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

Origin, pathogenicity, and transmissibility of a human isolated influenza A(H10N3) virus from China

Subtype H10 viruses are known to infect humans in Africa, Oceania, and Asia. In 2021, 2022, and recently in April 2024, a novel H10N3 subtype avian influenza virus was found cause human infection with severe pneumonia. Herein, we comprehensively studied the phylogenetic evolution and biological characteristics of the newly emerged influenza A(H10N3) virus. We found that the human isolated H10N3 virus was generated in early 2019 in domestic poultry. The viruses bound to salic acid α2, 3 receptors, indicating their insufficient ability to infect humans. Although a low pathogenic avian influenza virus, the human isolated H10N3 virus exhibited robust pathogenicity in both BALB/c and C57BL/6 mice, with MLD50 1000 times higher than a homologous environmental isolate. The human isolated H10N3 also showed respiratory droplet transmissibility in ferrets. Considering the continuous circulation in avian populations and repeated transmission to humans, strengthened surveillance of H10 subtype viruses in poultry should be put into effect.

The novel H10N3 avian influenza virus acquired airborne transmission among chickens: an increasing threat to public health

Following two human infections with the H10N3 avian influenza virus (AIV) in 2021 and 2022, a third case was discovered in Yunnan, China, in 2024, raising concerns about the potential for future pandemics. Recent studies have indicated that novel H10N3 viruses are highly pathogenic in mice and can be transmitted between guinea pigs via respiratory droplets without prior adaptation. However, the biological characteristics of novel H10N3 in poultry have not been fully elucidated. Our findings revealed that H10 subtype AIVs are predominantly prevalent in waterfowl. Notably, H10N8 and H10N3 viruses that have infected humans were primarily isolated from chickens. For the first time, double basic hemagglutinin cleavage sites (motif PEIKQGR↓GL) were identified in novel H10N3 AIVs, which exhibit enhanced replication in chickens, and can be transmitted between chickens through direct contact and respiratory droplets. Animal experimental studies demonstrated that ducks are also susceptible to H10N3 viruses and that the virus is transmissible through direct contact, suggesting a greater risk of transmission and recombination. Serological studies conducted among poultry workers suggest that while the human population was largely naïve to H10N3 infection, sporadic and undetected human infections did occur, indicating a potential increasing trend. These data further emphasize the growing threat to public health posed by zoonotic H10N3 subtype AIVs.IMPORTANCEExposure to poultry in live poultry markets (LPMs) is strongly associated with human infection with avian influenza viruses (AIVs), with chickens being the most common species found in these markets in China. The prevalence of AIVs in chickens, therefore, increases the risk of human infection. Notably, the main host of the novel H10N3 virus has shifted from waterfowl to chickens, and the virus can be transmitted between chickens via respiratory droplets, posing a potential risk of a pandemic within poultry populations. The novel H10N3 virus also remains sensitive to ducks and can be transmitted through direct contact, which means a greater risk of transmission and recombination. Significantly, the human population remains largely naïve to H10N3 infection, but sporadic seropositivity among poultry workers indicates previous exposure to H10 subtype AIVs. Therefore, a comprehensive surveillance of the novel H10N3 viruses in poultry is imperative. Effective control of the virus within poultry populations could significantly reduce the risk of emerging human infections.

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.

Evolution and biological characteristics of H11 avian influenza viruses isolated from migratory birds and pigeons

The emergence of novel avian influenza reassortants in wild birds in recent years is a public health concern. However, the viruses that circulate in migratory birds are not fully understood. In this study, we summarized and categorized global H11 avian influenza viruses and reported that waterfowl and shorebirds are the major reservoirs of the identified H11 viruses. The surveillance data of the 35,749 faecal samples collected from wild bird habitats in eastern China over the past seven years revealed a low prevalence of H11 viruses in birds, with a positive rate of 0.067% (24 isolates). The phylogenetic analysis of the twenty viruses indicated that H11 viruses have undergone complex reassortment with viruses circulating in waterfowl and shorebirds. These tested viruses do not acquire mammalian adaptive mutations in their genomes and preferentially bind to avian-type receptors. Experimental infection studies demonstrated that the two tested H11N9 viruses of wild bird origin replicated and transmitted more efficiently in ducks than in chickens, whereas the pigeon H11N2 virus isolated from a live poultry market was more adapted to replicate in chickens than in ducks. In addition, some H11 isolates replicated efficiently in mice and caused body weight loss but were not lethal. Our study revealed the role of waterfowl and shorebirds in the ecology and evolution of H11 viruses and the potential risk of introducing circulating H11 viruses into ducks or chickens, further emphasizing the importance of avian influenza surveillance at the interface of migratory birds and poultry.

Genetic characterization of low-pathogenic avian influenza subtypes H10N6 and H10N7 from free-grazing ducks in Thailand

Background and Aim

Free-grazing duck (FGD) raising is a unique domestic duck production system that is widely practiced in several Asian countries, including Thailand. FGD is a significant reservoir for influenza A viruses (IAVs). In this study, we genetically characterized IAV-H10N6 and IAV-H10N7 isolated from avian influenza surveillance in FGDs in Thailand.

Materials and Methods

We collected 640 swab samples from 29 FGD flocks located in 6 provinces of Thailand. IAVs were isolated from swab samples using egg inoculation. Hemagglutination test-positive samples were then subjected to IAV detection. Viral RNA was subjected to IAV detection using real-time reverse-transcription polymerase chain reaction (rRT-PCR) specific to matrix (M) gene. IAV subtypes were identified using the RT-PCR assay specific to all hemagglutinin and neuraminidase subtypes. Whole-genome sequencing of IAVs was performed to genetically characterize IAV-H10N6 and IAV-H10N7.

Results

Our results showed that 41 (6.41%) samples tested positive for IAV using rRT-PCR specific to the M gene. Among these, only two IAVs were subtypes as IAV-H10N6 and IAV-H10N7 and were subjected to whole-genome sequencing. IAV-H10N6 and IAV-H10N7 belonged to the Eurasian lineage and did not show any evidence of reassortment from the North American lineage. The viruses exhibited low-pathogenic characteristics and preferred binding to avian-type receptors. Genetic analysis revealed no mutations in PB2 and M genes, unlike human IAV-H10N3 and IAV-H10N8, which exhibited increased virulence in mammals.

Conclusion

IAV-H10N6 and IAV-H10N7 viruses have less potential as zoonotic viruses. However, IAV in FGDs should be monitored for novel reassortant or zoonotic viruses. This study provides information on the genetic characteristics and diversity of IAV-H10N6 and IAV-H10N7 that are circulated in FGDs in Thailand.

A Retrospective Investigation of a Case of Dual Infection by Avian-Origin Influenza A (H10N5) and Seasonal Influenza A (H3N2) Viruses - Anhui Province, China, December 2023-January 2024

What is known about this topic?

H10 avian influenza viruses circulate in wild birds and can reassort with other subtypes. H10N8 and H10N3 have previously caused sporadic human infections in China.

What is added by this report?

This report documents the first human case of co-infection with avian-origin H10N5 and seasonal H3N2 influenza viruses. Epidemiological investigations identified H10N5 in environmental samples linked to the patient, but no transmission to close contacts occurred.

What are the implications for public health practice?

Enhanced surveillance of avian influenza in live poultry markets and poultry populations is crucial for thoroughly characterizing the epidemiology, transmission, and pathogenesis of H10N5 viruses. Strengthening assessments of outbreak control measures is essential to guide effective management.

Ecological and Genetic Landscapes of Global H12 Avian Influenza Viruses and Biological Characteristics of an H12N5 Virus Isolated from Wild Ducks in Eastern China

Wild migratory birds are considered the central reservoirs of avian influenza viruses. H12 viruses are one of the 16 hemagglutinin (HA) subtypes of avian influenza viruses and are rarely reported because they are infrequently detected in birds. Consequently, the ecological and genetic profiles of H12 viruses and their adaptation in domestic birds and mammals remain unclear. Here, we found that H12N5 viruses were predominant in the nine identified H12NX subtypes, with the HA (H12) and neuraminidase (NA) (N5) genes showing combination bias in the categorized analysis of subtype combinations (H12 and N1-N9; H1-H12, H14, H15, and N5). These identified H12N5 viruses were primarily detected in birds of Anatidae and Scolopacidae in North America, excluding their possible characterization as chicken or mammalian viruses. The H12N5 viruses were divided into the North American lineage and Eurasian lineage according to their genetic differences, including the HA and NA surface genes and internal genes, although reassortment was observed between the two lineages. We isolated an Eurasian-lineage H12N5 virus from wild ducks in Eastern China, which was one of the 12 identified H12 viruses in China. Infectivity studies indicated that the H12N5 virus is poorly adapted to domestic ducks and chickens, although viral shedding could be detected in both inoculated and contact birds. Additionally, the naturally isolated H12N5 virus did not achieve good replication in mice. These results indicate that the rare subtype of H12 viruses was mainly pooled in wild migratory birds and has an established phylogeography, with low risks of spillover into domestic birds and mammals.

Development of Virus-like Particle Plant-Based Vaccines against Avian H5 and H9 Influenza A Viruses

Avian influenza A virus (AIV) is a significant cause of mortality in poultry, causing substantial economic loss, particularly in developing countries, and has zoonotic potential. For example, highly pathogenic avian influenza (HPAI) viruses of the H5 subtype have been circulating in Egypt for around two decades. In the last decade, H5N1 viruses of clade 2.2.1 have been succeeded by the antigenically distinct H5N8 clade 2.3.4.4b viruses. Furthermore, H9N2 viruses co-circulate with the H5N8 viruses in Egyptian poultry. It is widely recognised that effective vaccination against IAV requires a close antigenic match between the vaccine and viruses circulating in the field. Therefore, approaches to develop cost-effective vaccines that can be rapidly adapted to local virus strains are required for developing countries such as Egypt. In this project, the haemagglutinin (HA) proteins of Egyptian H5 and H9 viruses were expressed by transient transfection of plants (Nicotiana benthamiana). The formation of virus-like particles (VLPs) was confirmed by transmission electron microscopy. Mice were immunised with four doses of either H5 or H9 VLPs with adjuvant. Antibody and cellular immune responses were measured against the corresponding recombinant protein using ELISA and enzyme-linked immunosorbent assay (ELISpot), respectively. Chickens were immunised with one dose of H5 VLPs, eliciting HA-specific antibodies measured by ELISA and a pseudotyped virus neutralisation test using a heterologous H5 HA. In conclusion, plant-based VLP vaccines have potential for producing an effective vaccine candidate within a short time at a relatively low cost.

Prevalence, evolution, replication and transmission of H3N8 avian influenza viruses isolated from migratory birds in eastern China from 2017 to 2021

The continued evolution and emergence of novel influenza viruses in wild and domestic animals poses an increasing public health risk. Two human cases of H3N8 avian influenza virus infection in China in 2022 have caused public concern regarding the risk of transmission between birds and humans. However, the prevalence of H3N8 avian influenza viruses in their natural reservoirs and their biological characteristics are largely unknown. To elucidate the potential threat of H3N8 viruses, we analyzed five years of surveillance data obtained from an important wetland region in eastern China and evaluated the evolutionary and biological characteristics of 21 H3N8 viruses isolated from 15,899 migratory bird samples between 2017 and 2021. Genetic and phylogenetic analyses showed that the H3N8 viruses circulating in migratory birds and ducks have evolved into different branches and have undergone complicated reassortment with viruses in waterfowl. The 21 viruses belonged to 12 genotypes, and some strains induced body weight loss and pneumonia in mice. All the tested H3N8 viruses preferentially bind to avian-type receptors, although they have acquired the ability to bind human-type receptors. Infection studies in ducks, chickens and pigeons demonstrated that the currently circulating H3N8 viruses in migratory birds have a high possibility of infecting domestic waterfowl and a low possibility of infecting chickens and pigeons. Our findings imply that circulating H3N8 viruses in migratory birds continue to evolve and pose a high infection risk in domestic ducks. These results further emphasize the importance of avian influenza surveillance at the wild bird and poultry interface.

Genes, inflammatory response, tolerance, and resistance to virus infections in migratory birds, bats, and rodents

Normally, the host immunological response to viral infection is coordinated to restore homeostasis and protect the individual from possible tissue damage. The two major approaches are adopted by the host to deal with the pathogen: resistance or tolerance. The nature of the responses often differs between species and between individuals of the same species. Resistance includes innate and adaptive immune responses to control virus replication. Disease tolerance relies on the immune response allowing the coexistence of infections in the host with minimal or no clinical signs, while maintaining sufficient viral replication for transmission. Here, we compared the virome of bats, rodents and migratory birds and the molecular mechanisms underlying symptomatic and asymptomatic disease progression. We also explore the influence of the host physiology and environmental influences on RNA virus expression and how it impacts on the whole brain transcriptome of seemingly healthy semipalmated sandpiper (Calidris pusilla) and spotted sandpiper (Actitis macularius). Three time points throughout the year were selected to understand the importance of longitudinal surveys in the characterization of the virome. We finally revisited evidence that upstream and downstream regulation of the inflammatory response is, respectively, associated with resistance and tolerance to viral infections.

Global review of the H5N8 avian influenza virus subtype

Orthomyxoviruses are negative-sense, RNA viruses with segmented genomes that are highly unstable due to reassortment. The highly pathogenic avian influenza (HPAI) subtype H5N8 emerged in wild birds in China. Since its emergence, it has posed a significant threat to poultry and human health. Poultry meat is considered an inexpensive source of protein, but due to outbreaks of HPAI H5N8 from migratory birds in commercial flocks, the poultry meat industry has been facing severe financial crises. This review focuses on occasional epidemics that have damaged food security and poultry production across Europe, Eurasia, the Middle East, Africa, and America. HPAI H5N8 viral sequences have been retrieved from GISAID and analyzed. Virulent HPAI H5N8 belongs to clade 2.3.4.4b, Gs/GD lineage, and has been a threat to the poultry industry and the public in several countries since its first introduction. Continent-wide outbreaks have revealed that this virus is spreading globally. Thus, continuous sero- and viro-surveillance both in commercial and wild birds, and strict biosecurity reduces the risk of the HPAI virus appearing. Furthermore, homologous vaccination practices in commercial poultry need to be introduced to overcome the introduction of emergent strains. This review clearly indicates that HPAI H5N8 is a continuous threat to poultry and people and that further regional epidemiological studies are needed.

Continued evolution of the Eurasian avian-like H1N1 swine influenza viruses in China

Animal influenza viruses continue to pose a threat to human public health. The Eurasian avian-like H1N1 (EA H1N1) viruses are widespread in pigs throughout Europe and China and have caused human infections in several countries, indicating their pandemic potential. To carefully monitor the evolution of the EA H1N1 viruses in nature, we collected nasal swabs from 103,110 pigs in 22 provinces in China between October 2013 and December 2019, and isolated 855 EA H1N1 viruses. Genomic analysis of 319 representative viruses revealed that these EA H1N1 viruses formed eight different genotypes through reassortment with viruses of other lineages circulating in humans and pigs, and two of these genotypes (G4 and G5) were widely distributed in pigs. Animal studies indicated that some strains have become highly pathogenic in mice and highly transmissible in ferrets via respiratory droplets. Moreover, two-thirds of the EA H1N1 viruses reacted poorly with ferret serum antibodies induced by the currently used H1N1 human influenza vaccine, suggesting that existing immunity may not prevent the transmission of the EA H1N1 viruses in humans. Our study reveals the evolution and pandemic potential of EA H1N1 viruses and provides important insights for future pandemic preparedness.

Genetic analysis and biological characterization of H10N3 influenza A viruses isolated in China from 2014 to 2021

The H10 subtypes of avian influenza viruses pose a continual threat to the poultry industry and human health. The sporadic spillover of H10 subtypes viruses from poultry to humans is represented by the H10N8 human cases in 2013 and the recent H10N3 human infection in 2021. However, the genesis and characteristics of the recent reassortment H10N3 viruses have not been systemically investigated. In this study, we characterized 20 H10N3 viruses isolated in live poultry markets during routine nationwide surveillance in China from 2014 to 2021. The viruses in the recent reassortant genotype acquired their hemagglutinin (HA) and neuraminidase (NA) genes from the duck H10 viruses and H7N3 viruses, respectively, whereas the internal genes were derived from chicken H9N2 viruses as early as 2019. Receptor-binding analysis indicated that two of the tested H10N3 viruses had a higher affinity for human-type receptors than for avian-type receptors, highlighting the potential risk of avian-to-human transmission. Animal studies showed that only viruses belonging to the recent reassortant genotype were pathogenic in mice; two tested viruses transmitted via direct contact and one virus transmitted by respiratory droplets in guinea pigs, though with limited efficiency. These findings emphasize the need for enhanced surveillance of H10N3 viruses.