Avian Influenza Virus In China Research Articles

Cross-Species Transmission Potential of H4 Avian Influenza Viruses in China: Epidemiological and Evolutionary Study.

H4 avian influenza viruses (AIVs) have been widely detected in live poultry markets in China. However, the potential public health impact of H4 AIVs remains largely uncertain. Here, we fully analyzed the distribution and phylogenetic relationship of H4 AIVs in China. We obtained 31 isolates of H4 viruses in China during 2009-2022 through surveillance in poultry-associated environments, such as live poultry markets and poultry farms. Genomic sequence analysis together with publicly available data revealed that frequent reassortment and introduction of H4 AIV from wild birds to poultry may have occurred. We identified 62 genotypes among 127 whole genome sequences of H4 viruses in China, indicating that H4 AIVs had great genetic diversity in China. We also investigated molecular markers and found that drug resistance mutations frequently occurred in the M2 protein and a few mutations related to receptor binding and the host signature in H4 AIVs. Our study demonstrates the cross-species transmission potential of H4 AIVs in China and provides some reference significance for its risk assessment.

Reported human infections of H9N2 avian influenza virus in China in 2021.

The continued emergence of human infections of H9N2 avian influenza virus (AIV) poses a serious threat to public health. The prevalent Y280/G9 lineage of H9N2 AIV in Chinese poultry can directly bind to human receptors, increasing the risk of spillover infections to humans. Since 2013, the number of human cases of H9N2 avian influenza has been increasing continuously, and in 2021, China reported the highest number of human cases, at 25. In this study, we analyzed the age, geographic, temporal, and sex distributions of humans with H9N2 avian influenza in 2021 using data from the National Influenza Center (Beijing, China). We also conducted evolutionary, gene homology, and molecular characterization analyses of the H9N2 AIVs infecting humans. Our findings show that children under the age of 12 accounted for 80% of human cases in 2021, and females were more frequently affected than males. More cases occurred in winter than in summer, and most cases were concentrated in southern China. Human-infecting H9N2 viruses showed a high level of genetic homology and belonged to the prevalent G57 genotype. Several additional α2,6-SA-binding sites and sites of mammalian adaptation were also identified in the genomes of human-infecting H9N2 viruses. Therefore, continuous monitoring of H9N2 AIV and the implementation of further measures to control the H9N2 virus in poultry are essential to reduce the interspecies transmission of the virus.

Genetic and biological properties of H10Nx influenza viruses in China

H10 subtype avian influenza viruses (AIV) have been circulating in China for 40 years. H10 AIVs in China have expanded their host range from wild birds to domestic poultry and mammals, even human. Most of the H10 subtype AIVs reported in China were isolate from the southeast part. We isolated an H10N3 AIV, A/Chicken/Liaoning/SY1080/2021 (SY1080), from live poultry market (LPM) in Liaoning Province of the Northeast China. SY1080 replicated efficiently in mice lungs and nasal turbinates without prior adaptation. We systematically compared SY1080 with other H10 subtype isolates in China. Phylogenetic analysis showed that SY1080 and most of the H10 strains belonged to the Eurasian lineage. H10 AIVs in China have formed 63 genotypes. SY1080 as well as the H10N3 strains from human infections belonged to G60 genotype. H10Nx AIV acquired multiple mammalian adaptive and virulence related mutations during circulation and the recent reassortants derived internal genes from chicken H9N2 AIVs. The H10Nx subtypes AIVs posed potential threat to public health. These results suggested we should strengthen the surveillance and evaluation of H10 subtype strains.

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

ABSTRACT 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.

The emergence of new antigen branches of H9N2 avian influenza virus in China due to antigenic drift on hemagglutinin through antibody escape at immunodominant sites

ABSTRACT Vaccination is a crucial prevention and control measure against H9N2 avian influenza viruses (AIVs) that threaten poultry production and public health. However, H9N2 AIVs in China undergo continuous antigenic drift of hemagglutinin (HA) under antibody pressure, leading to the emergence of immune escape variants. In this study, we investigated the molecular basis of the current widespread antigenic drift of H9N2 AIVs. Specifically, the most prevalent h9.4.2.5-lineage in China was divided into two antigenic branches based on monoclonal antibody (mAb) hemagglutination inhibition (HI) profiling analysis, and 12 antibody escape residues were identified as molecular markers of these two branches. The 12 escape residues were mapped to antigenic sites A, B, and E (H3 was used as the reference). Among these, eight residues primarily increased 3`SLN preference and contributed to antigenicity drift, and four of the eight residues at sites A and B were positively selected. Moreover, the analysis of H9N2 strains over time and space has revealed the emergence of a new antigenic branch in China since 2015, which has replaced the previous branch. However, the old antigenic branch recirculated to several regions after 2018. Collectively, this study provides a theoretical basis for understanding the molecular mechanisms of antigenic drift and for developing vaccine candidates that contest with the current antigenicity of H9N2 AIVs.

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.

That H9N2 avian influenza viruses circulating in different regions gather in the same live-poultry market poses a potential threat to public health.

H9N2 avian influenza viruses are endemic and persistent in China, but those that are prevalent in different provinces are also causes of wide epidemics, related to the spread of wild birds and the cross-regional trade in live poultry. For the past 4 years, beginning in 2018, we have sampled a live-poultry market in Foshan, Guangdong, in this ongoing study. In addition to the prevalence of H9N2 avian influenza viruses in China during this period, we identified isolates from the same market belonging to clade A and clade B, which diverged in 2012-2013, and clade C, which diverged in 2014-2016, respectively. An analysis of population dynamics revealed that, after a critical divergence period from 2014 to 2016, the genetic diversity of H9N2 viruses peaked in 2017. Our spatiotemporal dynamics analysis found that clade A, B, and C, which maintain high rates of evolution, have different prevalence ranges and transmission paths. Clades A and B were mainly prevalent in East China in the early stage, and then spread to Southern China, becoming epidemic with clade C. Strains from different regions converge at the same live-poultry market to communicate, which may be one reasons the H9N2 viruses are difficult to eradicate and increasingly dominant throughout China. Selection pressure and molecular analysis have demonstrated that single amino acid polymorphisms at key receptor binding sites 156, 160, and 190 under positive selection pressure, suggesting that H9N2 viruses are undergoing mutations to adapt to new hosts. Live-poultry markets are important because people who visit them have frequent contact with poultry, H9N2 viruses from different regions converge at these markets and spread through contact between live birds and humans, generating increased risks of human exposure to these viruses and threatening public health safety. Thus, it is important to reducing the cross-regional trade of live poultry and strengthening the monitoring of avian influenza viruses in live-poultry markets to reduce the spread of avian influenza viruses.

Epidemiology, evolution, and biological characteristics of H6 avian influenza viruses in China

ABSTRACT H6 avian influenza virus (AIV) is one of the most prevalent AIV subtypes in birds globally. To investigate the current situation and characteristics of H6 AIVs circulating in China, we analysed the epidemiology, genetic evolution and pathogenic features of this subtype. During 2000-2021, H6 subtype AIVs spread widely through Southern China and presented high host diversity. On analysing 171 H6 viruses isolated during 2009-2021, dynamic reassortments were observed among H6 and other co-circulating AIV subtypes, and these generated a total of 16 different genotypes. A few H6N6 strains possessed L226 and S228 mutations of hemagglutinin (H3 numbering), which may enhance the affinity of H6 viruses to human receptors. H6N6 viruses also exhibited divergent pathogenicity and growth profiles in vivo and in vitro. Some of the H6N6 viruses could infect mice without mammalian adaptation, and even caused death in this species. Therefore, our study demonstrated that the H6 AIVs posed a potential threat to human health and highlighted the urgent need for continued surveillance and evaluation of the H6 influenza viruses circulating in the field.

Distribution and gene characteristics of H3, H4 and H6 subtypes of low pathogenic avian influenza viruses in environment related avian influenza viruses during 2014-2021 in China

Objective: To analyze the characteristics of low pathogenic H3, H4 and H6 subtypes of avian influenza viruses in environment related avian influenza viruses in China from 2014 to 2021. Methods: Surveillance sites were located in 31 provinces, autonomous region and municipalities to collect environmental samples related to avian influenza, detect the nucleic acid detection of influenza A virus, isolate virus, deeply sequence, analyze pathogenicity related molecular sites, and determine the distribution and variation characteristics of common H3, H4 and H6 subtypes of avian influenza virus in different regions, places and sample types. Results: A total of 388 645 samples were collected. The positive rate of low pathogenic H3 (0.56‰) and H6 (0.53‰) was higher than that of H4 (0.09‰). The positive rate of H4 subtype virus in live poultry market was higher than that in other places, and the difference was statistically significant. The positive rate of H3 and H6 subtypes in sewage samples was higher than that in other samples, and the difference was statistically significant. The positive rate of H3, H4 and H6 viruses in the south was higher than that in the north, and the difference was statistically significant. December was the most active time for virus. The analysis of pathogenicity related molecular sites showed that H3, H4 and H6 subtypes of viruses combined with avian influenza virus receptors, and some gene sites related to increased pathogenicity had mutations. Conclusion: The H3, H4 and H6 subtypes of low pathogenic avian influenza viruses have a high isolation positive rate in the live poultry market and sewage. The distribution of the three subtypes of viruses has obvious regional and seasonal characteristics, and the genetic characteristics still show the feature of low pathogenic avian influenza.

Surveillance of avian influenza viruses in live bird markets of Shandong province from 2013 to 2019.

Avian influenza viruses (AIVs) seriously affect the poultry industry and pose a great threat to humans. Timely surveillance of AIVs is the basis for preparedness of the virus. This study reported the long-term surveillance of AIVs in the live bird market (LBM) of 16 cities in Shandong province from 2013 to 2019. A total of 29,895 samples were obtained and the overall positive rate of AIVs was 9.7%. The H9 was found to be the most predominant subtype in most of the time and contributed most to the monthly positve rate of AIVs as supported by the univariate and multivariate analysis, while H5 and H7 only circulated in some short periods. Then, the whole-genome sequences of 62 representative H9N2 viruses including one human isolate from a 7-year-old boy in were determined and they were genetically similar to each other with the median pairwise sequence identities ranging from 0.96 to 0.98 for all segments. The newly sequenced viruses were most similar to viruses isolated in chickens in mainland China, especially the provinces in Eastern China. Phylogenetic analysis showed that these newly sequenced H9N2 viruses belonged to the same clade for all segments except PB1. Nearly all of these viruses belonged to the G57 genotype which has dominated in China since 2010. Finally, several molecular markers associated with human adaptation, mammalian virulence, and drug resistance were identified in the newly sequenced H9N2 viruses. Overall, the study deepens our understanding of the epidemic and evolution of AIVs and provides a basis for effective control of AIVs in China.

Status and Challenges for Vaccination against Avian H9N2 Influenza Virus in China.

In China, H9N2 avian influenza virus (AIV) has become widely prevalent in poultry, causing huge economic losses after secondary infection with other pathogens. Importantly, H9N2 AIV continuously infects humans, and its six internal genes frequently reassort with other influenza viruses to generate novel influenza viruses that infect humans, threatening public health. Inactivated whole-virus vaccines have been used to control H9N2 AIV in China for more than 20 years, and they can alleviate clinical symptoms after immunization, greatly reducing economic losses. However, H9N2 AIVs can still be isolated from immunized chickens and have recently become the main epidemic subtype. A more effective vaccine prevention strategy might be able to address the current situation. Herein, we analyze the current status and vaccination strategy against H9N2 AIV and summarize the progress in vaccine development to provide insight for better H9N2 prevention and control.

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.

Effect of the Interaction between Viral PB2 and Host SphK1 on H9N2 AIV Replication in Mammals.

The H9N2 avian influenza virus (AIV) is currently widespread worldwide, posing a severe threat to the poultry industry and public health. Reassortment is an important way for influenza viruses to adapt to a new host. In 2007, the PB2 gene of H9N2 AIV in China was reassorted, and the DK1-like lineage replaced the F/98-like lineage, forming a dominant genotype of G57. This genotype and its reassortants (such as H7N9, H10N8 and H5N6) showed higher mammalian adaptation, and caused increased human infections. However, the adaptive mechanisms of the DK1-like lineage PB2 gene remain unclear. Here, we confirmed that the PB2 lineage of the H9N2 AIV currently prevalent in China still belongs to the DK1-like lineage and, compared with the previously predominant F/98-like lineage, the DK1-like lineage PB2 gene significantly enhances H9N2 AIV to mammalian adaptation. Through transcriptomic analysis and qRT–PCR and western blot experiments, we identified a host factor, sphingosine kinase 1 (SphK1), that is closely related to viral replication. SphK1 inhibits the replication of DK1-like PB2 gene H9N2 AIV, but the ability of SphK1 protein to bind DK1-like PB2 protein is weaker than that of F/98-like PB2 protein, which may contribute to H9N2 AIV containing the DK1-like PB2 gene to escape the inhibitory effect of host factor SphK1 for efficient infection. This study broadens our understanding of the adaptive evolution of H9N2 AIV and highlights the necessity to pay close attention to the AIV that contains the adaptive PB2 protein in animals and humans.

Hemagglutinin Gene Variation Rate of H9N2 Avian Influenza Virus by Vaccine Intervention in China.

H9N2 subtype avian influenza virus (AIV) is widespread globally, with China being the main epidemic center. Inactivated virus vaccination was adopted as the main prevention method in China. In this study, 22 hemagglutinin (HA) sequences were obtained from all inactivated vaccine strains of H9N2 subtype AIVs in China since its introduction. A phylogenetic analysis of the vaccine sequences and HA sequences of all published H9N2 subtype AIVs was conducted to investigate the relationship between vaccine use and the virus genetic diversity of the virus. We found that during 2002–2006, when fewer vaccines were used, annual genetic differences between the HA sequences were mainly distributed between 0.025 and 0.075 and were mainly caused by point mutations. From 2009 to 2013, more vaccines were used, and the genetic distance between sequences was about 10 times greater than between 2002 and 2006, especially in 2013. In addition to the accumulation of point mutations, insertion mutations may be the main reason for the large genetic differences between sequences from 2009 to 2013. These findings suggest that the use of inactivated vaccines affected point mutations in the HA sequences and that the contribution of high-frequency replacement vaccine strains to the rate of virus evolution is greater than that of low-frequency replacement vaccine strains. The selection pressure of the vaccine antibody plays a certain role in regulating the variation of HA sequences in H9N2 subtype AIV.

Antigenic Evolution Characteristics and Immunological Evaluation of H9N2 Avian Influenza Viruses from 1994–2019 in China

The H9N2 subtype avian influenza viruses (AIVs) have been circulating in China for more than 20 years, attracting more and more attention due to the potential threat of them. At present, vaccination is a common prevention and control strategy in poultry farms, but as virus antigenicity evolves, the immune protection efficiency of vaccines has constantly been challenged. In this study, we downloaded the hemagglutinin (HA) protein sequences of the H9N2 subtype AIVs from 1994 to 2019 in China—with a total of 5138 sequences. The above sequences were analyzed in terms of time and space, and it was found that h9.4.2.5 was the most popular in various regions of China. Furthermore, the prevalence of H9N2 subtype AIVs in China around 2006 was different. The domestic epidemic branch was relatively diversified from 1994 to 2006. After 2006, the epidemic branch each year was h9.4.2.5. We compared the sequences around 2006 as a whole and screened out 15 different amino acid positions. Based on the HA protein of A/chicken/Guangxi/55/2005 (GX55), the abovementioned amino acid mutations were completed. According to the 12-plasmid reverse genetic system, the rescue of the mutant virus was completed using A/PuertoRico/8/1934 (H1N1) (PR8) as the backbone. The cross hemagglutination inhibition test showed that these mutant sites could transform the parental strain from the old to the new antigenic region. Animal experiments indicated that the mutant virus provided significant protection against the virus from the new antigenic region. This study revealed the antigenic evolution of H9N2 subtype AIVs in China. At the same time, it provided an experimental basis for the development of new vaccines.

Spatiotemporal Associations and Molecular Evolution of Highly Pathogenic Avian Influenza A H7N9 Virus in China from 2017 to 2021.

Highly pathogenic (HP) H7N9 avian influenza virus (AIV) emerged in China in 2016. HP H7N9 AIV caused at least 33 human infections and has been circulating in poultry farms continuously since wave 5. The genetic divergence, geographic patterns, and hemagglutinin adaptive and parallel molecular evolution of HP H7N9 AIV in China since 2017 are still unclear. Here, 10 new strains of HP H7N9 AIVs from October 2019 to April 2021 were sequenced. We found that HP H7N9 was primarily circulating in Northern China, particularly in the provinces surrounding the Bohai Sea (Liaoning, Hebei, and Shandong) since wave 6. Of note, HP H7N9 AIV phylogenies exhibit a geographical structure compatible with high levels of local transmission after unidirectional rapid geographical expansion towards the north of China in 2017. In addition, we showed that two major subclades were continually expanding with the viral population size undergoing a sharp increase after 2018 with an obvious seasonal tendency. Notably, the hemagglutinin gene showed signs of parallel evolution and positive selection. Our research sheds light on the current epidemiology, evolution, and diversity of HP H7N9 AIV that can help prevent and control the spreading of HP H7N9 AIV.

Genetic and antigenic diversity of H7N9 highly pathogenic avian influenza virus in China.

Avian influenza virus (AIV) H7N9 that emerged in 2013 in eastern China is a novel zoonotic agent mainly circulating in poultry without clinical signs but causing severe disease with high fatality in humans in more than 5 waves. Since the emergence of highly pathogenic (HP) H7N9 variants in 2016, it has induced heavy losses in the poultry industry leading to the implementation of an intensive nationwide vaccination program at the end of wave 5 (September 2017). To characterize the ongoing evolution of H7N9 AIV, we conducted analyses of H7N9 glycoprotein genes obtained from 2013 to 2019. Bayesian analyses revealed a decreasing population size of HP H7N9 variants post wave 5. Phylogenetic topologies revealed that two novel small subclades were formed and carried several fixed amino acid mutations that were along HA and NA phylogenetic trees since wave 5. Some of the mutations were located at antigenic sites or receptor binding sites. The antigenic analysis may reveal a significant antigenic drift evaluated by hemagglutinin inhibition (HI) assay and the antigenicity of H7N9 AIV might evolute in large leaps in wave 7. Molecular simulations found that the mutations (V135T, S145P, and L226Q) around the HA receptor pocket increased the affinity to α2,3-linked sialic acid (SIA) while decreased to α2,6-linked SIA. Altered affinity may suggest that HP H7N9 variations aggravate the pathogenicity to poultry but lessen the threat to public health. Selection analyses showed that the HP H7N9 AIV experienced an increasing selection pressure since wave 5, and the national implementation of vaccination might intensify the role of natural selection during the evolution waves 6 and 7. In summary, our data provide important insights about the genetic and antigenic diversity of circulating HP H7N9 viruses from 2017 to 2019. Enhanced surveillance is urgently warranted to understand the current situation of HP H7N9 AIV.

Epidemiological and Genetic Characteristics of the H3 Subtype Avian Influenza Viruses in China.

Epidemiological and Genetic Characteristics of the H3 Subtype Avian Influenza Viruses in China.

Variation and Molecular Basis for Enhancement of Receptor Binding of H9N2 Avian Influenza Viruses in China Isolates.

Currently, H9N2 avian influenza viruses (H9N2 AIVs) globally circulate in poultry and have acquired some adaptation to mammals. However, it is not clear what the molecular basis is for the variation in receptor-binding features of the H9N2 AIVs. The receptor-binding features of 92 H9N2 AIVs prevalent in China during 1994–2017 were characterized through solid-phase ELISA assay and reverse genetics. H9N2 AIVs that circulated in this period mostly belonged to clade h9.4.2. Two increasing incidents occurred in the ability of H9N2 AIVs to bind to avian-like receptors in 2002–2005 and 2011–2014. Two increasing incidents occurred in the strength of H9N2 AIVs to bind to human-like receptors in 2002–2005 and 2011–2017. We found that Q227M, D145G/N, S119R, and R246K mutations can significantly increase H9N2 AIVs to bind to both avian- and human-like receptors. A160D/N, Q156R, T205A, Q226L, V245I, V216L, D208E, T212I, R172Q, and S175N mutations can significantly enhance the strength of H9N2 AIVs to bind to human-like receptors. Our study also identified mutations T205A, D208E, V216L, Q226L, and V245I as the key sites leading to enhanced receptor binding of H9N2 AIVs during 2002–2005 and mutations S119R, D145G, Q156R, A160D, T212I, Q227M, and R246K as the key sites leading to enhanced receptor binding of H9N2 AIVs during 2011–2017. These findings further illustrate the receptor-binding characteristics of avian influenza viruses, which can be a potential threat to public health.

Dominant subtype switch in avian influenza viruses during 2016\u20132019 in China

We have surveyed avian influenza virus (AIV) genomes from live poultry markets within China since 2014. Here we present a total of 16,091 samples that were collected from May 2016 to February 2019 in 23 provinces and municipalities in China. We identify 2048 AIV-positive samples and perform next generation sequencing. AIV-positive rates (12.73%) from samples had decreased substantially since 2016, compared to that during 2014–2016 (26.90%). Additionally, H9N2 has replaced H5N6 and H7N9 as the dominant AIV subtype in both chickens and ducks. Notably, novel reassortants and variants continually emerged and disseminated in avian populations, including H7N3, H9N9, H9N6 and H5N6 variants. Importantly, almost all of the H9 AIVs and many H7N9 and H6N2 strains prefer human-type receptors, posing an increased risk for human infections. In summary, our nation-wide surveillance highlights substantial changes in the circulation of AIVs since 2016, which greatly impacts the prevention and control of AIVs in China and worldwide.