Antigenic analysis of highly pathogenic avian influenza virus H5N1 sublineages co-circulating in Egypt

Site-Specific Glycan-Masking/Unmasking Hemagglutinin Antigen Design to Elicit Broadly Neutralizing and Stem-Binding Antibodies Against Highly Pathogenic Avian Influenza H5N1 Virus Infections

The highly pathogenic avian influenza (HPAI) H5N1 viruses with the capability of transmission from birds to humans have a serious impact on public health. To date, HPAI H5N1 viruses have evolved into ten antigenically distinct clades that could cause a mismatch of vaccine strains and reduce vaccine efficacy. In this study, the glycan masking and unmasking strategies on hemagglutinin antigen were used for designing two antigens: H5-dm/st2 and H5-tm/st2, and investigated for their elicited immunity using two-dose recombinant H5 (rH5) immunization and a first-dose adenovirus vector prime, followed by a second-dose rH5 protein booster immunization. The H5-dm/st2 antigen was found to elicit broadly neutralizing antibodies against different H5N1 clade/subclade viruses, as well as more stem-binding antibodies to inhibit HA-facilitated membrane fusion activity. Mice immunized with the H5-dm/st2 antigen had a higher survival rate when challenged with homologous and heterologous clades of H5N1 viruses. Mutant influenza virus replaced with the H5-dm/st2 gene generated by reverse genetics (RG) technology amplified well in MDCK cells and embryonated chicken eggs. Again, the inactivated H5N1-dm/st2 RG virus elicited more potent cross-clade neutralizing and anti-fusion antibodies in sera. Therefore, the H5N1-dm/st2 RG virus with the site-specific glycan-masking on the globular head and the glycan-unmasking on the stem region of H5 antigen can be used for further development of cross-protective H5N1 vaccines.

Efficacy of recombinant Marek's disease virus vectored vaccines with computationally optimized broadly reactive antigen (COBRA) hemagglutinin insert against genetically diverse H5 high pathogenicity avian influenza viruses

The genetic and antigenic drift associated with the high pathogenicity avian influenza (HPAI) viruses of Goose/Guangdong (Gs/GD) lineage and the emergence of vaccine-resistant field viruses underscores the need for a broadly protective H5 influenza A vaccine. Here, we tested experimental vector herpesvirus of turkey (vHVT)-H5 vaccines containing either wild-type clade 2.3.4.4A-derived H5 inserts or computationally optimized broadly reactive antigen (COBRA) inserts with challenge by homologous and genetically divergent H5 HPAI Gs/GD lineage viruses in chickens. Direct assessment of protection was confirmed for all the tested constructs, which provided clinical protection against the homologous and heterologous H5 HPAI Gs/GD challenge viruses and significantly decreased oropharyngeal shedding titers compared to the sham vaccine. The cross reactivity was assessed by hemagglutinin inhibition (HI) and focus reduction assay against a panel of phylogenetically and antigenically diverse H5 strains. The COBRA-derived H5 inserts elicited antibody responses against antigenically diverse strains, while the wild-type-derived H5 vaccines elicited protection mostly against close antigenically related clades 2.3.4.4A and 2.3.4.4D viruses. In conclusion, the HVT vector, a widely used replicating vaccine platform in poultry, with H5 insert provides clinical protection and significant reduction of viral shedding against homologous and heterologous challenge. In addition, the COBRA-derived inserts have the potential to be used against antigenically distinct co-circulating viruses and future drift variants.

Crossroads of highly pathogenic H5N1: overlap between wild and domestic birds in the Black Sea-Mediterranean impacts global transmission

Understanding transmission dynamics that link wild and domestic animals is a key element of predicting the emergence of infectious disease, an event that has highest likelihood of occurring wherever human livelihoods depend on agriculture and animal trade. Contact between poultry and wild birds is a key driver of the emergence of highly pathogenic avian influenza (HPAI), a process that allows for host switching and accelerated reassortment, diversification, and spread of virus between otherwise unconnected regions. This study addresses questions relevant to the spillover of HPAI at a transmission hotspot: what is the nature of the wild bird-poultry interface in Egypt and adjacent Black Sea-Mediterranean countries and how has this contributed to outbreaks occurring worldwide? Using a spatiotemporal model of infection risk informed by satellite tracking of waterfowl and viral phylogenetics, this study identified ecological conditions that contribute to spillover in this understudied region. Results indicated that multiple ducks (Northern Shoveler and Northern Pintail) hosted segments that shared ancestry with HPAI H5 from both clade 2.2.1 and clade 2.3.4 supporting the role of Anseriformes in linking viral populations in East Asia and Africa over large distances. Quantifying the overlap between wild ducks and H5N1-infected poultry revealed an increasing interface in late winter peaking in early spring when ducks expanded their range before migration, with key differences in the timing of poultry contact risk between local and long-distance migrants.

Highly Pathogenic Avian Influenza H5 Hemagglutinin Fused with the A Subunit of Type IIb Escherichia coli Heat Labile Enterotoxin Elicited Protective Immunity and Neutralization by Intranasal Immunization in Mouse and Chicken Models

Highly pathogenic avian influenza viruses are classified by the World Organization for Animal Health (OIE) as causes of devastating avian diseases. This study aimed to develop type IIb Escherichiacoli heat-labile enterotoxin (LTIIb) as novel mucosal adjuvants for mucosal vaccine development. The fusion protein of H5 and LTIIb-A subunit was expressed and purified for mouse and chicken intranasal immunizations. Intranasal immunization with the H5-LTIIb-A fusion protein in mice elicited potent neutralizing antibodies in sera and bronchoalveolar lavage fluids, induced stronger Th1 and Th17 cellular responses in spleen and cervical lymph nodes, and improved protection against H5N1 influenza virus challenge. More interestingly, intranasal immunization with the H5-LTIIb-A fusion protein in chickens elicited high titers of IgY, IgA, hemagglutinin inhibition (HAI), and neutralizing antibodies in their antisera. This study employed the novel adjuvants of LTIIb for the development of a new generation of mucosal vaccines against highly pathogenic avian influenza viruses.

Respiratory disease due to mixed viral infections in poultry flocks in Egypt between 2017 and 2018: Upsurge of highly pathogenic avian influenza virus subtype H5N8 since 2018

For several years, poultry production in Egypt has been suffering from co-circulation of multiple respiratory viruses including highly pathogenic avian influenza virus (HPAIV) H5N1 (clade 2.2.1.2) and low pathogenic H9N2 (clade G1-B). Incursion of HPAIV H5N8 (clade 2.3.4.4b) to Egypt in November 2016 via wild birds followed by spread into commercial poultry flocks further complicated the situation. Current analyses focussed on 39 poultry farms suffering from respiratory manifestation and high mortality in six Egyptian governorates during 2017-2018. Real-time RT-PCR (RT-qPCR) substantiated the co-presence of at least two respiratory virus species in more than 80% of the investigated flocks. The percentage of HPAIV H5N1-positive holdings was fairly stable in 2017 (12.8%) and 2018 (10.2%), while the percentage of HPAIV H5N8-positive holdings increased from 23% in 2017 to 66.6% during 2018. The proportion of H9N2-positive samples was constantly high (2017:100% and 2018:63%), and H9N2 co-circulated with HPAIV H5N8 in 22 out of 39 (56.8%) flocks. Analyses of 26 H5, 18 H9 and 4 N2 new sequences confirmed continuous genetic diversification. In silico analysis revealed numerous amino acid substitutions in the HA and NA proteins suggestive of increased adaptation to mammalian hosts and putative antigenic variation. For sensitive detection of H9N2 viruses by RT-qPCR, an update of primers and probe sequences was crucial. Reasons for the relative increase of HPAIV H5N8 infections versus H5N1 remained unclear, but lack of suitable vaccines against clade 2.3.4.4b cannot be excluded. A reconsideration of surveillance and control measures should include updating of diagnostic tools and vaccination strategies.

Combined H5ND inactivated vaccine protects chickens against challenge by different clades of highly pathogenic avian influenza viruses subtype H5 and virulent Newcastle disease virus

Aim

The aim of the current study was to evaluate the efficacy of a trivalent-inactivated oil-emulsion vaccine against challenge by different clades highly pathogenic avian influenza (HPAI) viruses including HPAI-H5N8 and the virulent genotype VII Newcastle disease virus (NDV) (vNDV).

Materials and Methods

The vaccine studied herein is composed of reassortant AI viruses rgA/Chicken/Egypt/ME1010/2016 (clade 2.2.1.1), H5N1 rgA/Chicken/Egypt/RG-173CAL/2017 (clade 2.2.1.2), and "NDV" (LaSota NDV/CK/Egypt/11478AF/11); all used at a concentration of 10⁸ EID₅₀/bird and mixed with Montanide-ISA70 oil adjuvant. Two-week-old specific pathogen free (SPF) chickens were immunized subcutaneously with 0.5 ml of the vaccine, and hemagglutination inhibition (HI) antibody titers were monitored weekly. The intranasal challenge was conducted 4 weeks post-vaccination (PV) using 10⁶ EID₅₀/0.1 ml of the different virulent HPAI-H5N1 viruses representing clades 2.2.1, 2.2.1.1, 2.2.1.2, 2.3.4.4b-H5N8, and the vNDV.

Results

The vaccine induced HI antibody titers of >6log₂ against both H5N1 and NDV viruses at 2 weeks PV. Clinical protection against all HPAI H5N1 viruses and vNDV was 100%, except for HPAI H5N1 clade-2.2.1 and HPAI H5N8 clade-2.3.4.4b viruses that showed 93.3% protection. Challenged SPF chickens showed significant decreases in the virus shedding titers up to <3log₁₀ compared to challenge control chickens. No virus shedding was detected 6 "days post-challenge" in all vaccinated challenged groups.

Conclusion

Our results indicate that the trivalent H5ND vaccine provides significant clinical protection against different clades of the HPAI viruses including the newly emerging H5N8 HPAI virus. Availability of such potent multivalent oil-emulsion vaccine offers an effective tool against HPAI control in endemic countries and promises simpler vaccination programs.

Characterization of H5N1 Influenza Virus Quasispecies with Adaptive Hemagglutinin Mutations from Single-Virus Infections of Human Airway Cells

Transmission of avian influenza (AI) viruses to mammals involves phylogenetic bottlenecks that select small numbers of variants for transmission to new host species. However, little is known about the AI virus quasispecies diversity that produces variants for virus adaptation to humans. Here, we analyzed the hemagglutinin (HA) genetic diversity produced during AI H5N1 single-virus infection of primary human airway cells and characterized the phenotypes of these variants. During single-virus infection, HA variants emerged with increased fitness to infect human cells. These variants generally had decreased HA thermostability, an indicator of decreased transmissibility, that appeared to compensate for their increase in α2,6-linked sialic acid (α2,6 Sia) binding specificity and/or in the membrane fusion pH threshold, each of which is an advantageous mutational change for viral infection of human airway epithelia. An HA variant with increased HA thermostability also emerged but could not outcompete variants with less HA thermostability. These results provided data on HA quasispecies diversity in human airway cells.IMPORTANCE The diversity of the influenza virus quasispecies that emerges from a single infection is the starting point for viral adaptation to new hosts. A few studies have investigated AI virus quasispecies diversity during human adaptation using clinical samples. However, those studies could be appreciably affected by individual variability and multifactorial respiratory factors, which complicate identification of quasispecies diversity produced by selective pressure for increased adaptation to infect human airway cells. Here, we found that detectable HA genetic diversity was produced by H5N1 single-virus infection of human airway cells. Most of the HA variants had increased fitness to infect human airway cells but incurred a fitness cost of less HA stability. To our knowledge, this is the first report to characterize the adaptive changes of AI virus quasispecies produced by infection of human airway cells. These results provide a better perspective on AI virus adaptation to infect humans.

An Egyptian HPAI H5N1 isolate from clade 2.2.1.2 is highly pathogenic in an experimentally infected domestic duck breed (Sudani duck)

The highly pathogenic avian influenza (HPAI) H5N1 viruses continue to cause major problems in poultry and can, although rarely, cause human infection. Being enzootic in domestic poultry, Egyptian isolates are continuously evolving, and novel clades vary in their pathogenicity in avian hosts. Considering the importance of domestic ducks as natural hosts of HPAI H5N1 viruses and their likelihood of physical contact with other avian hosts and humans, it is of utmost importance to characterize the pathogenicity of newly emerged HPAI strains in the domestic duck. The most recently identified Egyptian clade 2.2.1.2 HPAI H5N1 viruses have been isolated from naturally infected pigeons, turkeys and humans. However, essentially nothing is known about their pathogenicity in domestic ducks. We therefore characterized the pathogenicity of an Egyptian HPAI H5N1 isolate A/chicken/Faquos/amn12/2011 (clade 2.2.1.2) in Sudani duck, a domestic duck breed commonly reared in Egypt. While viral transcription (HA mRNA) was highest in lung, heart and kidney peaking between 40 and 48 hpi, lower levels were detected in brain. Weight loss of infected ducks started at 16 hpi and persisted until 120 hpi. The first severe clinical signs were noted by 32 hpi and peaked in severity at 72 and 96 hpi. Haematological analyses showed a decline in total leucocytes, granulocytes, platelets and granulocyte/lymphocyte ratio, but lymphocytosis. Upon necropsy, lesions were obvious in heart, liver, spleen and pancreas and consisted mainly of necrosis and petechial haemorrhage. Histologically, lungs were the most severely affected organs, whereas brain only showed mild neuronal degeneration and gliosis at 48 hpi despite obvious neurological clinical signs. Taken together, our results provide first evidence that this HPAI H5N1 isolate (clade 2.2.1.2) is highly pathogenic to Sudani ducks and highlight the importance of this breed as potential reservoir and disseminator of HPAI strains from this clade.

Visualization of Alternative Functional Configurations of Influenza Virus Hemagglutinin Facilitates Rapid Selection of Complementing Vaccines in Emergency Situations

Successful immunization against avian influenza virus (AIV) requires eliciting an adequate polyclonal response to AIV hemagglutinin (HA) subunit 1 (HA1) epitopes. Outbreaks of highly-pathogenic (HP) AIV subtype H5N1 can occur in vaccinated flocks in many endemic areas. Protection against emerging AIV is partly hindered by the limitations of vaccine production and transport, the use of leaky vaccines, and the use of multiple, and often antigenically-diverse, vaccines. It was hypothesized that the majority of alternative functional configurations (AFC) within the AIV HA1 can be represented by the pool of vaccine seed viruses currently in production because only a finite number of AFC are possible within each substructure of the molecule. Therefore, combinations of commercial vaccines containing complementing structural units (CSU) to each HA1 substructure can elicit responses to the totality of a given emerging AIV HA1 substructure isoforms. Analysis of homology-based 3D models of vaccine seed and emerging viruses facilitated the definition of HA1 AFC isoforms. CSU-based plots were used to predict which commercial vaccine combinations could have been used to cover nine selected AFC isoforms on recent Egyptian HP AIV H5N1 outbreak viruses. It is projected that expansion of the vaccine HA1 3D model database will improve international emergency responses to AIV.

Host-adaptive mechanism of H5N1 avian influenza virus hemagglutininn

The H5N1 subtype is a highly pathogenic avian influenza virus currently circulating in birds in parts of Asia and northeast Africa, which has caused fatal human infections since 1997. Continuous circulation of the virus in endemic areas has allowed genetically diverse viruses to emerge, increasing the risk of H5N1 human infection. Although human infections with H5N1 have to date been limited, experimental evidence of the aerosol transmission of mutated viruses in a mammalian infection model has revealed the pandemic potential of H5N1 virus. One of the most important viral factors for host-adaptation of influenza virus is hemagglutinin (HA), which is the principal antigen on the viral surface and is responsible for viral binding to host receptors as well as endosomal membrane fusion. Our recent reports suggest that a fine balance of the HA properties, including receptor binding specificity and pH stability, is crucial for replication in human respiratory epithelia. This review provides an overview of current knowledge on the host-adaptive mechanism of H5N1 virus HA.

Continual Antigenic Diversification in China Leads to Global Antigenic Complexity of Avian Influenza H5N1 Viruses

The highly pathogenic avian influenza (HPAI) H5N1 virus poses a significant potential threat to human society due to its wide spread and rapid evolution. In this study, we present a comprehensive antigenic map for HPAI H5N1 viruses including 218 newly sequenced isolates from diverse regions of mainland China, by computationally separating almost all HPAI H5N1 viruses into 15 major antigenic clusters (ACs) based on their hemagglutinin sequences. Phylogenetic analysis showed that 12 of these 15 ACs originated in China in a divergent pattern. Further analysis of the dissemination of HPAI H5N1 virus in China identified that the virus's geographic expansion was co-incident with a significant divergence in antigenicity. Moreover, this antigenic diversification leads to global antigenic complexity, as typified by the recent HPAI H5N1 spread, showing extensive co-circulation and local persistence. This analysis has highlighted the challenge in H5N1 prevention and control that requires different planning strategies even inside China.

H5 influenza, a global update

H5 influenza viruses have caused much alarm globally due to their high pathogenic potential. As yet we have not seen sustained spread of the virus amongst humans despite a high prevalence of the virus in avian populations. Nevertheless, isolated human cases of infection have demonstrated high mortality and there are substantial efforts being taken to monitor the evolution of the virus and to undertake preparedness activities. Here we review and discuss the evolution of the A/goose/Guangdong/1/96 (H5N1) virus with emphasis on recent events.

Identification of polymerase gene mutations that affect viral replication in H5N1 influenza viruses isolated from pigeons

Highly pathogenic avian influenza virus H5N1 infects a wide range of host species, with a few cases of sporadic pigeon infections reported in the Middle East and Asia. However, the role of pigeons in the ecology and evolution of H5N1 viruses remains unclear. We previously reported two H5N1 virus strains, isolated from naturally infected pigeons in Egypt, that have several unique mutations in their viral polymerase genes. Here, we investigated the effect of these mutations on H5N1 polymerase activity and viral growth and identified three mutations that affected viral polymerase activity. The results showed that the PB1-V3D mutation significantly decreased polymerase activity and viral growth in both mammalian and avian cells. In contrast, the PB2-K627E and PA-K158R mutations had moderate effects: PB2-K627E decreased and PA-K158R increased polymerase activity. Structural homology modelling indicated that the PB1-V3D residue was located in the PB1 core region that interacts with PA, predicting that the PB1 mutation would produce a stronger interaction between PB1 and PA that results in decreased replication of pigeon-derived H5N1 viruses. Our results identified several unique mutations responsible for changes in polymerase activity in H5N1 virus strains isolated from infected pigeons, emphasizing the importance of avian influenza surveillance in pigeons and in studying the possible role of pigeon-derived H5N1 viruses in avian influenza virus evolution.

Enhanced virulence of clade 2.3.2.1 highly pathogenic avian influenza A H5N1 viruses in ferrets

Sporadic avian to human transmission of highly pathogenic avian influenza (HPAI) A(H5N1) viruses necessitates the analysis of currently circulating and evolving clades to assess their potential risk. Following the spread and sustained circulation of clade 2 viruses across multiple continents, numerous subclades and genotypes have been described. To better understand the pathogenesis associated with the continued diversification of clade 2A(H5N1) influenza viruses, we investigated the relative virulence of eleven human and poultry isolates collected from 2006 to 2013 by determining their ability to cause disease in the ferret model. Numerous clade 2 viruses, including a clade 2.2 avian isolate, a 2.2.2.1 human isolate, and two 2.2.1 human isolates, were found to be of low virulence in the ferret model, though lethality was detected following infection with one 2.2.1 human isolate. In contrast, three of six clade 2.3.2.1 avian isolates tested led to severe disease and death among infected ferrets. Clade 2.3.2.1b and 2.3.2.1c isolates, but not 2.3.2.1a isolates, were associated with ferret lethality. All A(H5N1) viruses replicated efficiently in the respiratory tract of ferrets regardless of their virulence and lethality. However, lethal isolates were characterized by systemic viral dissemination, including detection in the brain and enhanced histopathology in lung tissues. The finding of disparate virulence phenotypes between clade 2A(H5N1) viruses, notably differences between subclades of 2.3.2.1 viruses, suggests there are distinct molecular determinants present within the established subclades, the identification of which will assist in molecular-based surveillance and public health efforts against A(H5N1) viruses.

Genetic versus antigenic differences among highly pathogenic H5N1 avian influenza A viruses: Consequences for vaccine strain selection

Highly pathogenic H5N1 avian influenza A viruses display a remarkable genetic and antigenic diversity. We examined to what extent genetic distances between several H5N1 viruses from different clades correlate with antigenic differences and vaccine performance. H5-specific antisera were generated, and cross-reactivity and antigenic distances between 12 different viruses were determined. In general, antigenic distances increased proportional to genetic distances although notable exceptions were observed. Antigenic distances correlated better with genetic variation in 27 selected, antigenically-relevant H5 residues, than in the complete HA1 domain. Variation in these selected residues could accurately predict the antigenic distances for a novel H5N8 virus. Protection provided by vaccines against heterologous H5N1 challenge viruses indicated that cross-protection also correlates better with genetic variation in the selected antigenically-relevant residues than in complete HA1. When time is limited, variation at these selected residues may be used to accurately predict antigenic distance and vaccine performance.

Risk assessment of recent Egyptian H5N1 influenza viruses

Highly pathogenic avian influenza (HPAI) viruses of the H5N1 subtype are enzootic in poultry populations in different parts of the world, and have caused numerous human infections in recent years, particularly in Egypt. However, no sustained human-to-human transmission of these viruses has yet been reported. We tested nine naturally occurring Egyptian H5N1 viruses (isolated in 2014-2015) in ferrets and found that three of them transmitted via respiratory droplets, causing a fatal infection in one of the exposed animals. All isolates were sensitive to neuraminidase inhibitors. However, these viruses were not transmitted via respiratory droplets in three additional transmission experiments in ferrets. Currently, we do not know if the efficiency of transmission is very low or if subtle differences in experimental parameters contributed to these inconsistent results. Nonetheless, our findings heighten concern regarding the pandemic potential of recent Egyptian H5N1 influenza viruses.

Avian Influenza A(H5N1) Virus in Egypt

In Egypt, avian influenza A subtype H5N1 and H9N2 viruses are enzootic in poultry. The control plan devised by veterinary authorities in Egypt to prevent infections in poultry focused mainly on vaccination and ultimately failed. Recently, widespread H5N1 infections in poultry and a substantial increase in the number of human cases of H5N1 infection were observed. We summarize surveillance data from 2009 through 2014 and show that avian influenza viruses are established in poultry in Egypt and are continuously evolving genetically and antigenically. We also discuss the epidemiology of human infection with avian influenza in Egypt and describe how the true burden of disease is underestimated. We discuss the failures of relying on vaccinating poultry as the sole intervention tool. We conclude by highlighting the key components that need to be included in a new strategy to control avian influenza infections in poultry and humans in Egypt.

Phylodynamics of avian influenza clade 2.2.1 H5N1 viruses in Egypt

Background

Highly pathogenic avian influenza (HPAI) viruses of the H5N1 subtype are widely distributed within poultry populations in Egypt and have caused multiple human infections. Linking the epidemiological and sequence data is important to understand the transmission, persistence and evolution of the virus. This work describes the phylogenetic dynamics of H5N1 based on molecular characterization of the hemagglutinin (HA) gene of isolates collected from February 2006 to May 2014.

Methods

Full-length HA sequences of 368 H5N1 viruses were generated and were genetically analysed to study their genetic evolution. They were collected from different poultry species, production sectors, and geographic locations in Egypt. The Bayesian Markov Chain Monte Carlo (BMCMC) method was applied to estimate the evolutionary rates among different virus clusters; additionally, an analysis of selection pressures in the HA gene was performed using the Single Likelihood Ancestor Counting (SLAC) method.

Results

The phylogenetic analysis of the H5 gene from 2006–14 indicated the presence of one virus introduction of the classic clade (2.2.1) from which two main subgroups were originated, the variant subgroup which was further subdivided into 2 sub-divisions (2.2.1.1 and 2.2.1.1a) and the endemic subgroup (2.2.1.2). The clade 2.2.1.2 showed a high evolution rate over a period of 6 years (6.9 × 10⁻³ sub/site/year) in comparison to the 2.2.1.1a variant cluster (7.2 × 10⁻³ over a period of 4 years). Those two clusters are under positive selection as they possess 5 distinct positively selected sites in the HA gene. The mutations at 120, 154, and 162 HA antigenic sites and the other two mutations (129∆, I151T) that occurred from 2009–14 were found to be stable in the 2.2.1.2 clade. Additionally, 13 groups of H5N1 HPAI viruses were identified based on their amino acid sequences at the cleavage site and “EKRRKKR” became the dominant pattern beginning in 2013.

Conclusions

Continuous evolution of H5N1 HPAI viruses in Egypt has been observed in all poultry farming and production systems in almost all regions of the country. The wide circulation of the 2.2.1.2 clade carrying triple mutations (120, 129∆, I151T) associated with increased binding affinity to human receptors is an alarming finding of public health importance.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-016-0477-7) contains supplementary material, which is available to authorized users.

Introduction and enzootic of A/H5N1 in Egypt: Virus evolution, pathogenicity and vaccine efficacy ten years on

It is almost a decade since the highly pathogenic H5N1 avian influenza virus (A/H5N1) of clade 2.2.1 was introduced to Egypt in 2005, most likely, via wild birds; marking the longest endemic status of influenza viruses in poultry outside Asia. The endemic A/H5N1 in Egypt still compromises the poultry industry, poses serious hazards to public health and threatens to become potentially pandemic. The control strategies adopted for A/H5N1 in Egyptian poultry using diverse vaccines in commercialized poultry neither eliminated the virus nor did they decrease its evolutionary rate. Several virus clades have evolved, a few of them disappeared and others prevailed. Disparate evolutionary traits in both birds and humans were manifested by accumulation of clade-specific mutations across viral genomes driven by a variety of selection pressures. Viruses in vaccinated poultry populations displayed higher mutation rates at the immunogenic epitopes, promoting viral escape and reducing vaccine efficiency. On the other hand, viruses isolated from humans displayed changes in the receptor binding domain, which increased the viral affinity to bind to human-type glycan receptors. Moreover, viral pathogenicity exhibited several patterns in different hosts. This review aims to provide an overview of the viral evolution, pathogenicity and vaccine efficacy of A/H5N1 in Egypt during the last ten years.

Characterization of H5N1 influenza virus variants with hemagglutinin mutations isolated from patients

A change in viral hemagglutinin (HA) receptor binding specificity from α2,3- to α2,6-linked sialic acid is necessary for highly pathogenic avian influenza (AI) virus subtype H5N1 to become pandemic. However, details of the human-adaptive change in the H5N1 virus remain unknown. Our database search of H5N1 clade 2.2.1 viruses circulating in Egypt identified multiple HA mutations that had been selected in infected patients. Using reverse genetics, we found that increases in both human receptor specificity and the HA pH threshold for membrane fusion were necessary to facilitate replication of the virus variants in human airway epithelia. Furthermore, variants with enhanced replication in human cells had decreased HA stability, apparently to compensate for the changes in viral receptor specificity and membrane fusion activity. Our findings showed that H5N1 viruses could rapidly adapt to growth in the human airway microenvironment by altering their HA properties in infected patients and provided new insights into the human-adaptive mechanisms of AI viruses.

Circulation between bird and human hosts may allow H5N1 viruses to acquire amino acid changes that increase fitness for human infections. However, human-adaptive changes in H5N1 viruses have not been adequately investigated. In this study, we found that multiple HA mutations were actually selected in H5N1-infected patients and that H5N1 variants with some of these HA mutations had increased human-type receptor specificity and increased HA membrane fusion activity, both of which are advantageous for viral replication in human airway epithelia. Furthermore, HA mutants selected during viral replication in patients were likely to have less HA stability, apparently as a compensatory mechanism. These results begin to clarify the picture of the H5N1 human-adaptive mechanism.

A novel immunochromatographic system for easy-to-use detection of group 1 avian influenza viruses with acquired human-type receptor binding specificity

A switch of viral hemagglutinin receptor binding specificity from bird-type α2,3- to human-type α2,6-linked sialic acid is necessary for an avian influenza virus to become a pandemic virus. In this study, an easy-to-use strip test to detect receptor binding specificity of influenza virus was developed. A biotinylated anti-hemagglutinin antibody that bound a broad range of group 1 influenza A viruses and latex-conjugated α2,3 (blue) and α2,6 (red) sialylglycopolymers were used in an immunochromatographic strip test, with avidin and lectin immobilized on a nitrocellulose membrane at test and control lines, respectively. Accumulation of a sialylglycopolymer–virus–antibody complex at the test line was visualized by eye. The strip test could be completed in 30 min and did not require special equipment or skills, thereby avoiding some disadvantages of current methods for analyzing receptor binding specificity of influenza virus. The strip test could detect the receptor binding specificity of a wide range of influenza viruses, as well as small increases in the binding affinity of variant H5N1 viruses to α2,6 sialylglycans at viral titers >128 hemagglutination units. The strip test results were in agreement with those of ELISA virus binding assays, with correlations >0.95. In conclusion, the immunochromatographic strip test developed in this study should be useful for monitoring potential changes in the receptor binding specificity of group 1 influenza A viruses in the field.

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A novel immunochromatographic strip test system was developed.

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The strip test was developed to detect influenza virus receptor binding specificity.

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The strip test was applicable to a broad range of group 1 influenza A viruses.

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The strip detected faint increases in human-type specificity of variant H5N1 viruses.

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The system could be applied for easy monitoring the viral pandemic potential.

A human monoclonal antibody derived from a vaccinated volunteer recognizes heterosubtypically a novel epitope on the hemagglutinin globular head of H1 and H9 influenza A viruses

Most neutralizing antibodies elicited during influenza virus infection or by vaccination have a narrow spectrum because they usually target variable epitopes in the globular head region of hemagglutinin (HA). In this study, we describe a human monoclonal antibody (HuMAb), 5D7, that was prepared from the peripheral blood lymphocytes of a vaccinated volunteer using the fusion method. The HuMAb heterosubtypically neutralizes group 1 influenza A viruses, including seasonal H1N1, 2009 pandemic H1N1 (H1N1pdm) and avian H9N2, with a strong hemagglutinin inhibition activity. Selection of an escape mutant showed that the HuMAb targets a novel conformational epitope that is located in the HA head region but is distinct from the receptor binding site. Furthermore, Phe114Ile substitution in the epitope made the HA unrecognizable by the HuMAb. Amino acid residues in the predicted epitope region are also highly conserved in the HAs of H1N1 and H9N2. The HuMAb reported here may be a potential candidate for the development of therapeutic/prophylactic antibodies against H1 and H9 influenza viruses.

Broad cross-reactive epitopes of the H5N1 influenza virus identified by murine antibodies against the A/Vietnam/1194/2004 hemagglutinin

There is an urgent need for a rapid diagnostic system to detect the H5 subtype of the influenza A virus. We previously developed monoclonal antibodies (mAbs) against the H5 hemagglutinin (HA) for use in a rapid diagnostic kit. In this study, we determined the epitopes of the anti-H5 HA murine mAbs OM-b, AY-2C2, and YH-1A1. Binding assays of the mAbs to different strains of H5 HAs indicated that OM-b and AY-2C2 cross-reacted with HAs from clades 1, 2.1.3.2, 2.2, and 2.3.4, whereas YH-1A1 failed to bind to those of clades 2.1.3.2 and 2.3.4. HA chimeras revealed that the epitopes for each of the mAbs were in the HA1 region. Analysis of escape mutants revealed that OM-b and AY-2C2 mAbs interacted mainly with amino acid residues D43 and G46, and the YH-1A1 mAb interacted with G139 and K or R140 of H5 HA. Multiple alignments of H5 HA protein sequences showed that D43 and G46 were very conserved among H5N1 HAs, except those in clade 2.2.1 and clade 7 (88.7%). The epitope for YH-1A1 mAb was highly variable in the HAs of H5N1, although it was well conserved in those of H5N2-N9. The OM-b and AY-2C2 mAbs could bind to the HAs of clades 1.1 and 2.3.2.1 that are currently epidemic in Asia, and we conclude that these would be effective for the detection of H5N1 infections in this region.

Molecular characterization of avian influenza H5N1 virus in Egypt and the emergence of a novel endemic subclade

Clade 2.2 highly pathogenic H5N1 viruses have been in continuous circulation in Egyptian poultry since 2006. Their persistence caused significant genetic drift that led to the reclassification of these viruses into subclades 2.2.1 and 2.2.1.1. Here, we conducted full-genome sequence and phylogenetic analyses of 45 H5N1 isolated during 2006-2013 through systematic surveillance in Egypt, and 53 viruses that were sequenced previously and available in the public domain. Results indicated that H5N1 viruses in Egypt continue to evolve and a new distinct cluster has emerged. Mutations affecting viral virulence, pathogenicity, transmission, receptor-binding preference and drug resistance were studied. In light of our findings that H5N1 in Egypt continues to evolve, surveillance and molecular studies need to be sustained.

Immune escape mutants of Highly Pathogenic Avian Influenza H5N1 selected using polyclonal sera: identification of key amino acids in the HA protein

Evolution of Avian Influenza (AI) viruses--especially of the Highly Pathogenic Avian Influenza (HPAI) H5N1 subtype--is a major issue for the poultry industry. HPAI H5N1 epidemics are associated with huge economic losses and are sometimes connected to human morbidity and mortality. Vaccination (either as a preventive measure or as a means to control outbreaks) is an approach that splits the scientific community, due to the risk of it being a potential driving force in HPAI evolution through the selection of mutants able to escape vaccination-induced immunity. It is therefore essential to study how mutations are selected due to immune pressure. To this effect, we performed an in vitro selection of mutants from HPAI A/turkey/Turkey/1/05 (H5N1), using immune pressure from homologous polyclonal sera. After 42 rounds of selection, we identified 5 amino acid substitutions in the Haemagglutinin (HA) protein, most of which were located in areas of antigenic importance and suspected to be prone to selection pressure. We report that most of the mutations took place early in the selection process. Finally, our antigenic cartography studies showed that the antigenic distance between the selected isolates and their parent strain increased with passage number.

Natural history of highly pathogenic avian influenza H5N1

The ecology of highly pathogenic avian influenza (HPAI) H5N1 has significantly changed from sporadic outbreaks in terrestrial poultry to persistent circulation in terrestrial and aquatic poultry and potentially in wild waterfowl. A novel genotype of HPAI H5N1 arose in 1996 in Southern China and through ongoing mutation, reassortment, and natural selection, has diverged into distinct lineages and expanded into multiple reservoir hosts. The evolution of Goose/Guangdong-lineage highly pathogenic H5N1 viruses is ongoing: while stable interactions exist with some reservoir hosts, these viruses are continuing to evolve and adapt to others, and pose an un-calculable risk to sporadic hosts, including humans.

Antigenic analysis of H5N1 highly pathogenic avian influenza viruses circulating in Egypt (2006-2012)

The highly pathogenic avian influenza (HPAI) H5N1 in Egypt circulated continuously after its introduction in February 2006 with substantial economic losses and frequent human infections. Phylogenetic analysis of the available HA sequences revealed the presence of two main sublineages; the classic 2.2.1 and the variant 2.2.1.1. The classic 2.2.1 had subdivided into two clusters of viruses; cluster C1 contained the originally introduced virus and isolates from 2006 to 2009 and cluster C2 emerged in 2007 and continues to circulate. The variant 2.2.1.1 represents the isolates mainly from chickens and subdivided into two clusters; cluster V1 contains isolates from 2007 to 2009 and cluster V2 contains isolates from 2008 to 2011. Sequence analysis revealed 28 amino acid mutations in the previously reported antigenic sites and high evolution rate which may be due to selective pressure from vaccination and/or natural infection. Antigenic analysis of 18 H5N1 isolates from 2006 to 2012 that represent different clusters was conducted using hemagglutination inhibition (HI) and virus neutralization (VN) assays using hyperimmune sera produced by immunizing SPF chickens with inactivated whole-virus. Antigenic relatedness of ancestral Egyptian H5N1 isolate (459-3/06) with other isolates ranged from 30.7% to 79.1% indicating significant antigenic drift of the H5N1 viruses from the ancestral strains. The antigenic relatedness between C2 and V2 clusters ranged from 28.9% to 68% supporting the need for vaccine seed strains from both clusters. Interestingly, A/CK/EG/1709-6/2008 H5N1 strain showed a broad cross reactivity against viruses in different H5N1 clusters (antigenic relatedness ranged from 63.9% to 85.8%) demonstrating a potential candidate as a vaccine strain. Antigenic cartography which facilitates a quantitative interpretation and easy visualization of serological data was constructed based on HI results and further demonstrated the several antigenic groups among Egyptian H5N1 viruses. In conclusion, the cross reactivity between the co-circulating H5N1 strains may not be adequate for protection against each other and it is recommended to test vaccines that contain isolates from different antigenic groups in experimental infection trials for the selection of vaccine seed strain. Furthermore, the continuous monitoring for detecting the emerging variants followed by detailed antigenic analysis for updating vaccines is warranted.

Experimental challenge of chicken vaccinated with commercially available H5 vaccines reveals loss of protection to some highly pathogenic avian influenza H5N1 strains circulating in Hong Kong/China

Highly pathogenic avian influenza (HPAI) H5N1 virus continues to circulate in poultry in Asia and Africa posing a threat to both public and animal health. Vaccination, used as an adjunct to improved bio-security and stamping-out policies, contributed to protecting poultry in Hong Kong from HPAI H5N1 infection in 2004-2008 although the virus was repeatedly detected in dead wild birds. The detection of clade 2.3.4 H5N1 viruses in poultry markets and a farm in Hong Kong in 2008 raised the question whether this virus has changed to evade protection from the H5 vaccines in use. We tested the efficacy of three commercial vaccines (Nobilis, Poulvac and Harbin Re-5 vaccine) in specific pathogen free white leghorn chickens against a challenge with A/chicken/Hong Kong/8825-2/2008 (clade 2.3.4) isolated from vaccinated poultry in Hong Kong and A/chicken/Hong Kong/782/2009 (clade 2.3.2). Harbin Re5 vaccine provided the best, albeit not complete protection against challenge with the clade 2.3.4 virus. All three vaccines provided good protection from death and significantly reduced virus shedding following challenge with the clade 2.3.2 virus. Only Harbin Re-5 was able to completely protect chickens from virus shedding as well as mortality. Sera from vaccinated chickens had lower geometric hemagglutination inhibition titers against A/chicken/Hong Kong/8825-2/08, as compared to two other clade 2.3.4 and one clade 0 virus. Alignment of amino-acid sequences of the haemagglutinin of A/chicken/Hong Kong/8825-2/08 and the other H5 viruses revealed several mutations in positions including 69, 71, 83, 95, 133,140, 162, 183, 189, 194 and 270 (H5 numbering) which may correlate with loss of vaccine protection. Our results indicated that the tested HPAI H5N1 (2.3.4) virus has undergone antigenic changes that allow it to evade immunity from poultry vaccines. This highlights the need for continued surveillance and monitoring of vaccine induced immunity, with experimental vaccine challenge studies being done where indicated.

Antigenic diversity and cross-reactivity of avian influenza H5N1 viruses in Egypt between 2006 and 2011

Influenza epidemics are a major health concern worldwide. Highly pathogenic avian influenza (HPAI) H5N1 viruses in Egypt have been subject to rapid genetic and antigenic changes since the first outbreak in February 2006 and have been endemic in poultry in Egypt since 2008. In this study, 33 H5N1 viruses isolated from avian hosts were antigenically analysed by using a panel of eight mAbs raised against the A/Viet Nam/1203/04 (H5N1; clade 1) and A/bar-headed goose/Qinghai-lake/1A/05 (H5N1; clade 2.2) influenza viruses. Rats were immunized with inactivated whole-virus vaccine produced by reverse genetics with the haemagglutinin and neuraminidase genes of eight antigenically different HPAI H5N1 virus isolates and six internal genes from A/Puerto Rico/8/1934 (PR8) to produce polyclonal antibodies. Cross-reactivity between the obtained polyclonal antibodies and the isolated viruses was assayed. Antigenic cartography of the isolated viruses showed that three antigenic clusters were defined based on haemagglutination inhibition (HI) analysis using mAbs and the majority of viruses isolated in 2010 and 2011 fell into two of these clusters. An antigenic map based on polyclonal rat antisera showed that all virus isolates fell within one extended cluster. Accordingly, continuous surveillance and antigenic characterization will help us determine which virus isolate(s) should be used in poultry vaccine preparation.