Pandemic potential of avian influenza A (H7N9) viruses

3,4,5-tri-O-caffeoylquinic acid attenuates influenza A virus induced inflammation through Toll-like receptor 3/7 activated signaling pathway

BACKGROUND

3,4,5-tri-O-caffeoylquinic acid (3,4,5-TCQA), a natural polyphenolic acid, has been shown to be effective against influenza A virus (IAV) infection. Although it was found to inhibit the neuraminidase of IAV, it may also perturb other cellular functions, as polyphenolic acids have shown antioxidant, anti-inflammatory and other activities.

PURPOSE

This study aimed to investigate the effect of 3,4,5-TCQA at a cell level, which is critical for protecting host cell from IAV infection.

STUDY DESIGN AND METHODS

We explored the effect of 3,4,5-TCQA on H292 cells infected or un-infected with Pr8 IAV. The major genes and related pathway were identified through RNA sequencing. The pathway was confirmed by qRT-PCR and western blot analysis. The anti-inflammatory activity was evaluated using nitric oxide measurement assay.

RESULTS

We showed that 3,4,5-TCQA downregulated the immune response in H292 cells, and reduced the cytokine production in Pr8-infected cells, through Toll-like receptor (TLR) signaling pathway. In addition, 3,4,5-TCQA showed anti-inflammatory activity in LPS-activated RAW264.7 cells.

CONCLUSION

Collectively, our results indicated that 3,4,5-TCQA suppressed inflammation caused by IAV infection through TLR3/7 signaling pathway. This provides a new insight into the antiviral mechanism of 3,4,5-TCQA.

Nanomaterials-based immunosensors for avian influenza virus detection

Avian influenza viruses (AIV) are capable of infecting a considerable proportion of the world's population each year, leading to severe epidemics with high rates of morbidity and mortality. The methods now used to diagnose influenza virus A include the Western blot test (WB), hemagglutination inhibition (HI), and enzyme-linked immunosorbent assays (ELISAs). But because of their labor-intensiveness, lengthy procedures, need for costly equipment, and inexperienced staff, these approaches are considered inappropriate. The present review elucidates the recent advancements in the field of avian influenza detection through the utilization of nanomaterials-based immunosensors between 2014 and 2024. The classification of detection techniques has been taken into account to provide a comprehensive overview of the literature. The review encompasses a detailed illustration of the commonly employed detection mechanisms in immunosensors, namely, colorimetry, fluorescence assay, surface plasmon resonance (SPR), surface-enhanced Raman spectroscopy (SERS), electrochemical detection, quartz crystal microbalance (QCM) piezoelectric, and field-effect transistor (FET). Furthermore, the challenges and future prospects for the immunosensors have been deliberated upon. The present review aims to enhance the understanding of immunosensors-based sensing platforms for virus detection and to stimulate the development of novel immunosensors by providing novel ideas and inspirations. Therefore, the aim of this paper is to provide an updated information about biosensors, as a recent detection technique of influenza with its details regarding the various types of biosensors, which can be used for this review.

Virus versus host: influenza A virus circumvents the immune responses

Influenza A virus (IAV) is a highly contagious pathogen causing dreadful losses to humans and animals around the globe. As is known, immune escape is a strategy that benefits the proliferation of IAVs by antagonizing, blocking, and suppressing immune surveillance. The HA protein binds to the sialic acid (SA) receptor to enter the cytoplasm and initiate viral infection. The conserved components of the viral genome produced during replication, known as the pathogen-associated molecular patterns (PAMPs), are thought to be critical factors for the activation of effective innate immunity by triggering dependent signaling pathways after recognition by pattern recognition receptors (PRRs), followed by a cascade of adaptive immunity. Viral infection-induced immune responses establish an antiviral state in the host to effectively inhibit virus replication and enhance viral clearance. However, IAV has evolved multiple mechanisms that allow it to synthesize and transport viral components by "playing games" with the host. At its heart, this review will describe how host and viral factors interact to facilitate the viral evasion of host immune responses.

Targeted genomic sequencing of avian influenza viruses in wetland sediment from wild bird habitats

Diverse influenza A viruses (IAVs) circulate in wild birds, including highly pathogenic strains that infect poultry and humans. Consequently, surveillance of IAVs in wild birds is a cornerstone of agricultural biosecurity and pandemic preparedness. Surveillance is traditionally done by testing wild birds directly, but obtaining these specimens is labor intensive, detection rates can be low, and sampling is often biased toward certain avian species. As a result, local incursions of dangerous IAVs are rarely detected before outbreaks begin. Testing environmental specimens from wild bird habitats has been proposed as an alternative surveillance strategy. These specimens are thought to contain diverse IAVs deposited by a broad range of avian hosts, including species that are not typically sampled by surveillance programs. To enable this surveillance strategy, we developed a targeted genomic sequencing method for characterizing IAVs in these challenging environmental specimens. It combines custom hybridization probes, unique molecular index-based library construction, and purpose-built bioinformatic tools, allowing IAV genomic material to be enriched and analyzed with single-fragment resolution. We demonstrated our method on 90 sediment specimens from wetlands around Vancouver, Canada. We recovered 2,312 IAV genome fragments originating from all eight IAV genome segments. Eleven hemagglutinin subtypes and nine neuraminidase subtypes were detected, including H5, the current global surveillance priority. Our results demonstrate that targeted genomic sequencing of environmental specimens from wild bird habitats could become a valuable complement to avian influenza surveillance programs.IMPORTANCEIn this study, we developed genome sequencing tools for characterizing avian influenza viruses in sediment from wild bird habitats. These tools enable an environment-based approach to avian influenza surveillance. This could improve early detection of dangerous strains in local wild birds, allowing poultry producers to better protect their flocks and prevent human exposures to potential pandemic threats. Furthermore, we purposefully developed these methods to contend with viral genomic material that is diluted, fragmented, incomplete, and derived from multiple strains and hosts. These challenges are common to many environmental specimens, making these methods broadly applicable for genomic pathogen surveillance in diverse contexts.

Mutations in HA and PA affect the transmissibility of H7N9 avian influenza virus in chickens

Low pathogenic (LP) H7N9 avian influenza virus (AIV) emerged in 2013 and had spread widely over several months in China, experienced a noteworthy reduction in isolation rate in poultry and human since 2017. Here, we examined the transmission of H7N9 viruses to better understand viral spread and dissemination mechanisms. Three out of four viruses (2013-2016) could transmit in chickens through direct contact, and airborne transmission was confirmed in the JT157 (2016) virus. However, we did not detect the transmission of the two 2017 viruses, WF69 and AH395, through either direct or airborne exposure. Molecular analysis of genome sequence of two viruses identified eleven mutations located in viral proteins (except for matrix protein), such as PA (K362R and S364N) and HA (D167N, H7 numbering), etc. We explored the genetic determinants that contributed to the difference in transmissibility of the viruses in chickens by generating a series of reassortants in the JT157 background. We found that the replacement of HA gene in JT157 by that of WF69 abrogated the airborne transmission in recipient chickens, whereas the combination of HA and PA replacement led to the loss of airborne and direct contact transmission. Failure with contact transmission of the viruses has been associated with the emergence of the mutations D167N in HA and K362R and S364N in PA. Furthermore, the HA D167N mutation significantly reduced viral attachment to chicken lung and trachea tissues, while mutations K362R and S364N in PA reduced the nuclear transport efficiency and the PA protein expression levels in both cytoplasm and nucleus of CEF cells. The D167N substitution in HA reduced the H7N9 viral acid stability and avian-like receptor binding, while enhanced human-like receptor binding. Further analysis revealed these mutants grew poorly in vitro and in vivo. To conclude, H7N9 AIVs that contain mutations in the HA and PA protein reduced the viral transmissibility in chicken, and may pose a reduced threat for poultry but remain a heightened public health risk.

Fusion-inhibition peptide broadly inhibits influenza virus and SARS-CoV-2, including Delta and Omicron variants

Pandemic influenza virus and SARS-CoV-2 vaiants have posed major global threats to public health. Broad-spectrum antivirals blocking viral entry can be an effective strategy for combating these viruses. Here, we demonstrate a frog-defensin-derived basic peptide (FBP), which broadly inhibits the influenza virus by binding to haemagglutinin so as to block low pH-induced HA-mediated fusion and antagonizes endosomal acidification to inhibit the influenza virus. Moreover, FBP can bind to the SARS-CoV-2 spike to block spike-mediated cell–cell fusion in 293T/ACE2 cells endocytosis. Omicron spike shows a weak cell–cell fusion mediated by TMPRSS2 in Calu3 cells, making the Omicron variant sensitive to endosomal inhibitors. In vivo studies show that FBP broadly inhibits the A(H1N1)pdm09 virus in mice and SARS-CoV-2 (HKU001a and Delta)in hamsters. Notably, FBP shows significant inhibition of Omicron variant replication even though it has a high number of mutations in spike. In conclusion, these results suggest that virus-targeting FBP with a high barrier to drug resistance can be an effective entry-fusion inhibitor against influenza virus and SARS-CoV-2 in vivo.

ProbeTools: designing hybridization probes for targeted genomic sequencing of diverse and hypervariable viral taxa

Background

Sequencing viruses in many specimens is hindered by excessive background material from hosts, microbiota, and environmental organisms. Consequently, enrichment of target genomic material is necessary for practical high-throughput viral genome sequencing. Hybridization probes are widely used for enrichment in many fields, but their application to viral sequencing faces a major obstacle: it is difficult to design panels of probe oligo sequences that broadly target many viral taxa due to their rapid evolution, extensive diversity, and genetic hypervariability. To address this challenge, we created ProbeTools, a package of bioinformatic tools for generating effective viral capture panels, and for assessing coverage of target sequences by probe panel designs in silico. In this study, we validated ProbeTools by designing a panel of 3600 probes for subtyping the hypervariable haemagglutinin (HA) and neuraminidase (NA) genome segments of avian-origin influenza A viruses (AIVs). Using in silico assessment of AIV reference sequences and in vitro capture on egg-cultured viral isolates, we demonstrated effective performance by our custom AIV panel and ProbeTools’ suitability for challenging viral probe design applications.

Results

Based on ProbeTool’s in silico analysis, our panel provided broadly inclusive coverage of 14,772 HA and 11,967 NA reference sequences. For each reference sequence, we calculated the percentage of nucleotide positions covered by our panel in silico; 90% of HA and NA references sequences had at least 90.8 and 95.1% of their nucleotide positions covered respectively. We also observed effective in vitro capture on a representative collection of 23 egg-cultured AIVs that included isolates from wild birds, poultry, and humans and representatives from all HA and NA subtypes. Forty-two of forty-six HA and NA segments had over 98.3% of their nucleotide positions significantly enriched by our custom panel. These in vitro results were further used to validate ProbeTools’ in silico coverage assessment algorithm; 89.2% of in silico predictions were concordant with in vitro results.

Conclusions

ProbeTools generated an effective panel for subtyping AIVs that can be deployed for genomic surveillance, outbreak prevention, and pandemic preparedness. Effective probe design against hypervariable AIV targets also validated ProbeTools’ design and coverage assessment algorithms, demonstrating their suitability for other challenging viral capture applications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08790-4.

Improved method for avian influenza virus isolation from environmental water samples

Environmental water-targeted surveillance of migratory aquatic birds at overwintering sites is potentially one of the most effective approaches for understanding the ecology of avian influenza viruses (AIVs). In this study, we improved the method for AIV isolation from environmental water samples by making a minor modification to our previously reported process. We experimentally demonstrated that the AIV recovery efficiency of the modified method was 10-100-fold higher than that of the original method. This improved isolation method allowed us to isolate a considerably larger number of AIV isolates from environmental water samples collected at an overwintering site for tens of thousands of migratory aquatic birds in Japan during the 2018/19 winter season compared with those during previous winter seasons. Genetic and phylogenetic analyses revealed that AIVs of the same subtypes with multiple genetic constellations were circulating in a single overwintering site during a single winter season. These findings indicate that our improved isolation method contributes to enhance environmental water-targeted surveillance and to a better understanding of AIV ecology in migratory aquatic bird populations by monitoring ongoing AIV circulation. This article is protected by copyright. All rights reserved.

Adaptation of the H7N2 Feline Influenza Virus to Human Respiratory Cell Culture

During 2016–2017, the H7N2 feline influenza virus infected more than 500 cats in animal shelters in New York, USA. A veterinarian who had treated the cats became infected with this feline virus and showed mild respiratory symptoms. This suggests that the H7N2 feline influenza virus may evolve into a novel pandemic virus with a high pathogenicity and transmissibility as a result of mutations in humans. In this study, to gain insight into the molecular basis of the transmission of the feline virus to humans, we selected mutant viruses with enhanced growth in human respiratory A549 cells via successive passages of the virus and found almost all mutations to be in the envelope glycoproteins, such as hemagglutinin (HA) and neuraminidase (NA). The reverse genetics approach revealed that the HA mutations, HA1-H16Q, HA2-I47T, or HA2-Y119H, in the stalk region can lead to a high growth of mutant viruses in A549 cells, possibly by changing the pH threshold for membrane fusion. Furthermore, NA mutation, I28S/L, or three-amino-acid deletion in the transmembrane region can enhance viral growth in A549 cells, possibly by changing the HA–NA functional balance. These findings suggest that the H7N2 feline influenza virus has the potential to become a human pathogen by adapting to human respiratory cells, owing to the synergistic biological effect of the mutations in its envelope glycoproteins.

Coinfection of Chickens with H9N2 and H7N9 Avian Influenza Viruses Leads to Emergence of Reassortant H9N9 Virus with Increased Fitness for Poultry and a Zoonotic Potential

An H7N9 low-pathogenicity avian influenza virus (LPAIV) emerged in 2013 through genetic reassortment between H9N2 and other LPAIVs circulating in birds in China. This virus causes inapparent clinical disease in chickens, but zoonotic transmission results in severe and fatal disease in humans. To examine a natural reassortment scenario between H7N9 and G1 lineage H9N2 viruses predominant in the Indian subcontinent, we performed an experimental coinfection of chickens with A/Anhui/1/2013/H7N9 (Anhui/13) virus and A/Chicken/Pakistan/UDL-01/2008/H9N2 (UDL/08) virus. Plaque purification and genotyping of the reassortant viruses shed via the oropharynx of contact chickens showed H9N2 and H9N9 as predominant subtypes. The reassortant viruses shed by contact chickens also showed selective enrichment of polymerase genes from H9N2 virus. The viable "6+2" reassortant H9N9 (having nucleoprotein [NP] and neuraminidase [NA] from H7N9 and the remaining genes from H9N2) was successfully shed from the oropharynx of contact chickens, plus it showed an increased replication rate in human A549 cells and a significantly higher receptor binding to α2,6 and α2,3 sialoglycans compared to H9N2. The reassortant H9N9 virus also had a lower fusion pH, replicated in directly infected ferrets at similar levels compared to H7N9 and transmitted via direct contact. Ferrets exposed to H9N9 via aerosol contact were also found to be seropositive, compared to H7N9 aerosol contact ferrets. To the best of our knowledge, this is the first study demonstrating that cocirculation of H7N9 and G1 lineage H9N2 viruses could represent a threat for the generation of novel reassortant H9N9 viruses with greater virulence in poultry and a zoonotic potential. IMPORTANCE We evaluated the consequences of reassortment between the H7N9 and the contemporary H9N2 viruses of the G1 lineage that are enzootic in poultry across the Indian subcontinent and the Middle East. Coinfection of chickens with these viruses resulted in the emergence of novel reassortant H9N9 viruses with genes derived from both H9N2 and H7N9 viruses. The "6+2" reassortant H9N9 (having NP and NA from H7N9) virus was shed from contact chickens in a significantly higher proportion compared to most of the reassortant viruses, showed significantly increased replication fitness in human A549 cells, receptor binding toward human (α2,6) and avian (α2,3) sialic acid receptor analogues, and the potential to transmit via contact among ferrets. This study demonstrated the ability of viruses that already exist in nature to exchange genetic material, highlighting the potential emergence of viruses from these subtypes with zoonotic potential.

Designing a multi-epitope vaccine to provoke the robust immune response against influenza A H7N9

A new strain of Influenza A Virus (IAV), so-called "H7N9 Avian Influenza", is the first strain of this virus in which a human is infected by transmitting the N9 of influenza virus. Although continuous human-to-human transmission has not been reported, the occurrence of various H7N9-associated epidemics and the lack of production of strong antibodies against H7N9 in humans warn of the potential for H7N9 to become a new pandemic. Therefore, the need for effective vaccination against H7N9 as a life-threatening viral pathogen has become a major concern. The current study reports the design of a multi-epitope vaccine against Hemagglutinin (HA) and Neuraminidase (NA) proteins of H7N9 Influenza A virus by prediction of Cytotoxic T lymphocyte (CTL), Helper T lymphocyte (HTL), IFN-γ and B-cell epitopes. Human β-defensin-3 (HβD-3) and pan HLA DR-binding epitope (PADRE) sequence were considered as adjuvant. EAAAK, AAY, GPGPG, HEYGAEALERAG, KK and RVRR linkers were used as a connector for epitopes. The final construct contained 777 amino acids that are expected to be a recombinant protein of about ~ 86.38 kDa with antigenic and non-allergenic properties after expression. Modeled protein analysis based on the tertiary structure validation, docking studies, and molecular dynamics simulations results like Root-mean-square deviation (RMSD), Gyration, Root-mean-square fluctuation (RMSF) and Molecular Mechanics Poisson-Boltzmann Surface Area (MM/PBSA) showed that this protein has a stable construct and capable of being in interaction with Toll-like receptor 7 (TLR7), TLR8 and m826 antibody. Analysis of the obtained data the demonstrates that suggested vaccine has the potential to induce the immune response by stimulating T and Bcells, and may be utilizable for prevention purposes against Avian Influenza A (H7N9).

Identification and molecular characterization of H9N2 viruses carrying multiple mammalian adaptation markers in resident birds in central-western wetlands in India

We report here a targeted risk-based study to investigate the presence of influenza A viruses at the migratory-wild-domestic bird interface across the major wetlands of central India's Maharashtra state during the winter migration season. The H9N2 viruses have been isolated and confirmed in 3.86% (33/854) of the fecal samples of resident birds. To investigate the genetic pools of H9N2 circulating in resident birds, we sequenced two isolates of H9N2 from distant wetlands. Sequence and phylogenetic analyses have shown that these viruses are triple reassortants, with HA, NA, NP, and M genes belonging to G1 sub-lineage (A/quail/Hong Kong/G1/1997), PB2, PB1, and NS genes originating from the prototype Eurasian lineage (A/mallard/France/090360/2009) and PA gene deriving from Y439/Korean-like (A/duck/Hong Kong/Y439/97) sub-lineage. It was confirmed not only that four of their gene segments had a high genetic association with the zoonotic H9N2 virus, A/Human/India/TCM2581/2019, but also that they had many molecular markers associated with mammalian adaptation and enhanced virulence in mammals including the unique multiple basic amino acids, KSKR↓GLF at the HA cleavage site, and analog N-and O-glycosylation patterns on HA with that of the zoonotic H9N2 virus. Furthermore, future experiments would be to characterize these isolates biologically to address the public health concern. Importantly, due to the identification of these viruses at a strategic geographical location in India (a major stop-over point in the Central Asian flyway), these novel viruses also pose a possible threat to be exported to other regions via migratory/resident birds. Consequently, systematic investigation and active monitoring are a prerequisite for identifying and preventing the spread of viruses of zoonotic potential by enforcing strict biosecurity measures.

Antiviral effect of fufang yinhua jiedu (FFYH) granules against influenza A virus through regulating the inflammatory responses by TLR7/MyD88 signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Fufang-Yinhua-Jiedu Granules (FFYH) optimized from a Yin-Qiao-San, as traditional Chinese medicine (TCM), was used to treat influenza and upper respiratory tract infection and was recommended for the prevention and treatment of SARS in 2003 and current COVID-19 in Anhui Province in 2020.

AIM OF STUDY

In the clinical studies, FFYH was very effective for the treatment of influenza, but the mechanism of action against influenza A virus remains unclear. In the present study, we investigated the antiviral effect of FFYH against influenza A virus in vitro and vivo. Moreover, the potential mechanism of FFYH against influenza A virus in vivo was investigated for the first time.

MATERIALS AND METHODS

CPE inhibition assay and HA assay were used to evaluate the in vitro antiviral effects of FFYH against influenza A virus H1N1, H3N2, H5N1, H7N9 and H9N2. Mice were used to evaluate the antiviral effect of FFYH in vivo with ribavirin and lianhuaqingwen as positive controls. RT-PCR was used to quantify the mRNA transcription of TNF-α, IL-6, IFN-γ, IP10, and IL-1β mRNA. ELISA was used to examine the expression of inflammatory factors such as TNF-α, IL-6, IFN-γ, IP10, and IL-1β in sera. The blood parameters were analyzed with auto hematology analyzer. Moreover, the potential mechanism of FFYH against influenza A virus in vivo was also investigated.

RESULTS

FFYH showed a broad-spectrum of antiviral activity against H1N1, H3N2, H5N1, H7N9, and H9N2 influenza A viruses. Furthermore, FFYH dose-dependently increased the survival rate, significantly prolonged the median survival time of mice, and markedly reduced lung injury caused by influenza A virus. Also, FFYH significantly improve the sick signs, food taken, weight loss, blood parameters, lung index, and lung pathological changes. Moreover, FFYH could markedly inhibit the inflammatory cytokine expression of TNF-α, IL-6, IFN-γ, IP10, IL-10, and IL-1β mRNA or protein via inhibition of the TLR7/MyD88/NF-κB signaling pathway in vivo.

CONCLUSION

FFYH not only showed a broad-spectrum of anti-influenza virus activity in vitro, but also exhibited a significant protective effect against lethal influenza virus infection in vivo. Furthermore, our results indicated that the in vivo antiviral effect of FFYH against influenza virus may be attributed to suppressing the expression of inflammatory cytokines via regulating the TLR7/MyD88/NF-κB signaling pathway. These findings provide evidence for the clinical treatment of influenza A virus infection with FFYH.

Avian Influenza H7N9 Virus Adaptation to Human Hosts

Avian influenza virus A (H7N9), after circulating in avian hosts for decades, was identified as a human pathogen in 2013. Herein, amino acid substitutions possibly essential for human adaptation were identified by comparing the 4706 aligned overlapping nonamer position sequences (1–9, 2–10, etc.) of the reported 2014 and 2017 avian and human H7N9 datasets. The initial set of virus sequences (as of year 2014) exhibited a total of 109 avian-to-human (A2H) signature amino acid substitutions. Each represented the most prevalent substitution at a given avian virus nonamer position that was selectively adapted as the corresponding index (most prevalent sequence) of the human viruses. The majority of these avian substitutions were long-standing in the evolution of H7N9, and only 17 were first detected in 2013 as possibly essential for the initial human adaptation. Strikingly, continued evolution of the avian H7N9 virus has resulted in avian and human protein sequences that are almost identical. This rapid and continued adaptation of the avian H7N9 virus to the human host, with near identity of the avian and human viruses, is associated with increased human infection and a predicted greater risk of human-to-human transmission.

Identification of H7N9 hemagglutinin novel protein epitopes that elicit strong antibody-dependent, cell-mediated cytotoxic activities with protection from influenza infection in mouse model

BACKGROUND

Antibody-dependent cell-mediated cytotoxicity (ADCC) is one of the mechanisms connecting humoral immunity and cellular immunity and has been well-demonstrated in recent studies. Neutralizing antibodies and antibodies can mediate ADCC effects and both build a strong defense against H7N9 influenza virus infection. In our previous study, we found that H7N9 patients' plasma displayed low neutralizing activities that were not sufficient for host protection; however, the plasma of some patients can mediate strong ADCC effects.

METHODS

Based on the plasma samples of H7N9 infected patients collected, we measured the ADCC activities of these samples and selected the best to locate the dominant epitopes on H7N9 hemagglutinin (HA) protein that can elicit antibodies and strong ADCC activities. We constructed a yeast surface-display H7N9 HA protein epitope library and screened this library against plasma samples with different potencies in mediating ADCC effects.

RESULTS

Two dominant epitopes were selected from the screening. Plasma samples with depleted antibodies that were specific to the epitopes showed reduced ADCC activities. The serum of mice immunized with the epitopes elicited strong ADCC activities. Three monoclonal antibodies were isolated which showed high ADCC effects in vitro. Vaccination with isolated ADCC activating epitopes can provide partial protection from influenza infection in mouse model. And mice with vaccinated with combination of epitopes and extracellular domain can provide full protection from influenza infection in the same mouse model.

CONCLUSIONS

In this study, the epitopes isolated on H7N9 HA were immunogenic and elicited antibodies and strong ADCC activities in mice. Although the protective effect of the epitopes is partial, the combination of epitopes and extracellular domain can provide 100% protection from influenza virus infection in the same mouse model. Our study provides information on the potential use of epitope vaccine design against H7N9 viral infection.

Improving immunogenicity of influenza virus H7N9 recombinant hemagglutinin for vaccine development

Human infections of novel avian influenza A virus (H7N9) emerged in early 2013 and caused about 40% case-fatality through 2017. Therefore, development of influenza H7N9 vaccines is critical for pandemic preparedness. Currently, there are three means of production of commercial influenza vaccines: egg-based, mammalian cell-based, and insect cell-based platforms. The insect cell-based platform has the advantage of high speed in producing recombinant protein. In this study, we evaluate the stability and immunogenicity of two different influenza H7 HA expression constructs generated using the baculovirus system, including membrane-based full-length HA (mH7) and secreted ectodomain-based H7 (sH7). The mH7 construct could form an oligomer-rosette structure and had a high hemagglutinin (HA) titer 8192. In contrast to mH7, the sH7 construct could not form an oligomer-rosette structure and did not have HA titer before cross-linking with anti-His antibody. Thermal stability tests showed that the sH7 and mH7 constructs were unstable at 43 °C and 52 °C, respectively. In a mice immunization study, the mH7 construct but not the sH7 construct could induce robust HI and neutralizing antibody titers. In conclusion, further development of the mH7 vaccine candidate is desirable.

Substitutions in the PB2 methionine 283 residue affect H5 subtype avian influenza virus virulence

The influenza A virus (IAV) PB2 subunit modulates viral polymerase activity, replication kinetics and pathogenicity. Here we identified novel PB2 substitutions at position 283 of H5 subtype IAV and evaluated their biological characteristics and virulence. The substitution PB2-M283L enhanced the growth capacity and polymerase activity in human and mammalian cells in comparison to the rWT virus. The substitution PB2-M283L displayed high virulence, resulting in a greater virus load in different tissues, more severe histopathological lesions and proinflammatory cytokines burst in mice. The substitution PB2-M283I had an opposite phenotype. Our data extend the important role of PB2 substitutions in the adaptation of H5 subtype IAVs to mammalian hosts.

Emergence of human avian influenza A(H7N9) virus infections in Wenshan City in Southwest China, 2017

BACKGROUND

The emergence of human infection with avian influenza A(H7N9) virus was reported in Wenshan City, southwestern China in 2017. The study describes the epidemiological and virological features of the outbreak and discusses the origin of the infection.

METHODS

Poultry exposure and timelines of key events for each patient were collected. Samples derived from the patients, their close contacts, and environments were tested for influenza A(H7N9) virus by real-time reverse transcription polymerase chain reaction. Genetic sequencing and phylogenetic analysis were also conducted.

RESULTS

Five patients were reported in the outbreak. An epidemiological investigation showed that all patients had been exposed at live poultry markets. The A(H7N9) isolates from these patients had low pathogenicity in avian species. Both epidemiological investigations of chicken sources and phylogenetic analysis of viral gene sequences indicated that the source of infection was from Guangxi Province, which lies 100 km to the east of Wenshan City.

CONCLUSIONS

In the study, a sudden emergence of human cases of H7N9 was documented in urban area of Wenshan City. Chickens were an important carrier in the H7N9 virus spreading from Guangxi to Wenshan. Hygienic management of live poultry markets and virological screening of chickens transported across regions should be reinforced to limit the spread of H7N9 virus.

Avian influenza viruses in humans: lessons from past outbreaks

BACKGROUND

Human infections with avian influenza viruses (AIV) represent a persistent public health threat. The principal risk factor governing human infection with AIV is from direct contact with infected poultry and is primarily observed in Asia and Egypt where live-bird markets are common.

AREAS OF AGREEMENT

Changing patterns of virus transmission and a lack of obvious disease manifestations in avian species hampers early detection and efficient control of potentially zoonotic AIV.

AREAS OF CONTROVERSY

Despite extensive studies on biological and environmental risk factors, the exact conditions required for cross-species transmission from avian species to humans remain largely unknown.

GROWING POINTS

The development of a universal ('across-subtype') influenza vaccine and effective antiviral therapeutics are a priority.

AREAS TIMELY FOR DEVELOPING RESEARCH

Sustained virus surveillance and collection of ecological and physiological parameters from birds in different environments is required to better understand influenza virus ecology and identify risk factors for human infection.

Molecular Characterization of a Novel Avian Influenza A (H2N9) Strain Isolated from Wild Duck in Korea in 2018

A novel avian influenza virus (A/wild duck/Korea/K102/2018) (H2N9) was isolated from wild birds in South Korea in 2018, and phylogenetic and molecular analyses were conducted on complete gene sequences obtained by next-generation sequencing. Phylogenetic analysis indicated that the hemagglutinin (HA) and neuraminidase (NA) genes of the A/wild duck/Korea/K102/2018 (H2N9) virus belonged to the Eurasian countries, whereas other internal genes (polymerase basic protein 1 (PB1), PB2, nucleoprotein (NP), polymerase acidic protein (PA), matrix protein (M), and non-structural protein (NS)) belonged to the East Asian countries. A monobasic amino acid (PQIEPR/GLF) at the HA cleavage site, E627 in the PB2 gene, and no deletion of the stalk region in the NA gene indicated that the A/wild duck/Korea/K102/2018 (H2N9) isolate was a typical low pathogenicity avian influenza (LPAI). Nucleotide sequence similarity analysis of HA revealed that the highest homology (98.34%) is to that of A/duck/Mongolia/482/2015 (H2N3), and amino acid sequence of NA was closely related to that of A/duck/Bangladesh/8987/2010 (H10N9) (96.45%). In contrast, internal genes showed homology higher than 98% compared to those of other isolates derived from duck and wild birds of China or Japan in 2016–2018. The newly isolated A/wild duck/Korea/K102/2018 (H2N9) strain is the first reported avian influenza virus in Korea, and may have evolved from multiple genotypes in wild birds and ducks in Mongolia, China, and Japan.

Rapid isolation of a potent human antibody against H7N9 influenza virus from an infected patient

Influenza virus A H7N9 remains a serious threat to public health due to the lack of effective vaccines and drugs. In this study, a neutralizing human antibody named 3L11 was rapidly isolated from the switched memory B cells of a patient infected with H7N9. The antibody 3L11 was encoded by the heavy-chain VH1-8 gene and the light-chain VL2-13 gene that had undergone somatic mutations, and conferred high affinity binding to H7N9 hemagglutinins (HAs). It promoted killing of infected cells by antibody-dependent cell-mediated cytotoxicity (ADCC). Epitope mapping by mass spectroscopy (MS) indicated that 3L11 bound to the peptide 149-175 of HAs that contained the 150-loop of the receptor-binding site (RBS). Additionally, the 3L11 escape strains had G151R (Gly¹⁵¹→Arg¹⁵¹) and S152P (Ser¹⁵²→Pro¹⁵²) mutations within a conserved antigenic site A near the RBS that were not observed in field strains. Importantly, 3L11 fully protected mice against a lethal H7N9 virus challenge, in both pre- and postexposure administration regimens. Altogether, this work demonstrates the feasibility of rapid isolation of neutralizing H7N9 antibodies from infected patients and provides a potential prophylactic and therapeutic agent against H7N9 viruses.

Identification of key hemagglutinin residues responsible for cleavage, acid stability, and virulence of fifth-wave highly pathogenic avian influenza A(H7N9) viruses

We previously demonstrated that despite no airborne transmissibility increase compared to low pathogenic avian influenza viruses, select human isolates of highly pathogenic avian influenza A(H7N9) virus exhibit greater virulence in animal models and a lower threshold pH for fusion. In the current study, we utilized both in vitro and in vivo approaches to identify key residues responsible for hemagglutinin (HA) intracellular cleavage, acid stability, and virulence in mice. We found that the four amino acid insertion (-KRTA-) at the HA cleavage site of A/Taiwan/1/2017 virus is essential for HA intracellular cleavage and contributes to disease in mice. Furthermore, a lysine to glutamic acid mutation at position HA2-64 increased the threshold pH for HA activation, reduced virus stability, and replication in mice. Identification of a key residue responsible for enhanced acid stability of A(H7N9) viruses is of great significance for future surveillance activities and improvements in vaccine stability.

A hospital cluster combined with a family cluster of avian influenza H7N9 infection in Anhui Province, China

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We reported a hospital cluster combined with family cluster of H7N9 infection. A poultry farm was the initially infectious source of the H7N9 virus infection. Airborne transmission may result in the hospital cluster.

Objectives

To identify human-to-human transmission of H7N9 avian influenza virus, we investigated a hospital cluster combined with family cluster in this study.

Methods

We obtained and analyzed clinical, epidemiological and virological data from the three patients. RT-PCR, viral culture and sequencing were conducted for determination of causative pathogen.

Results

The index case presented developed pneumonia with fever after exposure to chicken in a poultry farm. Case A presented pneumonia with high fever on day 3 after she shared a hospital room with the index case. Case B, the father of the index case, presented pneumonia with high fever on day 15 after he took care of the index case. H7N9 virus circulated in the local farm to which the index case was exposed. Full genomic sequence of virus showed 99.8–100% identity shared between the index case and case A or case B. Compared to the earliest virus of Anhui, a total of 29 amino acid variation sites were observed in the 8 segments.

Conclusions

A hospital cluster combined with family cluster of H7N9 avian influenza infection was identified. Air transmission resulted in the hospital cluster possibly. A poultry farm was the initially infectious source of the cluster.

Recent Updates on Mouse Models for Human Immunodeficiency, Influenza, and Dengue Viral Infections

Well-developed mouse models are important for understanding the pathogenesis and progression of immunological response to viral infections in humans. Moreover, to test vaccines, anti-viral drugs and therapeutic agents, mouse models are fundamental for preclinical investigations. Human viruses, however, seldom infect mice due to differences in the cellular receptors used by the viruses for entry, as well as in the innate immune responses in mice and humans. In other words, a species barrier exists when using mouse models for investigating human viral infections. Developing transgenic (Tg) mice models expressing the human genes coding for viral entry receptors and knock-out (KO) mice models devoid of components involved in the innate immune response have, to some extent, overcome this barrier. Humanized mouse models are a third approach, developed by engrafting functional human cells and tissues into immunodeficient mice. They are becoming indispensable for analyzing human viral diseases since they nearly recapitulate the human disease. These mouse models also serve to test the efficacy of vaccines and antiviral agents. This review provides an update on the Tg, KO, and humanized mouse models that are used in studies investigating the pathogenesis of three important human-specific viruses, namely human immunodeficiency (HIV) virus 1, influenza, and dengue.

Emerging Influenza D Virus Threat: What We Know so Far!

Influenza viruses, since time immemorial, have been the major respiratory pathogen known to infect a wide variety of animals, birds and reptiles with established lineages. They belong to the family Orthomyxoviridae and cause acute respiratory illness often during local outbreaks or seasonal epidemics and occasionally during pandemics. Recent studies have identified a new genus within the Orthomyxoviridae family. This newly identified pathogen, D/swine/Oklahoma/1334/2011 (D/OK), first identified in pigs with influenza-like illness was classified as the influenza D virus (IDV) which is distantly related to the previously characterized human influenza C virus. Several other back-to-back studies soon suggested cattle as the natural reservoir and possible involvement of IDV in the bovine respiratory disease complex was established. Not much is known about its likelihood to cause disease in humans, but it definitely poses a potential threat as an emerging pathogen in cattle-workers. Here, we review the evolution, epidemiology, virology and pathobiology of influenza D virus and the possibility of transmission among various hosts and potential to cause human disease.

A Novel Reassortant Avian H7N6 Influenza Virus Is Transmissible in Guinea Pigs via Respiratory Droplets

Since 2013, H7N9 and H5N6 avian influenza viruses (AIVs) have caused sporadic human infections and deaths and continued to circulate in the poultry industry. Since 2014, H7N6 viruses which might be reassortants of H7N9 and H5N6 viruses, have been isolated in China. However, the biological properties of H7N6 viruses are unknown. Here, we characterize the receptor binding preference, pathogenicity and transmissibility of a H7N6 virus A/chicken/Hubei/00095/2017(H7N6) (abbreviated HB95), and a closely related H7N9 virus, A/chicken/Hubei/00093/2017(H7N9) (abbreviated HB93), which were isolated from poultry in Hubei Province, China, in 2017. Phylogenetic analyses demonstrated that the hemagglutinin (HA) gene of HB95 is closely related to those of HB93 and human-origin H7N9 viruses, and that the neuraminidase (NA) gene of HB95 shared the highest nucleotide similarity with those of H5N6 viruses. HB95 and HB93 had binding affinity for human-like α2, 6-linked sialic acid receptors and were virulent in mice without prior adaptation. In addition, in guinea pig model, HB93 was transmissible by direct contact, but HB95 was transmissible via respiratory droplets. These results revealed the potential threat to public health posed by H7N6 influenza viruses and emphasized the need for continued surveillance of the circulation of this subtype in poultry.

Risk Assessment of Fifth-Wave H7N9 Influenza A Viruses in Mammalian Models

The fifth wave of the H7N9 influenza epidemic in China was distinguished by a sudden increase in human infections, an extended geographic distribution, and the emergence of highly pathogenic avian influenza (HPAI) viruses. Genetically, some H7N9 viruses from the fifth wave have acquired novel amino acid changes at positions involved in mammalian adaptation, antigenicity, and hemagglutinin cleavability. Here, several human low-pathogenic avian influenza (LPAI) and HPAI H7N9 virus isolates from the fifth epidemic wave were assessed for their pathogenicity and transmissibility in mammalian models, as well as their ability to replicate in human airway epithelial cells. We found that an LPAI virus exhibited a similar capacity to replicate and cause disease in two animal species as viruses from previous waves. In contrast, HPAI H7N9 viruses possessed enhanced virulence, causing greater lethargy and mortality, with an extended tropism for brain tissues in both ferret and mouse models. These HPAI viruses also showed signs of adaptation to mammalian hosts by acquiring the ability to fuse at a lower pH threshold than other H7N9 viruses. All of the fifth-wave H7N9 viruses were able to transmit among cohoused ferrets but exhibited a limited capacity to transmit by respiratory droplets, and deep sequencing analysis revealed that the H7N9 viruses sampled after transmission showed a reduced amount of minor variants. Taken together, we conclude that the fifth-wave HPAI H7N9 viruses have gained the ability to cause enhanced disease in mammalian models and with further adaptation may acquire the ability to cause an H7N9 pandemic.IMPORTANCE The potential pandemic risk posed by avian influenza H7N9 viruses was heightened during the fifth epidemic wave in China due to the sudden increase in the number of human infections and the emergence of antigenically distinct LPAI and HPAI H7N9 viruses. In this study, a group of fifth-wave HPAI and LPAI viruses was evaluated for its ability to infect, cause disease, and transmit in small-animal models. The ability of HPAI H7N9 viruses to cause more severe disease and to replicate in brain tissues in animal models as well as their ability to fuse at a lower pH threshold than LPAI H7N9 viruses suggests that the fifth-wave H7N9 viruses have evolved to acquire novel traits with the potential to pose a higher risk to humans. Although the fifth-wave H7N9 viruses have not yet gained the ability to transmit efficiently by air, continuous surveillance and risk assessment remain essential parts of our pandemic preparedness efforts.

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.

An easy, rapid, and sensitive method for detection of drug-resistant influenza virus by using a sialidase fluorescent imaging probe, BTP3-Neu5Ac

Immunochromatographic kits and RT-PCR are widely used as diagnostic tools for influenza detection in clinical and hygiene fields. Immunochromatographic kits are useful for differential typing of influenza A and influenza B but cannot show if the detected virus strains have acquired drug resistance against neuraminidase inhibitors that target sialidase activity of viral neuraminidase. Although RT-PCR enables determination of drug-resistant mutants, its efficacy is limited to viruses carrying a known substitution in their neuraminidase genome sequence. In the present study, an easy, rapid and sensitive method for detection of drug-resistant influenza viruses regardless of major antigenic changes or genomic mutations was developed. By using the method in combination with virus-concentrated membranes in centrifugal filter units and a sialidase imaging probe, 2-(benzothiazol-2-yl)-4-bromophenyl-N-acetylneuraminic acid (BTP3-Neu5Ac), sialidase activity of influenza neuraminidase was visualized on membranes by the green fluorescence of produced hydrophobic BTP3 under UV irradiation with a handheld UV flashlight. Fluorescence images in the presence or absence of neuraminidase inhibitors clearly discriminated drug-resistant influenza viruses from drug-sensitive ones. The assay can be done within 15 min. The detection sensitivity was shown to be equal to or higher than the sensitivities of commercial immunochromatographic kits. The assay will be a powerful tool for screening and monitoring of emerging drug-resistant influenza viruses and would help clinicians decide effective antiviral treatment strategies when such mutants have become prevalent.

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.

Unexpected infection outcomes of China-origin H7N9 low pathogenicity avian influenza virus in turkeys

The China-origin H7N9 low pathogenicity avian influenza virus (LPAIV) emerged as a zoonotic threat in 2013 where it continues to circulate in live poultry markets. Absence of overt clinical signs in poultry is a typical LPAIV infection outcome, and has contributed to its insidious maintenance in China. This study is the first description of H7N9 LPAIV (A/Anhui/1/13) infection in turkeys, with efficient transmission to two additional rounds of introduced contact turkeys which all became infected during cohousing. Surprisingly, mortality was observed in six of eight (75%) second-round contact turkeys which is unusual for LPAIV infection, with unexpected systemic dissemination to many organs beyond the respiratory and enteric tracts, but interestingly no accompanying mutation to highly pathogenic AIV. The intravenous pathogenicity index score for a turkey-derived isolate (0.39) affirmed the LPAIV phenotype. However, the amino acid change L235Q in the haemagglutinin gene occurred in directly-infected turkeys and transmitted to the contacts, including those that died and the two which resolved infection to survive to the end of the study. This polymorphism was indicative of a reversion from mammalian to avian adaptation for the H7N9 virus. This study underlined a new risk to poultry in the event of H7N9 spread beyond China.

Towards the Application of Human Defensins as Antivirals

Defensins are antimicrobial peptides that participate in the innate immunity of hosts. Humans constitutively and/or inducibly express α- and β-defensins, which are known for their antiviral and antibacterial activities. This review describes the application of human defensins. We discuss the extant experimental results, limited though they are, to consider the potential applicability of human defensins as antiviral agents. Given their antiviral effects, we propose that basic research be conducted on human defensins that focuses on RNA viruses, such as human immunodeficiency virus (HIV), influenza A virus (IAV), respiratory syncytial virus (RSV), and dengue virus (DENV), which are considered serious human pathogens but have posed huge challenges for vaccine development for different reasons. Concerning the prophylactic and therapeutic applications of defensins, we then discuss the applicability of human defensins as antivirals that has been demonstrated in reports using animal models. Finally, we discuss the potential adjuvant-like activity of human defensins and propose an exploration of the ‘defensin vaccine’ concept to prime the body with a controlled supply of human defensins. In sum, we suggest a conceptual framework to achieve the practical application of human defensins to combat viral infections.

RIP3 deficiency ameliorates inflammatory response in mice infected with influenza H7N9 virus infection

Influenza H7N9 virus infection causes an acute, highly contagious respiratory illness that triggers cell death of infected cells and airway epithelial destruction. RIP3 is a key regulator of cell death responses to a growing number of viral and microbial agents. This study aimed to investigate the role of RIP3 in inflammation of influenza H7N9 virus infection. Here, RIP3 knock out (RIP3−/−) mice and littermate wild type mice were infected intranasally with influenza H7N9 virus (A/Fujian/S03/2015) to determine the contribution of RIP3 to the inflammatory response of influenza H7N9 virus infection. It was found that RIP3−/− mice infected with H7N9 virus showed higher survival and less weight loss, compared with wild type littermate mice. In addition, RIP3−/− mice had fewer regions of edema, infiltration with inflammatory cells, and alveolar collapses, and the secretions of IL-1β, IL-6, RANTES and MIP-1 in BALF were significantly decreased on days 3 and 7 p.i. when compared with WT mice. Moreover, caspase 1/IL1β signaling was found to be involved in RIP3 associated inflammation of influenza H7N9 virus, but not RIP3/MLKL dependent necrosis. In the conclusion, our results indicated that RIP3 deficiency can protect mice from the infection of influenza H7N9 virus by downregulating caspase 1/IL1β signaling, which provided evidence of the RIP3 involved necroptosis independent manner.

Hydrogen Bond Variations of Influenza A Viruses During Adaptation in Human

Many host specific mutations have been detected in influenza A viruses (IAVs). However, their effects on hydrogen bond (H-bond) variations have rarely been investigated. In this study, 60 host specific sites were identified in the internal proteins of avian and human IAVs, 27 of which contained mutations with effects on H-bonds. Besides, 30 group specific sites were detected in HA and NA. Twenty-six of 36 mutations existing at these group specific sites caused H-bond loss or formation in at least one subtype. The number of mutations in isolations of 2009 pandemic H1N1, human-infecting H5N1 and H7N9 varied. The combinations of mutations and H-bond changes in these three subtypes of IAVs were also different. In addition, the mutations in isolations of H5N1 distributed more scattered than those in 2009 pandemic H1N1 and H7N9. Eight wave specific mutations in isolations of the fifth H7N9 wave were also identified. Three of them, R140K in HA, Y170H in NA, and R340K in PB2, were capable of resulting in H-bond loss. As mentioned above, these host or group or wave specific H-bond variations provide us with a new field of vision for understanding the changes of structural features in the human adaptation of IAVs.

Emodin Inhibition of Influenza A Virus Replication and Influenza Viral Pneumonia via the Nrf2, TLR4, p38/JNK and NF-kappaB Pathways

Lasting activations of toll-like receptors (TLRs), MAPK and NF-κB pathways can support influenza A virus (IAV) infection and promote pneumonia. In this study, we have investigated the effect and mechanism of action of emodin on IAV infection using qRT-PCR, western blotting, ELISA, Nrf2 luciferase reporter, siRNA and plaque inhibition assays. The results showed that emodin could significantly inhibit IAV (ST169, H1N1) replication, reduce IAV-induced expressions of TLR2/3/4/7, MyD88 and TRAF6, decrease IAV-induced phosphorylations of p38/JNK MAPK and nuclear translocation of NF-κB p65. Emodin also activated the Nrf2 pathway, decreased ROS levels, increased GSH levelss and GSH/GSSG ratio, and upregulated the activities of SOD, GR, CAT and GSH-Px after IAV infection. Suppression of Nrf2 via siRNA markedly blocked the inhibitory effects of emodin on IAV-induced activations of TLR4, p38/JNK, and NF-κB pathways and on IAV-induced production of IL-1β, IL-6 and expression of IAV M2 protein. Emodin also dramatically increased the survival rate of mice, reduced lung edema, pulmonary viral titer and inflammatory cytokines, and improved lung histopathological changes. In conclusion, emodin can inhibit IAV replication and influenza viral pneumonia, at least in part, by activating Nrf2 signaling and inhibiting IAV-induced activations of the TLR4, p38/JNK MAPK and NF-κB pathways.

Virtual screening approach to identifying influenza virus neuraminidase inhibitors using molecular docking combined with machine-learning-based scoring function

In recent years, an epidemic of the highly pathogenic avian influenza H7N9 virus has persisted in China, with a high mortality rate. To develop novel anti-influenza therapies, we have constructed a machine-learning-based scoring function (RF-NA-Score) for the effective virtual screening of lead compounds targeting the viral neuraminidase (NA) protein. RF-NA-Score is more accurate than RF-Score, with a root-mean-square error of 1.46, Pearson’s correlation coefficient of 0.707, and Spearman’s rank correlation coefficient of 0.707 in a 5-fold cross-validation study. The performance of RF-NA-Score in a docking-based virtual screening of NA inhibitors was evaluated with a dataset containing 281 NA inhibitors and 322 noninhibitors. Compared with other docking–rescoring virtual screening strategies, rescoring with RF-NA-Score significantly improved the efficiency of virtual screening, and a strategy that averaged the scores given by RF-NA-Score, based on the binding conformations predicted with AutoDock, AutoDock Vina, and LeDock, was shown to be the best strategy. This strategy was then applied to the virtual screening of NA inhibitors in the SPECS database. The 100 selected compounds were tested in an in vitro H7N9 NA inhibition assay, and two compounds with novel scaffolds showed moderate inhibitory activities. These results indicate that RF-NA-Score improves the efficiency of virtual screening for NA inhibitors, and can be used successfully to identify new NA inhibitor scaffolds. Scoring functions specific for other drug targets could also be established with the same method.

Recombinant influenza H7 hemagglutinin containing CFLLC minidomain in the transmembrane domain showed enhanced cross-protection in mice

Since February 2013, H7N9 influenza virus, causing human infections with high mortality in China, has been a potential pandemic threat. The H7N9 viruses are found to diverge into distinct genotypes as other influenza viruses; thus a vaccine that can provide sufficient cross-protection against different genotypes of H7N9 viruses is urgently needed. Our previous studies demonstrated that the HA-based structural design approach by introducing a CFLLC minidomain into transmembrane domain (TM) of H1, H5 or H9 hemagglutinin (HA) proteins by replacing with H3 subtype HA TM could enhance their cross-protection. In this study, we used Sf9 insect cell expression system to express recombinant H7 HA proteins H7-53WT, in which HA gene was derived from H7N9-53 strain, and H7-53TM containing CFLLC minidomian by replacing its TM domain with H3 HA TM. We investigated whether introduction of CFLLC minidomain into H7 HA (H7-53TM) could increase its cross-reactivity and cross-protection against different genotypes of H7N9 viruses. The results showed that the H7-53TM either with or without squalene adjuvant induced increased HI antibodies, serum IgG antibodies, and IFN-γ production to a panel of 7 H7N9 viruses in mice. Vaccinated animals with H7-53TM alone showed complete protection against challenge with heterologous H7N9-MCX strain, while H7-53WT alone showed incomplete protection (80%). Furthermore, mice vaccinated with H7-53TM HA showed less body weight loss and less pulmonary lesions and inflammation after challenge with homologous or heterologous H7N9 viruses, comparing to H7-53WT. In summary, this study presents a better subunit vaccine candidate (H7-53TM) against potential H7N9 pandemic.

Novel Influenza D virus: Epidemiology, pathology, evolution and biological characteristics

In 2011, a new virus was isolated from pigs with influenza-like symptoms and subsequently also from cattle, which are the main reservoir of the virus. It is similar to Influenza C virus (ICV), a (predominantly) human pathogen, causing respiratory disease in children. Since the virus is unable to reassort with ICV (and based on several other criteria as discussed in the text) it is now officially named as Influenzavirus D (IDV), a new genus of the Orthomyxoviridae. We summarize the epidemiology, pathology and evolution of IDV and its biological characteristics with emphasis on the only glycoprotein HEF. Based on the limited data available we finally consider whether IDV represent a public health threat.

An avian influenza H7 DNA priming vaccine is safe and immunogenic in a randomized phase I clinical trial

A novel avian influenza subtype, A/H7N9, emerged in 2013 and represents a public health threat with pandemic potential. We have previously shown that DNA vaccine priming increases the magnitude and quality of antibody responses to H5N1 monovalent inactivated boost. We now report the safety and immunogenicity of a H7 DNA-H7N9 monovalent inactivated vaccine prime-boost regimen. In this Phase 1, open label, randomized clinical trial, we evaluated three H7N9 vaccination regimens in healthy adults, with a prime-boost interval of 16 weeks. Group 1 received H7 DNA vaccine prime and H7N9 monovalent inactivated vaccine boost. Group 2 received H7 DNA and H7N9 monovalent inactivated vaccine as a prime and H7N9 monovalent inactivated vaccine as a boost. Group 3 received H7N9 monovalent inactivated vaccine in a homologous prime-boost regimen. Overall, 30 individuals between 20 to 60 years old enrolled and 28 completed both vaccinations. All injections were well tolerated with no serious adverse events. 2 weeks post-boost, 50% of Group 1 and 33% of Group 2 achieved a HAI titer ≥1:40 compared with 11% of Group 3. Also, at least a fourfold increase in neutralizing antibody responses was seen in 90% of Group 1, 100% of Group 2, and 78% of Group 3 subjects. Peak neutralizing antibody geometric mean titers were significantly greater for Group 1 (GMT = 440.61, p < 0.05) and Group 2 (GMT = 331, p = 0.02) when compared with Group 3 (GMT = 86.11). A novel H7 DNA vaccine was safe, well-tolerated, and immunogenic when boosted with H7N9 monovalent inactivated vaccine, while priming for higher HAI and neutralizing antibody titers than H7N9 monovalent inactivated vaccine alone.

A vaccine candidate to treat a deadly subtype of avian influenza was shown to induce protective antibodies in initial clinical trials. As of March 2017, avian influenza strain A/H7N9 has killed 497 people since 2013, with 1349 confirmed cases. Julie Ledgerwood and her team from the United States’ National Institutes of Health in collaboration with colleagues at the Centers for Disease Control and Prevention tested their two-stage vaccine protocol in humans, showing it to be effective and safe. The vaccine consists of an initial injection of viral DNA, which ‘primes’ the immune system to the pathogen, followed by a follow-up injection of an inactivated purified viral protein, which further boosts the host’s production of protective antibodies. The study shows the viability of this vaccine regimen and suggests further investigation into its appropriateness for treating avian influenza in humans.

A humanized mouse model identifies key amino acids for low immunogenicity of H7N9 vaccines

Influenza vaccines of H7N9 subtype are consistently less immunogenic in humans than vaccines developed for other subtypes. Although prior immunoinformatic analysis identified T-cell epitopes in H7 hemagglutinin (HA) which potentially enhance regulatory T cell response due to conservation with the human genome, the links between the T-cell epitopes and low immunogenicity of H7 HA remains unknown due to the lack of animal models reproducing the response observed in humans. Here, we utilized a humanized mouse model to recapitulate the low immunogenicity of H7 HA. Our analysis demonstrated that modification of a single H7 epitope by changing 3 amino acids so that it is homologous with a known H3 immunogenic epitope sequence significantly improved the immunogenicity of the H7 HA in the humanized mouse model, leading to a greater than 4-fold increase in HA-binding IgG responses. Thus, we provide experimental evidence for the important contribution of this H7-specific T cell epitope in determining the immunogenicity of an influenza vaccine. Furthermore, this study delineates strategies that can be used for screening and selecting vaccine strains using immunoinformatics tools and a humanized mouse model.

Genetics and biological property analysis of Korea lineage of influenza A H9N2 viruses

H9N2 influenza viruses have been detected from wild and domestic avian species including chickens and ducks worldwide. Few studies have compared the biological properties of different H9N2 lineages or determined whether certain lineages might pose a higher risk to mammals, especially H9N2 viruses of Korean lineage. The objective of this study was to characterize the genetic and biological properties of 22 Korean H9N2 viruses and assess their potential risks to mammals. Their complete genomes were analyzed. Some Korean H9N2 viruses were found to carry mammalian host-specific mutations. Based on genomic diversities, these H9N2 viruses were divided into 12 genotypes. All 22 showed preferential binding to human-like receptor. Two of eight H9N2 viruses were highly lethal to mice, causing 90-100% mortality without prior adaptation and severe respiratory syndromes associated with diffuse lung injury, severe pneumonia, and alveolar damage. These findings suggest that recent Korean H9N2 viruses might have established a stable sublineage with enhanced pathogenicity to mice. Various H9N2 strains pathogenic to mice were endemic in wild bird, poultry farm, and live bird markets, suggesting that Korean H9N2 viruses could evolve to become a threat to humans. The findings emphasize the necessity of careful, continuous, and thorough surveillance paired with risk-assessment for circulating H9N2 influenza viruses.

In vivo evasion of MxA by avian influenza viruses requires human signature in the viral nucleoprotein

Deeg et al. show a novel line of transgenic mice expressing restriction factor MxA exhibits robust resistance to influenza viruses of avian but not human origin. In vivo evasion of MxA is mediated by distinct amino acids in the nucleoprotein of human influenza viruses.

Zoonotic transmission of influenza A viruses can give rise to devastating pandemics, but currently it is impossible to predict the pandemic potential of circulating avian influenza viruses. Here, we describe a new mouse model suitable for such risk assessment, based on the observation that the innate restriction factor MxA represents an effective species barrier that must be overcome by zoonotic viruses. Our mouse lacks functional endogenous Mx genes but instead carries the human MX1 locus as a transgene. Such transgenic mice were largely resistant to highly pathogenic avian H5 and H7 influenza A viruses, but were almost as susceptible to infection with influenza viruses of human origin as nontransgenic littermates. Influenza A viruses that successfully established stable lineages in humans have acquired adaptive mutations which allow partial MxA escape. Accordingly, an engineered avian H7N7 influenza virus carrying a nucleoprotein with signature mutations typically found in human virus isolates was more virulent in transgenic mice than parental virus, demonstrating that a few amino acid changes in the viral target protein can mediate escape from MxA restriction in vivo. Similar mutations probably need to be acquired by emerging influenza A viruses before they can spread in the human population.

Identification of Rare PB2-D701N Mutation from a Patient with Severe Influenza: Contribution of the PB2-D701N Mutation to the Pathogenicity of Human Influenza

Several amino acid changes have been previously implicated in adaptation of avian influenza viruses to human hosts, among them the D701N change in the PB2 polymerase subunit that also is the main determinant of avian virus pathogenesis in animal models. However, previous studies using recombinant viruses did not provide conclusive information of the contribution of this PB2 residue to pathogenicity in human influenza virus strains. We identified this mutation in an A(H1N1)pdm09-like human influenza virus isolated from an infected patient with pneumonia and acute respiratory failure, admitted to the intensive care unit. An exhaustive search has revealed PB2-D701 as a highly conserved position in all available H1N1 human virus sequences in NCBI database, showing a very low prevalence of PB2-D701N change. Presence of PB2-701N amino acid correlates with severe or fatal outcome in those scarce cases with known disease outcome of the infection. In these patients, the residue PB2-701N may contribute to pathogenicity as it was previously reported in humans infected with avian viruses. This study helps to clarify a debate that has arisen regarding the role of PB2-D701N in human influenza virus pathogenicity.

Challenges of Treating Adenovirus Infection: Application of a Deployable Rapid-Assembly Shelter Hospital

This article outlines the evolution of a rescue team in responding to adenovirus prevention with a deployable field hospital. The local governments mobilized a shelter hospital and a rescue team consisting of 59 members to assist with rescue and response efforts after an epidemic outbreak of adenovirus. We describe and evaluate the challenges of preparing for deployment, field hospital maintenance, treatment mode, and primary treatment methods. The field hospital established at the rescue scene consisted of a medical command vehicle, a computed tomography shelter, an X-ray shelter, a special laboratory shelter, an oxygen and electricity supply vehicle, and epidemic prevention and protection equipment. The rescue team comprised paramedics, physicians, X-ray technicians, respiratory therapists, and logistical personnel. In 22 days, more than 3000 patients with suspected adenovirus infection underwent initial examinations. All patients were properly treated, and no deaths occurred. After emergency measures were implemented, the spread of adenovirus was eventually controlled. An emergency involving infectious diseases in less-developed regions demands the rapid development of a field facility with specialized medical personnel when local hospital facilities are either unavailable or unusable. An appropriate and detailed prearranged action plan is important for infectious diseases prevention. (Disaster Med Public Health Preparedness. 2018;12:109-114).

NEDDylation of PB2 Reduces Its Stability and Blocks the Replication of Influenza A Virus

Post-translational modifications of viral proteins play important roles in regulating viral replication. Here we demonstrated that the PB2 of influenza A virus (IAV) can be modified by NEDD8. We revealed that E3 ligase HDM2 can promote PB2 NEDDylation. Overexpression of either NEDD8 or HDM2 can inhibit IAV replication, while knockdown of HDM2 has the opposite effect. Then we identified residue K699 in PB2 as the major NEDDylation site. We found that NEDDylation deficient PB2 mutant (PB2 K699R) has a longer half-life than wild-type PB2, indicating that NEDDylation of PB2 reduces its stability. We generated an IAV mutant in which PB2 was mutated to PB2 K699R (WSN-PB2 K699R) and examined the replication of WSN and WSN-PB2 K699R viruses in both MDCK and A549 cells and found that the replication of WSN-PB2 K699R was more efficient than wild-type WSN. In addition, we observed that overexpression of NEDD8 significantly inhibited the replication of WSN, but not WSN-PB2 K699R. The infection assay in mice showed that WSN-PB2 K699R exhibited enhanced virulence in mice compared to WSN, suggesting that NEDDylation of PB2 reduced IAV replication in vivo. In conclusion, we demonstrated that NEDDylation of PB2 by HDM2 negatively regulates IAV infection.

Avian and Human Seasonal Influenza Hemagglutinin Proteins Elicit CD4 T Cell Responses That Are Comparable in Epitope Abundance and Diversity

Avian influenza viruses remain a significant concern due to their pandemic potential. Vaccine trials have suggested that humans respond poorly to avian influenza vaccines relative to seasonal vaccines. It is important to understand, first, if there is a general deficiency in the ability of avian hemagglutinin (HA) proteins to generate immune responses and, if so, what underlies this defect. This question is of particular interest because it has been suggested that in humans, the poor immunogenicity of H7 vaccines may be due to a paucity of CD4 T cell epitopes. Because of the generally high levels of cross-reactive CD4 T cells in humans, it is not possible to compare the inherent immunogenicities of avian and seasonal HA proteins in an unbiased manner. Here, we empirically examine the epitope diversity and abundance of CD4 T cells elicited by seasonal and avian HA proteins. HLA-DR1 and HLA-DR4 transgenic mice were vaccinated with purified HA proteins, and CD4 T cells to specific epitopes were identified and quantified. These studies revealed that the diversity and abundance of CD4 T cells specific for HA do not segregate on the basis of whether the HA was derived from human seasonal or avian influenza viruses. Therefore, we conclude that failure in responses to avian vaccines in humans is likely due to a lack of cross-reactive CD4 T cell memory perhaps coupled with competition with or suppression of naive, HA-specific CD4 T cells by memory CD4 T cells specific for more highly conserved proteins.