Human H1N1 Influenza Research Articles

Vaccine models predict rules for updating vaccines against evolving pathogens such as SARS-CoV-2 and influenza in the context of pre-existing immunity.

Currently, vaccines for SARS-CoV-2 and influenza viruses are updated if the new vaccine induces higher antibody-titers to circulating variants than current vaccines. This approach does not account for complex dynamics of how prior immunity skews recall responses to the updated vaccine. We: (i) use computational models to mechanistically dissect how prior immunity influences recall responses; (ii) explore how this affects the rules for evaluating and deploying updated vaccines; and (iii) apply this to SARS-CoV-2. Our analysis of existing data suggests that there is a strong benefit to updating the current SARS-CoV-2 vaccines to match the currently circulating variants. We propose a general two-dose strategy for determining if vaccines need updating as well as for vaccinating high-risk individuals. Finally, we directly validate our model by reanalysis of earlier human H5N1 influenza vaccine studies.

Egg-adaptive mutations of human influenza H3N2 virus are contingent on natural evolution.

Egg-adaptive mutations in influenza hemagglutinin (HA) often emerge during the production of egg-based seasonal influenza vaccines, which contribute to the largest share in the global influenza vaccine market. While some egg-adaptive mutations have minimal impact on the HA antigenicity (e.g. G186V), others can alter it (e.g. L194P). Here, we show that the preference of egg-adaptive mutation in human H3N2 HA is strain-dependent. In particular, Thr160 and Asn190, which are found in many recent H3N2 strains, restrict the emergence of L194P but not G186V. Our results further suggest that natural amino acid variants at other HA residues also play a role in determining the preference of egg-adaptive mutation. Consistently, recent human H3N2 strains from different clades acquire different mutations during egg passaging. Overall, these results demonstrate that natural mutations in human H3N2 HA can influence the preference of egg-adaptation mutation, which has important implications in seed strain selection for egg-based influenza vaccine.

An epitope-optimized human H3N2 influenza vaccine induces broadly protective immunity in mice and ferrets

There is a crucial need for an improved H3N2 influenza virus vaccine due to low vaccine efficacy rates and increased morbidity and mortality associated with H3N2-dominated influenza seasons. Here, we utilize a computational design strategy to produce epitope-optimized, broadly cross-reactive H3 hemagglutinins in order to create a universal H3N2 influenza vaccine. The Epigraph immunogens are designed to maximize the viral population frequency of epitopes incorporated into the immunogen. We compared our Epigraph H3 vaccine to the traditional egg-based inactivated influenza vaccine from 2018–19, FluZone. Epigraph vaccination-induced stronger cross-reactive antibody responses than FluZone against 18 H3N2 viruses isolated from 1968 to 2019 in both mice and ferrets, with protective hemagglutination inhibition titers against 93–100% of the contemporary H3N2 strains compared to only 27% protection measured from FluZone. In addition, Epigraph vaccination-induced strong cross-reactive T-cell immunity which significantly contributes to protection against lethal influenza virus infection. Finally, Epigraph vaccination protected ferrets from influenza disease after challenge with two H3N2 viruses. The superior cross-reactive immunity induced by these Epigraph immunogens supports their development as a universal H3N2 influenza vaccine.

Lipid biophysics and/or soft matter-inspired approach for controlling enveloped virus infectivity.

Proven as a natural barrier against viral infection, pulmonary surfactant phospholipids have a biophysical and immunological role within the respiratory system, acting against microorganisms including viruses. Enveloped viruses have, in common, an outer bilayer membrane that forms the underlying structure for viral membrane proteins to function in an optimal way to ensure infectivity. Perturbating the membrane of viruses using exogenous lipids can be envisioned as a generic way to reduce their infectivity. In this context, the potential of exogenous lipids to be used against enveloped virus infectivity would be indicated by the resulting physical stress imposed to the viral membrane, and conical lipids, i.e. lyso-lipids, would be expected to generate stronger biophysical disturbances. We confirm that when treated with lyso-lipids the infectivity three strains of influenza virus (avian H2N3, equine H3N8 or pandemic human influenza H1N1) is reduced by up to 99% in a cell-based model. By contrast, lipids with a similar head group but two aliphatic chains were less effective (reducing infection by only 40–50%). This work opens a new path to merge concepts from different research fields, i.e. ‘soft matter physics' and virology.

Characterization of Immune Response towards Generation of Universal Anti-HA-Stalk Antibodies after Immunization of Broiler Hens with Triple H5N1/NA-HA-M1 VLPs.

(1) Background: Avian influenza viruses (AIVs) promptly evade preexisting immunity by constantly altering the immunodominant neutralizing antibody epitopes (antigenic drift) or by procuring new envelope serotypes (antigenic shift). As a consequence, the majority of antibodies elicited by infection or vaccination protect only against closely related strains. The immunodominance of the globular head of the main glycoprotein has been shown to mask the immunogenicity of the conserved regions located within the hemagglutinin (HA) protein. It has been shown that the broadly neutralizing universal antibodies recognize the HA2 domain in headless hemagglutinin (HA-stalk). Therefore, the HA-stalk is a highly conserved antigen, which makes it a good candidate to be used in universal vaccine development against AIVs. (2) Methods: Sf9 insect cells were used to produce triple H5N1/NA-HA-M1 influenza virus-like particles (VLPs) via co-expression of neuraminidase, hemagglutinin and matrix proteins from a tricistronic expression cassette. Purified influenza VLPs were used to immunize broiler hens. An in-depth characterization of the immune response was performed with an emphasis on the pool of elicited universal antibodies. (3) Results: Our findings suggest, that after vaccination with triple H5N1/NA-HA-M1 VLPs, hens generate a pool of broad-spectrum universal anti-HA-stalk antibodies. Furthermore, these universal antibodies are able to recognize the mammalian-derived HA-stalk recombinant proteins from homologous H5N1 and heterologous H7N9 AIVs as well as from the heterosubtypic human H1N1 influenza strain. (4) Conclusions: Our findings may suggest that highly pathogenic avian influenza H5 HA protein contain functional epitopes that are attractive targets for the generation of broad-spectrum antibodies against AIVs in their native hosts.

In Vitro and In Vivo Antiviral Studies of New Heteroannulated 1,2,3-Triazole Glycosides Targeting the Neuraminidase of Influenza A Viruses.

There is an urgent need to develop and synthesize new anti-influenza drugs with activity against different strains, resistance to mutations, and suitability for various populations. Herein, we tested in vitro and in vivo the antiviral activity of new 1,2,3-triazole glycosides incorporating benzimidazole, benzooxazole, or benzotriazole cores synthesized by using a click approach. The Cu-catalyzation strategy consisted of 1,3-dipolar cycloaddition of the azidoalkyl derivative of the respective heterocyclic and different glycosyl acetylenes with five or six carbon sugar moieties. The antiviral activity of the synthesized glycosides against wild-type and neuraminidase inhibitor resistant strains of the avian influenza H5N1 and human influenza H1N1 viruses was high in vitro and in mice. Structure–activity relationship studies showed that varying the glycosyl moiety in the synthesized glycosides enhanced antiviral activity. The compound (2R,3R,4S,5R)-2-((1-(Benzo[d]thiazol-2-ylmethyl)-1H-1,2,3-triazol-4-yl)methoxy)tetrahydro-2H-pyran-3,4,5-triyl triacetate (Compound 9c) had a 50% inhibitory concentration (IC50) = 2.280 µM and a ligand lipophilic efficiency (LLE) of 6.84. The compound (2R,3R,4S,5R)-2-((1-((1H-Benzo[d]imidazol-2-yl)methyl)-1H-1,2,3-triazol-4-yl)methoxy)tetrahydro-2H-pyran-3,4,5-triyl triacetate had IC50 = 2.75 µM and LLE = 7.3 after docking analysis with the H5N1 virus neuraminidase. Compound 9c achieved full protection from H1N1 infection and 80% protection from H5N1 in addition to a high binding energy with neuraminidase and was safe in vitro and in vivo. This compound is suitable for further clinical studies as a new neuraminidase inhibitor.

The PB1 gene from H9N2 avian influenza virus showed high compatibility and increased mutation rate after reassorting with a human H1N1 influenza virus

BackgroundReassortment between human and avian influenza viruses (AIV) may result in novel viruses with new characteristics that may threaten human health when causing the next flu pandemic. A particular risk may be posed by avian influenza viruses of subtype H9N2 that are currently massively circulating in domestic poultry in Asia and have been shown to infect humans. In this study, we investigate the characteristics and compatibility of a human H1N1 virus with avian H9N2 derived genes.MethodsThe polymerase activity of the viral ribonucleoprotein (RNP) complex as combinations of polymerase-related gene segments derived from different reassortment events was tested in luciferase reporter assays. Reassortant viruses were generated by reverse genetics. Gene segments of the human WSN-H1N1 virus (A/WSN/1933) were replaced by gene segments of the avian A2093-H9N2 virus (A/chicken/Jiangsu/A2093/2011), which were both the Hemagglutinin (HA) and Neuraminidase (NA) gene segments in combination with one of the genes involved in the RNP complex (either PB2, PB1, PA or NP). The growth kinetics and virulence of reassortant viruses were tested on cell lines and mice. The reassortant viruses were then passaged for five generations in MDCK cells and mice lungs. The HA gene of progeny viruses from different passaging paths was analyzed using Next-Generation Sequencing (NGS).ResultsWe discovered that the avian PB1 gene of H9N2 increased the polymerase activity of the RNP complex in backbone of H1N1. Reassortant viruses were able to replicate in MDCK and DF1 cells and mice. Analysis of the NGS data showed a higher substitution rate for the PB1-reassortant virus. In particular, for the PB1-reassortant virus, increased virulence for mice was measured by increased body weight loss after infection in mice.ConclusionsThe higher polymerase activity and increased mutation frequency measured for the PB1-reassortant virus suggests that the avian PB1 gene of H9N2 may drive the evolution and adaptation of reassortant viruses to the human host. This study provides novel insights in the characteristics of viruses that may arise by reassortment of human and avian influenza viruses. Surveillance for infections with H9N2 viruses and the emergence of the reassortant viruses in humans is important for pandemic preparedness.

Antigenic evolution of human influenza H3N2 neuraminidase is constrained by charge balancing.

As one of the main influenza antigens, neuraminidase (NA) in H3N2 virus has evolved extensively for more than 50 years due to continuous immune pressure. While NA has recently emerged as an effective vaccine target, biophysical constraints on the antigenic evolution of NA remain largely elusive. Here, we apply combinatorial mutagenesis and next-generation sequencing to characterize the local fitness landscape in an antigenic region of NA in six different human H3N2 strains that were isolated around 10 years apart. The local fitness landscape correlates well among strains and the pairwise epistasis is highly conserved. Our analysis further demonstrates that local net charge governs the pairwise epistasis in this antigenic region. In addition, we show that residue coevolution in this antigenic region is correlated with the pairwise epistasis between charge states. Overall, this study demonstrates the importance of quantifying epistasis and the underlying biophysical constraint for building a model of influenza evolution.

H3N2 Influenza Viruses with 12- or 16-Amino Acid Deletions in the Receptor-Binding Region of Their Hemagglutinin Protein.

ABSTRACTHuman influenza viruses evade host immune responses by accumulating mutations around the receptor-binding region of the hemagglutinin (HA) protein, which is composed of three key elements, the 130-loop, the 190-helix, and the 220-loop. Here, we characterized two human H3N2 influenza viruses with 12- and 16-amino acid deletions around the HA receptor-binding site that were isolated after antigenic selection of mutated H3N2 viruses. Structural modeling suggested that the 12-amino acid deletion eliminated the 190-helix. The 16-amino acid deletion comprises two stretches of 11- and 5-amino acid deletions. As the result of a frameshift, “novel” amino acids (not found in wild-type HA at these positions) are encoded between the deleted regions. Interestingly, structural modeling predicted that the novel sequence forms a structure resembling the 190-helix. However, compared to wild-type HA, the 16-amino acid deletion mutant lacks two antiparallel beta-sheets that connect the 190-helix and the 220-loop in wild-type HA. Nonetheless, both HA deletion mutants replicated in mammalian cells, and the 16-amino acid deletion mutant (with a remodeled 190-helix) also replicated in Syrian hamsters, albeit at low titers. Wild-type virus bound preferentially to α2,6-linked sialic acids, whereas both mutants gained affinity for α2,3-linked sialic acids. Moreover, the 12- and 16-amino acid deletions may affect the antigenic properties of the viruses. Thus, viruses with sizeable deletions around the HA receptor-binding site are viable but may display altered sialic acid preferences, altered antigenic properties, and attenuated replicative ability in cultured cells and virulence in Syrian hamsters.

Antigenic Distance between North American Swine and Human Seasonal H3N2 Influenza A Viruses as an Indication of Zoonotic Risk to Humans.

Human-to-swine transmission of influenza A virus (IAV) repeatedly occurs, leading to sustained transmission and increased diversity in swine; human seasonal H3N2 introductions occurred in the 1990s and 2010s and were maintained in North American swine. Swine H3N2 strains were subsequently associated with zoonotic infections, highlighting the need to understand the risk of endemic swine IAV to humans. We quantified antigenic distances between swine H3N2 and human seasonal vaccine strains from 1973 to 2014 using a panel of monovalent antisera raised in pigs in hemagglutination inhibition (HI) assays. Swine H3N2 lineages retained the closest antigenic similarity to human vaccine strains from the decade of incursion. Swine lineages from the 1990s were antigenically more similar to human vaccine strains of the mid-1990s but had substantial distance from recent human vaccine strains. In contrast, lineages from the 2010s were closer to human vaccine strains from 2011 and 2014 and the most antigenically distant from human vaccine strains prior to 2007. HI assays using ferret antisera demonstrated that swine lineages from the 1990s and 2010s had significant fold reductions compared to the homologous HI titer of the nearest pandemic preparedness candidate vaccine virus (CVV) or seasonal vaccine strain. The assessment of postinfection and postvaccination human serum cohorts demonstrated limited cross-reactivity to swine H3N2 from the 1990s, especially in older adults born before the 1970s. We identified swine strains to which humans are likely to lack population immunity or are not protected against by a current human seasonal vaccine or CVV to use in prioritizing future human CVV strain selection. IMPORTANCE Human H3N2 influenza A viruses spread to pigs in North America in the 1990s and more recently in the 2010s. These cross-species events led to sustained circulation and increased H3N2 diversity in pig populations. The evolution of H3N2 in swine led to a reduced similarity to human seasonal H3N2 and the vaccine strains used to protect human populations. We quantified the antigenic phenotypes and found that North American swine H3N2 lineages retained more antigenic similarity to historical human vaccine strains from the decade of incursion but had substantial differences compared to recent human vaccine strains. Additionally, pandemic preparedness vaccine strains demonstrated a loss of similarity to contemporary swine strains. Finally, human sera revealed that although these adults had antibodies against human H3N2 strains, many had limited immunity to swine H3N2, especially older adults born before 1970. Antigenic assessment of swine H3N2 provides critical information for pandemic preparedness and candidate vaccine development.

A Cross-Reactive Monoclonal Antibody Against Neuraminidases of Both H9N2 and H3N2 Influenza Viruses Shows Protection in Mice Challenging Models.

Neuraminidases (NAs) of H9N2 avian influenza virus (AIV) and H3N2 human seasonal influenza virus (HSIV) share similar antigenic structures. However, there are few reports on epitopes shared by these two NAs. We previously reported a monoclonal antibody (mAb) 1G8 against the NA of H9N2 AIV with neuraminidase inhibition (NI) ability. In this study, 1G8 was shown to cross-react with and inhibit the NA of H3N2 HSIV. In a passive transfer experiment, 1G8 provided protection to mice challenged with rescued H1N2 viruses carrying H9N2 NA or H3N2 NA. Mutation at amino acid position 199 was also selected and proved to be crucial for H3N2 HSIV to escape from mAb 1G8. Moreover, we found that residue 199 contributed to inducing broad protective antibodies without the influence of the N-linked glycosylation at amino acid position 200 in NAs. Residues as residue 199, which are not shielded by glycosylation modification, would form ideal epitopes for developing universal vaccine and protective antibodies.

SARS-CoV-2 spike and its adaptable furin cleavage site

SARS-CoV-2 spike and its adaptable furin cleavage site

Evolution of the PB1 gene of human influenza A (H3N2) viruses circulating between 1968 and 2019.

One avian H3N2 influenza virus, providing its PB1 and HA segments, reassorted with one human H2N2 virus and caused a pandemic outbreak in 1968, killing over 1 million people. After its introduction to humanity, the pandemic H3N2 virus continued adapting to humans and has resulted in epidemic outbreaks every influenza season. To understand the functional roles of the originally avian PB1 gene in the circulating strains of human H3N2 influenza viruses, we analyzed the evolution of the PB1 gene in all human H3N2 isolates from 1968 to 2019. We found several specific residues dramatically changed around 2002-2009 and remained stable through to 2019. Then, we verified the functions of these PB1 mutations in the genetic background of the early pandemic virus, A/Hong Kong/1/1968(HK/68), as well as a recent seasonal strain, A/Jiangsu/34/2016 (JS/16). The PB1 V709I or PB1 V113A/K586R/D619N/V709I induced higher polymerase activity of HK/68 in human cells. And the four mutations acted cooperatively that had an increased replication capacity in vitro and in vivo at an early stage of infection. In contrast, the backward mutant, A113V/R586K/N619D/I709V, reduced polymerase activity in human cells. The PB1 I709V decreased viral replication in vitro, but this mutant only showed less effect on mice infection experiment, which suggested influenza A virus evolved in human host was not always consisted with highly replication efficiency and pathogenicity in other mammalian host. Overall, our results demonstrated that the identified PB1 mutations contributed to the viral evolution of human influenza A (H3N2) viruses.

Sulfated glycans containing NeuAcα2-3Gal facilitate the propagation of human H1N1 influenza A viruses in eggs

When human influenza viruses are isolated and passaged in chicken embryos, variants with amino acid substitutions around the receptor binding site of hemagglutinin (HA) are selected; however, the mechanisms that underlie this phenomenon have yet to be elucidated. Here, we analyzed the receptor structures that contributed to propagation of egg-passaged human H1N1 viruses. The analysis included seasonal and 2009 pandemic strains, both of which have amino acid substitutions of HA found in strains isolated or passaged in eggs. These viruses exhibited high binding to sulfated glycans containing NeuAcα2-3Gal. In MDCK cells overexpressing the sulfotransferase that synthesize Galβ1-4(SO3--6)GlcNAc, production of human H1N1 viruses was increased up to 90-fold. Furthermore, these sulfated glycans were expressed on the allantoic and amniotic membranes of chicken embryos. These results suggest that 6-sulfo sialyl Lewis X and/or NeuAcα2-3Galβ1-4(SO3--6)GlcNAc are involved in efficient propagation of human H1N1 viruses in chicken embryos.

Pathogenicity and transmissibility of current H3N2 swine influenza virus in Southern China: A zoonotic potential.

Swine are considered as 'mixing vessels' of influenza A viruses and play an important role in the generation of novel influenza pandemics. In this study, we described that the H3N2 swine influenza (swH3N2) viruses currently circulating in pigs in Guangdong province carried six internal genes from 2009 pandemic H1N1 virus (pmd09), and their antigenicity was obviously different from that of current human H3N2 influenza viruses or recommended vaccine strains (A/Guangdong/1194/2019, A/Hong Kong/4801/2014). These swH3N2 viruses preferentially bonded to the human-like receptors, and efficiently replicated in human, canine and swine cells. In addition, the virus replicated in turbinate and trachea of guinea pigs, and efficiently transmitted among guinea pigs, and virus shedding last for 6 days post-infection (dpi). The virus replicated in the respiratory tract of pigs, effectively transmitted among pigs, and virus shedding last until 9 dpi. Taken together, these current swH3N2 viruses might have the zoonotic potential. Strengthening surveillance and monitoring the pathogenicity of such swH3N2 viruses are urgently needed.

Organochlorine Pesticide Dieldrin Suppresses Cellular Interferon-Related Antiviral Gene Expression.

Organochlorine pesticides (OCPs) are persistent pollutants linked to diverse adverse health outcomes. Environmental exposure to OCPs has been suggested to negatively impact the immune system but their effects on cellular antiviral responses remain unknown. Transcriptomic analysis of N27 rat dopaminergic neuronal cells unexpectedly detected high level expression of genes in the interferon (IFN)-related antiviral response pathways including the IFN-induced protein with tetratricopeptide repeats 1 and 2 (Ifit1/2) and the MX Dynamin Like GTPases Mx1 and Mx2. Interestingly, treatment of N27 cells with dieldrin markedly downregulated the expression of many of these genes. Dieldrin exterted a similar effect in inhibiting IFIT2 and MX1 gene expression in human SH-SY5Y neuronal cells induced by an RNA viral mimic, polyinosinic: polycytidylic acid (poly I:C) and IFIT2/3 gene expression in human pulmonary epithelial cells exposed to human influenza H1N1 virus. Mechanistically, dieldrin induced a rapid rise in levels of intracellular reactive oxygen species (iROS) and a decrease in intracellular glutathione (GSH) levels in SH-SY5Y cells. Treatment with N-acetylcysteine, an antioxidant and GSH biosynthesis precursor, effectively blocked both dieldrin-induced increases in iROS and its inhibition of poly I:C-induced upregulation of IFIT and MX gene expression, suggesting a role for intracellular oxidative status in dieldrin's modulation of antiviral gene expression. This study demonstrates that dieldrin modulates key genes of the cellular innate immune responses that are normally involved in the host's cellular defense against viral infections. Our findings have potential relevance to understanding the organismal effects of environmentally persistent organochlorine contaminants on the mammalian cellular immune system.

The pandemic matrix gene is associated with increased pro-inflammatory immune responses during influenza virus infection

Abstract The 2009 H1N1 influenza pandemic (pdmH1N1) arose from multiple genetic reassortment events between three swine influenza A virus (swIAV) lineages and became established as a seasonal H1N1 human influenza virus. Through reverse-zoonotic events, the pdmH1N1 strain contributed gene segments to endemic swIAVs and the pandemic matrix gene (pdmM) completely replaced the classical swine matrix gene (swM), suggesting a fitness benefit. We assessed a panel of swIAVs in the BALB/c mouse model and demonstrated that swIAVs containing the pdmM gene caused increased morbidity, lung pathology, and mortality compared to swIAVs containing the swM gene. We hypothesized that swIAVs containing the pdmM gene induce dysregulation of the innate response, causing increased disease. To test this, mice were infected with swIAVs containing either the pdmM or the swM gene segment, and immune cell infiltrates, cytokine production, and histopathology were assessed. We found that pdmM viruses elicited increased cellular infiltration, NK cell activation and increased IFNγ production in bronchial alveolar lavage (BAL) fluid compared to mice infected with swM viruses. We also detected increased numbers of infiltrating macrophages, neutrophils, DCs, and eosinophils, as well as increased proinflammatory cytokine production. Additionally, elevated myeloperoxidase content was detected in BAL fluid, suggesting increased neutrophil activation. Finally, infection with pdmM viruses resulted in greater histologic lesion scores compared to swM viruses. We conclude the pdmM gene elicits increased innate immune responses, causing greater disease in a mouse model of infection. Future studies will identify determinants of increased disease severity.

Rapid and Efficient Cell-to-Cell Transmission of Avian Influenza H5N1 Virus in MDCK Cells Is Achieved by Trogocytosis.

Viruses have developed direct cell-to-cell transfer strategies to enter target cells without being released to escape host immune responses and antiviral treatments. These strategies are more rapid and efficient than transmission through indirect mechanisms of viral infection between cells. Here, we demonstrate that an H5N1 influenza virus can spread via direct cell-to-cell transfer in Madin-Darby canine kidney (MDCK) cells. We compared cell-to-cell transmission of the H5N1 virus to that of a human influenza H1N1 virus. The H5N1 virus has been found to spread to recipient cells faster than the human influenza H1N1 virus. Additionally, we showed that plasma membrane exchange (trogocytosis) occurs between co-cultured infected donor cells and uninfected recipient cells early point, allowing the intercellular transfer of viral material to recipient cells. Notably, the H5N1 virus induced higher trogocytosis levels than the H1N1 virus, which could explain the faster cell-to-cell transmission rate of H5N1. Importantly, this phenomenon was also observed in A549 human lung epithelial cells, which are representative cells in the natural infection site. Altogether, our results provide evidence demonstrating that trogocytosis could be the additional mechanism utilized by the H5N1 virus for rapid and efficient cell-to-cell transmission.

Molecular Characteristics, Antigenicity, Pathogenicity, and Zoonotic Potential of a H3N2 Canine Influenza Virus Currently Circulating in South China.

Canine influenza viruses (CIVs) could be a source of influenza viruses which infect humans because canine are important companion pets. To assess the potential risk of H3N2 CIVs currently circulating in southern China to public health, biological characteristics of A/canine/Guangdong/DY1/2019 (CADY1/2019) were detected. CADY1/2019 bound to both avian-type and human-type receptors. CADY1/2019 had a similar pH value for HA protein fusion to human viruses, but its antigenicity was obviously different from those of current human H3N2 influenza viruses (IVs) or the vaccine strains recommended in the North hemisphere. CADY1/2019 effectively replicated in the respiratory tract and was transmitted by physical contact among guinea pigs. Compared to human H3N2 IV, CADY1/2019 exhibited higher replication in MDCK, A549, 3D4/21, ST, and PK15 cells. Sequence analysis indicated that CADY1/2019 is an avian-origin virus, and belongs to the novel clade and has acquired many adaptation mutations to infect other mammals, including human. Taken together, currently circulating H3N2 CIVs have a zoonotic potential, and there is a need for strengthening surveillance and monitoring of their pathogenicity.

Infection and risk factors of human and avian influenza in pigs in south China

The coinfection of swine influenza (SI) strains and avian/human-source influenza strains in piggeries can contribute to the evolution of new influenza viruses with pandemic potential. This study analyzed surveillance data on SI in south China and explored the spatial predictor variables associated with different influenza infection scenarios in counties within the study area. Blood samples were collected from 7670 pigs from 534 pig farms from 2015 to 2017 and tested for evidence of infection with influenza strains from swine, human and avian sources. The herd prevalences for EA H1N1, H1N1pdm09, classic H1N1, HS-like H3N2, seasonal human H1N1 and avian influenza H9N2 were 88.5, 64.5, 60.3, 57.8, 12.9 and 10.3 %, respectively. Anthropogenic factors including detection frequency, chicken density, duck density, pig density and human population density were found to be better predictor variables for three influenza infection scenarios (infection with human strains, infection with avian strains, and coinfection with H9N2 avian strain and at least one swine strain) than were meteorological and geographical factors. Predictive risk maps generated for the four provinces in south China highlighted that the areas with a higher risk of the three infection scenarios were predominantly clustered in the delta area of the Pearl River in Guangdong province and counties surrounding Poyang Lake in Jiangxi province. Identification of higher risk areas can inform targeted surveillance for influenza in humans and pigs, helping public health authorities in designing risk-based SI control strategies to address the pandemic influenza threat in south China.