Novel Zoonotic Avian Influenza A(H3N8) Virus in Chicken, Hong Kong, China

Structural basis of receptor-binding adaptation of human-infecting H3N8 influenza A virus

Recent avian-origin H3N8 influenza A virus (IAV) that have infected humans pose a potential public health concern. Alterations in the viral surface glycoprotein, hemagglutinin (HA), are typically required for IAVs to cross the species barrier for adaptation to a new host, but whether H3N8 has adapted to infect humans remains elusive. The observation of a degenerative codon in position 228 of HA in human H3N8 A/Henan/4-10/2022 protein sequence, which could be residue G or S, suggests a dynamic viral adaptation for human infection. Previously, we found this human-isolated virus has shown the ability to transmit between ferrets via respiratory droplets, with the HA-G228S substitution mutation emerging as a critical determinant for the airborne transmission of the virus in ferrets. Here, we investigated the receptor-binding properties of these two H3N8 HAs. Our results showed H3N8 HAs have dual receptor-binding properties with a preference for avian receptor binding, and G228S slightly increased binding to human receptors. Cryo-electron microscopy structures of the two H3N8 HAs with avian and human receptor analogs revealed the basis for dual receptor binding. Mutagenesis studies reveal that the Q226L mutation shifts H3N8 HA's receptor preference from avian to human, while the G228S substitution enhances binding to both receptor types. H3N8 exhibits distinct antigenic sites compared to H3N2, prompting concerns regarding vaccine efficacy. These findings suggest that the current H3N8 human isolates are yet to adapt for efficient human-to-human transmission and further continuous surveillance should be implemented.IMPORTANCEInfluenza virus transmission remains a public health concern currently. H3N8 subtype influenza A viruses infect humans and their HAs acquire the ability to bind to both human and avian receptors, posing a threat to human health. We have solved and analyzed the structural basis of dual receptor binding of recently human-infecting H3N8 HA, and we demonstrate that the G228S enhances human receptor binding and adaptation. We also found that HN/4-10 H3N8 HA has distinct antigenic sites, which challenges vaccine efficacy. Taken together, our work is critical to the prevention and control of human H3 influenza virus infection.

Emergence of a novel reassortant H3N3 avian influenza virus with enhanced pathogenicity and transmissibility in chickens in China

H3N3 avian influenza viruses (AIVs) are less prevalent in poultry than H3N8 viruses. However, although relatively rare, reassortant H3N3 viruses have been known to appear in both domestic poultry and wild birds. In this study, we isolated the H3N3 virus in chickens sourced from a live poultry market in China. A comprehensive genomic analysis revealed that the virus possessed a single basic amino acid in the cleavage site of the hemagglutinin (HA) gene. Phylogenetic analysis indicated that eight genes in the H3N3 virus belong to the Eurasian lineage. Specifically, the HA and NA genes were clustered with H3N2 and H11N3, respectively, while the internal genes were closely related to the H3N8 and H9N2 viruses. Furthermore, the H3N3 virus exhibited high and moderate stability in thermal and acidic conditions and efficient replication capabilities in mammalian cells. The H3N3 virus demonstrated that it could infect and replicate in the upper and lower respiratory tract of BALB/c mice without prior adaptation, triggering hemagglutination inhibition (HI) antibody titres ranging from 80 to 160; notably, the H3N3 virus replicated vigorously within the chicken respiratory and digestive tracts. The virus also transmitted efficiently and swiftly among chickens through direct contact, leading to higher levels of HI antibodies in both the inoculated and contact birds. These findings suggest that the H3N3 virus may be a novel reassortant originating from viruses circulating in domestic poultry, thus demonstrating an increased pathogenicity and transmissibility in chickens. Our study determines that H3N3 AIV potentially threatens the poultry industry and public health, highlighting the importance of active surveillance of AIVs.

Pandemic risk characterisation of zoonotic influenza A viruses using the Tool for Influenza Pandemic Risk Assessment (TIPRA)

A systematic risk assessment approach is essential for evaluating the relative risk of influenza A viruses (IAVs) with pandemic potential. To achieve this, the Tool for Influenza Pandemic Risk Assessment (TIPRA) was developed under the Global Influenza Programme of WHO. Since its release in 2016 and update in 2020, TIPRA has been used to assess the pandemic risk of 11 zoonotic IAVs across ten evaluation rounds. Notably, A(H7N9), A(H9N2), and A(H5) clade 2.3.4.4 viruses were re-evaluated owing to changes in epidemiological characteristics or virus properties. A(H7N9) viruses had the highest relative risk at the time of assessment, highlighting the importance of continuous monitoring and reassessment as changes in epidemiological trends within animal and human populations can alter risk profiles. The knowledge gaps identified throughout the ten risk assessments should help to guide the efficient use of resources for future research, including surveillance. The TIPRA tool reflects the One Health approach and has proven crucial for closely monitoring virus dynamics in both human and non-human populations to enhance preparedness for potential IAV pandemics.

Pathogenicity of Novel H3 Avian Influenza Viruses in Chickens and Development of a Promising Vaccine

Since 2022, three cases of human infections of novel H3N8 avian influenza viruses (AIVs) have been confirmed in China. Given the potential for significant public health implications, the prompt detection and containment of the virus is particularly important. Comprehensive analyses were conducted of the complete viral gene sequences of five H3 subtype AIVs that were isolated from chickens, pigeons, and geese in live poultry markets in China in 2023. Four strains exhibited a high degree of homology with the H3N8 viruses responsible for human infections in 2022 and 2023. A subsequent study was conducted to investigate the pathogenicity differences among multiple subtypes of the H3 AIVs in chickens. The study revealed that all infected chickens exhibited clinical signs and viral shedding. Notably, two H3N8 viruses, which were highly homologous to human strains, demonstrated significant differences in adaptability to chickens. The goose-derived H3N5 strain displayed high adaptability to chickens and could replicate in multiple organs, with the highest titer in the cloaca. Additionally, a potential vaccine strain, designated CK/NT308/H3N3, was successfully developed that provided complete clinical protection and effectively prevented viral shedding against both H3N3 and H3N8 viruses. In conclusion, CK/NT308/H3N3 presents a promising vaccine candidate.

Addressing unexpected bacterial RNA safety concerns of E. coli produced influenza NP through CpG loaded mutant

Influenza virus nucleoprotein (NP) is a promising target for universal influenza vaccines due to its conservation and high immunogenicity. Here, we uncovered a previously unknown factor that E. coli-produced NP carries bacterial RNA, which is crucial for its high immunogenicity but may pose safety and consistency concerns due to batch variability. To address these concerns, we developed a NP mutant (NPmut) that lacks RNA binding activity but can be loaded with CpG1826, a synthetic oligodeoxynucleotide adjuvant that has been used in the FDA-approved Hepatitis B vaccine. The CpG1826-loaded NPmut induced immune responses comparable to RNA-bound NP while eliminating safety risks. Additionally, the mixture of CpG1826-loaded NPmut and 3M2e protein (three tandem copies of the ectodomain of influenza M2 protein) provided enhanced protection against influenza viruses challenge. Our findings highlight the adjuvant activity of bacterial RNA in E. coli-produced NP and propose a safer strategy for developing universal influenza vaccines.

Recombinant avian-derived antiviral proteins cIFITM1, cIFITM3, and cViperin as effective adjuvants in inactivated H9N2 subtype avian influenza vaccines

Vaccine adjuvants, serving as non-specific immune enhancers, play a pivotal role in the immunoprevention and control of animal diseases. This study utilized prokaryotic expression systems to express and purify chicken-derived cIFITM1, cIFITM3, and cViperin, which were then formulated as adjuvants with H9N2 avian influenza virus antigens to create inactivated vaccines. These vaccines were administered to SPF chickens to investigate their immunopotentiating functions. Additionally, the proteins were assessed for their ability to act as standalone immune enhancers. The results demonstrated that cIFITM1, cIFITM3, and cViperin significantly elevated serum hemagglutination inhibition (HI) antibody titers. Notably, when used individually, these proteins markedly enhanced the antiviral capabilities of challenged chickens, leading to alleviated clinical symptoms, reduced tracheal virus replication, diminished virus shedding, and lessened histopathological damage, with cIFITM1 exhibiting the most pronounced effect. Furthermore, the protective efficacy of two H9N2 recombinant virus inactivated vaccines supplemented with cIFITM1 adjuvant was validated, achieving a 100 % vaccine protection efficiency. In conclusion, cIFITM1, cIFITM3, and cViperin as adjuvants for influenza vaccines effectively inhibit virus replication and shedding, highlighting their significant potential in influenza prevention and control.

Zoonotic infections by avian influenza virus: changing global epidemiology, investigation, and control

Avian influenza virus continues to pose zoonotic, epizootic, and pandemic threats worldwide, as exemplified by the 2020-23 epizootics of re-emerging H5 genotype avian influenza viruses among birds and mammals and the fatal jump to humans of emerging A(H3N8) in early 2023. Future influenza pandemic threats are driven by extensive mutations and reassortments of avian influenza viruses rooted in frequent interspecies transmission and genetic mixing and underscore the urgent need for more effective actions. We examine the changing global epidemiology of human infections caused by avian influenza viruses over the past decade, including dramatic increases in both the number of reported infections in humans and the spectrum of avian influenza virus subtypes that have jumped to humans. We also discuss the use of advanced surveillance, diagnostic technologies, and state-of-the-art analysis methods for tracking emerging avian influenza viruses. We outline an avian influenza virus-specific application of the One Health approach, integrating enhanced surveillance, tightened biosecurity, targeted vaccination, timely precautions, and timely clinical management, and fostering global collaboration to control the threats of avian influenza viruses.

Evaluating the Impact of Low-Pathogenicity Avian Influenza H6N1 Outbreaks in United Kingdom and Republic of Ireland Poultry Farms during 2020

In January 2020, increased mortality was reported in a small broiler breeder flock in County Fermanagh, Northern Ireland. Gross pathological findings included coelomitis, oophoritis, salpingitis, visceral gout, splenomegaly, and renomegaly. Clinical presentation included inappetence, pronounced diarrhoea, and increased egg deformation. These signs, in combination with increased mortality, triggered a notifiable avian disease investigation. High pathogenicity avian influenza virus (HPAIV) was not suspected, as mortality levels and clinical signs were not consistent with HPAIV. Laboratory investigation demonstrated the causative agent to be a low-pathogenicity avian influenza virus (LPAIV), subtype H6N1, resulting in an outbreak that affected 15 premises in Northern Ireland. The H6N1 virus was also associated with infection on 13 premises in the Republic of Ireland and six in Great Britain. The close genetic relationship between the viruses in Ireland and Northern Ireland suggested a direct causal link whereas those in Great Britain were associated with exposure to a common ancestral virus. Overall, this rapidly spreading outbreak required the culling of over 2 million birds across the United Kingdom and the Republic of Ireland to stamp out the incursion. This report demonstrates the importance of investigating LPAIV outbreaks promptly, given their substantial economic impacts.

European Food Safety Authority, European Centre for Disease Prevention and Control, European Union Reference Laboratory for Avian Influenza, Alexakis L, Fusaro A, Kuiken T, Mirinavičiūtė G, Ståhl K, Staubach C, Svartström O, Terregino C, Willgert K, Delacourt R, Goudjihounde SM, Grant M, Tampach S, Kohnle L. Avian influenza overview March-June 2024

Between 16 March and 14 June 2024, 42 highly pathogenic avian influenza (HPAI) A(H5) virus detections were reported in domestic (15) and wild (27) birds across 13 countries in Europe. Although the overall number of detections in Europe has not been this low since the 2019-2020 epidemiological year, HPAI viruses continue to circulate at a very low level. Most detections in poultry were due to indirect contact with wild birds, but there was also secondary spread. Outside Europe, the HPAI situation intensified particularly in the USA, where a new A(H5N1) virus genotype (B3.13) has been identified in >130 dairy herds in 12 states. Infection in cattle appears to be centred on the udder, with milk from infected animals showing high viral loads and representing a new vehicle of transmission. Apart from cattle, HPAI viruses were identified in two other mammal species (alpaca and walrus) for the first time. Between 13 March and 20 June 2024, 14 new human cases with avian influenza virus infection were reported from Vietnam (one A(H5N1), one A(H9N2)), Australia (with travel history to India, one A(H5N1)), USA (three A(H5N1)), China (two A(H5N6), three A(H9N2), one A(H10N3)), India (one A(H9N2)), and Mexico (one fatal A(H5N2) case). The latter case was the first laboratory-confirmed human infection with avian influenza virus subtype A(H5N2). Most of the human cases had reported exposure to poultry, live poultry markets, or dairy cattle prior to avian influenza virus detection or onset of illness. Human infections with avian influenza viruses remain rare and no human-to-human transmission has been observed. The risk of infection with currently circulating avian A(H5) influenza viruses of clade 2.3.4.4b in Europe remains low for the general public in the EU/EEA. The risk of infection remains low-to-moderate for those occupationally or otherwise exposed to infected animals or contaminated environments.

First Known Human Death After Infection With the Avian Influenza A/H3N8 Virus: Guangdong Province, China, March 2023

Here, we report on a case of human infection with the H3N8 avian influenza virus. The patient had multiple myeloma and died of severe infection. Genome analysis showed multiple gene mutations and reassortments without mammalian-adaptive mutations. This suggests that avian influenza (A/H3N8) virus infection could be lethal for immunocompromised persons.

Characterization of a human H3N8 influenza virus

BACKGROUND

In 2022 and 2023, novel reassortant H3N8 influenza viruses infected three people, marking the first human infections with viruses of this subtype.

METHODS

Here, we generated one of these viruses (A/Henan/4-10CNIC/2022; hereafter called A/Henan/2022 virus) by using reverse genetics and characterized it.

FINDINGS

In intranasally infected mice, reverse genetics-generated A/Henan/2022 virus caused weight loss in all five animals (one of which had to be euthanized) and replicated efficiently in the respiratory tract. Intranasal infection of ferrets resulted in minor weight loss and moderate fever but no mortality. Reverse genetics-generated A/Henan/2022 virus replicated efficiently in the upper respiratory tract of ferrets but was not detected in the lungs. Virus transmission via respiratory droplets occurred in one of four pairs of ferrets. Deep-sequencing of nasal swab samples from inoculated and exposed ferrets revealed sequence polymorphisms in the haemagglutinin protein that may affect receptor-binding specificity. We also tested 90 human sera for neutralizing antibodies against reverse genetics-generated A/Henan/2022 virus and found that some of them possessed neutralizing antibody titres, especially sera from older donors with likely exposure to earlier human H3N2 viruses.

INTERPRETATION

Our data demonstrate that reverse genetics-generated A/Henan/2022 virus is a low pathogenic influenza virus (of avian influenza virus descent) with some antigenic resemblance to older human H3N2 viruses and limited respiratory droplet transmissibility in ferrets.

FUNDING

This work was supported by the Japan Program for Infectious Diseases Research and Infrastructure (JP23wm0125002), and the Japan Initiative for World-leading Vaccine Research and Development Centers (JP233fa627001) from the Japan Agency for Medical Research and Development (AMED).

European Food Safety Authority, European Centre for Disease Prevention and Control, European Union Reference Laboratory for Avian Influenza, Fusaro A, Gonzales JL, Kuiken T, Mirinavičiūtė G, Niqueux É, Ståhl K, Staubach C, Svartström O, Terregino C, Willgert K, Baldinelli F, Delacourt R, Georganas A, Kohnle L. Avian influenza overview December 2023-March 2024

Between 2 December 2023 and 15 March 2024, highly pathogenic avian influenza (HPAI) A(H5) outbreaks were reported in domestic (227) and wild (414) birds across 26 countries in Europe. Compared to previous years, although still widespread, the overall number of HPAI virus detections in birds was significantly lower, among other reasons, possibly due to some level of flock immunity in previously affected wild bird species, resulting in reduced contamination of the environment, and a different composition of circulating A(H5N1) genotypes. Most HPAI outbreaks reported in poultry were primary outbreaks following the introduction of the virus by wild birds. Outside Europe, the majority of outbreaks in poultry were still clustered in North America, while the spread of A(H5) to more naïve wild bird populations on mainland Antarctica is of particular concern. For mammals, A(H5N5) was reported for the first time in Europe, while goat kids in the United States of America represented the first natural A(H5N1) infection in ruminants. Since the last report and as of 12 March 2024, five human avian influenza A(H5N1) infections, including one death, three of which were clade 2.3.2.1c viruses, have been reported by Cambodia. China has reported two human infections, including one fatal case, with avian influenza A(H5N6), four human infections with avian influenza A(H9N2) and one fatal case with co-infection of seasonal influenza A(H3N2) and avian influenza A(H10N5). The latter case was the first documented human infection with avian influenza A(H10N5). Human infections with avian influenza remain rare and no sustained human-to-human infection has been observed. The risk of infection with currently circulating avian H5 influenza viruses of clade 2.3.4.4b in Europe remains low for the general population in the EU/EEA. The risk of infection remains low to moderate for those occupationally or otherwise exposed to infected animals.

European Food Safety Authority, European Centre for Disease Prevention and Control, European Union Reference Laboratory for Avian Influenza, Adlhoch C, Fusaro A, Gonzales JL, Kuiken T, Mirinavičiūtė G, Niqueux É, Ståhl K, Staubach C, Terregino C, Willgert K, Baldinelli F, Chuzhakina K, Delacourt R, Georganas A, Georgiev M, Kohnle L. Avian influenza overview September-December 2023

Between 2 September and 1 December 2023, highly pathogenic avian influenza (HPAI) A(H5) outbreaks were reported in domestic (88) and wild (175) birds across 23 countries in Europe. Compared to previous years, the increase in the number of HPAI virus detections in waterfowl has been delayed, possibly due to a later start of the autumn migration of several wild bird species. Common cranes were the most frequently affected species during this reporting period with mortality events being described in several European countries. Most HPAI outbreaks reported in poultry were primary outbreaks following the introduction of the virus by wild birds, with the exception of Hungary, where two clusters involving secondary spread occurred. HPAI viruses identified in Europe belonged to eleven different genotypes, seven of which were new. With regard to mammals, the serological survey conducted in all fur farms in Finland revealed 29 additional serologically positive farms during this reporting period. Wild mammals continued to be affected mostly in the Americas, from where further spread into wild birds and mammals in the Antarctic region was described for the first time. Since the last report and as of 1 December 2023, three fatal and one severe human A(H5N1) infection with clade 2.3.2.1c viruses have been reported by Cambodia, and one A(H9N2) infection was reported from China. No human infections related to the avian influenza detections in animals in fur farms in Finland have been reported, and human infections with avian influenza remain a rare event. The risk of infection with currently circulating avian H5 influenza viruses of clade 2.3.4.4b in Europe remains low for the general population in the EU/EEA. The risk of infection remains low to moderate for occupationally or otherwise exposed people to infected birds or mammals (wild or domesticated); this assessment covers different situations that depend on the level of exposure.

European Food Safety Authority, European Centre for Disease Prevention and Control, European Union Reference Laboratory for Avian Influenza, Adlhoch C, Fusaro A, Gonzales JL, Kuiken T, Mirinavičiūtė G, Niqueux É, Staubach C, Terregino C, Baldinelli F, Rusinà A, Kohnle L. Avian influenza overview June-September 2023

Between 24 June and 1 September 2023, highly pathogenic avian influenza (HPAI) A(H5) outbreaks were reported in domestic (25) and wild (482) birds across 21 countries in Europe. Most of these outbreaks appeared to be clustered along coastlines with only few HPAI virus detections inland. In poultry, all HPAI outbreaks were primary and sporadic with most of them occurring in the United Kingdom. In wild birds, colony-breeding seabirds continued to be most heavily affected, but an increasing number of HPAI virus detections in waterfowl is expected in the coming weeks. The current epidemic in wild birds has already surpassed the one of the previous epidemiological year in terms of total number of HPAI virus detections. As regards mammals, A(H5N1) virus was identified in 26 fur animal farms in Finland. Affected species included American mink, red and Arctic fox, and common raccoon dog. The most likely source of introduction was contact with gulls. Wild mammals continued to be affected worldwide, mostly red foxes and different seal species. Since the last report and as of 28 September 2023, two A(H5N1) clade 2.3.4.4b virus detections in humans have been reported by the United Kingdom, and three human infections with A(H5N6) and two with A(H9N2) were reported from China, respectively. No human infection related to the avian influenza detections in animals on fur farms in Finland or in cats in Poland have been reported, and human infections with avian influenza remain a rare event. The risk of infection with currently circulating avian H5 influenza viruses of clade 2.3.4.4b in Europe remains low for the general population in the EU/EEA. The risk of infection remains low to moderate for occupationally or otherwise exposed people to infected birds or mammals (wild or domesticated); this assessment covers different situations that depend on the level of exposure.

The International Virus Bioinformatics Meeting 2023

The 2023 International Virus Bioinformatics Meeting was held in Valencia, Spain, from 24-26 May 2023, attracting approximately 180 participants worldwide. The primary objective of the conference was to establish a dynamic scientific environment conducive to discussion, collaboration, and the generation of novel research ideas. As the first in-person event following the SARS-CoV-2 pandemic, the meeting facilitated highly interactive exchanges among attendees. It served as a pivotal gathering for gaining insights into the current status of virus bioinformatics research and engaging with leading researchers and emerging scientists. The event comprised eight invited talks, 19 contributed talks, and 74 poster presentations across eleven sessions spanning three days. Topics covered included machine learning, bacteriophages, virus discovery, virus classification, virus visualization, viral infection, viromics, molecular epidemiology, phylodynamic analysis, RNA viruses, viral sequence analysis, viral surveillance, and metagenomics. This report provides rewritten abstracts of the presentations, a summary of the key research findings, and highlights shared during the meeting.

Airborne transmission of human-isolated avian H3N8 influenza virus between ferrets

H3N8 avian influenza viruses (AIVs) in China caused two confirmed human infections in 2022, followed by a fatal case reported in 2023. H3N8 viruses are widespread in chicken flocks; however, the zoonotic features of H3N8 viruses are poorly understood. Here, we demonstrate that H3N8 viruses were able to infect and replicate efficiently in organotypic normal human bronchial epithelial (NHBE) cells and lung epithelial (Calu-3) cells. Human isolates of H3N8 virus were more virulent and caused severe pathology in mice and ferrets, relative to chicken isolates. Importantly, H3N8 virus isolated from a patient with severe pneumonia was transmissible between ferrets through respiratory droplets; it had acquired human-receptor-binding preference and amino acid substitution PB2-E627K necessary for airborne transmission. Human populations, even when vaccinated against human H3N2 virus, appear immunologically naive to emerging mammalian-adapted H3N8 AIVs and could be vulnerable to infection at epidemic or pandemic proportion.

European Food Safety Authority, European Centre for Disease Prevention and Control, European Union Reference Laboratory for Avian Influenza, Adlhoch C, Fusaro A, Gonzales JL, Kuiken T, Melidou A, Mirinavičiūtė G, Niqueux É, Ståhl K, Staubach C, Terregino C, Baldinelli F, Broglia A, Kohnle L. Avian influenza overview April - June 2023

Between 29 April and 23 June 2023, highly pathogenic avian influenza (HPAI) A(H5N1) virus (clade 2.3.4.4b) outbreaks were reported in domestic (98) and wild (634) birds across 25 countries in Europe. A cluster of outbreaks in mulard ducks for foie gras production was concentrated in Southwest France, whereas the overall A(H5N1) situation in poultry in Europe and worldwide has eased. In wild birds, black-headed gulls and several new seabird species, mostly gulls and terns (e.g. sandwich terns), were heavily affected, with increased mortality being observed in both adults and juveniles after hatching. Compared to the same period last year, dead seabirds have been increasingly found inland and not only along European coastlines. As regards mammals, A(H5N1) virus was identified in 24 domestic cats and one caracal in Poland between 10 and 30 June 2023. Affected animals showed neurological and respiratory signs, sometimes mortality, and were widely scattered across nine voivodeships in the country. All cases are genetically closely related and identified viruses cluster with viruses detected in poultry (since October 2022, but now only sporadic) and wild birds (December 2022-January 2023) in the past. Uncertainties still exist around their possible source of infection, with no feline-to-feline or feline-to-human transmission reported so far. Since 10 May 2023 and as of 4 July 2023, two A(H5N1) clade 2.3.4.4b virus detections in humans were reported from the United Kingdom, and two A(H9N2) and one A(H5N6) human infections in China. In addition, one person infected with A(H3N8) in China has died. The risk of infection with currently circulating avian H5 influenza viruses of clade 2.3.4.4b in Europe remains low for the general population in the EU/EEA, low to moderate for occupationally or otherwise exposed people to infected birds or mammals (wild or domesticated).

A Novel Triple Reassortment H3N8 Avian Influenza Virus: Characteristics, Pathogenicity, and Transmissibility

An increasing number of new subtypes of avian influenza viruses (AIVs) are reported to be infecting humans, including H3N2, H5N1, H7N9, H10N8, and the recently emerged H3N8 virus in China in 2022. However, the genetic and biological properties of the currently prevalent H3N8 AIVs are not yet fully understood. This study reports the isolation of a novel triple reassortment H3N8 virus (GD-H3N8) from chicken flocks in Guangdong province, China, in 2022. The GD-H3N8 virus contains the Eurasian avian duck-origin H3 gene, the North American avian N8 gene, and dynamic internal genes of the H9N2 virus, and shows high homology with human H3N8 strains. The GD-H3N8 isolate has multiple mammalian adaptive mutations associated with receptor binding and virulence. Growth kinetics assays demonstrate that the GD-H3N8 isolate is capable of efficient replication in avian, mammalian, and human cells in vitro. In vivo, the GD-H3N8 isolate can replicate efficiently in mice without preadaptation, in addition to establishing systemic infection and transmission by direct contact in chickens. These findings underscore the need for continued surveillance of H3N8 viruses to identify circulating strains that may potentially threaten human health.

Characterization of an Emergent Chicken H3N8 Influenza Virus in Southern China: a Potential Threat to Public Health

Although influenza A viruses of several subtypes have occasionally infected humans, to date only those of the H1, H2, and H3 subtypes have led to pandemics and become established in humans. The detection of two human infections by avian H3N8 viruses in April and May of 2022 raised pandemic concerns. Recent studies have shown the H3N8 viruses were introduced into humans from poultry, although their genesis, prevalence, and transmissibility in mammals have not been fully elucidated. Findings generated from our systematic influenza surveillance showed that this H3N8 influenza virus was first detected in chickens in July 2021 and then disseminated and became established in chickens over wider regions of China. Phylogenetic analyses revealed that the H3 HA and N8 NA were derived from avian viruses prevalent in domestic ducks in the Guangxi-Guangdong region, while all internal genes were from enzootic poultry H9N2 viruses. The novel H3N8 viruses form independent lineages in the glycoprotein gene trees, but their internal genes are mixed with those of H9N2 viruses, indicating continuous gene exchange among these viruses. Experimental infection of ferrets with three chicken H3N8 viruses showed transmission through direct contact and inefficient transmission by airborne exposure. Examination of contemporary human sera detected only very limited antibody cross-reaction to these viruses. The continuing evolution of these viruses in poultry could pose an ongoing pandemic threat. IMPORTANCE A novel H3N8 virus with demonstrated zoonotic potential has emerged and disseminated in chickens in China. It was generated by reassortment between avian H3 and N8 virus(es) and long-term enzootic H9N2 viruses present in southern China. This H3N8 virus has maintained independent H3 and N8 gene lineages but continues to exchange internal genes with other H9N2 viruses to form novel variants. Our experimental studies showed that these H3N8 viruses were transmissible in ferrets, and serological data suggest that the human population lacks effective immunological protection against it. With its wide geographical distribution and continuing evolution in chickens, other spillovers to humans can be expected and might lead to more efficient transmission in humans.

European Food Safety Authority, European Centre for Disease Prevention and Control, European Union Reference Laboratory for Avian Influenza, Adlhoch C, Fusaro A, Gonzales JL, Kuiken T, Mirinaviciute G, Niqueux É, Stahl K, Staubach C, Terregino C, Broglia A, Kohnle L, Baldinelli F. Avian influenza overview March - April 2023

Between 2 March and 28 April 2023, highly pathogenic avian influenza (HPAI) A(H5Nx) virus, clade 2.3.4.4b, outbreaks were reported in domestic (106) and wild (610) birds across 24 countries in Europe. Poultry outbreaks occurred less frequently compared to the previous reporting period and compared to spring 2022. Most of these outbreaks were classified as primary outbreaks without secondary spread and some of them associated with atypical disease presentation, in particular low mortality. In wild birds, black-headed gulls continued to be heavily affected, while also other threatened wild bird species, such as the peregrine falcon, showed increased mortality. The ongoing epidemic in black-headed gulls, many of which breed inland, may increase the risk for poultry, especially in July-August, when first-year birds disperse from the breeding colonies. HPAI A(H5N1) virus also continued to expand in the Americas, including in mammalian species, and is expected to reach the Antarctic in the near future. HPAI virus infections were detected in six mammal species, particularly in marine mammals and mustelids, for the first time, while the viruses currently circulating in Europe retain a preferential binding for avian-like receptors. Since 13 March 2022 and as of 10 May 2023, two A(H5N1) clade 2.3.4.4b virus detections in humans were reported from China (1), and Chile (1), as well as three A(H9N2) and one A(H3N8) human infections in China. The risk of infection with currently circulating avian H5 influenza viruses of clade 2.3.4.4b in Europe remains low for the general population in the EU/EEA, and low to moderate for occupationally or otherwise exposed people.

Emergence of an ancient and pathogenic mammarenavirus

ABSTRACTEmerging zoonoses of wildlife origin caused by previously unknown agents are one of the most important challenges for human health. The Qinghai-Tibet Plateau represents a unique ecological niche with diverse wildlife that harbors several human pathogens and numerous previously uncharacterized pathogens. In this study, we identified and characterized a novel arenavirus (namely, plateau pika virus, PPV) from plateau pikas (Ochotona curzoniae) on the Qinghai-Tibet Plateau by virome analysis. Isolated PPV strains could replicate in several mammalian cells. We further investigated PPV pathogenesis using animal models. PPV administered via an intraventricular route caused trembling and sudden death in IFNαβR^-/- mice, and pathological inflammatory lesions in brain tissue were observed. According to a retrospective serological survey in the geographical region where PPV was isolated, PPV-specific IgG antibodies were detected in 8 (2.4%) of 335 outpatients with available sera. Phylogenetic analyses revealed that this virus was clearly separated from previously reported New and Old World mammarenaviruses. Under the co-speciation framework, the estimated divergence time of PPV was 77-88 million years ago (MYA), earlier than that of OW and NW mammarenaviruses (26-34 MYA).

Prevalence of the H5N8 influenza virus in birds: Systematic review with meta-analysis

INTRODUCTION

Avian influenza viruses are members of the Orthomyxoviridae family, considered highly pathogenic (HPAI). They result from genetic variations from their low virulence predecessors. HPAI is a global problem. Large outbreaks of HAPI have significant health and economic impacts.

OBJECTIVE

The objective of this study was to assess the prevalence of the H5N8 Influenza virus in birds, as well as to assess its variability according to the countries and years.

METHODS

A systematic review of the literature was carried out in six databases (Web of Sciences, Scopus, PubMed, SciELO, Lilacs and Google Scholar) to evaluate the proportion of birds infected with the H5N8 Influenza virus, by molecular and immunological techniques. A meta-analysis was performed using a random-effects model to calculate the pooled prevalence, 95% confidence intervals (95%CI). A 2-tailed 5% alpha level was used for hypothesis testing. Measures of heterogeneity were estimated and reported, including the Cochrane Q statistic, the I² index, and the tau-squared test. In addition, bird species performed subgroup analyzes.

RESULTS

152 data groups were analyzed, a combined prevalence of 1.6% (95% CI 1.3-1.9%) was found for molecular studies, and the ELISA study yielded a seroprevalence of 66.7%; those results of molecular detection varied by year, from 0.2% in 2014 to 52.6% in 2020 and 96.9% in 2015.

CONCLUSION

The combined prevalence was substantial because large outbreaks have caused severe economic repercussions. In addition, it is considered a serious concern for public health due to its possible zoonotic activity.