated greatly in 2000 and 2006. Since 2010, a single genotype became predominant in poultry throughout China, and the eastern coastal region became the newly identified epidemic center. Throughout their 20-year prevalence in China, H9N2 influenza viruses have emerged and adapted from aquatic birds to chickens. The minor avian species and wild birds exacerbated H9N2 genotypes by providing diversified genes, and chickens were the most prevalent vector in which the viruses evolved and expanded their prevalence. It is the necessity for surveillance and disease control on live-bird markets, poultry farms and wild-bird habitats in China.

Universal influenza virus vaccines: what can we learn from the human immune response following exposure to H7 subtype viruses?

Several universal influenza virus vaccine candidates based on eliciting antibodies against the hemagglutinin stalk domain are in development. Typically, these vaccines induce responses that target group 1 or group 2 hemagglutinins with little to no cross-group reactivity and protection. Similarly, the majority of human anti-stalk monoclonal antibodies that have been isolated are directed against group 1 or group 2 hemagglutinins with very few that bind to hemagglutinins of both groups. Here we review what is known about the human humoral immune response to vaccination and infection with H7 subtype influenza viruses on a polyclonal and monoclonal level. It seems that unlike vaccination with H5 hemagglutinin, which induces antibody responses mostly restricted to the group 1 stalk domain, H7 exposure induces both group 2 and cross-group antibody responses. A better understanding of this phenomenon and the underlying mechanisms might help to develop future universal influenza virus vaccine candidates.

Natural Reassortants of Potentially Zoonotic Avian Influenza Viruses H5N1 and H9N2 from Egypt Display Distinct Pathogenic Phenotypes in Experimentally Infected Chickens and Ferrets

The cocirculation of zoonotic highly pathogenic avian influenza virus (HPAIV) of subtype H5N1 and avian influenza virus (AIV) of subtype H9N2 among poultry in Egypt for at least 6 years should render that country a hypothetical hot spot for the emergence of reassortant, phenotypically altered viruses, yet no reassortants have been detected in Egypt. The present investigations proved that reassortants of the Egyptian H5N1 clade 2.2.1.2 virus and H9N2 virus of the G1-B lineage can be generated by coamplification in embryonated chicken eggs. Reassortants were restricted to the H5N1 subtype and acquired between two and all six of the internal segments of the H9N2 virus. Five selected plaque-purified reassortant clones expressed a broad phenotypic spectrum both in vitro and in vivo Two groups of reassortants were characterized to have retarded growth characteristics in vitro compared to the H5N1 parent virus. One clone provoked reduced mortality in inoculated chickens, although the characteristics of a highly pathogenic phenotype were retained. Enhanced zoonotic properties were not predicted for any of these clones, and this prediction was confirmed by ferret inoculation experiments: neither the H5N1 parent virus nor two selected clones induced severe clinical symptoms or were transmitted to sentinel ferrets by contact. While the emergence of reassortants of Egyptian HPAIV of subtype H5N1 with internal gene segments of cocirculating H9N2 viruses is possible in principle, the spread of such viruses is expected to be governed by their fitness to outcompete the parental viruses in the field. The eventual spread of attenuated phenotypes, however, would negatively impact syndrome surveillance on poultry farms and might foster enzootic virus circulation.IMPORTANCE Despite almost 6 years of the continuous cocirculation of highly pathogenic avian influenza virus H5N1 and avian influenza virus H9N2 in poultry in Egypt, no reassortants of the two subtypes have been reported. Here, the principal compatibility of the two subtypes is shown by forcing the reassortment between copassaged H5N1 und H9N2 viruses in embryonated chicken eggs. The resulting reassortant viruses displayed a wide range of pathogenicity including attenuated phenotypes in chickens, but did not show enhanced zoonotic propensities in the ferret model.

Investigation of antiviral state mediated by interferon-inducible transmembrane protein 1 induced by H9N2 virus and inactivated viral particle in human endothelial cells

Background

Endothelial cells are believed to play an important role in response to virus infection. Our previous microarray analysis showed that H9N2 virus infection and inactivated viral particle inoculation increased the expression of interferon-inducible transmembrane protein 1 (IFITM1) in human umbilical vein endothelial cells (HUVECs). In present study, we deeply investigated the expression patterns of IFITM1 and IFITM1-mediated antiviral response induced by H9N2 virus infection and inactivated viral particle inoculation in HUVECs. Epithelial cells that are considered target cells of the influenza virus were selected as a reference control.

Methods

First, we quantified the expression levels of IFITM1 in HUVECs induced by H9N2 virus infection or viral particle inoculation using quantitative real-time PCR and western blot. Second, we observed whether hemagglutinin or neuraminidase affected IFITM1 expression in HUVECs. Finally, we investigated the effect of induced-IFITM1 on the antiviral state in HUVECs by siRNA and activation plasmid transfection.

Results

Both H9N2 virus infection and viral particle inoculation increased the expression of IFITM1 without elevating the levels of interferon-ɑ/β in HUVECs. HA or NA protein binding alone is not sufficient to increase the levels of IFITM1 and interferon-ɑ/β in HUVECs. IFITM1 induced by viral particle inoculation significantly decreased the virus titers in culture supernatants of HUVECs.

Conclusions

Our results showed that inactivated viral particle inoculation increased the expression of IFITM1 at mRNA and protein levels. Moreover, the induction of IFITM1 expression mediated the antiviral state in HUVECs.

Spatio-temporal pattern analysis for evaluation of the spread of human infections with avian influenza A(H7N9) virus in China, 2013-2014

BACKGROUND

A large number (n = 460) of A(H7N9) human infections have been reported in China from March 2013 through December 2014, and H7N9 outbreaks in humans became an emerging issue for China health, which have caused numerous disease outbreaks in domestic poultry and wild bird populations, and threatened human health severely. The aims of this study were to investigate the directional trend of the epidemic and to identify the significant presence of spatial-temporal clustering of influenza A(H7N9) human cases between March 2013 and December 2014.

METHODS

Three distinct epidemic phases of A(H7N9) human infections were identified in this study. In each phase, standard deviational ellipse analysis was conducted to examine the directional trend of disease spreading, and retrospective space-time permutation scan statistic was then used to identify the spatio-temporal cluster patterns of H7N9 outbreaks in humans.

RESULTS

The ever-changing location and the increasing size of the three identified standard deviational ellipses showed that the epidemic moved from east to southeast coast, and hence to some central regions, with a future epidemiological trend of continue dispersing to more central regions of China, and a few new human cases might also appear in parts of the western China. Furthermore, A(H7N9) human infections were clustering in space and time in the first two phases with five significant spatio-temporal clusters (p < 0.05), but there was no significant cluster identified in phase III.

CONCLUSIONS

There was a new epidemiologic pattern that the decrease in significant spatio-temporal cluster of A(H7N9) human infections was accompanied with an obvious spatial expansion of the outbreaks during the study period, and identification of the spatio-temporal patterns of the epidemic can provide valuable insights for better understanding the spreading dynamics of the disease in China.

Internal Gene Cassette from a Genotype S H9N2 Avian Influenza Virus Attenuates the Pathogenicity of H5 Viruses in Chickens and Mice

H9N2 avian influenza virus (AIV) of genotype S frequently donate internal genes to facilitate the generation of novel reassortants such as H7N9, H10N8, H5N2 and H5N6 AIVs, posing an enormous threat to both human health and poultry industry. However, the pathogenicity and transmission of reassortant H5 viruses with internal gene cassette of genotype S H9N2-origin in chickens and mice remain unknown. In this study, four H5 reassortants carrying the HA and NA genes from different clades of H5 viruses and the remaining internal genes from an H9N2 virus of the predominant genotype S were generated by reverse genetics. We found that all four H5 reassortant viruses showed attenuated virulence in both chickens and mice, thus leading to increased the mean death times compared to the corresponding parental viruses. Consistently, the polymerase activity and replication ability in mammalian and avian cells, and the cytokine responses in the lungs of chickens and mice were also decreased when compared to their respective parental viruses. Moreover, these reassortants transmitted from birds to birds by direct contact but not by an airborne route. Our data indicate that the internal genes as a whole cassette from genotype S H9N2 viruses play important roles in reducing the pathogenicity of the H5 recombinants in chickens and mice, and might contribute to the circulation in avian or mammalian hosts.

Phylogenetic and genetic characterization of a 2017 clinical isolate of H7N9 virus in Guangzhou, China during the fifth epidemic wave

Pathogenic H7N9 influenza viruses continue to pose a public health concern. The H7N9 virus has caused five outbreak waves of human infections in China since 2013. In the present study, a novel H7N9 strain (A/Guangdong/8H324/2017) was isolated from a female patient with severe respiratory illness during the fifth wave of the 2017 H7N9 epidemic. Phylogenetic analysis showed that the H7N9 viruses collected during the fifth wave belong to two different lineages: the Pearl River Delta lineage and the Yangtze River Delta lineage. The novel isolate is closely related to the Pearl River Delta H7N9 viruses, which were isolated from patients in Guangdong Province. The novel H7N9 isolate has an insertion of three basic amino acids in the cleavage site of hemagglutinin (HA), which may enhance virulence in poultry. The 2017 isolate also possesses an R292K substitution in the neuraminidase (NA) protein, which confers oseltamivir resistance. This study highlights the pandemic potential of the novel H7N9 virus in mammals; thus, future characterization and surveillance is warranted.

Avian influenza overview October 2016-August 2017

The A(H5N8) highly pathogenic avian influenza (HPAI) epidemic occurred in 29 European countries in 2016/2017 and has been the largest ever recorded in the EU in terms of number of poultry outbreaks, geographical extent and number of dead wild birds. Multiple primary incursions temporally related with all major poultry sectors affected but secondary spread was most commonly associated with domestic waterfowl species. A massive effort of all the affected EU Member States (MSs) allowed a descriptive epidemiological overview of the cases in poultry, captive birds and wild birds, providing also information on measures applied at the individual MS level. Data on poultry population structure are required to facilitate data and risk factor analysis, hence to strengthen science-based advice to risk managers. It is suggested to promote common understanding and application of definitions related to control activities and their reporting across MSs. Despite a large number of human exposures to infected poultry occurred during the ongoing outbreaks, no transmission to humans has been identified. Monitoring the avian influenza (AI) situation in other continents indicated a potential risk of long-distance spread of HPAI virus (HPAIV) A(H5N6) from Asia to wintering grounds towards Western Europe, similarly to what happened with HPAIV A(H5N8) and HPAIV A(H5N1) in previous years. Furthermore, the HPAI situation in Africa with A(H5N8) and A(H5N1) is rapidly evolving. Strengthening collaborations at National, EU and Global levels would allow close monitoring of the AI situation, ultimately helping to increase preparedness. No human case was reported in the EU due to AIVs subtypes A(H5N1), A(H5N6), A(H7N9) and A(H9N2). Direct transmission of these viruses to humans has only been reported in areas, mainly in Asia and Egypt, with a substantial involvement of wild bird and/or poultry populations. It is suggested to improve the collection and reporting of exposure events of people to AI.

Clusters of Human Infections With Avian Influenza A(H7N9) Virus in China, March 2013 to June 2015

Multiple clusters of human infections with novel avian influenza A(H7N9) virus have occurred since the virus was first identified in spring 2013. However, in many situations it is unclear whether these clusters result from person-to-person transmission or exposure to a common infectious source. We analyzed the possibility of person-to-person transmission in each cluster and developed a framework to assess the likelihood that person-to-person transmission had occurred. We described 21 clusters with 22 infected contact cases that were identified by the Chinese Center for Disease Control and Prevention from March 2013 through June 2015. Based on detailed epidemiological information and the timing of the contact case patients' exposures to infected persons and to poultry during their potential incubation period, we graded the likelihood of person-to-person transmission as probable, possible, or unlikely. We found that person-to-person transmission probably occurred 12 times and possibly occurred 4 times; it was unlikely in 6 clusters. Probable nosocomial transmission is likely to have occurred in 2 clusters. Limited person-to-person transmission is likely to have occurred on multiple occasions since the H7N9 virus was first identified. However, these transmission events represented a small fraction of all identified cases of H7N9 human infection, and sustained person-to-person transmission was not documented.

Evolutionary genotypes of influenza A (H7N9) viruses over five epidemic waves in China

Since the first human case of influenza A (H7N9) infection was identified in March 2013, five epidemics have emerged in China. Diverse H7N9 virus genotypes created through reassortments were already detected in the first epidemic wave, but how the H7N9 virus genetic diversities have evolved during the subsequent epidemics remained unclear. Here, to assess the ongoing genetic evolution of H7N9 viruses, we performed in-depth investigations of the dynamic H7N9 genotypes in these waves. We found that the H7N9 genotypes in the second and third epidemic waves are more diverse than those in the first wave, due to new reassortments that occurred during the second wave. However, the number of different H7N9 genotypes identified in the fourth and fifth waves decreased significantly. Furthermore, we found that different dominant genotypes existed in each of the five epidemic waves, and these wave-specific genotypes possess unique mutations that are enriched in the PB2 protein.

Recombinant hemagglutinin proteins formulated in a novel PELC/CpG adjuvant for H7N9 subunit vaccine development

Humans infected with H7N9 avian influenza viruses can result in severe pneumonia and acute respiratory syndrome with an approximately 40% mortality rate, and there is an urgent need to develop an effective vaccine to reduce its pandemic potential. In this study, we used a novel PELC/CpG adjuvant for recombinant H7HA (rH7HA) subunit vaccine development. After immunizing BALB/c mice intramuscularly, rH7HA proteins formulated in this adjuvant instead of an alum adjuvant elicited higher IgG, hemagglutination-inhibition, and virus neutralizing antibodies in sera; induced higher numbers of H7HA-specific IFN-γ-secreting T cells and antibody secreting cells in spleen; and provided improved protection against live virus challenges. Our results indicate that rH7HA proteins formulated in PELC/CpG adjuvant can induce potent anti-H7N9 immunity that may provide useful information for H7N9 subunit vaccine development.

Antiviral effect of forsythoside A from Forsythia suspensa (Thunb.) Vahl fruit against influenza A virus through reduction of viral M1 protein

ETHNOPHARMACOLOGICAL RELEVANCE

Yinqiaosan is a classical traditional Chinese medicine formula, which has been used to treat respiratory diseases since ancient China. It consists of nine herbs and among them, Forsythia suspensa (Thunb.) Vahl fruit is one of the major herbal components. Despite the long history of Yinqiaosan, the active compounds and the mechanisms of action of this formula remain elusive.

AIM OF THE STUDY

The present study aimed to examine the suppressive effect of Yinqiaosan on influenza virus and to identify the active components in the formula targeting influenza.

MATERIALS AND METHODS

Anti-influenza virus effect of Yinqiaosan was assessed by tissue culture infective dose assay, and was also tested in an in vivo mouse model. Active compound from the formula was identified with a bioactivity-guided fractionation scheme. The potential mode of action of the compound was further investigated by identifying the host cell signaling pathways and viral protein production using in vitro cell culture models.

RESULTS

Our results showed that forsythoside A from Forsythia suspensa (Thunb.) Vahl fruit, a major herbal component in Yinqiaosan, reduced the viral titers of different influenza virus subtypes in cell cultures and increased the survival rate of the mice in an in vivo influenza virus infection model. Further experiments on the mode of action of forsythoside A showed that it reduced the influenza M1 protein, which in turn intervened the budding process of the newly formed virions and eventually limited the virus spread.

CONCLUSION

Results of our present study provides scientific evidence to support to the application of a traditional herbal formula. We also identify novel candidate compound for future drug development against influenza virus.

Transmission and immunopathology of the avian influenza virus A/Anhui/1/2013 (H7N9) human isolate in three commonly commercialized avian species

H7N9 virus infection is a global concern, given that it can cause severe infection and mortality in humans. However, the understanding of H7N9 epidemiology, animal reservoir species and zoonotic risk remains limited. This work evaluates the pathogenicity, transmissibility and local innate immune response of three avian species harbouring different respiratory distribution of α2,6 and α2,3 SA receptors. Muscovy ducks, European quails and SPF chickens were intranasally inoculated with 10⁵ embryo infectious dose (EID)₅₀ of the human H7N9 (A/Anhui/1/2013) influenza isolate. None of the avian species showed clinical signs or macroscopic lesions, and only mild microscopic lesions were observed in the upper respiratory tract of quail and chickens. Quail presented more severe histopathologic lesions and avian influenza virus (AIV) positivity by immunohistochemistry (IHC), which correlated with higher IL-6 responses. In contrast, Muscovy ducks were resistant to disease and presented higher IFNα and TLR7 response. In all species, viral shedding was higher in the respiratory than in the digestive tract. Higher viral shedding was observed in quail, followed by chicken and ducks, which presented similar viral titres. Efficient transmission was observed in all contact quail and half of the Muscovy ducks, while no transmission was observed between chicken. All avian species showed viral shedding in drinking water throughout infection.

Hemagglutinin-specific CD4+ T-cell responses following 2009-pH1N1 inactivated split-vaccine inoculation in humans

Influenza A virus remains a major threat to public health, and the inactivated split-virus vaccine is the most prevalent vaccine used worldwide. However, our knowledge about cellular immune responses to the inactivated influenza virus vaccine and its correlation with humoral responses are yet limited, which has restricted our understanding of the vaccine's protective mechanisms. Herein, in two clinical trials, T-cell responses specific for both previously identified human leucocyte antigen (HLA)-I-restricted epitopes from influenza virus and hemagglutinin (HA) protein were longitudinally investigated before, during, and after a two-dose vaccination with the inactivated 2009 pandemic H1N1 (2009-pH1N1) vaccine. A robust antibody response in all of the donors after vaccination was observed. Though no CD8⁺ T-cell responses to known epitopes were detected, HA-specific T-cell responses were primed following vaccination, and the responses were found to be mainly CD4⁺ T-cell dependent. However, HA-specific T-cells circulating in peripheral blood dropped to baseline levels 6weeks after vaccination, but humoral immune responses maintained a high level for 4months post-vaccination. Significant correlations between the magnitude of the HA-specific T-cell responses and hemagglutination inhibition antibody titers were demonstrated, indicating a priming role of HA-specific T-cells for humoral immune responses. In conclusion, our study indicates that HA-specific CD4⁺ T-cell responses can be primed by the inactivated 2009-pH1N1 vaccine, which may coordinate with the elicitation of antibody protection. These findings would benefit a better understanding of the immune protective mechanisms of the widely used inactivated 2009-pH1N1 vaccine.

Adaptation of influenza A (H7N9) virus in primary human airway epithelial cells

Influenza A (H7N9) is an emerging zoonotic pathogen with pandemic potential. To understand its adaptation capability, we examined the genetic changes and cellular responses following serial infections of A (H7N9) in primary human airway epithelial cells (hAECs). After 35 serial passages, six amino acid mutations were found, i.e. HA (R54G, T160A, Q226L, H3 numbering), NA (K289R, or K292R for N2 numbering), NP (V363V/I) and PB2 (L/R332R). The mutations in HA enabled A(H7N9) virus to bind with higher affinity (from 39.2% to 53.4%) to sialic acid α2,6-galactose (SAα2,6-Gal) linked receptors. A greater production of proinflammatory cytokines in hAECs was elicited at later passages together with earlier peaking at 24 hours post infection of IL-6, MIP-1α, and MCP-1 levels. Viral replication capacity in hAECs maintained at similar levels throughout the 35 passages. In conclusion, during the serial infections of hAECs by influenza A(H7N9) virus, enhanced binding of virion to cell receptors with subsequent stronger innate cell response were noted, but no enhancement of viral replication could be observed. This indicates the existence of possible evolutional hurdle for influenza A(H7N9) virus to transmit efficiently from human to human.

Avian Influenza A (H7N9) viruses isolated from patients with mild and fatal infection differ in pathogenicity and induction of cytokines

Since 2013, a novel Influenza A (H7N9) virus strain has continued to circulate within poultry and causing human disease. Influenza A (H7N9) virus results in two types of infection: mild and severe. The different results of clinical findings may be related with host susceptibility and characteristics of the virus itself. In order to investigate potential pathogenesis of Influenza A (H7N9) virus, we performed pathogenecity and cytokines analysis of two isolates, A/Guangdong/6/2013 H7N9 virus (GD-6) from a patient with a mild infection, and A/Guangdong/7/2013 H7N9 virus (GD-7) from a patient with a fatal infection. We found that GD-7 replicated to higher levels than GD-6 in human peripheral blood mononuclear cells (PBMCs), lung tissues, and mice. Furthermore, GD-7 infection resulted in more severe lung damage in mice lung tissues than GD-6 infection. GD-7 elicited higher levels of interleukin-6 (IL-6) and tumor necrosis factor-α(TNF-α) than GD-6 did. In conclusion, GD-7 was more pathogenic and induced higher levels of proinflammatory cytokines than GD-6 did.

The H7N9 influenza A virus infection results in lethal inflammation in the mammalian host via the NLRP3-caspase-1 inflammasome

The avian origin influenza A virus (IAV) H7N9 has caused a considerable number of human infections associated with high rates of death since its emergence in 2013. As a vital component of the host innate immune system, the nucleotide-binding domain leucine-rich repeat containing receptor, pyrin domain containing 3 (NLRP3) inflammasome plays a critical role against H1N1 viral infection. However, the function of NLRP3 inflammasome in host immunological responses to the lethal H7N9 virus is still obscure. Here, we demonstrated that mice deficient for NLRP3 inflammasome components, including NLRP3, caspase-1, and Apoptosis-associated speck-like protein containing a CARD (ASC), were less susceptible to H7N9 viral challenge than wild type (WT) controls. Inflammasome deficiency in these animals led to significantly milder mortality and less pulmonary inflammation compared with WT mice. Furthermore, IL-1 receptor deficient mice also exhibited a higher survival rate than WT controls. Thus, our study reveals that the NLRP3 inflammasome is deleterious for the host during H7N9 infection in mice, which is due to an overwhelming inflammatory response via caspase-1 activation and associated IL-1 signal. Therefore, fine-tuning the activity of NLRP3 inflammasome or IL-1 signaling may be beneficial for the host to control H7N9 associated lethal pathogenesis.

Spatial characteristics and the epidemiology of human infections with avian influenza A(H7N9) virus in five waves from 2013 to 2017 in Zhejiang Province, China

Background

The five-wave epidemic of H7N9 in China emerged in the second half of 2016. This study aimed to compare the epidemiological characteristics among the five waves, estimating the possible infected cases and inferring the extent of the possible epidemic in the areas that have not reported cases before.

Methods

The data for the H7N9 cases from Zhejiang Province between 2013 and 2017 was obtained from the China Information Network System of Disease Prevention and Control. The start date of each wave was 16 March 2013, 1 July 2013, 1 July 2014, 1 July 2015 and 1 July 2016. The F test or Pearson’s chi-square test were used to compare the characteristics of the five waves. Global and local autocorrelation analysis was carried out to identify spatial autocorrelations. Ordinary kriging interpolation was analyzed to estimate the number of human infections with H7N9 virus and to infer the extent of infections in the areas with no cases reported before.

Result

There were 45, 94, 45, 34 and 80 cases identified from the first wave to the fifth, respectively. The death rate was significantly different among the five waves of epidemics (χ² = 10.784, P = 0.029). The age distribution (F = 0.903, P = 0.462), gender (χ² = 2.674, P = 0.614) and occupation(χ² = 19.764, P = 0.407) were similar in each period. Most of the cases were males and farmers. A significant trend (χ² = 70.328, P<0.001) was identified that showed a growing proportion of rural cases. There were 31 high-high clusters and 3 high-low clusters at the county level among the five waves and 12, 8, 2, 9 and 3 clusters in each wave, respectively. The total cases infected with the H7N9 virus were far more than those that have been reported now, and the affected areas continue to expand. The epidemic in the north of Zhejiang Province persisted in all five waves. Since the second wave, the virus spread to the south areas and central areas. There was an obvious decline in the infected cases in the urban areas, and the epidemics mostly occurred in the rural areas after the fourth wave. The epidemic was relatively dispersed since the third wave had fewer than two cases in most of the areas and showed a reinforcing trend again in the fifth wave.

Conclusions

The study revealed that there were few differences in the epidemiologic characteristics among the five waves of the epidemic. However, the areas where the possible epidemic circulated was larger than reported. The epidemic cross-regional expansion continued and mostly occurred in rural areas. Continuous closure of the live poultry market (LPM) is strongly recommended in both rural and urban areas. Illegal and scattered live poultry trading, especially in rural areas, must be forbidden. It is suggested too that a more rigorous management be performed on live poultry trade and wholesale across the area. Health education, surveillance of cases and pathogenicity should also be strengthened.

Epidemiology, Evolution, and Pathogenesis of H7N9 Influenza Viruses in Five Epidemic Waves since 2013 in China

H7N9 influenza viruses were first isolated in 2013 and continue to cause human infections. H7N9 infections represent an ongoing public health threat that has resulted in 1344 cases with 511 deaths as of April 9, 2017. This highlights the continued threat posed by the current poultry trade and live poultry market system in China. Until now, there have been five H7N9 influenza epidemic waves in China; however, the steep increase in the number of humans infected with H7N9 viruses observed in the fifth wave, beginning in October 2016, the spread into western provinces, and the emergence of highly pathogenic (HP) H7N9 influenza outbreaks in chickens and infection in humans have caused domestic and international concern. In this review, we summarize and compare the different waves of H7N9 regarding their epidemiology, pathogenesis, evolution, and characteristic features, and speculate on factors behind the recent increase in the number of human cases and sudden outbreaks in chickens. The continuous evolution of the virus poses a long-term threat to public health and the poultry industry, and thus it is imperative to strengthen prevention and control strategies.

Detection of Avian H7N9 Influenza A Viruses in the Yangtze Delta Region of China During Early H7N9 Outbreaks

Since the first H7N9 human case in Shanghai, February 19, 2013, the emerging avian-origin H7N9 influenza A virus has become an epizootic virus in China, posing a potential pandemic threat to public health. From April 2 to April 28, 2013, some 422 oral-pharyngeal and cloacal swabs were collected from birds and environmental surfaces at five live poultry markets (LPMs) and 13 backyard poultry farms (BPFs) across three cities, Wuxi, Suzhou, and Nanjing, in the Yangtze Delta region. In total 22 isolates were recovered, and six were subtyped as H7N9, nine as H9N2, four as H7N9/H9N2, and three unsubtyped influenza A viruses. Genomic sequences showed that the HA and NA genes of the H7N9 viruses were similar to those of the H7N9 human isolates, as well as other avian-origin H7N9 isolates in the region, but the PB1, PA, NP, and MP genes of the sequenced viruses were more diverse. Among the four H7N9/H9N2 mixed infections, three were from LPM, whereas the other one was from the ducks at one BPF, which were H7N9 negative in serologic analyses. A survey of the bird trading records of the LPMs and BPFs indicates that trading was a likely route for virus transmission across these regions. Our results suggested that better biosecurity and more effective vaccination should be implemented in backyard farms, in addition to biosecurity management in LPMs.

M Gene Reassortment in H9N2 Influenza Virus Promotes Early Infection and Replication: Contribution to Rising Virus Prevalence in Chickens in China

Segment reassortment and base mutagenesis of influenza A viruses are the primary routes to the rapid evolution of high-fitness virus genotypes. We recently described a predominant G57 genotype of avian H9N2 viruses that caused countrywide outbreaks in chickens in China during 2010 to 2013, which led to the zoonotic emergence of H7N9 viruses. One of the key features of the G57 genotype is the replacement of the earlier A/chicken/Beijing/1/1994 (BJ/94)-like M gene with the A/quail/Hong Kong/G1/1997 (G1)-like M gene of quail origin. We report here the functional significance of the G1-like M gene in H9N2 viruses in conferring increased infection severity and infectivity in primary chicken embryonic fibroblasts and chickens. H9N2 virus housing the G1-like M gene, in place of the BJ/94-like M gene, showed an early surge in viral mRNA and viral RNA (vRNA) transcription that was associated with enhanced viral protein production and with an early elevated release of progeny virus comprising largely spherical rather than filamentous virions. Importantly, H9N2 virus with the G1-like M gene conferred extrapulmonary virus spread in chickens. Five highly represented signature amino acid residues (37A, 95K, 224N, and 242N in the M1 protein and 21G in the M2 protein) encoded by the prevalent G1-like M gene were demonstrated to be prime contributors to enhanced infectivity. Therefore, the genetic evolution of the M gene in H9N2 virus increases reproductive virus fitness, indicating its contribution to the rising virus prevalence in chickens in China.IMPORTANCE We recently described the circulation of a dominant genotype (genotype G57) of H9N2 viruses in countrywide outbreaks in chickens in China, which was responsible, through reassortment, for the emergence of H7N9 viruses that cause severe human infections. A key feature of the genotype G57 H9N2 virus is the presence of the quail-origin G1-like M gene, which had replaced the earlier BJ/94-like M gene. We found that H9N2 virus with the G1-like M gene, but not the BJ/94-like M gene, showed an early surge in progeny virus production and more severe pathology and extrapulmonary virus spread in chickens. Five highly represented amino acid residues in the M1 and M2 proteins derived from the G1-like M gene were shown to mediate enhanced virus infectivity. These observations enhance what we currently know about the roles of reassortment and mutations in virus fitness and have implications for assessing the potential of variant influenza viruses that can cause a rising prevalence in chickens.

Carbon nanotag based visual detection of influenza A virus by a lateral flow immunoassay

The authors report on a rapid and direct visual test for the detection of influenza A virus using a carbon nanotag based lateral flow assay. Carbon nanoparticles in the form of nanostrings are acting as reporters. As carbon nanotags accumulate in the test zone due to formation of an antibody-antigen-carbon nanotag antibody complex, and this allows for the direct visualization of the analytical signal. Under optimal conditions, influenza A virus can be determined in allantoic fluid inoculated with the virus with a limit of detection of 350 TCID₅₀.mL⁻¹ (i.e., the 50% tissue culture infectious dose). No interference is found for several other tested proteins, and for closely related viruses. Cell lysates containing different seasonal strains of influenza A viruses (including the H1N1 and H3N2 strains) collected from clinical samples were analyzed. It is demonstrated that the method can detect both influenza A viruses without interference by biological matrices. In our perception, this method has a wide potential in that it may be extended to a generally applicable platform for rapid diagnosis influenza A viruses.

Graphical abstract

Risk factors for avian influenza virus contamination of live poultry markets in Zhejiang, China during the 2015-2016 human influenza season

Live bird markets (LBMs), being a potential source of avian influenza virus, require effective environmental surveillance management. In our study, a total of 2865 environmental samples were collected from 292 LBMs during the 2015–2016 human influenza season from 10 cities in Zhejiang province, China. The samples were tested by real-time quantitative polymerase chain reaction (RT-PCR). Field investigations were carried out to investigate probable risk factors. Of the environmental samples, 1519 (53.0%) were contaminated by A subtype. The highest prevalence of the H9 subtype was 30.2%, and the frequencies of the H5 and H7 subtype were 9.3% and 17.3%, respectively. Hangzhou and Jinhua cities were contaminated more seriously than the others. The prevalence of H5/H7/H9 in drinking water samples was highest, at 50.9%, and chopping board swabs ranked second, at 49.3%. Duration of sales per day, types of live poultry, LBM location and the number of live poultry were the main risk factors for environmental contamination, according to logistic regression analysis. In conclusion, LBMs in Zhejiang were contaminated by avian influenza. Our study has provided clues for avian influenza prevention and control during the human influenza season, especially in areas where LBMs are not closed.

Inference and forecast of H7N9 influenza in China, 2013 to 2015

The recent emergence of A(H7N9) avian influenza poses a significant challenge to public health in China and around the world; however, understanding of the transmission dynamics and progression of influenza A(H7N9) infection in domestic poultry, as well as spillover transmission to humans, remains limited. Here, we develop a mathematical model–Bayesian inference system which combines a simple epidemic model and data assimilation method, and use it in conjunction with data on observed human influenza A(H7N9) cases from 19 February 2013 to 19 September 2015 to estimate key epidemiological parameters and to forecast infection in both poultry and humans. Our findings indicate a high outbreak attack rate of 33% among poultry but a low rate of chicken-to-human spillover transmission. In addition, we generated accurate forecasts of the peak timing and magnitude of human influenza A(H7N9) cases. This work demonstrates that transmission dynamics within an avian reservoir can be estimated and that real-time forecast of spillover avian influenza in humans is possible.

Quantifying predictors for the spatial diffusion of avian influenza virus in China

Background

Avian influenza virus (AIV) causes both severe outbreaks and endemic disease among poultry and has caused sporadic human infections in Asia, furthermore the routes of transmission in avian species between geographic regions can be numerous and complex. Using nucleotide sequences from the internal protein coding segments of AIV, we performed a Bayesian phylogeographic study to uncover regional routes of transmission and factors predictive of the rate of viral diffusion within China.

Results

We found that the Central area and Pan-Pearl River Delta were the two main sources of AIV diffusion, while the East Coast areas especially the Yangtze River delta, were the major targets of viral invasion. Next we investigated the extent to which economic, agricultural, environmental and climatic regional data was predictive of viral diffusion by fitting phylogeographic discrete trait models using generalised linear models.

Conclusions

Our results highlighted that the economic-agricultural predictors, especially the poultry population density and the number of farm product markets, are the key determinants of spatial diffusion of AIV in China; high human density and freight transportation are also important predictors of high rates of viral transmission; Climate features (e.g. temperature) were correlated to the viral invasion in the destination to some degree; while little or no impacts were found from natural environment factors (such as surface water coverage). This study uncovers the risk factors and enhances our understanding of the spatial dynamics of AIV in bird populations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0845-3) contains supplementary material, which is available to authorized users.

Estimating Risks of Inapparent Avian Exposure for Human Infection: Avian Influenza Virus A (H7N9) in Zhejiang Province, China

Inapparent avian exposure was suspected for the sporadic infection of avian influenza A(H7N9) occurring in China. This type of exposure is usually unnoticed and difficult to model and measure. Infected poultry with avian influenza H7N9 virus typically remains asymptomatic, which may facilitate infection through inapparent poultry/bird exposure, especially in a country with widespread practice of backyard poultry. The present study proposed a novel approach that integrated ecological and case-control methods to quantify the risk of inapparent avian exposure on human H7N9 infection. Significant associations of the infection with chicken and goose densities, but not with duck density, were identified after adjusting for spatial clustering effects of the H7N9 cases across multiple geographic scales of neighborhood, community, district and city levels. These exposure risks varied geographically in association with proximity to rivers and lakes that were also proxies for inapparent exposure to avian-related environment. Males, elderly people, and farmers were high-risk subgroups for the virus infection. These findings enable health officials to target educational programs and awareness training in specific locations to reduce the risks of inapparent exposure.

Humoral and Cellular Immunogenicity Induced by Avian Influenza A (H7N9) DNA Vaccine in Mice

BACKGROUND

In March 2013, human infection with avian influenza A (H7N9) virus emerged in China, causing serious public health concerns and raising the possibility of avian-source pandemic influenza. Thus, the development of an effective vaccine for preventing and rapidly controlling avian influenza A (H7N9) virus is needed. In this study, we evaluated the immunogenicity of a synthetic DNA vaccine against H7 HA antigens in mice.

MATERIALS AND METHODS

The synthetic consensus H7 HA DNA vaccine (25 or 50 μg) was administered to BALB/c mice at 0, 14, and 28 days by intramuscular injection followed by electroporation. Humoral and cellular immune responses were analyzed in a hemagglutination inhibition test and interferon-gamma enzyme-linked immunospot (ELISpot) assay, respectively.

RESULTS

H7 HA-vaccinated mice showed 100% seroprotection and seroconversion rate against H7N9 reassortant influenza virus after both second and third immunizations. The geometric mean titer by the hemagglutination inhibition test increased with an increasing number of immunizations. However, there was no significant difference in geometric titer between the two groups injected with 25 and 50 μg of H7 HA DNA vaccine after two (79.98 vs. 107.65, P = 0.39) and three (159.96 vs. 215.28, P = 0.18) doses. In addition, the ELISpot assay revealed that administration of H7 HA DNA vaccine induced potent interferon-gamma production from mouse splenocytes.

CONCLUSIONS

This study demonstrated the humoral and cellular immunogenicity of synthetic consensus H7 HA DNA vaccine in mice. This work demonstrates the potential of the H7 HA DNA vaccine as an efficient tool for the rapid control of emerging influenza A (H7N9) virus.

Proteomic Analysis of Differential Expression of Cellular Proteins in Response to Avian H9N2 Virus Infection of A549 Cells

In this study, differentially expressed proteins in A549 cells (human lung adenocarcinoma epithelial cell line) infected with H9N2 avian influenza virus (AIV) were investigated by two-dimensional electrophoresis (2-DE). Sixteen different spots between the groups (ratio > 2, p < 0.05) were identified with mass spectrometry identification. Proteins located in the downstream of the NF-κB and IFN transcription factor pathways were identified, e.g., ISG15. Actin and keratin were also identified, suggesting that the cytoskeleton may plays an important role in the AIV infection of mammalian cells. These findings could provide insights into the interaction between host and influenza viruses and might provide valuable information for clarifying the pathogenesis of viral infections as well.

Biological Characteristics of H9N2 Avian Influenza Viruses from Healthy Chickens in Shanghai, China

Background

H9N2 avian influenza viruses that circulate in domestic poultry in eastern China pose challenges to human health. However, few studies have compared the biological characteristics of H9N2 viruses isolated from healthy chickens in Shanghai.

Material/Methods

Three H9N2 viruses – CK/SH/Y1/07, CK/SH/Y1/02, and CK/SH/23/13 – isolated from healthy chickens in Shanghai between 2002 and 2013, were selected and their biological characteristics were determined.

Results

All 3 H9N2 viruses showed a preference for both the avian- and human-like receptors, and they replicated well in MDCK and A549 cells. All H9N2 viruses were non-pathogenic to mini-pigs and were detected in the trachea and lung tissues. The CK/SH/Y1/07 and CK/SH/Y1/02 viruses were transmitted to mini-pigs through direct-contact or respiratory droplet exposure, but CK/SH/23/13 virus was not.

Conclusions

These results suggest that H9N2 viruses isolated from healthy chickens in Shanghai efficiently replicate and transmit among pigs and other mammals.

Pattern transitions in spatial epidemics: Mechanisms and emergent properties

Infectious diseases are a threat to human health and a hindrance to societal development. Consequently, the spread of diseases in both time and space has been widely studied, revealing the different types of spatial patterns. Transitions between patterns are an emergent property in spatial epidemics that can serve as a potential trend indicator of disease spread. Despite the usefulness of such an indicator, attempts to systematize the topic of pattern transitions have been few and far between. We present a mini-review on pattern transitions in spatial epidemics, describing the types of transitions and their underlying mechanisms. We show that pattern transitions relate to the complexity of spatial epidemics by, for example, being accompanied with phenomena such as coherence resonance and cyclic evolution. The results presented herein provide valuable insights into disease prevention and control, and may even be applicable outside epidemiology, including other branches of medical science, ecology, quantitative finance, and elsewhere.

Genesis, Evolution and Prevalence of H5N6 Avian Influenza Viruses in China

Constant surveillance of live poultry markets (LPMs) is currently the best way to predict and identify emerging avian influenza viruses (AIVs) that pose a potential threat to public health. Through surveillance of LPMs from 16 provinces and municipalities in China during 2014-2016, we identified 3,174 AIV-positive samples and isolated and sequenced 1,135 AIVs covering 31 subtypes. Our analysis shows that H5N6 has replaced H5N1 as one of the dominant AIV subtypes in southern China, especially in ducks. Phylogenetic analysis reveals that H5N6 arose from reassortments of H5 and H6N6 viruses, with the hemagglutinin and neuraminidase combinations being strongly lineage specific. H5N6 viruses constitute at least 34 distinct genotypes derived from various evolutionary pathways. Notably, genotype G1.2 virus, with internal genes from the chicken H9N2/H7N9 gene pool, was responsible for at least five human H5N6 infections. Our findings highlight H5N6 AIVs as potential threats to public health and agriculture.

Nonlinear dynamics of avian influenza epidemic models

Avian influenza is a zoonotic disease caused by the transmission of the avian influenza A virus, such as H5N1 and H7N9, from birds to humans. The avian influenza A H5N1 virus has caused more than 500 human infections worldwide with nearly a 60% death rate since it was first reported in Hong Kong in 1997. The four outbreaks of the avian influenza A H7N9 in China from March 2013 to June 2016 have resulted in 580 human cases including 202 deaths with a death rate of nearly 35%. In this paper, we construct two avian influenza bird-to-human transmission models with different growth laws of the avian population, one with logistic growth and the other with Allee effect, and analyze their dynamical behavior. We obtain a threshold value for the prevalence of avian influenza and investigate the local or global asymptotical stability of each equilibrium of these systems by using linear analysis technique or combining Liapunov function method and LaSalle's invariance principle, respectively. Moreover, we give necessary and sufficient conditions for the occurrence of periodic solutions in the avian influenza system with Allee effect of the avian population. Numerical simulations are also presented to illustrate the theoretical results.

The complexity of human infected AIV H5N6 isolated from China

BACKGROUND

Novel avian influenza viruses (AIVs) of H7N9, H10N8, and H5N6 are currently circulating in China's poultry flocks, occasionally infecting human and other mammals. Human infected AIV H5N6 in China during 2014-2015 is believed to be a triple reassortant originated from H6N6 and two clades of H5 viruses. The current report suggests that its reassortment history is more complicated.

METHODS

Genomes of human infected isolates of AIV H5N6 were searched from the NCBI Influenza Virus Sequence Database and the Global Initiative on Sharing Avian Influenza Data. Sequences shared high identities with each segment of their genomes were obtained through the Basic Local Alignment Search Tool. Alignments were done by mafft-7.037-win32 program; 8 large-scale and then 8 gradually converged phylogenetic trees were constructed by using MEGA5.1/5.2/6.0 Software.

RESULTS

The events that each segment of the genomes of human infected AIV H5N6 isolates circulated in China had evolved into its current status might have happened before 2013, and so were they then reassorted into the epidemic AIV H5N6. A/Guangzhou/39715/2014(H5N6) and A/Sichuan/26221/2014(H5N6) had their six internal segments (PB2, PB1, PA, NP, NEP, and M) in common, and were reassorted from AIVs H5N1 in the same period and same region as that of HA, while A/Yunnan/0127/2015(H5N6) derived its six internal segments from AIV H9N2 that has been prevalent in Eastern China since 2008.

CONCLUSIONS

AIV H5N6 isolates established from both human and poultry in China during 2014-2015 were heterogeneous; both AIVs H5N1 and H9N2 were involved in the reassortment of AIV H5N6 in China.

Cross-immunity Against Avian Influenza A(H7N9) Virus in the Healthy Population Is Affected by Antigenicity-Dependent Substitutions

BACKGROUND

 The emergence of infections by the novel avian influenza A(H7N9) virus has posed a threat to human health. Cross-immunity between A(H7N9) and other heterosubtypic influenza viruses affected by antigenicity-dependent substitutions needs to be investigated.

METHODS

 We investigated the cellular and humoral immune responses against A(H7N9) and 2009 pandemic influenza A(H1N1) virus (A[H1N1]pdm09), by serological and T-cell-specific assays, in a healthy population. The molecular bases of the cellular and humoral antigenic variability of A(H7N9) were illuminated by structural determination.

RESULTS

 We not only found that antibodies against A(H7N9) were lacking in the studied population, but also revealed that both CD4⁺ and CD8⁺ T cells that cross-reacted with A(H7N9) were at significantly lower levels than those against the A(H1N1)pdm09 peptides with substitutions. Moreover, individual peptides for A(H7N9) with low cross-reactivity were identified. Structural determination indicated that substitutions within these peptides influence the antigenic variability of A(H7N9) through both major histocompatibility complex (MHC) binding and T-cell receptor docking.

CONCLUSIONS

 The impact of antigenicity-dependent substitutions on cross-reactivity of T-cell immunity against the novel influenza virus A(H7N9) in the healthy population benefits the understanding of immune evasion of influenza viruses and provides a useful reference for universal vaccine development.