Evolution and extensive reassortment of H5 influenza viruses isolated from wild birds in China over the past decade

Isoleucine at position 137 of haemagglutinin acts as a mammalian adaptation marker of H9N2 avian influenza virus

The H9N2 subtype of avian influenza virus (AIV) is widely distributed among poultry and wild birds and is also a threat to humans. During AIV active surveillance in Liaoning province from 2015 to 2016, we identified 10 H9N2 strains exhibiting different lethality to chick embryos. Two representative strains, A/chicken/China/LN07/2016 (CKLN/07) and A/chicken/China/LN17/2016 (CKLN/17), with similar genomic background but different chick embryo lethality, were chosen to evaluate the molecular basis for this difference. A series of reassortants between CKLN/07 and CKLN/17 were generated and their chick embryo lethality was assessed. We found that the isoleucine (I) residue at position 137 (H3 numbering) in the haemagglutinin (HA) was responsible for the chick embryo lethality of the H9N2 virus. Further studies revealed that the threonine (T) to I mutation at HA position 137 enhanced viral replication in vitro and in vivo. Moreover, the HA-T137I substitution in H9N2 avian influenza virus increased the guinea pig transmission efficiency. We also found that the HA-T137I substitution was critical for α2,6-linked sialic acid binding preference and HA activation and stability of H9N2 virus. Our findings demonstrated that HA-137I is a key molecular marker for mammalian adaptation of H9N2 AIV.

Evaluation of global distribution, genetic evolution, and mammalian infectivity and pathogenicity of H13 and H16 avian influenza viruses

H13 and H16 subtype avian influenza viruses (AIVs) typically infect Charadriiformes, are widely distributed throughout coastal regions worldwide, and pose a risk of spill-over to mammals. Systematic research on the epidemiology, transmission dynamics, and biological characteristics of these subtypes remains limited. To address this gap, we analyzed 20 years of wild bird influenza surveillance data from China integrated with global influenza database information to reconstruct the global spatiotemporal distribution, transmission dynamics and public health implications of H13 and H16. During influenza surveillance, 28 H13 and 19 H16 viruses were isolated. The phylogenetic trees for the H13 and H16 viruses revealed that both subtypes could be classified into three distinct groups. Viruses from H13 Group A, H13 Group C, and H16 Group C demonstrated frequent genetic exchanges and intercontinental transmission on a global scale. Mapping host migration revealed overlap between virus spread and host migration pathways. Our results suggest that host migration is a key driver of widespread distribution, cross-regional spread, and gene exchange for some H13 and H16 lineages. Virus isolates exhibit high genetic diversity with rich genotypic variation. Most isolates carry mammalian-adaptive mutations, such as the G228S mutation in the HA protein. H13 and H16 isolates of multiple genotypes infected mice without prior adaptation and exhibited varying tissue tropism. In summary, these findings indicate that host migration patterns are closely associated with the evolution of H13 and H16 AIVs. The potential risk of mammalian infection is highlighted, as viruses carrying mammalian-adaptive mutations may lead to new infection cases.

Avian influenza A(H5N6) virus detected during live-poultry market surveillance linked to a human infection in Changsha, China, from 2020 to 2023

In November 2022, we reported a fatal case of human infection caused by a highly pathogenic avian influenza A(H5N6) virus bearing a clade 2.3.4.4b HA gene in Changsha City. We investigated the transmission route and distribution of the H5N6 virus in the largest live-poultry market (LPM), which is linked to the human infection. A total of 1357 samples from the LPM were collected for avian influenza A virus detection from 2020 to 2023. The proportion of LPM samples positive for H5 subtype avian influenza virus was 14.30% (194/1357). Sequences of H5N6 (n = 10) and H5N1 (n = 4) avian influenza viruses were obtained from the LPM samples using next-generation sequencing. The complete genome sequence of the H5N6 virus from the human infection case, A/Changsha/1/2022(EPI_ISL_16466440), was determined and analyzed. The PB1 and PB2 segments shared 99.65% and 99.23% sequence identity with A/duck/Hunan/S40199/2021(H5N6) and A/Whooper swan/Sanmenxia/H615/2020(H5N8), respectively. The other segments showed the highest sequence similarity to strain A/Guangdong/1/2021(H5N6), which was isolated in Guangzhou. L89V and I292V substitutions in the PB2 protein were predicted from the A/Changsha/1/2022 genome sequence. Phylogenetic analysis based on the HA gene showed that A/Changsha/1/2022 and other H5 subtype isolates obtained from the LPM grouped together in the 2.3.4.4b branch. Bayesian evolutionary analysis of the HA gene showed that clade 2.3.4.4b of the H5N6 virus is likely to have been prevalent in Hunan Province around October 2021. In conclusion, we confirmed that the clade 2.3.4.4b HA gene of A/Changsha/1/2022 virus recombined with those of local strains. These results demonstrate the importance of continuous surveillance of H5N6 influenza viruses.

Emergence, migration and spreading of the high pathogenicity avian influenza virus H5NX of the Gs/Gd lineage into America

The high pathogenicity avian influenza virus H5N1, which first emerged in the winter of 2021, has resulted in multiple outbreaks across the American continent through the summer of 2023 and they continue based on early 2025 records, presenting significant challenges for global health and food security. The viruses causing the outbreaks belong to clade 2.3.4.4b, which are descendants of the lineage A/Goose/Guangdong/1/1996 (Gs/Gd) through genetic reassortments with several low pathogenicity avian influenza viruses present in populations of Anseriformes and Charadriiformes orders. This review addresses these issues by thoroughly analysing available epidemiological databases and specialized literature reviews. This project explores the mechanisms behind the resurgence of the H5N1 virus. It provides a comprehensive overview of the origin, timeline and factors contributing to its prevalence among wild bird populations on the American continent.

Genomic Characterization and Phylogenetic Analysis of Five Avian Influenza H5N1 Subtypes from Wild Anser indicus in Yunnan, China

Highly pathogenic avian influenza (HPAI) H5 viruses have been found to have a substantial geographic distribution since they were first reported in Guangdong Province, China. The emergence of new genotypes threatens the poultry industry and human health worldwide. Here, we report five HPAI H5N1 variants isolated from Anser indicus in Yunnan Province, China. A phylogenetic analysis of the hemagglutinin (HA) gene showed that all isolates belong to the highly pathogenic H5 clade 2.3.4.4b and formed two distinct genetic clusters. Bayesian phylogenetic analysis also revealed that the viruses were initially disseminated from wild birds to Anser indicus, implying that infected birds most likely contributed to viral transmission in the region. Genomic sequence analysis revealed several amino acid substitutions, also implying that the infected birds contributed to the spread of the virus throughout the region. Substitutions in the HA glycoprotein increased the virus's binding affinity to human α-2,6 sialic acid residues. Substitutions in the PB1, PA, and PB2 motifs increased viral polymerase activity and replication in hosts, whereas substitutions in the NP, M1, and NS motifs increased viral pathogenicity in chickens and mice.

Genetic diversity of highly pathogenic avian influenza H5N6 and H5N8 viruses in poultry markets in Guangdong, China, 2020-2022

H5 highly pathogenic avian influenza (HPAI) viruses of the A/Goose/Guangdong/1/96 (Gs/Gd) lineage continue to evolve and cause outbreaks in domestic poultry and wild birds, with sporadic spillover infections in mammals. The global spread of clade 2.3.4.4b viruses via migratory birds since 2020 has facilitated the introduction of novel reassortants to China, where avian influenza of various subtypes have been epizootic or enzootic among domestic birds. To determine the impact of clade 2.3.4.4b re-introduction on local HPAI dynamics, we analyzed the genetic diversity of H5N6 and H5N8 detected from monthly poultry market surveillance in Guangdong, China, between 2020 and 2022. Our findings reveal that H5N6 viruses clustered in clades 2.3.4.4b and 2.3.4.4h, while H5N8 viruses were exclusively clustered in clade 2.3.4.4b. After 2020, the re-introduced clade 2.3.4.4b viruses replaced the clade 2.3.4.4h viruses detected in 2020. The N6 genes were divided into two clusters, distinguished by an 11 amino acid deletion in the stalk region, while the N8 genes clustered with clade 2.3.4.4 H5N8 viruses circulating among wild birds. Genomic analysis identified 10 transient genotypes. H5N6, which was more prevalently detected, was also clustered into more genotypes than H5N8. Specifically, H5N6 isolates contained genes derived from HPAI H5Nx viruses and low pathogenic avian influenza in China, while the H5N8 isolates contained genes derived from HPAI A(H5N8) 2.3.4.4b and A(H5N1) 2.3.2.1c. No positive selection on amino acid residues associated with mammalian adaptation was found. Our results suggest expanded genetic diversity of H5Nx viruses in China since 2021 with increasing challenges for pandemic preparedness.IMPORTANCESince 2016/2017, clade 2.3.4.4b H5Nx viruses have spread via migratory birds to all continents except Oceania. Here, we evaluated the impact of the re-introduction of clade of 2.3.4.4b on highly pathogenic avian influenza (HPAI) virus genetic diversity in China. Twenty-two H5N6 and H5N8 HPAI isolated from monthly surveillance in two poultry markets in Guangdong between 2020 and 2022 were characterized. Our findings showed that clade 2.3.4.4h, detected in 2020, was replaced by clade 2.3.4.4b in 2021-2022. H5N6 (n = 18) were clustered into more genotypes than H5N8 (n = 4), suggesting that H5N6 may possess better replication fitness in poultry. Conversely, the H5N8 genotypes are largely derived from the clade 2.3.4.4b wild bird isolates. As clade 2.3.4.4b continues to spread via migratory birds, it is anticipated that the genetic diversity of H5N6 viruses circulating in China may continue to expand in the coming years. Continuous efforts in surveillance, genetic analysis, and risk assessment are therefore crucial for pandemic preparedness.

Novel H16N3 avian influenza viruses isolated from migratory gulls in China in 2023

As a rare subtype of avian influenza virus, H16 viruses are predominant in gulls but rarely found in domestic birds. The low prevalence of H16 viruses has limited our understanding of their epidemiology and evolutionary dynamics. In this study, we isolated three novel H16N3 viruses from migratory gulls in East Asian-Australasian Flyway in eastern China in 2023, which are significantly different from previously identified isolates. To fully understand the epidemiology and genetics characteristics of the global H16 viruses, we compared the host divergence of several rare subtypes and determined that the H13 and H16 subtypes were predominantly pooled into different species of gulls by sharing their internal genes, whereas the waterfowl of Anatidae served as the primary natural reservoirs of the H8, H11, H12, H14, and H15 subtypes. Detailed phylogenetic analysis revealed the evolutionary divergence of globally circulating H16 viruses and their frequent gene reassortment. Furthermore, the gull origin H13 and H16 viruses collectively served as gene donors for the newly emerged highly pathogenic clade 2.3.4.4b H5N1 viruses because the H13/H16-like PA, NP, and NS genes have been introduced into circulating H5N1 viruses since May 2022 in Europe. To date, the H5N1 reassortants containing the H13/H16-like gene segments have been detected in wild and domestic birds and resulted in mammal and human infections. These results improve our knowledge of the ecology and genetics of H16 viruses and emphasize the need for surveillance to monitor the emergence of novel avian influenza viruses in migratory birds.

Detection and characterisation of high pathogenicity avian influenza virus (H5N1/H5N8) clade 2.3.4.4b, Hong Kong SAR, China, 2021 to 2024

We isolated three genotypes of highly pathogenic avian influenza virus (HPAIV) clade 2.3.4.4b from wild birds infected with H5N1 (n = 12) and H5N8 (n = 1) in Hong Kong SAR 2021-2024. Viruses from two spoonbills from late 2022 were genetically related to a virus from a human in China. Four tested viruses exhibited variable virulence in mice but were susceptible to approved antivirals. No neutralising antibody was detected in 63 age-stratified human sera, suggesting potential risk should the virus adapt to humans.

A Model H5N2 Vaccine Strain for Dual Protection Against H5N1 and H9N2 Avian Influenza Viruses

Background/Objective: Highly pathogenic (HP) H5Nx and low-pathogenicity (LP) H9N2 avian influenza viruses (AIVs) pose global threats to the poultry industry and public health, highlighting the critical need for a dual-protective vaccine. Methods: In this study, we generated a model PR8-derived recombinant H5N2 vaccine strain with hemagglutinin (HA) and neuraminidase (NA) genes from clade 2.3.2.1c H5N1 and Y439-like H9N2 viruses, respectively. To enhance the immunogenicity of the recombinant H5N2 vaccine strain, N-glycans of the HA2 subunit, NA, and M2e were modified. Additionally, we replaced M2e with avian M2e to enhance the antigenic homogeneity of AIVs for better protection. We also replaced PR8 PB2 with 01310 PB2, which is the PB2 gene derived from an LP H9N2 avian influenza virus, to eliminate pathogenicity in mammals. The productivity of the model vaccine strain (rvH5N2-aM2e-vPB2) in embryonated chicken eggs (ECEs), its potential risk of mammalian infection, and the immunogenicity associated with different inactivation methods (formaldehyde (F/A) vs. binary ethyleneimine (BEI)) were evaluated. Results: The rvH5N2-aM2e-vPB2 strain demonstrated high productivity in ECEs and exhibited complete inhibition of replication in mammalian cells. Furthermore, compared with using F/A inactivation, inactivation using BEI significantly enhanced the immune response, particularly against NA. This enhancement resulted in increased virus neutralization titers, supporting its efficacy for dual protection against H5Nx and H9N2 avian influenza viruses. Furthermore, we demonstrated that M2e-specific immune responses, difficult to induce with inactivated vaccines, can be effectively elicited with live vaccines, suggesting a strategy to enhance M2e immunogenicity in whole influenza virus vaccines. Conclusions: Finally, the successful development of the model rH5N2 vaccine strain is described; this strain provides dual protection, has potential applicability in regions where avian influenza is endemic, and can be used to promote the development of versatile H5N2 recombinant vaccines for effective avian influenza control.

Combination Adjuvants Enhance Recombinant H5 Hemagglutinin Vaccine Protection Against High-Dose Viral Challenge in Chickens

BACKGROUND

Recombinant avian influenza subunit vaccines often require adjuvants to enhance immune responses. This study aims to evaluate the immune-enhancing potential of seven combination adjuvants in specific pathogen-free (SPF) chickens.

METHODS

SPF chickens were vaccinated with combinations of ISA78VG and adjuvants, including Quil-A, CpG, and monophosphoryl lipid A (MPLA). Their immune responses were assessed using a vaccination and viral challenge protection model.

RESULTS

The combinations of ISA78VG with Quil-A, CpG&MPLA or CpG&Quil-A significantly enhanced antibody responses and provided cross-protection against the H5N8-20135 strain. The ISA78VG&MPLA and ISA78VG&CpG&MPLA combinations induced the stronger IFN-γ production, with CpG further amplifying the immune response. The ISA78VG&Quil-A formulation, in particular, stimulated rapid antibody responses, achieving a 100% seroconversion by day 14 and high titers of hemagglutination inhibition (HI) antibodies against both the recombinant HA antigen and the H5N6-20053 virus.

CONCLUSIONS

The ISA78VG&Quil-A combination is an ideal adjuvant for enhancing the immunogenicity of avian influenza rHA subunit vaccines, offering a promising strategy for H5 subtype vaccine development.

The panzootic spread of highly pathogenic avian influenza H5N1 sublineage 2.3.4.4b: a critical appraisal of One Health preparedness and prevention

Changes in the epidemiology and ecology of H5N1 highly pathogenic avian influenza are devastating wild bird and poultry populations, farms and communities, and wild mammals worldwide. Having originated in farmed poultry, H5N1 viruses are now spread globally by wild birds, with transmission to many mammal and avian species, resulting in 2024 in transmission among dairy cattle with associated human cases. These ecological changes pose challenges to mitigating the impacts of H5N1 highly pathogenic avian influenza on wildlife, ecosystems, domestic animals, food security, and humans. H5N1 highly pathogenic avian influenza highlights the need for One Health approaches to pandemic prevention and preparedness, emphasising multisectoral collaborations among animal, environmental, and public health sectors. Action is needed to reduce future pandemic risks by preventing transmission of highly pathogenic avian influenza among domestic and wild animals and people, focusing on upstream drivers of outbreaks, and ensuring rapid responses and risk assessments for zoonotic outbreaks. Political commitment and sustainable funding are crucial to implementing and maintaining prevention programmes, surveillance, and outbreak responses.

Evolution and biological characterization of H5N1 influenza viruses bearing the clade 2.3.2.1 hemagglutinin gene

H5N1 avian influenza viruses bearing the clade 2.3.2.1 hemagglutinin (HA) gene have been widely detected in birds and poultry in several countries. During our routine surveillance, we isolated 28 H5N1 viruses between January 2017 and October 2020. To investigate the genetic relationship of the globally circulating H5N1 viruses and the biological properties of those detected in China, we performed a detailed phylogenic analysis of 274 representative H5N1 strains and analyzed the antigenic properties, receptor-binding preference, and virulence in mice of the H5N1 viruses isolated in China. The phylogenic analysis indicated that the HA genes of the 274 viruses belonged to six subclades, namely clades 2.3.2.1a to 2.3.2.1f; these viruses acquired gene mutations and underwent complicated reassortment to form 58 genotypes, with G43 being the dominant genotype detected in eight Asian and African countries. The 28 H5N1 viruses detected in this study carried the HA of clade 2.3.2.1c (two strains), 2.3.2.1d (three strains), or 2.3.2.1f (23 strains), and formed eight genotypes. These viruses were antigenically well-matched with the H5-Re12 vaccine strain used in China. Animal studies showed that the pathogenicity of the H5N1 viruses ranged from non-lethal to highly lethal in mice. Moreover, the viruses exclusively bound to avian-type receptors and have not acquired the ability to bind to human-type receptors. Our study reveals the overall picture of the evolution of clade 2.3.2.1 H5N1 viruses and provides insights into the control of these viruses.

Epidemiology and biological characteristics of influenza A (H4N6) viruses from wild birds

During the active surveillance, we isolated nine H4N6 subtype influenza A viruses from wild birds in China. To reveal the epidemiology and biology characteristics of H4 subtype influenza A virus from wild birds, we investigated H4 subtype viruses available in the public source, and found that the H4 viruses have been detected in at least 37 countries to date, and more than 73.6% of the viruses were from wild Anseriformes. Bayesian phylogeographic analysis showed that Mongolia worked as the important transmission centre for Eurasian lineage H4 viruses spreading. Phylogenetic analysis of HA genes indicated that global H4 influenza A viruses were divided into Eurasian and North American lineage, our nine H4N6 isolates fell into the Eurasian lineage. Recombination analysis suggested that nine H4N6 isolates underwent complex gene recombination with various subtypes of influenza A viruses and formed two genotypes. Notably, nine H4N6 isolates acquired mammalian virulence-increasing residues. Two representative H4N6 viruses possessed dual receptor binding specificity, they could efficiently replicate in MDCK and 293 T cells in vitro infection, also could cross the species barrier to infect mice directly without prior adaption in vivo experiments. These findings emphasize the public health issues represented by H4 viruses, and highlight the need to strengthen the active surveillance of H4 viruses from wild birds.

Recombinant duck enteritis virus bearing the hemagglutinin genes of H5 and H7 influenza viruses is an ideal multivalent live vaccine in ducks

Due to the fact that many avian influenza viruses that kill chickens are not lethal to ducks, farmers are reluctant to use avian influenza inactivated vaccines on ducks. Large numbers of unvaccinated ducks play an important role in the transmission of avian influenza viruses from wild birds to domestic poultry, creating a substantial challenge to vaccination strategies for avian influenza control. To solve this problem, we constructed a recombinant duck enteritis virus (DEV), rDEV-dH5/H7, using a live attenuated DEV vaccine strain (vDEV) as a vector. rDEV-dH5/H7 carries the hemagglutinin gene of two H5 viruses [GZ/S4184/17 (H5N6) (clade 2.3.4.4 h) and LN/SD007/17 (H5N1) (clade 2.3.2.1d)] and an H7 virus [GX/SD098/17 (H7N9)]. These three hemagglutinin genes were stably inherited in rDEV-dH5/H7 and expressed in rDEV-dH5/H7-infected cells. Animal studies revealed that rDEV-dH5/H7 and vDEV induced similar neutralizing antibody responses and protection against lethal DEV challenge. Importantly, rDEV-dH5/H7 induced strong and long-lasting hemagglutinin inhibition antibodies against different H5 and H7 viruses and provided complete protection against challenges with homologous and heterologous highly pathogenic H5 and H7 influenza viruses in ducks. Our study shows that rDEV-dH5/H7 could serve as an ideal live attenuated vaccine to protect ducks against infection with lethal DEV and highly pathogenic avian influenza viruses.

Emergence of HPAI H5N6 Clade 2.3.4.4b in Wild Birds: A Case Study From South Korea, 2023

The emergence and evolution of avian influenza A viruses (AIVs) pose significant challenges to both public health and animal husbandry worldwide. Here, we characterized a novel reassortant highly pathogenic avian influenza virus (HPAIV), clade 2.3.4.4b H5N6, that was isolated from a mandarin duck in South Korea in December 2023. Phylogenetic and molecular analyses show that the hemagglutinin (HA) gene of the 23-JBN-F12-36/H5N6 virus clustered with HPAIV clade 2.3.4.4b H5N1 viruses, which were circulating in South Korea and Japan in 2022-2023. The M and polymerase acidic (PA) genes also revealed a close association with the HPAIV clade 2.3.4.4b H5N1 AIV that was identified previously in South Korea during November 2022. Notably, the neuraminidase (NA) gene of the 23-JBN-F12-36/H5N6 virus was estimated to have its origins in the HPAIV clade 2.3.4.4h H5N6 prevalent in poultry in China, and it is clustered with the AIVs that are associated with human infection cases. Taken together, these results show that the virus has been produced by reassortment with H5N1 HPAIV, which is prevalent in wild birds; H5N6 HPAIV, which is circulated in poultry in China; and the internal genes of low pathogenic avian influenza viruses (LPAIVs). In light of the reassortment of HPAIVs circulating in existing wild birds and HPAIVs circulating in poultry in China within the 2.3.4.4b H5Nx clade, it is imperative to strengthen active surveillance across wild bird populations, poultry farms, and live poultry markets, and to inform for the effective design of improved prevention and control strategies.

The Alarming Situation of Highly Pathogenic Avian Influenza Viruses in 2019-2023

Avian influenza viruses (AIVs) have the potential to cause severe illness in wild birds, domestic poultry, and humans. The ongoing circulation of highly pathogenic avian influenza viruses (HPAIVs) has presented significant challenges to global poultry industry and public health in recent years. This study aimed to elucidate the circulation of HPAIVs during 2019 to 2023. Specifically, we assess the alarming global spread and continuous evolution of HPAIVs. Moreover, we discuss their transmission and prevention strategies to provide valuable references for future prevention and control measures against AIVs.

Spatiotemporal and Species-Crossing Transmission Dynamics of Subclade 2.3.4.4b H5Nx HPAIVs

Subclade 2.3.4.4b H5Nx highly pathogenic avian influenza (HPAI) viruses, emerged in 2013 with multiple subtypes of H5N8, H5N1, and H5N6, had unprecedently caused a global epizootic by H5N1 since 2021, which had devasted multiple species of wild birds, poultry, and wild mammals (terrestrial and marine) with a high mortality, causing severe ecological damage. The infected wild mammals may become new "mixers" for influenza viruses, posing the potential transmission to human. Frequent outbreaks of subclade 2.3.4.4b H5Nx viruses among wild birds and poultry had exposed major gaps in our knowledge on their evolution, spatiotemporal diffusion, and species-crossing transmission. Here, we integrated the phylogenetic and epidemiological data of subclade 2.3.4.4b H5Nx viruses in public database and used Bayesian phylodynamic analysis to reveal the pattern of the global large-scale transmission. Phylogenic analysis demonstrated that the HA gene of these viruses diverged into two dominant clusters around 2015 and 2016. The Bayesian phylodynamic analysis illustrated that the viruses presented spatiotemporally complex transmission network with geographical and host relative expansion and recombination with different subtypes of NA segment. Spatially, the Russian Federation (Siberia) was identified as the primary hub for virus transmission, which was further facilitated by the establishment of strong epidemiological linkages between West Europe and broader regions, such as North America. As for hosts, wild Anseriformes were the primary species for the virus spillover, contributing to the spatial expansion and rapid diffusion globally of subclade 2.3.4.4b viruses. We investigated the phylogeny of subclade 2.3.4.4b H5Nx viruses and the spatiotemporal pattern of transmission with initial location and the primary host, which could provide comprehensive insights for subclade 2.3.4.4b H5Nx viruses. Due to the wild birds involved the widespread of subclade 2.3.4.4b H5Nx viruses, the epizootics in poultry are inevitable, so we highly recommend to apply the policy of culling plus with vaccination to protect the poultry industry and potentially protect the public health.

Bio-Chemoinformatics-Driven Analysis of nsp7 and nsp8 Mutations and Their Effects on Viral Replication Protein Complex Stability

The nonstructural proteins 7 and 8 (nsp7 and nsp8) of SARS-CoV-2 are highly important proteins involved in the RNA-dependent polymerase (RdRp) protein replication complex. In this study, we analyzed the global mutation of nsp7 and nsp8 in 2022 and 2023 and analyzed the effects of mutation on the viral replication protein complex using bio-chemoinformatics. Frequently occurring variants are found to be single amino acid mutations for both nsp7 and nsp8. The most frequently occurring mutations for nsp7 which include L56F, L71F, S25L, M3I, D77N, V33I and T83I are predicted to cause destabilizing effects, whereas those in nsp8 are predicted to cause stabilizing effects, with the threonine to isoleucine mutation (T89I, T145I, T123I, T148I, T187I) being a frequent mutation. A conserved domain database analysis generated critical interaction residues for nsp7 (Lys-7, His-36 and Asn-37) and nsp8 (Lys-58, Pro-183 and Arg-190), which, according to thermodynamic calculations, are prone to destabilization. Trp-29, Phe-49 of nsp7 and Trp-154, Tyr-135 and Phe-15 of nsp8 cause greater destabilizing effects to the protein complex based on a computational alanine scan suggesting them as possible new target sites. This study provides an intensive analysis of the mutations of nsp7 and nsp8 and their possible implications for viral complex stability.

Virulence and transmission characteristics of clade 2.3.4.4b H5N6 subtype avian influenza viruses possessing different internal gene constellations

Clade 2.3.4.4 H5N6 avian influenza virus (AIV) has been predominant in poultry in China, and the circulating haemagglutinin (HA) gene has changed from clade 2.3.4.4h to clade 2.3.4.4b in recent years. In 2021, we isolated four H5N6 viruses from ducks during the routine surveillance of AIV in China. The whole-genome sequencing results demonstrated that the four isolates all belonged to the currently prevalent clade 2.3.4.4b but had different internal gene constellations, which could be divided into G1 and G2 genotypes. Specifically, G1 possessed H9-like PB2 and PB1 genes on the H5-like genetic backbone while G2 owned an H3-like PB1 gene and the H5-like remaining internal genes. By determining the characteristics of H5N6 viruses, including growth performance on different cells, plaque-formation ability, virus attachment ability, and pathogenicity and transmission in different animal models, we found that G1 strains were more conducive to replication in mammalian cells (MDCK and A549) and BALB/c mice than G2 strains. However, G2 strains were more advantageously replicated in avian cells (CEF and DF-1) and slightly more transmissible in waterfowls (mallards) than G1 strains. This study enriched the epidemiological data of H5 subtype AIV to further understand its dynamic evolution, and laid the foundation for further research on the mechanism of low pathogenic AIV internal genes in generating novel H5 subtype reassortants.

Alarming situation of emerging H5 and H7 avian influenza and effective control strategies

Avian influenza viruses continue to present challenges to animal and human health. Viruses bearing the hemagglutinin (HA) gene of the H5 subtype and H7 subtype have caused 2634 human cases around the world, including more than 1000 deaths. These viruses have caused numerous disease outbreaks in wild birds and domestic poultry, and are responsible for the loss of at least 422 million domestic birds since 2005. The H5 influenza viruses are spread by migratory wild birds and have caused three waves of influenza outbreaks across multiple continents, and the third wave that started in 2020 is ongoing. Many countries in Europe and North America control highly pathogenic avian influenza by culling alone, whereas some countries, including China, have adopted a "cull plus vaccination" strategy. As the largest poultry-producing country in the world, China lost relatively few poultry during the three waves of global H5 avian influenza outbreaks, and nearly eliminated the pervasive H7N9 viruses that emerged in 2013. In this review, we briefly summarize the damages the H5 and H7 influenza viruses have caused to the global poultry industry and public health, analyze the origin, evolution, and spread of the H5 viruses that caused the waves, and discuss how and why the vaccination strategy in China has been a success. Given that the H5N1 viruses are widely circulating in wild birds and causing problems in domestic poultry around the world, we recommend that any unnecessary obstacles to vaccination strategies should be removed immediately and forever.

Key Amino Acid Residues That Determine the Antigenic Properties of Highly Pathogenic H5 Influenza Viruses Bearing the Clade 2.3.4.4 Hemagglutinin Gene

The H5 subtype highly pathogenic avian influenza viruses bearing the clade 2.3.4.4 HA gene have been pervasive among domestic poultry and wild birds worldwide since 2014, presenting substantial risks to human and animal health. Continued circulation of clade 2.3.4.4 viruses has resulted in the emergence of eight subclades (2.3.4.4a-h) and multiple distinct antigenic groups. However, the key antigenic substitutions responsible for the antigenic change of these viruses remain unknown. In this study, we analyzed the HA gene sequences of 5713 clade 2.3.4.4 viruses obtained from a public database and found that 23 amino acid residues were highly variable among these strains. We then generated a series of single-amino-acid mutants based on the H5-Re8 (a vaccine seed virus) background and tested their reactivity with a panel of eight monoclonal antibodies (mAbs). Six mutants bearing amino acid substitutions at positions 120, 126, 141, 156, 185, or 189 (H5 numbering) led to reduced or lost reactivity to these mAbs. Further antigenic cartography analysis revealed that the amino acid residues at positions 126, 156, and 189 acted as immunodominant epitopes of H5 viruses. Collectively, our findings offer valuable guidance for the surveillance and early detection of emerging antigenic variants.

Highly Pathogenic Avian Influenza Virus (H5N1) Clade 2.3.4.4b Introduced by Wild Birds, China, 2021

Highly pathogenic avian influenza (HPAI) subtype H5N1 clade 2.3.4.4b virus has spread globally, causing unprecedented large-scale avian influenza outbreaks since 2020. In 2021, we isolated 17 highly pathogenic avian influenza H5N1 viruses from wild birds in China. To determine virus origin, we genetically analyzed 1,529 clade 2.3.4.4b H5N1 viruses reported globally since October 2020 and found that they formed 35 genotypes. The 17 viruses belonged to genotypes G07, which originated from eastern Asia, and G10, which originated from Russia. The viruses were moderately pathogenic in mice but were highly lethal in ducks. The viruses were in the same antigenic cluster as the current vaccine strain (H5-Re14) used in China. In chickens, the H5/H7 trivalent vaccine provided complete protection against clade 2.3.4.4b H5N1 virus challenge. Our data indicate that vaccination is an effective strategy for preventing and controlling the globally prevalent clade 2.3.4.4b H5N1 virus.

Genetic characteristics of waterfowl-origin H5N6 highly pathogenic avian influenza viruses and their pathogenesis in ducks and chickens

Waterfowl, such as ducks, are natural hosts for avian influenza viruses (AIVs) and act as a bridge for transmitting the virus to humans or susceptible chickens. Since 2013, chickens and ducks have been threatened by waterfowl-origin H5N6 subtype AIVs in China. Therefore, it is necessary to investigate the genetic evolution, transmission, and pathogenicity of these viruses. In this study, we determined the genetic characteristics, transmission, and pathogenicity of waterfowl-origin H5N6 viruses in southern China. The hemagglutinin (HA) genes of H5N6 viruses were classified into the MIX-like branch of clade 2.3.4.4h. The neuraminidase (NA) genes belonged to the Eurasian lineage. The PB1 genes were classified into MIX-like and VN 2014-like branches. The remaining five genes were clustered into the MIX-like branch. Therefore, these viruses belonged to different genotypes. The cleavage site of the HA proteins of these viruses was RERRRKR/G, a molecular characteristic of the H5 highly pathogenic AIV. The NA stalk of all H5N6 viruses contained 11 amino acid deletions at residues 58-68. All viruses contained 627E and 701D in the PB2 proteins, which were molecular characteristics of typical bird AIVs. Furthermore, this study showed that Q135 and S23 viruses could replicate systematically in chickens and ducks. They did not cause death in ducks but induced mild clinical signs in them. All the infected chickens showed severe clinical signs and died. These viruses were shed from the digestive and respiratory tracts and transmitted horizontally in chickens and ducks. Our results provide valuable information for preventing H5N6 avian influenza outbreaks.

Highly Pathogenic H5 Influenza Viruses Isolated between 2016 and 2017 in Vietnamese Live Bird Markets

Routine surveillance in live poultry markets in the northern regions of Vietnam from 2016 to 2017 resulted in the isolation of 27 highly pathogenic avian H5N1 and H5N6 viruses of 3 different clades (2.3.2.1c, 2.3.4.4f, and 2.3.4.4g). Sequence and phylogenetic analysis of these viruses revealed reassortment with various subtypes of low pathogenic avian influenza viruses. Deep-sequencing identified minor viral subpopulations encoding variants that may affect pathogenicity and sensitivity to antiviral drugs. Interestingly, mice infected with two different clade 2.3.2.1c viruses lost body weight rapidly and succumbed to virus infection, whereas mice infected with clade 2.3.4.4f or 2.3.4.4g viruses experienced non-lethal infections.

Evolution and mammalian adaptation of H3 and H10 subtype avian influenza viruses in wild birds in Yancheng Wetland of China

Wild birds play a critical role in avian influenza virus (AIV) ecology and some outbreaks of avian influenza in human originate from wild birds, suggesting that epidemiological surveillance and interspecies-transmission analysis of AIVs in wild birds are critical. Since 2019, we have performed sampling in Yancheng Wetland along the East Asian-Australasian Flyway. Totally, 2054 fecal swabs were collected and one H3N8, two H3N1, one H10N8, and three H10N1 were isolated. Three H3 gene of AIVs we isolated belonged to Eurasian lineage, but the four H10 gene clustered into North American lineage. What's more, the H3 and the foreign H10 gene had generated novel reassortants in Yancheng wetland. Receptor binding assay indicated that nearly all strains, except D369/H10N1, presented a dual receptor-binding profile and bound to avian-type receptor preferentially. In animal experiment, all isolates could infect mice without prior adaptation and induce histopathological changes in mice lungs, moreover, all H3 subtype AIVs obviously triggered weight loss of mice. In addition to lung and turbinate, D322/H3N1, D338/H3N8, D211/H10N8 and D266/H10N1 could spread to brain and kidney or liver or spleen, showing a wider range of tissue tropism. Multiple mutants associated with mammalian adaptation were also detected in all isolates according to molecular analysis. These findings revealed that H3 and H10 AIVs circulating in wild birds in Yancheng Wetland underwent complex reassortment and increased mammalian adaptation, which highlighted the necessity to monitor the diverse reassortment of AIVs in wild birds and evaluate the risks of H3 and H10 viruses to human health.

Emerging Highly Pathogenic Avian Influenza (H5N8) Virus in Podiceps nigricollis in Northwest China in 2021

Three highly pathogenic avian influenza (H5N8) viruses were detected in the migratory bird Podiceps nigricollis in Northwest China in June 2021. Phylogenetic analysis indicated that these H5N8 isolates belonged to clade 2.3.4.4b, which were highly homologous to strains isolated in China and South Korea. In this study, H5N8 virus infection in Podiceps nigricollis was detected using Oxford Nanopore Technologies sequencing technology and caused pathological changes in multiple organs.

Superinfection exclusion creates spatially distinct influenza virus populations

Interactions between viruses during coinfections can influence viral fitness and population diversity, as seen in the generation of reassortant pandemic influenza A virus (IAV) strains. However, opportunities for interactions between closely related viruses are limited by a process known as superinfection exclusion (SIE), which blocks coinfection shortly after primary infection. Using IAVs, we asked whether SIE, an effect which occurs at the level of individual cells, could limit interactions between populations of viruses as they spread across multiple cells within a host. To address this, we first measured the kinetics of SIE in individual cells by infecting them sequentially with 2 isogenic IAVs, each encoding a different fluorophore. By varying the interval between addition of the 2 IAVs, we showed that early in infection SIE does not prevent coinfection, but that after this initial lag phase the potential for coinfection decreases exponentially. We then asked how the kinetics of SIE onset controlled coinfections as IAVs spread asynchronously across monolayers of cells. We observed that viruses at individual coinfected foci continued to coinfect cells as they spread, because all new infections were of cells that had not yet established SIE. In contrast, viruses spreading towards each other from separately infected foci could only establish minimal regions of coinfection before reaching cells where coinfection was blocked. This created a pattern of separate foci of infection, which was recapitulated in the lungs of infected mice, and which is likely to be applicable to many other viruses that induce SIE. We conclude that the kinetics of SIE onset segregate spreading viral infections into discrete regions, within which interactions between virus populations can occur freely, and between which they are blocked.

H3N8 subtype avian influenza virus originated from wild birds exhibited dual receptor-binding profiles

We present the phylogeny, receptor binding property, growth in mammal cells and pathogenicity in mammal model of H3N8 viruses, which were isolated from wild birds in China. The human receptor preference and efficient replication in mice without prior adaption highlight that the H3N8 virus possesses the public threat potential.

Highly Pathogenic Avian Influenza A(H5N1) Virus Clade 2.3.4.4b in Wild Birds and Live Bird Markets, Egypt

Clade 2.3.4.4 H5Nx influenza viruses have further diversified into several subclades. Sub-clade 2.3.4.4b H5N1 viruses have been widely circulating in wild birds and detected in Europe, Africa, Asia, and North America since October 2020. In this study, we report the first detection of highly pathogenic avian influenza H5N1 clade 2.3.4.4b viruses in wild birds and domestic ducks from live bird markets in Egypt. Phylogenetic analysis revealed that the Egyptian H5N1 virus retained the genomic composition of Eurasian strains. Mutations in the viral proteins associated with zoonotic potential and pathogenicity were detected in Egyptian isolates. Egypt is considered a hot spot for the evolution of the influenza virus, so active surveillance of avian influenza viruses in Egypt is warranted.

Global dissemination of H5N1 influenza viruses bearing the clade 2.3.4.4b HA gene and biologic analysis of the ones detected in China

H5N1 avian influenza viruses bearing the clade 2.3.4.4b hemagglutinin gene have been widely circulating in wild birds and are responsible for the loss of over 70 million domestic poultry in Europe, Africa, Asia, and North America since October 2020. During our routine surveillance, 13 H5N1 viruses were isolated from 26,767 wild bird and poultry samples that were collected between September 2021 and March 2022 in China. To investigate the origin of these Chinese isolates and understand their genetic relationship with the globally circulating H5N1 viruses, we performed a detailed phylogenic analysis of 233 representative H5N1 strains that were isolated from 28 countries. We found that, after they emerged in the Netherlands, the H5N1 viruses encountered complicated gene exchange with different viruses circulating in wild birds and formed 16 genotypes. Genotype one (G1) was predominant, being detected in 22 countries, whereas all other genotypes were only detected in one or two continents. H5N1 viruses of four genotypes (G1, G7, G9, and G10) were detected in China; three of these genotypes have been previously reported in other countries. The H5N1 viruses detected in China replicated in mice, with pathogenicity varying among strains; the G1 virus was highly lethal in mice. Moreover, we found that these viruses were antigenically similar to and well matched with the H5-Re14 vaccine strain currently used in China. Our study reveals the overall picture of H5N1 virus evolution and provides insights for the control of these viruses.

H5N8 Subtype avian influenza virus isolated from migratory birds emerging in Eastern China possessed a high pathogenicity in mammals

Novel H5N8 highly pathogenic avian influenza viruses (HPAIVs) bearing the clade 2.3.4.4b HA gene have been widely spread through wild migratory birds since 2020. One H5N8 HPAIV (A/Wild bird/Cixi/Cixi02/2020; here after Cixi02) was isolated from migratory birds in Zhejiang Province, Eastern China in 25 November 2020. However, its pathogenicity in avian and mammal remains unknown. Hemagglutinin gene genetic analysis indicated that Cixi02 virus belonged to the branch II of H5 clade 2.3.4.4b originated from Iraq in May 2020. Cixi02 virus showed a binding affinity to both SA α-2, 3-galactose (Gal) and SA α-2, 6 Gal receptors, good pH stability, thermostability, and replication ability in both avian and mammal cells. The poultry pathogenicity indicated that Cixi02 virus was lethal to chickens. Moreover, the mammalian pathogenicity showed that the 50% mouse lethal dose (MLD50 ) is 2.14 lgEID50 /50 μl, indicating a high pathogenicity in mice. Meanwhile, Cixi02 virus was widely detected in multiple organs, including heart, liver, spleen, lung, kidney, turbinate, and brain after nasal infection. In addition, we found high level gene expressions of TNF-α, IL-12p70, CXCL10, and IFN-α in lungs, IL-8 and IL-1β in brains, and observed severe histopathological change in lungs and brains. Collectedly, this study provided new insights on the pathogenic and zoonotic features of an H5N8 subtype AIV isolated from migratory birds.

H1N1 Influenza A Virus Protein NS2 Inhibits Innate Immune Response by Targeting IRF7

Influenza A virus (IAV) is a globally distributed zoonotic pathogen and causes a highly infectious respiratory disease with high morbidity and mortality in humans and animals. IAV has evolved various strategies to counteract the innate immune response, using different viral proteins. However, the mechanisms are not fully elucidated. In this study, we demonstrated that the nonstructural protein 2 (NS2) of H1N1 IAV negatively regulate the induction of type-I interferon. Co-immunoprecipitation experiments revealed that NS2 specifically interacts with interferon regulatory factor 7 (IRF7). NS2 blocks the nuclear translocation of IRF7 by inhibiting the formation of IRF7 dimers, thereby prevents the activation of IRF7 and inhibits the production of interferon-beta. Taken together, these findings revealed a novel mechanism by which the NS2 of H1N1 IAV inhibits IRF7-mediated type-I interferon production.

Clinical features of the first critical case of acute encephalitis caused by avian influenza A (H5N6) virus

Highly pathogenic avian influenza viruses (HPAIV), such as H5N1, H5N6, and H7N9, have been reported to frequently infect humans, but acute encephalitis caused by HPAIV in humans has been rarely reported. We report the first critical case of acute encephalitis with mild pneumonia caused by the H5N6 virus. On January 25 of 2022, a 6-year-old girl with severe neurological symptoms was admitted to our hospital and rapidly developed into seizures and coma. Brain imaging showed abnormalities. Electroencephalogram (EEG) presented abnormal slow waves. Cerebrospinal fluid (CSF) contained elevated protein (1.64 g/L) and white cells (546 × 10⁶/L). Laboratory investigations revealed abnormally elevated transaminases, lactate dehydrogenase, and cytokines in serum. A novel reassortant H5N6 virus was identified from the patient’s serum, CSF, and tracheal aspirate specimens. Phylogenic analysis indicated that this virus was a novel reassortant avian-origin influenza A (H5N6) virus that belonged to clade 2.3.4.4b. This patient was diagnosed with acute encephalitis and discharged from the hospital accompanied by a language barrier. An epidemiological investigation confirmed that wild waterfowls were the direct source of infection in this case. Our study highlights the urgent need to pay attention to acute encephalitis caused by HPAIV.

Evolutionary features of a prolific subtype of avian influenza A virus in European waterfowl

Avian influenza A virus (AIV) is ubiquitous in waterfowl and is detected annually at high prevalence in waterfowl during the Northern Hemisphere autumn. Some AIV subtypes are globally common in waterfowl, such as H3N8, H4N6, and H6N2, and are detected in the same populations at a high frequency, annually. In order to investigate genetic features associated to the long-term maintenance of common subtypes in migratory ducks, we sequenced 248 H4 viruses isolated across 8 years (2002-9) from mallards (Anas platyrhynchos) sampled in southeast Sweden. Phylogenetic analyses showed that both H4 and N6 sequences fell into three distinct lineages, structured by year of isolation. Specifically, across the 8 years of the study, we observed lineage replacement, whereby a different HA lineage circulated in the population each year. Analysis of deduced amino acid sequences of the HA lineages illustrated key differences in regions of the globular head of hemagglutinin that overlap with established antigenic sites in homologous hemagglutinin H3, suggesting the possibility of antigenic differences among these HA lineages. Beyond HA, lineage replacement was common to all segments, such that novel genome constellations were detected across years. A dominant genome constellation would rapidly amplify in the duck population, followed by unlinking of gene segments as a result of reassortment within 2-3 weeks following introduction. These data help reveal the evolutionary dynamics exhibited by AIV on both annual and decadal scales in an important reservoir host.

Phylogenetic and Phylogeographic Analysis of the Highly Pathogenic H5N6 Avian Influenza Virus in China

The clade 2.3.4.4b H5N8 avian influenza viruses (AIVs) have caused the loss of more than 33 million domestic poultry worldwide since January 2020. Novel H5N6 reassortants with hemagglutinin (HA) from clade 2.3.4.4b H5N8 AIVs are responsible for multiple human infections in China. Therefore, we conducted an epidemiological survey on waterfowl farms in Sichuan and Guangxi provinces and performed a comprehensive spatiotemporal analysis of H5N6 AIVs in China. At the nucleotide level, the H5N6 AIVs isolated in the present study exhibited high homology with the H5N6 AIVs that caused human infections. Demographic history indicates that clade 2.3.4.4b seemingly replaced clade 2.3.4.4h to become China’s predominant H5N6 AIV clade. Based on genomic diversity, we classified clade 2.3.4.4b H5N6 AIV into ten genotypes (2.3.4.4bG1–G10), of which the 2.3.4.4bG5 and G10 AIVs can cause human infections. Phylogeographic results suggest that Hong Kong and Jiangxi acted as important epicentres for clades 2.3.4.4b and 2.3.4.4h, respectively. Taken together, our study provides critical insight into the evolution and spread of H5N6 AIVs in China, which indicates that the novel 2.3.4.4b reassortants pose challenges for public health and poultry.

Epidemiologic, Clinical, and Genetic Characteristics of Human Infections with Influenza A(H5N6) Viruses, China

The recent rise in the frequency of influenza A(H5N6) infections in China has raised serious concerns about whether the risk for human infection has increased. We surveyed epidemiologic, clinical, and genetic data of human infections with A(H5N6) viruses. Severe disease occurred in 93.8% of cases, and the fatality rate was 55.4%. Median patient age was 51 years. Most H5N6 hemagglutinin (HA) genes in human isolates in 2021 originated from subclade 2.3.4.4b; we estimated the time to most recent common ancestor as June 16, 2020. A total of 13 genotypes with HA genes from multiple subclades in clade 2.3.4.4 were identified in human isolates. Of note, 4 new genotypes detected in 2021 were the major causes of increased H5N6 virus infections. Mammalian-adapted mutations were found in HA and internal genes. Although we found no evidence of human-to-human transmission, continuous evolution of H5N6 viruses may increase the risk for human infections.

Comparative Antigenicity and Pathogenicity of Two Distinct Genotypes of Highly Pathogenic Avian Influenza Viruses (H5N8) From Wild Birds in China, 2020-2021

To date, there have been three epidemic waves of H5N8 avian influenza worldwide. The current third epidemic wave began in October 2020 and has expanded to at least 46 countries. Active and passive surveillance were conducted to monitor H5N8 viruses from wild birds in China. Genetic analysis of 10 H5N8 viruses isolated from wild birds identified two different genotypes. Animal challenge experiments indicated that the H5N8 isolates are highly pathogenic in chickens, mildly pathogenic in ducks, while pathogenicity varied in BALB/c mice. Moreover, there were significant differences in antigenicity as compared to Re-11 vaccine strain and vaccinated chickens were not completely protected against challenge with the high dose of H5N8 virus. With the use of the new matched vaccine and increased poultry immune density, surveillance should be intensified to monitor the emergence of mutant strains and potential worldwide spread via wild birds.

Emergence, Evolution, and Biological Characteristics of H10N4 and H10N8 Avian Influenza Viruses in Migratory Wild Birds Detected in Eastern China in 2020

H10Nx influenza viruses have caused increasing public concern due to their occasional infection of humans. However, the genesis and biological characteristics of H10 viruses in migratory wild birds are largely unknown. In this study, we conducted active surveillance to monitor circulation of avian influenza viruses in eastern China and isolated five H10N4 and two H10N8 viruses from migratory birds in 2020. Genetic analysis indicated that the hemagglutinin (HA) genes of the seven H10 viruses were clustered into the North American lineage and established as a novel Eurasian branch in wild birds in South Korea, Bangladesh, and China. The neuraminidase (NA) genes of the H10N4 and H10N8 viruses originated from the circulating HxN4 and H5N8 viruses in migratory birds in Eurasia. We further revealed that some of the novel H10N4 and H10N8 viruses acquired the ability to bind human-like receptors. Animal studies indicated that these H10 viruses can replicate in mice, chickens, and ducks. Importantly, we found that the H10N4 and H10N8 viruses can transmit efficiently among chickens and ducks but induce lower HA inhibition (HI) antibody titers in ducks. These findings emphasized that annual surveillance in migratory waterfowl should be strengthened to monitor the introduction of wild-bird H10N4 and H10N8 reassortants into poultry.

IMPORTANCE The emerging avian influenza reassortants and mutants in birds pose an increasing threat to poultry and public health. H10 avian influenza viruses are widely prevalent in wild birds, poultry, seals, and minks and pose an increasing threat to human health. The occasional human infections with H10N8 and H10N3 viruses in China have significantly increased public concern about the potential pandemic risk posed by H10 viruses. In this study, we found that the North American H10 viruses have been successfully introduced to Asia by migratory birds and further reassorted with other subtypes to generate novel H10N4 and H10N8 viruses in eastern China. These emerging H10 reassortants have a high potential to threaten the poultry industry and human health due to their efficient replication and transmission in chickens, ducks, and mice.

WITHDRAWN: Molecular Evolution and Amino Acid Characteristics of Main Antigen Genes of Clinical Duck-Derived H5N6 Subtype Avian Influenza Virus in East China from 2015 to 2019

This article has been withdrawn at the request of the authors. The Publisher apologizes for any inconvenience this may cause.

Phylogenetic and phenotypic characterization of two novel clade 2.3.2.1 H5N2 subtype avian influenza viruses from chickens in China

The extended co-circulation of H5 subtype highly pathogenic avian influenza (HPAI) viruses and H9N2 low pathogenic avian influenza (LPAI) viruses has inevitably facilitated gene reassortment between the two subtypes in fields. And, novel reassortant H5NX viruses harboring partial or even whole sets of H9N2 internal genes have continuously been detected, such as clade 2.3.4.4 H5N2 or H5N6 reassortants. Here, we report two novel H5N2 subtype HPAI isolates of HF9 and QY5 from chickens in live poultry markets during routine surveillance in 2018. Phylogenetic analysis showed that those two H5N2 strains both possessed the HA genes from clade 2.3.2.1e of H5N1 viruses but all the other seven gene segments consistently from the endemic S genotype of H9N2 subtype viruses. Further analysis revealed that HF9 and QY5 differed only in six sites including K353R, A588T and T661I in PB2, I682V and L704S in PB1 plus G631S in PA at the amino acid level. A chicken regression experiment confirmed that both HF9 and QY5 were lethal infection to all tested chickens via contact transmission. Moreover, those two isolates could immediately replicate in mice lungs without adaptation. However, mortality rate of those two variants were distinct in mice model, HF9 with 100% but QY5 with just 20% at the infection dosage of 10^6.0EID₅₀ per mouse. We suppose that the phenotypic difference may probably be attributed to the amino acid substitutions in the polymerase genes between the two isolates that constitute of a subject of further ongoing research.

The molecular determinants of antigenic drift in a novel avian influenza A (H9N2) variant virus

Background

In early 2020, a novel H9N2 AIV immune escape variant emerged in South China and rapidly spread throughout mainland China. The effectiveness of the current H9N2 vaccine is being challenged by emerging immune escape strains. Assessing key amino acid substitutions that contribute to antigenic drift and immune escape in the HA gene of circulating strains is critical for understanding virus evolution and in selecting more effective vaccine components.

Methods

In this study, a representative immune escape strain, A/chicken/Fujian/11/2020 (FJ/20), differed from current H9N2 vaccine strain, A/chicken/Anhui/LH99/2017 (AH/17) by 18 amino acids in the head domain in HA protein. To investigate the molecular determinants of antigenic drift of FJ/20, a panel of mutants were generated by reverse genetics including specific amino acids changes in the HA genes of FJ/20 and AH/17. The antigenic effect of the substitutions was evaluated by hemagglutination inhibition (HI) assay and antigenic cartography.

Results

Fujian-like H9N2 viruses had changed antigenicity significantly, having mutated into an antigenically distinct sub-clade. Relative to the titers of the vaccine virus AH/17, the escape strain FJ/20 saw a 16-fold reduction in HI titer against antiserum elicited by AH/17. Our results showed that seven residue substitutions (D127S, G135D, N145T, R146Q, D179T, R182T and T183N) near the HA receptor binding sites were critical for converting the antigenicity of both AH/17 and FJ/20. Especially, the combined mutations 127D, 135G, 145N, and 146R could be a major factor of antigenic drift in the current immune escape variant FJ/20. The avian influenza A (H9N2) variant virus need further ongoing epidemiological surveillance.

Conclusions

In this study, we evaluated the relative contributions of different combinations of amino acid substitutions in the HA globular head domain of the immune escape strain FJ/20 and the vaccine strain AH/17. Our study provides more insights into the molecular mechanism of the antigenic drift of the H9N2 AIV immune escape strain. This work identified important markers for understanding H9N2 AIV evolution as well as for improving vaccine development and control strategies in poultry.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-022-01755-9.

MicroRNA-200c-targeted contactin 1 facilitates the replication of influenza A virus by accelerating the degradation of MAVS

Influenza A viruses (IAVs) continuously challenge the poultry industry and human health. Elucidation of the host factors that modulate the IAV lifecycle is vital for developing antiviral drugs and vaccines. In this study, we infected A549 cells with IAVs and found that host protein contactin-1 (CNTN1), a member of the immunoglobulin superfamily, enhanced viral replication. Bioinformatic prediction and experimental validation indicated that the expression of CNTN1 was reduced by microRNA-200c (miR-200c) through directly targeting. We further showed that CNTN1-modulated viral replication in A549 cells is dependent on type I interferon signaling. Co-immunoprecipitation experiments revealed that CNTN1 specifically interacts with MAVS and promotes its proteasomal degradation by removing its K63-linked ubiquitination. Moreover, we discovered that the deubiquitinase USP25 is recruited by CNTN1 to catalyze the deubiquitination of K63-linked MAVS. Consequently, the CNTN1-induced degradation cascade of MAVS blocked RIG-I-MAVS-mediated interferon signaling, leading to enhanced viral replication. Taken together, our data reveal novel roles of CNTN1 in the type I interferon pathway and regulatory mechanism of IAV replication.

Sequence characteristics and phylogenetic analysis of H9N2 subtype avian influenza A viruses detected from poultry and the environment in China, 2018

H9N2 subtype avian influenza A virus (AIV) is a causative agent that poses serious threats to both the poultry industry and global public health. In this study, we performed active surveillance to identify H9N2 AIVs from poultry (chicken, duck, and goose) and the environment of different regions in China, and we phylogenetically characterized the sequences. AIV subtype-specific reverse transcription polymerase chain reaction (RT-PCR) showed that 5.43% (83/1529) samples were AIV positive, and 87.02% (67/77) of which were H9N2 AIVs. Phylogenetic analysis revealed that all H9N2 field viruses belonged to the Y280-like lineage, exhibiting 93.9-100% and 94.6-100% of homology in the hemagglutinin (HA) gene and 94.4-100% and 96.3-100% in the neuraminidase (NA) gene, at the nucleotide (nt) and amino acid (aa) levels, respectively. All field viruses shared relatively lower identities with vaccine strains, ranging from 89.4% to 97.7%. The aa sequence at the cleavage site (aa 333-340) in HA of all the isolated H9N2 AIVs was PSRSSRG/L, which is a characteristic of low pathogenic avian influenza virus (LPAIV). Notably, all the H9N2 field viruses harbored eight glycosylation sites, whereas a glycosylation site 218 NRT was missing and a new site 313 NCS was inserted. All field viruses had NGLMR as their receptor binding sites (RBS) at aa position 224-229, showing high conservation with many recently-isolated H9N2 strains. All H9N2 field isolates at position 226 had the aa Leucine (L), indicating their ability to bind to sialic acid (SA) α, a 2-6 receptor of mammals that poses the potential risk of transmission to humans. Our results suggest that H9N2 AIVs circulating in poultry populations that have genetic variation and the potential of infecting mammalian species are of great significance when monitoring H9N2 AIVs in China.

SUMOylation of matrix protein M1 and filamentous morphology collectively contribute to the replication and virulence of highly pathogenic H5N1 avian influenza viruses in mammals

The matrix protein (M1) of influenza A virus plays an important role in replication, assembly, and budding. A previous study found that aspartic acid (D) at position 30 and alanine (A) at position 215 of M1 contribute to the high pathogenicity of H5N1 viruses in mice, and double mutations of D to asparagine (N) at position 30 (D30N) and A to threonine (T) at position 215 (A215T) in M1 dramatically attenuate H5N1 viruses in mice. However, the underlying mechanisms by which these M1 mutations attenuate the virulence of H5N1 viruses are unknown. Here, we found that the amino acid mutation A215T eliminates the SUMOylation of M1 by reducing its interaction with the host SUMO1 protein, significantly reducing the stability of M1, slowing the export of the M1-vRNP complex from the nucleus to the cytoplasm, and reducing viral replication in MDCK cells. We further found that the D30N mutation in M1 alters the shape of progeny viruses from filamentous to spherical virions. Our findings reveal an essential role for M1 215A SUMOylation and M1 30D-related filamentous morphology in the pathogenesis of avian influenza viruses, which could be targeted in novel antiviral drug designs.

IMPORTANCE Identification of the pathogenic mechanism of highly pathogenic avian influenza viruses in mammals is helpful to develop novel anti-influenza virus strategies. Two amino acid mutations (D30N and A215T) in M1 were found to collectively attenuate H5N1 influenza viruses in mice, but the underlying mechanism remained unknown. This study found that the A215T mutation significantly decreases the SUMOylation of M1, which in turn attenuates the replication of H5N1 virus in mammalian cells. The D30N mutation in M1 was found to change the virion shape from filamentous to spherical. These findings are important for understanding the molecular mechanism of virulence of highly pathogenic avian influenza viruses in mammals.

A single-amino-acid mutation at position 225 in hemagglutinin attenuates H5N6 influenza virus in mice

The highly pathogenic avian influenza H5N6 viruses are widely circulating in poultry and wild birds, and have caused 38 human infections including 21 deaths; however, the key genetic determinants of the pathogenicity of these viruses have yet to be fully investigated. Here, we characterized two H5N6 avian influenza viruses - A/duck/Guangdong/S1330/2016 (GD/330) and A/environment/Fujian/S1160/2016 (FJ/160) - that have similar viral genomes but differ markedly in their lethality in mice. GD/330 is highly pathogenic with a 50% mouse lethal dose (MLD50) of 2.5 log10 50% egg infectious doses (EID50), whereas FJ/160 exhibits low pathogenicity with an MLD50 of 7.4 log10 EID50. We explored the molecular basis for the difference in virulence between these two viruses. By using reverse genetics, we created a series of reassortants and mutants in the GD/330 background and assessed their virulence in mice. We found that the HA gene of FJ/160 substantially attenuated the virulence of GD/330 and that the mutation of glycine (G) to tryptophan (W) at position 225 (H3 numbering) in HA played a key role in this function. We further found that the amino acid mutation G225W in HA decreased the acid and thermal stability and increased the pH of HA activation, thereby attenuating the H5N6 virus in mice. Our study thus identifies a novel molecular determinant in the HA protein and provides a new target for the development of live attenuated vaccines and antiviral drugs against H5 influenza viruses.

H5 low pathogenic avian influenza viruses maintained in wild birds in China

Low pathogenic avian influenza virus, H5 or H7 subtype, possesses the potential capability to change to highly pathogenic variant, which damages wild waterfowl, domestic poultry, and mammalian hosts. In regular active surveillance of avian influenza virus from wild birds in China in 2020, we isolated six H5 avian influenza viruses, including one H5N2, two H5N3, and three H5N8. Phylogenetic analysis indicated that the H5N2 and H5N3 isolates clustered into Eurasian lineage, whereas the H5N8 viruses were originated in North America. The HA proteins of six viruses carried the cleavage-site motif PQRETR↓GLF, which indicated low pathogenicity of the viruses in chickens. However, the N30D, I43M, and T215A mutations in M1 protein and the P42S, I106M, and C138F residues changed in NS1 protein, implying all viruses could exhibit increased virulence in mice. Viral replication kinetics in mammalian cells demonstrated that the three representative viruses had the ability to replicate in both MDCK cells and A549 cells with low titers. Even though two of three representatives, WS/SX/S3-620/2020(H5N3) and ML/AH/A3-770/2020(H5N8), did not replicate and transmit efficiently in poultry (chickens), they did replicate and transmit efficiently in waterfowl (ducks). Viral pathogenicity in mice indicated that both H5N2 and H5N3 viruses are able to replicate in the nasal turbinates and lungs of mice without prior adaptation, while the H5N8 virus could not. The intercontinental and cross-species transmission of viruses may continuously exist in China, thereby providing constant opportunities for virus reassortment with local resident AIVs. Thus, it is crucial to continuously monitor migration routes for AIVs by systematic surveillance.