Human infections with recently-emerging highly pathogenic H7N9 avian influenza virus in China

Molecular Evolution, Diversity, and Adaptation of Influenza A(H7N9) Viruses in China

The substantial increase in prevalence and emergence of antigenically divergent or highly pathogenic influenza A(H7N9) viruses during 2016–17 raises concerns about the epizootic potential of these viruses. We investigated the evolution and adaptation of H7N9 viruses by analyzing available data and newly generated virus sequences isolated in Guangdong Province, China, during 2015–2017. Phylogenetic analyses showed that circulating H7N9 viruses belong to distinct lineages with differing spatial distributions. Hemagglutination inhibition assays performed on serum samples from patients infected with these viruses identified 3 antigenic clusters for 16 strains of different virus lineages. We used ancestral sequence reconstruction to identify parallel amino acid changes on multiple separate lineages. We inferred that mutations in hemagglutinin occur primarily at sites involved in receptor recognition or antigenicity. Our results indicate that highly pathogenic strains likely emerged from viruses circulating in eastern Guangdong Province during March 2016 and are associated with a high rate of adaptive molecular evolution.

Targeting Hemagglutinin: Approaches for Broad Protection against the Influenza A Virus

Influenza A viruses are dynamically epidemic and genetically diverse. Due to the antigenic drift and shift of the virus, seasonal vaccines are required to be reformulated annually to match with current circulating strains. However, the mismatch between vaccinal strains and circulating strains occurs frequently, resulting in the low efficacy of seasonal vaccines. Therefore, several “universal” vaccine candidates based on the structure and function of the hemagglutinin (HA) protein have been developed to meet the requirement of a broad protection against homo-/heterosubtypic challenges. Here, we review recent novel constructs and discuss several important findings regarding the broad protective efficacy of HA-based universal vaccines.

Light chain modulates heavy chain conformation to change protection profile of monoclonal antibodies against influenza A viruses

The isolation of human monoclonal antibodies with broadly neutralizing breadth can provide a promising countermeasure for influenza A viruses infection. Most broadly neutralizing antibodies against influenza A viruses bind to the conserved stem region or the receptor-binding cavity of hemagglutinin and the interaction is dominated by the heavy chain. The light chain, however, contributes few or no direct contacts to the antigen. Here we report an H3-clade neutralizing human monoclonal antibody, AF4H1K1, which recognizes the hemagglutinin glycoproteins of all group 2 influenza A viruses. This human monoclonal antibody has been obtained through the screening by pairing different heavy and light chains from an H7N9-infected patient based on the next-generation sequencing technology. Further structural studies revealed that light chains modulate the neutralizing spectrum by affecting the local conformation of heavy chains, instead of direct interaction with the antigen. These findings provide important clues to understand the molecular basis of light chains in antigen recognition and to explore the strategies in particular of the use of light chain modification to develop broadly protective monoclonal antibodies against influenza A viruses and other emerging viruses.

Inhibition of avian-origin influenza A(H7N9) virus by the novel cap-dependent endonuclease inhibitor baloxavir marboxil

Human infections with avian-origin influenza A(H7N9) virus represent a serious threat to global health; however, treatment options are limited. Here, we show the inhibitory effects of baloxavir acid (BXA) and its prodrug baloxavir marboxil (BXM), a first-in-class cap-dependent endonuclease inhibitor, against A(H7N9), in vitro and in vivo. In cell culture, BXA at four nanomolar concentration achieved a 1.5-2.8 log reduction in virus titers of A(H7N9), including the NA-R292K mutant virus and highly pathogenic avian influenza viruses, whereas NA inhibitors or favipiravir required approximately 20-fold or higher concentrations to achieve the same levels of reduction. A(H7N9)-specific amino acid polymorphism at position 37, implicated in BXA binding to the PA endonuclease domain, did not impact on BXA susceptibility. In mice, oral administration of BXM at 5 and 50 mg/kg twice a day for 5 days completely protected from a lethal A/Anhui/1/2013 (H7N9) challenge, and reduced virus titers more than 2-3 log in the lungs. Furthermore, the potent therapeutic effects of BXM in mice were still observed when a higher virus dose was administered or treatment was delayed up to 48 hours post infection. These findings support further investigation of BXM for A(H7N9) treatment in humans.

Enhanced Replication of Highly Pathogenic Influenza A(H7N9) Virus in Humans

To clarify the threat posed by emergence of highly pathogenic influenza A(H7N9) virus infection among humans, we characterized the viral polymerase complex. Polymerase basic 2–482R, polymerase basic 2–588V, and polymerase acidic–497R individually or additively enhanced virus polymerase activity, indicating that multiple replication-enhancing mutations in 1 isolate may contribute to virulence.

Characterization of Mouse Monoclonal Antibodies Against the HA of A(H7N9) Influenza Virus

Many cases of human infection with the H7N9 virus have been detected in China since 2013. H7N9 viruses are maintained in chickens and are transmitted to humans at live bird markets. During circulation in birds, H7N9 viruses have accumulated amino acid substitutions in their hemagglutinin (HA), which resulted in an antigenically change in the recent H7N9 viruses. Here, we characterized 46 mouse monoclonal antibodies against the HA of the prototype strain. 16 H7-HA-specific monoclonal antibodies (mAbs) possessed hemagglutination inhibition (HI) and neutralization activities by recognizing the major antigenic site A; four other H7-HA-specific clones also showed HI and neutralizing activities via recognition of the major antigenic sites A and D; seven mAbs that reacted with several HA subtypes and possibly recognized the HA stem partially protected mice from lethal infection with prototype H7N9 virus; and the remaining 19 mAbs had neither HI nor neutralization activity. All human H7N9 viruses tested showed a similar neutralization sensitivity to the first group of 16 mAbs, whereas human H7N9 viruses isolated in 2016–2017 were not neutralized by a second group of 4 mAbs. These results suggest that amino acid substitutions at the epitope of the second mAb group appear to be involved in the antigenic drift of the H7N9 viruses. Further analysis is required to fully understand the antigenic change in H7N9 viruses.

Structure-function analysis of neutralizing antibodies to H7N9 influenza from naturally infected humans

Little is known about the specificities and neutralization breadth of the H7-reactive antibody repertoire induced by natural H7N9 infection in humans. We have isolated and characterized 73 H7-reactive monoclonal antibodies from peripheral B cells from four donors infected in 2013 and 2014. Of these, 45 antibodies were H7-specific, and 17 of these neutralized the virus, albeit with few somatic mutations in their variable domain sequences. An additional set of 28 antibodies, isolated from younger donors born after 1968, cross-reacted between H7 and H3 haemagglutinins in binding assays, and had accumulated significantly more somatic mutations, but were predominantly non-neutralizing in vitro. Crystal structures of three neutralizing and protective antibodies in complex with the H7 haemagglutinin revealed that they recognize overlapping residues surrounding the receptor-binding site of haemagglutinin. One of the antibodies, L4A-14, bound into the sialic acid binding site and made contacts with haemagglutinin residues that were conserved in the great majority of 2016-2017 H7N9 isolates. However, only 3 of the 17 neutralizing antibodies retained activity for the Yangtze River Delta lineage viruses isolated in 2016-2017 that have undergone antigenic change, which emphasizes the need for updated H7N9 vaccines.

Recombinant baculovirus vaccine expressing hemagglutinin of H7N9 avian influenza virus confers full protection against lethal highly pathogenic H7N9 virus infection in chickens

The emergent highly pathogenic avian influenza A (H7N9) (HPAI) virus is a major public concern in China. Therefore, it is crucially important to develop an effective vaccine against this virus. In this study, we constructed a baculovirus vaccine expressing the hemagglutinin (HA) of H7N9 strain A/Chicken/Jiaxing/148/2014 (JX148). The recombinant baculovirus (rBac-JX148HA) generated in this study showed good growth in insect cells and good safety, and it stably expressed the HA protein. We compared the immunogenicity and efficacy of the inactivated whole-virus vaccine JX148 and rBac-JX148HA. One chicken in the JX148-treated group died on day 4 post-challenge, and three chickens had typical clinical symptoms (survival rate, 90%; morbidity, 40%). However, no chickens immunized with rBac-JX148HA showed clinical signs during the 14-day observation period. An analysis of viral shedding and viral replication demonstrated that rBac-JX148HA more efficiently inhibited viral shedding and viral replication than the inactivated whole-virus vaccine. Taken together, these results indicate that the inactivated recombinant baculovirus vaccine induces a high hemagglutination inhibition antibody titer, provides complete protection against challenge with the highly pathogenic H7N9 virus, and effectively inhibits viral shedding. Therefore, the candidate vaccine has potential utility in the prevention and control of H7N9 avian influenza and is also appropriate for veterinary vaccines using cell suspension culture technology.

Comparison between human infections caused by highly and low pathogenic H7N9 avian influenza viruses in Wave Five: Clinical and virological findings

OBJECTIVE

The newly emerged highly pathogenic (HP) H7N9 avian influenza virus during Wave Five has caused 28 human infections, while differences in disease severity between low pathogenic (LP)- and HP-H7N9 human infections remain unclear.

METHODS

Clinical data, concentrations of serum cytokines, dynamics of virus shedding and PaO₂/FiO₂ from patients infected with LP-H7N9 (n = 7, LP group) and HP-H7N9 (n = 5, HP group) viruses during Wave Five were compared. In addition, critical mutations associated with H7N9 virulence in mammal/human were analyzed.

RESULTS

Lymphopenia, elevated aspartate aminotransferase, alanine aminotransferase, C-reactive protein and lactate dehydrogenase were common features, with higher incidences of leukopenia and thrombocytopenia in the LP group. The acute phase of both groups was accompanied with elevated cytokines associated with disease severity, including MIF, MCP-1 and IP-10. Diffuse exudation of the lungs and consolidation were observed from all patients. The dynamics of virus shedding and PaO₂/FiO₂ were similar between both groups. Notably, a higher prevalence of neuraminidase inhibitors (NAIs) resistance in the HP-H7N9 virus was found.

CONCLUSIONS

Our results indicate that this newly emerged HP-H7N9 virus caused similar disease severity in humans compared with LP-H7N9 virus, while higher case fatality rate and prevalence of NAI-resistance in human HP-H7N9 infections were of great concern.

Safety, Tolerability, and Pharmacokinetics of the Novel Anti-influenza Agent Baloxavir Marboxil in Healthy Adults: Phase I Study Findings

Background and Objective

Baloxavir marboxil, a prodrug that is metabolized to baloxavir acid, suppresses viral replication by inhibiting cap-dependent endonuclease. This first-in-human phase I study evaluated the safety, tolerability, and pharmacokinetics of baloxavir marboxil/baloxavir acid in healthy Japanese volunteers (Study 1), while food effects were evaluated in a separate phase I, crossover study in healthy Japanese volunteers (Study 2).

Methods

Study 1 participants were randomized to single-dose oral baloxavir marboxil (6, 20, 40, 60, or 80 mg; n = 6 per dose) or placebo (n = 10), while Study 2 participants (n = 15) received single-dose oral baloxavir marboxil 20 mg in fasted, fed, and before-meal states.

Results

Baloxavir marboxil was well tolerated; there were few treatment-emergent adverse events and no serious adverse events/deaths. The mean plasma baloxavir acid concentration 24 h after single-dose (C₂₄) oral baloxavir marboxil 6 mg was 6.92 ng/mL, exceeding the target C₂₄ (6.85 ng/mL) estimated in nonclinical studies. In Study 1, baloxavir acid exposure demonstrated dose-proportional increases in the fasted state, with maximum plasma concentration generally attained within 3.5 h. Terminal elimination half-life ranged from 49 to 91 h. In Study 2, exposure was decreased and apparent clearance increased in the fed and before-meal states versus the fasted state; however, exposure exceeded the target C₂₄ in all states.

Conclusion

Single-dose oral baloxavir marboxil was well tolerated, had a favorable safety profile, and had favorable pharmacokinetic characteristics, including a long half-life, supporting single oral dosing. The baloxavir acid area under the plasma concentration-time curve decreased with food intake by approximately 40%.

Multiple amino acid substitutions involved in the adaption of three avian-origin H7N9 influenza viruses in mice

Background

Avian influenza A H7N9 virus has caused five outbreak waves of human infections in China since 2013 and posed a dual challenge to public health and poultry industry. The number of reported H7N9 virus human cases confirmed by laboratory has surpassed that of H5N1 virus. However, the mechanism for how H7N9 influenza virus overcomes host range barrier has not been clearly understood.

Methods

To generate mouse-adapted H7N9 influenza viruses, we passaged three avian-origin H7N9 viruses in mice by lung-to-lung passages independently. Then, the characteristics between the parental and mouse-adapted H7N9 viruses was compared in the following aspects, including virulence in mice, tropism of different tissues, replication in MDCK cells and molecular mutations.

Results

After ten passages in mice, MLD₅₀ of the H7N9 viruses reduced >750-3,160,000 folds, and virus titers in MDCK cells increased 10-200 folds at 48 hours post-inoculation. Moreover, the mouse-adapted H7N9 viruses showed more expanded tissue tropism and more serious lung pathological lesions in mice. Further analysis of the amino acids changes revealed 10 amino acid substitutions located in PB2 (E627K), PB1 (W215R and D638G), PA (T97I), HA (H3 numbering: R220G, L226S, G279R and G493R) and NA (P3Q and R134I) proteins. Moreover, PB2 E627K substitution was shared by the three mouse-adapted viruses (two viruses belong to YRD lineage and one virus belongs to PRD lineage), and PA T97A substitution was shared by two mouse-adapted viruses (belong to YRD lineage).

Conclusions

Our result indicated that the virulence in mice and virus titer in MDCK cells of H7N9 viruses significantly increased after adapted in mouse model. PB2 E627K and PA T97A substitutions are vital in mouse adaption and should be monitored during epidemiological study of H7N9 virus.

Electronic supplementary material

The online version of this article (10.1186/s12985-018-1109-1) contains supplementary material, which is available to authorized users.

Pathogenicity of two novel human-origin H7N9 highly pathogenic avian influenza viruses in chickens and ducks

Human infection by low-pathogenic avian influenza viruses of the H7N9 subtype was first reported in March 2013 in China. Subsequently, these viruses caused five outbreaks through September 2017. In the fifth outbreak, H7N9 virus possessing a multiple basic amino acid insertion in the cleavage site of hemagglutinin emerged and caused 4% of all human infections in that period. To date, H7N9 highly pathogenic avian influenza viruses (HPAIVs) have been isolated from poultry, mostly chickens, as well as the environment. To evaluate the relative infectivity of these viruses in poultry, chickens and ducks were subjected to experimental infection with two H7N9 HPAIVs isolated from humans, namely A/Guangdong/17SF003/2016 and A/Taiwan/1/2017. When chickens were inoculated with the HPAIVs at a dose of 10⁶ 50% egg infectious dose (EID₅₀), all chickens died within 2-5 days after inoculation, and the viruses replicated in most of the internal organs examined. The 50% lethal doses of A/Guangdong/17SF003/2016 and A/Taiwan/1/2017 in chickens were calculated as 10^3.3 and 10^4.7 EID₅₀, respectively. Conversely, none of the ducks inoculated with either virus displayed any clinical signs, and less-efficient virus replication and less shedding were observed in ducks compared to chickens. These findings indicate that chickens, but not ducks, are highly permissive hosts for emerging H7N9 HPAIVs.

Epidemiological and molecular analysis of avian influenza A(H7N9) virus in Shanghai, China, 2013-2017

Background

Human infections with a novel avian influenza A virus (H7N9) were reported in Shanghai municipality, China, at the beginning of 2013. High-pathogenic avian influenza (HPAI) H7N9 virus emerged in late February 2017 along with existing low-pathogenic avian influenza (LPAI) H7N9 virus, and this has the potential to develop into a pandemic that could be harmful to humans.

Methods

To elucidate the epidemiological characteristics of H7N9-infected cases from 2013 to 2017 in Shanghai, data on the 59 laboratory-confirmed human cases and 26 bird and environmental contamination cases were collected from the WHO website and Food and Agriculture Organization Emergency Prevention System for Animal Health (FAO EMPRES-AH). Full-length sequences of H7N9 viruses that emerged in Shanghai were collected from the Global Initiative on Sharing Avian Influenza Data to analyze the evolutionary and genetic features.

Results

We found that genetically different strains emerged in every epidemic in Shanghai, and most of the circulating H7N9 strains had affinity to human-type receptors, with the characteristics of high-virulence and low-pathogenic influenza viruses. Furthermore, our findings suggest that the Shanghai chicken strains are closely related to the HPAI H7N9 virus A/Guangdong/17SF003/2016, indicating that this viral strain is of avian origin and generated from the LPAI H7N9 viruses in Shanghai. The gradual decrease in H7N9 human infection in Shanghai was probably due to the control measures taken by the Shanghai government and the enhanced public awareness leading to a reduced risk of H7N9 virus infection. However, LPAI H7N9 viruses from poultry and environmental samples were continually detected in Shanghai across the epidemics, increasing the risk of new emerging H7N9 outbreaks.

Conclusion

It is important to consistently obtain sufficient surveillance data and implement prevention measures against H7N9 viruses in Shanghai municipality.

Broad neutralizing activity of a human monoclonal antibody against H7N9 strains from 2013 to 2017

H7N9 influenza virus has been circulating among humans for five epidemic waves since it was first isolated in 2013 in China. The recent increase in H7N9 infections during the fifth outbreak in China has caused concerns of a possible pandemic. In this study, we describe a previously characterized human monoclonal antibody, HNIgGA6, obtained by isolating rearranged heavy-chain and light-chain genes from patients who had recovered from H7N9 infections. HNIgGA6 recognized multiple HAs and neutralized the infectivity of 11 out of the 12 H7N9 strains tested, as well as three emerging HPAI H7N9 isolates. The only resistant strain was A/Shanghai/1/2013 (H7N9-SH1), which carries the avian receptor alleles 186V and 226Q in the sialic acid-binding pocket. The mAb broadly neutralized divergent H7N9 strains from 2013 to 2017 and represents a potential alternative treatment for H7N9 interventions.

Deciphering the Sharp Decrease in H7N9 Human Infections

The H7N9 virus has caused five waves of human infections since 2013. However, human infections have almost disappeared in the past year. In a recent study, Shi et al. revealed that the usage of a bivalent H5/H7 vaccine successfully prevented chicken infections, and thus prevented, and nearly eliminated, human infections.

Identification of two residues within the NS1 of H7N9 influenza A virus that critically affect the protein stability and function

The emerging avian-origin H7N9 influenza A virus, which causes mild to lethal human respiratory disease, continues to circulate in China, posing a great threat to public health. Influenza NS1 protein plays a key role in counteracting host innate immune responses, allowing the virus to efficiently replicate in the host. In this study, we compared NS1 amino acid sequences of H7N9 influenza A virus with those of other strains, and determined NS1 protein variability within the H7N9 virus and then evaluated the impact of amino acid substitutions on ability of the NS1 proteins to inhibit host innate immunity. Interestingly, the amino acid residue S212 was identified to have a profound effect on the primary function of NS1, since S212P substitution disabled H7N9 NS1 in suppressing the host RIG-I-dependent interferon response, as well as the ability to promote the virus replication. In addition, we identified another amino acid residue, I178, serving as a key site to keep NS1 protein high steady-state levels. When the isoleucine was replaced by valine at 178 site (I178V mutation), NS1 of H7N9 underwent rapid degradation through proteasome pathway. Furthermore, we observed that P212S and V178I mutation in NS1 of PR8 virus enhanced virulence and promoted the virus replication in vivo. Together, these results indicate that residues I178 and S212 within H7N9 NS1 protein are critical for stability and functioning of the NS1 protein respectively, and may contribute to the enhanced pathogenicity of H7N9 influenza virus.

AS03-adjuvanted H5N1 vaccine promotes antibody diversity and affinity maturation, NAI titers, cross-clade H5N1 neutralization, but not H1N1 cross-subtype neutralization

Immune responses to inactivated vaccines against avian influenza are poor due in part to lack of immune memory. Adjuvants significantly increased virus neutralizing titers. We performed comprehensive analyses of polyclonal antibody responses following FDA-approved adjuvanted H5N1-A/Indonesia vaccine, administered in presence or absence of AS03. Using Whole Genome Fragment Phage Display Libraries, we observed that AS03 induced antibody epitope diversity to viral hemagglutinin (HA) and neuraminidase compared with unadjuvanted vaccine. Furthermore, AS03 promoted significant antibody affinity maturation to properly folded H5-HA1 (but not to HA2) domain, which correlated with neutralization titers against both vaccine and heterologous H5N1 strains. However, no increase in heterosubtypic cross-neutralization of Group1-H1N1 seasonal strains was observed. AS03-H5N1 vaccine also induced higher neuraminidase inhibition antibody titers. This study provides insight into the differential impacts of AS03 adjuvant on H5N1 vaccine-induced antibody responses that may help optimize vaccine platforms for future vaccines with improved protection against seasonal and pandemic influenza strains.

Differences in the ease with which mutant viruses escape from human monoclonal antibodies against the HA stem of influenza A virus

BACKGROUND

Broadly protective human monoclonal antibodies that recognize the conserved epitopes in the HA of influenza A virus are being developed as therapeutic agents. Emergence of resistant viruses must always be considered when developing therapeutic agents against influenza.

OBJECTIVES

We examined human hetero-reactive mAbs against the HA stem of influenza A virus for the ease with which escape mutant viruses emerged.

STUDY DESIGN

We attempted to generate the mutant viruses escaped from the hetero-reactive anti-HA stem antibodies. We also evaluated their protective efficacy, binding affinity, and epitopes.

RESULTS

We obtained several human monoclonal antibodies (mAbs) that react with the HA of different HA subtypes of influenza A virus belonging to group 1. Upon attempting to generate escape mutant viruses, we found that the ease with which such viruses emerged differed among the mAbs; viruses barely escaped from two of the mAbs (clones S9-3-37 and F20C77), whereas escape from the third mAb (clone F5B7) occurred readily. Comparisons of the mAbs revealed that the HA stem epitopes, in vitro neutralization potency, binding affinity to H1-HA, and protective efficacy against lethal challenge with H1N1pdm09 virus were all comparable.

CONCLUSIONS

These results demonstrate the importance of determining the ease with which escape mutant viruses emerge when evaluating anti-HA stem antibodies as antiviral agents during preclinical testing.

Did the Highly Pathogenic Avian Influenza A(H7N9) Viruses Emerged in China Raise Increased Threat to Public Health?

The low pathogenic avian influenza A(H7N9) viruses (LPAI) were first identified in 2013 and have continued to infect humans since then. It was reported in February 2017 that the LPAI H7N9 virus has evolved into highly pathogenic avian influenza (HPAI) viruses, potentially increasing the risk for human and poultry. We in this study overviewed the emergence, epidemiology, and biological characterizations of the HPAI H7N9 viruses for the risk assessment.

A live attenuated vaccine prevents replication and transmission of H7N9 highly pathogenic influenza viruses in mammals

H7N9 influenza viruses emerged in 2013 and have caused severe disease and deaths in humans in China. Some H7N9 viruses circulating in chickens have mutated to highly pathogenic viruses that have caused several disease outbreaks in chickens. Studies have shown that when the H7N9 highly pathogenic viruses replicate in ferrets or humans, they easily acquire certain mammalian-adapting mutations and become highly lethal in mice and highly transmissible in ferrets by respiratory droplet, creating the potential for human-to-human transmission. Therefore, the development of effective control measures is a top priority for H7N9 pandemic preparedness. In this study, we evaluated the protective efficacy of a cold-adapted, live attenuated H7N9 vaccine (H7N9/AAca) against two heterologous H7N9 highly pathogenic viruses in mice and guinea pigs. Our results showed that one dose of the H7N9/AAca vaccine prevented disease and death in mice challenged with two different H7N9 highly pathogenic viruses, but did not prevent replication of the challenge viruses; after two doses of H7N9/AAca, the mice were completely protected from challenge with A/chicken/Hunan/S1220/2017(H7N9) virus, and very low viral titers were detected in mice challenged with H7N9 virus CK/SD008-PB2/627 K. More importantly, we found that one dose of H7N9/AAca could efficiently prevent transmission of CK/SD008-PB2/627 K in guinea pigs. Our study suggests that H7N9/AAca has the potential to be an effective H7N9 vaccine and should be evaluated in humans.

Impacts of age and gender at the risk of underlying medical conditions and death in patients with avian influenza A (H7N9): a meta-analysis study

Objective

The objective of our study was to conduct a series of analyses that examined the impacts of age and gender at the risk of underlying medical conditions (UMCs) and death in patients with influenza A (H7N9).

Methods

We began by searching for potentially relevant articles in English or Chinese before February 28, 2018. Additionally, we reviewed our own files and reference lists of articles identified by this search.

Results

The association between death and UMCs was significant in H7N9 patients, with an OR of 1.49 (95% CI: 1.24–1.78). Subgroup analyses showed that having two or more UMCs of any type (OR: 2.24; P=0.044), chronic respiratory diseases (OR: 1.81; P=0.032), and chronic cardiovascular disease (OR: 1.63; P=0.013) had an association with increased fatality in H7N9 patients. Age (60 years or older) [adjusted OR (AOR): 1.86; P=0.032] and gender (male: AOR: 1.68, P=0.006; female: AOR: 1.88, P=0.044) were significantly associated with death in H7N9 patients with UMCs compared to H7N9 patients without any UMC. Stratification analyses found statistically significant increased death in H7N9 patients with UMCs who were 60 years of age and older (AOR: 2.72; P<0.001) and gender (male; AOR=1.64; P=0.033), compared to H7N9 patients without these respective conditions.

Conclusion

Impacts of age are substantial and significant at the risk of UMCs and death in H7N9 patients. This analysis did not find a significant difference in gender comparisons. Efforts should particularly focus on reducing fatality rates in patients with combined risks from UMCs and other significant impact factor such as age (60 years or older).

Evolutionary dynamics of avian influenza A H7N9 virus across five waves in mainland China, 2013-2017

Since its emergence in March 2013, novel avian influenza A H7N9 virus has triggered five epidemics of human infections in China. This raises concerns about the pandemic threat of this quickly evolving H7N9 subtype for humans. In this study, we evaluated all available genomes for H7N9 and H9N2 influenza A viruses. Our assessment discovered that H7N9 of the 1st wave had the lowest nucleotide diversity, which then experienced substantial and rapid population expansion from a small founder population. From the 2nd wave, their nucleotide diversity increased quickly, indicating that H7N9 viruses had acquired larger populations and mutations after their initial emergence in 2013. After the phylogeographic divergence in the 2nd wave, although the HA and NA genes from different regions differed, compared to previous epidemics, the evolving H7N9 viruses in the 5th wave lost most of their previous clades. The highly pathogenic avian influenza (HPAI) H7N9 viruses in the 5th wave clustered together, and clustered close to the low pathogenic avian influenza (LPAI) virus isolated from the Pearl River Delta in the 3rd and 4th waves. This result supports the origin of HPAI H7N9 viruses was in the Pearl River Delta. In the 5th wave, although both HPAI and LPAI H7N9 viruses were isolated from the Pearl River Delta, their HA and NA genes were phylogenetically distinct.

Development of a Colloidal Gold-Based Immunochromatographic Strip for Rapid Detection of H7N9 Influenza Viruses

Both high- and low-pathogenic H7N9 influenza A virus (IAV) infections have been found in human and poultry in China, and most human cases are related to contact with infected poultry. It is necessary to develop a rapid and simple method to detect H7N9 IAV in poultry. In this study, 13 monoclonal antibodies (McAbs) against the H7N9 IAV hemagglutinin were developed, and three critical amino acid epitopes (198, 227, 235) were identified based on the reactivity of these variant and wild-type strains with the McAbs. We developed an immunochromatographic assay for H7N9 AIVs using two McAbs recognizing the epitope position 227 and 235. The assay had good specificity, stability, and sensitivity, with a detection limit of swab and tissue samples of 2.5 log₁₀EID₅₀/0.1 mL, which is suitable for the analysis of clinical samples. This assay provides an effective method for the rapid detection of H7N9 AIVs in poultry.

The Pandemic Threat of Emerging H5 and H7 Avian Influenza Viruses

The 1918 H1N1 Spanish Influenza pandemic was the most severe pandemic in modern history. Unlike more recent pandemics, most of the 1918 H1N1 virus' genome was derived directly from an avian influenza virus. Recent avian-origin H5 A/goose/Guangdong/1/1996 (GsGd) and Asian H7N9 viruses have caused several hundred human infections with high mortality rates. While these viruses have not spread beyond infected individuals, if they evolve the ability to transmit efficiently from person-to-person, specifically via the airborne route, they will initiate a pandemic. Therefore, this review examines H5 GsGd and Asian H7N9 viruses that have caused recent zoonotic infections with a focus on viral properties that support airborne transmission. Several GsGd H5 and Asian H7N9 viruses display molecular changes that potentiate transmission and/or exhibit ability for limited transmission between ferrets. However, the hemagglutinin of these viruses is unstable; this likely represents the most significant obstacle to the emergence of a virus capable of efficient airborne transmission. Given the global disease burden of an influenza pandemic, continued surveillance and pandemic preparedness efforts against H5 GsGd and Asian lineage H7N9 viruses are warranted.

Broadly Reactive Human Monoclonal Antibodies Elicited following Pandemic H1N1 Influenza Virus Exposure Protect Mice against Highly Pathogenic H5N1 Challenge

Broadly cross-reactive antibodies (Abs) that recognize conserved epitopes within the influenza virus hemagglutinin (HA) stalk domain are of particular interest for their potential use as therapeutic and prophylactic agents against multiple influenza virus subtypes, including zoonotic virus strains. Here, we characterized four human HA stalk-reactive monoclonal antibodies (MAbs) for their binding breadth and affinity, in vitro neutralization capacity, and in vivo protective potential against an highly pathogenic avian influenza virus. The monoclonal antibodies were isolated from individuals shortly following infection with (70-1F02 and 1009-3B05) or vaccination against (05-2G02 and 09-3A01) A(H1N1)pdm09. Three of the MAbs bound HAs from multiple strains of group 1 viruses, and one MAb, 05-2G02, bound to both group 1 and group 2 influenza A virus HAs. All four antibodies prophylactically protected mice against a lethal challenge with the highly pathogenic A/Vietnam/1203/04 (H5N1) strain. Two MAbs, 70-1F02 and 09-3A01, were further tested for their therapeutic efficacy against the same strain and showed good efficacy in this setting as well. One MAb, 70-1F02, cocrystallized with H5 HA and showed heavy-chain-only interactions similar to those seen with the previously described CR6261 anti-stalk antibody. Finally, we show that antibodies that compete with these MAbs are prevalent in serum from an individual recently infected with the A(H1N1)pdm09 virus. The antibodies described here can be developed into broad-spectrum antiviral therapeutics that could be used to combat infections by zoonotic or emerging pandemic influenza viruses.IMPORTANCE The rise in zoonotic infections of humans by emerging influenza viruses is a worldwide public health concern. The majority of recent zoonotic human influenza cases were caused by H7N9 and H5Nx viruses and were associated with high morbidity and mortality. In addition, seasonal influenza viruses are estimated to cause up to 650,000 deaths annually worldwide. Currently available antiviral treatment options include only neuraminidase inhibitors, but some influenza viruses are naturally resistant to these drugs, and others quickly develop resistance-conferring mutations. Alternative therapeutics are urgently needed. Broadly protective antibodies that target the conserved "stalk" domain of the hemagglutinin represent potential potent antiviral prophylactic and therapeutic agents that can assist pandemic preparedness. Here, we describe four human monoclonal antibodies that target conserved regions of influenza HA and characterize their binding spectrum as well as their protective capacity in prophylactic and therapeutic settings against a lethal challenge with a zoonotic influenza virus.

Structural and Molecular Characterization of the Hemagglutinin from the Fifth-Epidemic-Wave A(H7N9) Influenza Viruses

The avian influenza A(H7N9) virus continues to cause human infections in China and is a major ongoing public health concern. Five epidemic waves of A(H7N9) infection have occurred since 2013, and the recent fifth epidemic wave saw the emergence of two distinct lineages with elevated numbers of human infection cases and broader geographic distribution of viral diseases compared to the first four epidemic waves. Moreover, highly pathogenic avian influenza (HPAI) A(H7N9) viruses were also isolated during the fifth epidemic wave. Here, we present a detailed structural and biochemical analysis of the surface hemagglutinin (HA) antigen from viruses isolated during this recent epidemic wave. Results highlight that, compared to the 2013 virus HAs, the fifth-wave virus HAs remained a weak binder to human glycan receptor analogs. We also studied three mutations, V177K-K184T-G219S, that were recently reported to switch a 2013 A(H7N9) HA to human-type receptor specificity. Our results indicate that these mutations could also switch the H7 HA receptor preference to a predominantly human binding specificity for both fifth-wave H7 HAs analyzed in this study.IMPORTANCE The A(H7N9) viruses circulating in China are of great public health concern. Here, we report a molecular and structural study of the major surface proteins from several recent A(H7N9) influenza viruses. Our results improve the understanding of these evolving viruses and provide important information on their receptor preference that is central to ongoing pandemic risk assessment.

Development of a quadruple qRT-PCR assay for simultaneous identification of highly and low pathogenic H7N9 avian influenza viruses and characterization against oseltamivir resistance

Background

During the fifth wave of human H7N9 infections, a novel highly pathogenic (HP) H7N9 variant emerged with an insertion of multiple basic amino acids in the HA cleavage site. Moreover, a neuraminidase inhibitor (NAI) resistance (R292K in NA) mutation was found in H7N9 isolates from humans, poultry and the environment. In this study, we set out to develop and validate a multiplex quantitative reverse transcript polymerase chain reaction (qRT-PCR) to simultaneously detect the presence of H7N9 and further identify the HP and NAI-resistance mutations.

Methods

A quadruple qRT-PCR to simultaneously detect the presence of H7N9 and further identify the HP and NAI-resistance mutations was designed based on the analyses of the HA and NA genes of H7N9. This assay was further tested for specificity and sensitivity, and validated using clinical samples.

Results

The assay was highly specific and able to detect low pathogenic (LP)- or HP-H7N9 with/without the NAI-resistance mutation. The detection limit of the assay was determined to be 50 genome-equivalent copies and 2.8 × 10^− 3 50% tissue culture infectious doses (TCID₅₀) of live H7N9 per reaction. Clinical validation was confirmed by commercial kits and Sanger sequencing with ten clinical samples.

Conclusions

We developed and validated a rapid, single-reaction, one-step, quadruple real-time qRT-PCR to simultaneously detect the presence of H7N9 and further identify the HP- and NAI-resistance strains with excellent performance in specificity and sensitivity. This assay could be used to monitor the evolution of H7N9 viruses in the laboratory, field and the clinic for early-warning and the prevention of H7N9 infections.

Avian Influenza A Virus Pandemic Preparedness and Vaccine Development

Influenza A viruses can infect a wide range of hosts, creating opportunities for zoonotic transmission, i.e., transmission from animals to humans, and placing the human population at constant risk of potential pandemics. In the last hundred years, four influenza A virus pandemics have had a devastating effect, especially the 1918 influenza pandemic that took the lives of at least 40 million people. There is a constant risk that currently circulating avian influenza A viruses (e.g., H5N1, H7N9) will cause a new pandemic. Vaccines are the cornerstone in preparing for and combating potential pandemics. Despite exceptional advances in the design and development of (pre-)pandemic vaccines, there are still serious challenges to overcome, mainly caused by intrinsic characteristics of influenza A viruses: Rapid evolution and a broad host range combined with maintenance in animal reservoirs, making it near impossible to predict the nature and source of the next pandemic virus. Here, recent advances in the development of vaccination strategies to prepare against a pandemic virus coming from the avian reservoir will be discussed. Furthermore, remaining challenges will be addressed, setting the agenda for future research in the development of new vaccination strategies against potentially pandemic influenza A viruses.

A comprehensive comparison of the fifth-wave highly pathogenic and low-pathogenic H7N9 avian influenza viruses reveals potential threat posed by both types of viruses in mammals

Before 2013, zoonotic influenza infections were dominated by H5N1 viruses in China. However, the emergence of the H7N9 viruses in early 2013 changed this dominance greatly, and more than 1,600 laboratory-confirmed human cases of H7N9 infections have been reported since then. To understand the underlying mechanism of the emergence of the fifth epidemic wave that shows an unexpected sharp increase, we systematically investigated the biological characteristics of the highly pathogenic (HP) and low-pathogenic (LP) H7N9 AIVs during this period. We first systematically analysed the haemagglutination assay gene of all the isolates available from the website and found that the HP and LP viruses differed a little in the well-established receptor binding sites and in other potentially important sites. Phylogenetic analysis showed that both the HP and LP viruses belong to the branch of the Yangtze River Delta, whereas they diverged to different small branches. To further compare the biological variations in the HP and LP viruses, we selected six HP and six LP strains for in-depth analysis, including receptor binding characteristics, thermal stability, viral replication and virulence in mice. The three major findings of this study were as follows: (a) Other potential site/sites may affect the receptor binding property of the H7N9 viruses; (b) the HP viruses displayed a higher thermostability than did the LP viruses, quite consistent with the epidemiological data during the summer period; and (c) one-third of the HP viruses were moderately pathogenic in mice, whereas all the LP viruses were nonpathogenic in this animal model. However, the LP viruses replicated more efficiently in the mouse lung and can spread to the extrarespiratory organs (spleen, kidney and brain). Taken together, our results suggest that both the HP and LP H7N9 viruses can pose a potential threat to public health, highlighting the importance of the continual surveillance of the H7N9 AIVs.

Highly Pathogenic H5N1 Influenza A Virus Spreads Efficiently in Human Primary Monocyte-Derived Macrophages and Dendritic Cells

Influenza A viruses cause recurrent epidemics and occasional global pandemics. Wild birds are the natural reservoir of influenza A virus from where the virus can be transmitted to poultry or to mammals including humans. Mortality among humans in the highly pathogenic avian influenza H5N1 virus infection is even 60%. Despite intense research, there are still open questions in the pathogenicity of the H5N1 virus in humans. To characterize the H5N1 virus infection in human monocyte-derived macrophages (Mɸs) and dendritic cells (DCs), we used human isolates of highly pathogenic H5N1/2004 and H5N1/1997 and low pathogenic H7N9/2013 avian influenza viruses in comparison with a seasonal H3N2/1989 virus. We noticed that the H5N1 viruses have an overwhelming ability to replicate and spread in primary human immune cell cultures, and even the addition of trypsin did not equalize the infectivity of H7N9 or H3N2 viruses to the level seen with H5N1 virus. H5N1 virus stocks contained more often propagation-competent viruses than the H7N9 or H3N2 viruses. The data also showed that human DCs and Mɸs maintain 1,000- and 10,000-fold increase in the production of infectious H5N1 virus, respectively. Both analyzed highly pathogenic H5N1 viruses showed multi-cycle infection in primary human DCs and Mɸs, whereas the H3N2 and H7N9 viruses were incapable of spreading in immune cells. Interestingly, H5N1 virus was able to spread extremely efficiently despite the strong induction of antiviral interferon gene expression, which may in part explain the high pathogenicity of H5N1 virus infection in humans.

H7 virus-like particles assembled by hemagglutinin containing H3N2 transmembrane domain and M1 induce broad homologous and heterologous protection in mice

•

H7 VLPs-WT and H7 VLPs-TM have similar morphological and cleavage characteristics.

•

H7 VLPs-TM has more HA trimers and better resists thermal changes than H7 VLPs-WT.

•

H7 VLPs-TM induces stronger Th1 immune response than H7 VLPs-WT.

•

H7 VLPs-TM induces broad homologous and heterologous protection in mice.

Influenza A H7N9 virus has caused five outbreak waves of human infections in China since 2013 and posed a dual challenge to public health and poultry industry. There is an urgent need to develop an effective vaccine to reduce its pandemic potential. In the present study, we evaluated the biochemical characteristics and immunogenicity of two H7 virus-like particles (VLPs) composed of the matrix 1 (M1) and hemagglutinin of wild-type (HA-WT) or hemagglutinin of whose transmembrane domain replaced by that from H3N2 subtype (HA-TM). H7 VLPs-WT and H7 VLPs-TM could assemble and release into the supernatant of Sf9 cells and they had similar morphological characteristics. However, compared to H7 VLPs-WT, H7 VLPs-TM had more trimeric HA proteins and could better resist thermal changes. In mice H7 VLPs-TM induced higher titers of HI, IgG, IgG2a and IFN-γ, and provided better protection against homologous and heterologous H7N9 viruses (no matter belonging to Yangtze River Delta or Pearl River Delta) challenge with less weight loss and higher survival rate. In summary, H7 VLPs-TM represents a potential strategy for the development of H7N9 vaccines.

Development of an Influenza Rapid Diagnostic Kit Specific for the H7 Subtype

Since the spring of 2013, human infections with H7N9 viruses have been detected in China. Some of these viruses have become highly pathogenic. Highly and low pathogenic avian influenza H7N9 viruses are currently co-circulating with the seasonal influenza A viruses H3N2 and H1N1pdm09. Prompt identification and isolation of H7N9 patients is one measure to prevent the spread of H7N9 virus and help prevent a pandemic. The majority of commercially available point-of-care rapid influenza diagnostic kits can differentiate between influenza A and B viruses, but cannot distinguish between H7N9 viruses and seasonal influenza A viruses. Accordingly, we have developed a rapid diagnostic kit specific for the H7 subtype that is accessible, easy to use. Although the detection limit of this H7 kit is one-tenth lower than that of a commercially available rapid influenza A and B diagnostic kit of similar design, except for the specificity of the monoclonal antibodies used, this kit is highly specific, detecting only H7-subtype influenza viruses, including the recent highly pathogenic H7N9 viruses from humans, and does not show any non-specific reactions with other HA subtypes. This H7 kit will be of value for the early detection of H7N9-infected patients.

Westward Spread of Highly Pathogenic Avian Influenza A(H7N9) Virus among Humans, China

We report infection of humans with highly pathogenic avian influenza A(H7N9) virus in Shaanxi, China, in May 2017. We obtained complete genomes for samples from 5 patients and from live poultry markets or farms in 4 cities. Results indicate that H7N9 is spreading westward from southern and eastern China.

New Threats from H7N9 Influenza Virus: Spread and Evolution of High- and Low-Pathogenicity Variants with High Genomic Diversity in Wave Five

H7N9 virus has caused five infection waves since it emerged in 2013. The highest number of human cases was seen in wave 5; however, the underlying reasons have not been thoroughly elucidated. In this study, the geographical distribution, phylogeny, and genetic evolution of 240 H7N9 viruses in wave 5, including 35 new isolates from patients and poultry in nine provinces, were comprehensively analyzed together with strains from first four waves. Geographical distribution analysis indicated that the newly emerging highly pathogenic (HP) and low-pathogenicity (LP) H7N9 viruses were cocirculating, causing human and poultry infections across China. Genetic analysis indicated that dynamic reassortment of the internal genes among LP-H7N9/H9N2/H6Ny and HP-H7N9, as well as of the surface genes, between the Yangtze and Pearl River Delta lineages resulted in at least 36 genotypes, with three major genotypes (G1 [A/chicken/Jiangsu/SC537/2013-like], G3 [A/Chicken/Zhongshan/ZS/2017-like], and G11 [A/Anhui/40094/2015-like]). The HP-H7N9 genotype likely evolved from G1 LP-H7N9 by the insertion of a KRTA motif at the cleavage site (CS) and then evolved into 15 genotypes with four different CS motifs, including PKGKRTAR/G, PKGKRIAR/G, PKRKRAAR/G, and PKRKRTAR/G. Approximately 46% (28/61) of HP strains belonged to G3. Importantly, neuraminidase (NA) inhibitor (NAI) resistance (R292K in NA) and mammalian adaptation (e.g., E627K and A588V in PB2) mutations were found in a few non-human-derived HP-H7N9 strains. In summary, the enhanced prevalence and diverse genetic characteristics that occurred with mammalian-adapted and NAI-resistant mutations may have contributed to increased numbers of human infections in wave 5.IMPORTANCE The highest numbers of human H7N9 infections were observed during wave 5 from October 2016 to September 2017. Our results showed that HP-H7N9 and LP-H7N9 had spread virtually throughout China and underwent dynamic reassortment with different subtypes (H7N9/H9N2 and H6Ny) and lineages (Yangtze and Pearl River Delta lineages), resulting in totals of 36 and 3 major genotypes, respectively. Notably, the NAI drug-resistant (R292K in NA) and mammalian-adapted (e.g., E627K in PB2) mutations were found in HP-H7N9 not only from human isolates but also from poultry and environmental isolates, indicating increased risks for human infections. The broad dissemination of LP- and HP-H7N9 with high levels of genetic diversity and host adaptation and drug-resistant mutations likely accounted for the sharp increases in the number of human infections during wave 5. Therefore, more strategies are needed against the further spread and damage of H7N9 in the world.

The fifth influenza A(H7N9) epidemic: A family cluster of infection in Suzhou city of China, 2016

OBJECTIVE

Influenza A(H7N9) virus is known for its high pathogenicity in human. A family cluster of influenza A(H7N9) virus infection was identified in Suzhou, China. This study aimed to investigate the possibility of human-to-human transmission of the virus and examine the virologic features of this family cluster.

METHODS

The clinical and epidemiologic data of two patients in the family cluster of influenza A(H7N9) virus infection were collected. Viral RNA in samples derived from the two patients, their close contacts, and the environments with likely influenza A(H7N9) virus transmission were tested by real-time reverse transcriptase polymerase chain reaction (rRT-PCR) assay. Hemagglutination inhibition (HI) assay was used to detect virus-specific antibodies. Genetic sequencing and phylogenetic analysis were also performed.

RESULTS

The index patient (Case 1), a 66-year old man, was virologically diagnosed with influenza A(H7N9) virus infection 12days after experiencing influenza-like symptoms, then died of multi-organ failure. His 39-year old daughter (Case 2), denying any other exposure to influenza A(H7N9) virus, became infected with influenza A(H7N9) virus following taking care of her father during his illness. Sequencing viral genomes isolated from the two patients showed nearly identical nucleotide sequence, and genetically resembled the viral genome isolated from a chicken in the wet market where the index patient once visited. All three influenza A(H7N9) viruses shared S138A, G186V, Q226L mutations in HA (H3) protein and a single basic amino acid (PEIPKGR↓G) at the cleavage site.

CONCLUSIONS

Human-to-human transmission of influenza A(H7N9) virus most likely occurred in this household. The three-amino-acid mutations in HA protein were discovered in this study, which might have increased the binding affinity of influenza A(H7N9) virus to the receptor on trachea epithelial cells to facilitate viral transmission among humans.

Avian-to-Human Receptor-Binding Adaptation by Influenza A Virus Hemagglutinin H4

Low-pathogenicity avian influenza viruses (LPAIVs) have caused a global concern to public health since the first novel LPAIV H7N9 outbreak occurred. The receptor-binding properties of the viral hemagglutinin are one key factor for efficient transmission and infection in humans. Recent evidence shows that H4 subtype viruses have been widely circulating in domestic poultry and human asymptomatic infections might have occurred. Here, we evaluated the receptor-binding properties of two representative isolates, avian H4N6 (containing Q226 and G228) and swine H4N6 (containing L226 and S228), and found that the avian isolate preferentially binds to avian receptors, whereas the swine isolate preferentially binds to human receptors. The Q226L and G228S substitutions are pivotal for the receptor-binding switch, which resulted in similar human receptor-binding features to the pandemic H2 and H3, implying that H4 has the potential to cause human infections. This early-warning study calls for future extensive surveillance.

Sudden emergence of human infections with H7N9 avian influenza A virus in Hubei province, central China

There have been five waves of H7N9 avian influenza virus (AIV) infection in humans since its initial emergence in China in 2013, posing a significant threat to public health. Hubei province was free local transmission during the first four waves of H7N9 AIV. However, multiple cases of human H7N9 infection were reported in Hubei during January 2017. To understand the molecular epidemiology that underlies this sudden emergence, we collected samples from 14 human cases of H7N9 influenza virus from Hubei province, along with environmental samples from different locations in Hubei. Our analysis revealed that the newly emerged human H7N9 viruses were all from persons exposed to poultry and shared the same origin as the environmental sampled viruses in the Yangtze River lineage of H7N9. Notably, we also documented an earlier and distinct importation from Jiangsu province that may have established a local environmental reservoir. Our study highlights the need for continued surveillance of H7N9 in both human and avian populations in central China.

Emergence and Adaptation of a Novel Highly Pathogenic H7N9 Influenza Virus in Birds and Humans from a 2013 Human-Infecting Low-Pathogenic Ancestor

Since its emergence in 2013, the H7N9 low-pathogenic avian influenza virus (LPAIV) has been circulating in domestic poultry in China, causing five waves of human infections. A novel H7N9 highly pathogenic avian influenza virus (HPAIV) variant possessing multiple basic amino acids at the cleavage site of the hemagglutinin (HA) protein was first reported in two cases of human infection in January 2017. More seriously, those novel H7N9 HPAIV variants have been transmitted and caused outbreaks on poultry farms in eight provinces in China. Herein, we demonstrate the presence of three different amino acid motifs at the cleavage sites of these HPAIV variants which were isolated from chickens and humans and likely evolved from the preexisting LPAIVs. Animal experiments showed that these novel H7N9 HPAIV variants are both highly pathogenic in chickens and lethal to mice. Notably, human-origin viruses were more pathogenic in mice than avian viruses, and the mutations in the PB2 gene associated with adaptation to mammals (E627K, A588V, and D701N) were identified by next-generation sequencing (NGS) and Sanger sequencing of the isolates from infected mice. No polymorphisms in the key amino acid substitutions of PB2 and HA in isolates from infected chicken lungs were detected by NGS. In sum, these results highlight the high degree of pathogenicity and the valid transmissibility of this new H7N9 variant in chickens and the quick adaptation of this new H7N9 variant to mammals, so the risk should be evaluated and more attention should be paid to this variant.IMPORTANCE Due to the recent increased numbers of zoonotic infections in poultry and persistent human infections in China, influenza A(H7N9) virus has remained a public health threat. Most of the influenza A(H7N9) viruses reported previously have been of low pathogenicity. Now, these novel H7N9 HPAIV variants have caused human infections in three provinces and outbreaks on poultry farms in eight provinces in China. We analyzed the molecular features and compared the relative characteristics of one H7N9 LPAIV and two H7N9 HPAIVs isolated from chickens and two human-origin H7N9 HPAIVs in chicken and mouse models. We found that all HPAIVs both are highly pathogenic and have valid transmissibility in chickens. Strikingly, the human-origin viruses were more highly pathogenic than the avian-origin viruses in mice, and dynamic mutations were confirmed by NGS and Sanger sequencing. Our findings offer important insight into the origin, adaptation, pathogenicity, and transmissibility of these viruses to both poultry and mammals.

Potential Pandemic of H7N9 Avian Influenza A Virus in Human

Since 2013, the H7N9 avian influenza A virus (AIV) has caused human infections and to the extent of now surpassing H5N1. This raises an alarm about the potential of H7N9 to become a pandemic problem. Our compilation of the amino acid changes required for AIVs to cross the species-barrier discovers 58 that have very high proportions in both the human- and avian-isolated H7N9 viruses. These changes correspond with sporadic human infections that continue to occur in regions of avian infections. Among the six internal viral genes, amino acid changes do not differ significantly between H9N2 and H7N9, except for V100A in PA, and K526R, D627K, and D701N in PB2. H9N2 AIVs provide internal genes to H7N9. Most of the amino acid changes in H7N9 appear to come directly from H9N2. Seventeen amino acid substitutions appear to have fixed quickly by the 5th wave. Among these, six amino acid sites in HA1 are receptor binding sites, and PB2-A588V was shown to promote the adaptation of AIVs to mammals. The accelerated fixation of mutations may promote the adaptation of H7N9 to human, but need further functional evidence. Although H7N9 AIVs still cannot efficiently transmit between humans, they have the genetic makeup associated with human infections. These viruses must be controlled in poultry to remove the threat of it becoming a human pandemic event.

Epidemiology of human infections with highly pathogenic avian influenza A(H7N9) virus in Guangdong, 2016 to 2017

We describe the epidemiology of highly pathogenic avian influenza (HPAI) A(H7N9) based on poultry market environmental surveillance and laboratory-confirmed human cases (n = 9) in Guangdong, China. We also compare the epidemiology between human cases of high- and low-pathogenic avian influenza A(H7N9) (n = 51) in Guangdong. Case fatality and severity were similar. Touching sick or dead poultry was the most important risk factor for HPAI A(H7N9) infections and should be highlighted for the control of future influenza A(H7N9) epidemics.

Human protective monoclonal antibodies against the HA stem of group 2 HAs derived from an H3N2 virus-infected human

OBJECTIVES

Broadly reactive human monoclonal antibodies against the HA stem of influenza A virus are being developed as therapeutic agents as well as to understand the epitopes that are essential for a universal influenza virus vaccine.

METHODS

We isolated and characterized two hetero-reactive human monoclonal antibodies from an H3N2 virus-infected human.

RESULTS

These antibodies, which are predominantly bound to the HA stem of group 2 HAs, used IGHV3-66 and IGHV4-38-2 germline genes, respectively. They possessed in vitro neutralizing ability, and in vivo protective efficacy against lethal infection with H3N2 or H7N9 virus. Escape mutations revealed that one of the protective antibodies recognized the α-helix A of HA2, and the other recognized the C-terminal portion of the fusion peptide and the β-sheet that precedes the α-helix A of HA2.

CONCLUSIONS

Of many human protective monoclonal antibodies against the HA stem, two human protective monoclonal antibodies were isolated in this study that predominantly recognize epitopes on the HA stem of group 2 and use unique IGHV3-66 and IGHV4-38-2 germline genes.