Iceland: an underestimated hub for the spread of high-pathogenicity avian influenza viruses in the North Atlantic.

High-pathogenicity avian influenza viruses (HPAIVs) of the goose/Guangdong lineage are enzootically circulating in wild bird populations worldwide. This increases the risk of entry into poultry production and spill-over to mammalian species, including humans. Better understanding of the ecological and epizootiological networks of these viruses is essential to optimize mitigation measures. Based on full genome sequences of 26 HPAIV samples from Iceland, which were collected between spring and autumn 2022, as well as 1 sample from the 2023 summer period, we show that 3 different genotypes of HPAIV H5N1 clade 2.3.4.4b were circulating within the wild bird population in Iceland in 2022. Furthermore, in 2023 we observed a novel introduction of HPAIV H5N5 of the same clade to Iceland. The data support the role of Iceland as an utmost northwestern distribution area in Europe that might act also as a potential bridging point for intercontinental spread of HPAIV across the North Atlantic.

Bird flu appears entrenched in U.S. dairy herds.

New measures to control H5N1 in cows are "a drop in the bucket," scientists say.

Modelling the transmission dynamics of H9N2 avian influenza viruses in a live bird market.

H9N2 avian influenza viruses (AIVs) are a major concern for the poultry sector and human health in countries where this subtype is endemic. By fitting a model simulating H9N2 AIV transmission to data from a field experiment, we characterise the epidemiology of the virus in a live bird market in Bangladesh. Many supplied birds arrive already exposed to H9N2 AIVs, resulting in many broiler chickens entering the market as infected, and many indigenous backyard chickens entering with pre-existing immunity. Most susceptible chickens become infected within one day spent at the market, owing to high levels of viral transmission within market and short latent periods, as brief as 5.3 hours. Although H9N2 AIV transmission can be substantially reduced under moderate levels of cleaning and disinfection, effective risk mitigation also requires a range of additional interventions targeting markets and other nodes along the poultry production and distribution network.

Blowflies are potential vector for avian influenza virus at enzootic area in Japan.

High pathogenicity avian influenza (HPAI) poses a significant threat to both domestic and wild birds globally. The avian influenza virus, known for environmental contamination and subsequent oral infection in birds, necessitates careful consideration of alternative introduction routes during HPAI outbreaks. This study focuses on blowflies (genus Calliphora), in particular Calliphora nigribarbis, attracted to decaying animals and feces, which migrate to lowland areas of Japan from northern or mountainous regions in early winter, coinciding with HPAI season. Our investigation aims to delineate the role of blowflies as HPAI vectors by conducting a virus prevalence survey in a wild bird HPAI-enzootic area. In December 2022, 648 Calliphora nigribarbis were collected. Influenza virus RT-PCR testing identified 14 virus-positive samples (2.2% prevalence), with the highest occurrence observed near the crane colony (14.9%). Subtyping revealed the presence of H5N1 and HxN1 in some samples. Subsequent collections in December 2023 identified one HPAI virus-positive specimen from 608 collected flies in total, underscoring the potential involvement of blowflies in HPAI transmission. Our observations suggest C. nigribarbis may acquire the HPAI virus from deceased wild birds directly or from fecal materials from infected birds, highlighting the need to add blowflies as a target of HPAI vector control.

Cross-species spill-over potential of the H9N2 bat influenza A virus.

In 2017, a novel influenza A virus (IAV) was isolated from an Egyptian fruit bat. In contrast to other bat influenza viruses, the virus was related to avian A(H9N2) viruses and was probably the result of a bird-to-bat transmission event. To determine the cross-species spill-over potential, we biologically characterize features of A/bat/Egypt/381OP/2017(H9N2). The virus has a pH inactivation profile and neuraminidase activity similar to those of human-adapted IAVs. Despite the virus having an avian virus-like preference for α2,3 sialic acid receptors, it is unable to replicate in male mallard ducks; however, it readily infects ex-vivo human respiratory cell cultures and replicates in the lungs of female mice. A/bat/Egypt/381OP/2017 replicates in the upper respiratory tract of experimentally-infected male ferrets featuring direct-contact and airborne transmission. These data suggest that the bat A(H9N2) virus has features associated with increased risk to humans without a shift to a preference for α2,6 sialic acid receptors.

The virus is out of the barn: the emergence of HPAI as a pathogen of avian and mammalian wildlife around the globe.

Highly pathogenic avian influenza (HPAI) has persisted as a One Health threat whose current circulation and impact are addressed in the companion Currents in One Health by Puryear and Runstadler, JAVMA, May 2024. Highly pathogenic avian influenza emerged as a by-product of agricultural practices and adapted to endemic circulation in wild bird species. Over more than 20 years, continued evolution in a complex ecology involving multiple hosts has produced a lineage that expanded globally over the last 2 years. Understanding the continued evolution and movement of HPAI relies on understanding how the virus is infecting different hosts in different contexts. This includes understanding the environmental factors and the natural ecology of viral transmission that impact host exposure and ultimately evolutionary trajectories. Particularly with the rapid host expansion, increased spillover to mammalian hosts, and novel clinical phenotypes in infected hosts, despite progress in understanding the impact of specific mutations to HPAI viruses that are associated with spillover potential, the threat to public health is poorly understood. Active research is focusing on new approaches to understanding the relationship of viral genotype to phenotype and the implementation of research and surveillance pipelines to make sense of the enormous potential for diverse HPAI viruses to emerge from wild reservoirs amid global circulation.

Complex N-glycans are important for interspecies transmission of H7 influenza A viruses.

Influenza A viruses (IAVs) can overcome species barriers by adaptation of the receptor-binding site of the hemagglutinin (HA). To initiate infection, HAs bind to glycan receptors with terminal sialic acids, which are either N-acetylneuraminic acid (NeuAc) or N-glycolylneuraminic acid (NeuGc); the latter is mainly found in horses and pigs but not in birds and humans. We investigated the influence of previously identified equine NeuGc-adapting mutations (S128T, I130V, A135E, T189A, and K193R) in avian H7 IAVs in vitro and in vivo. We observed that these mutations negatively affected viral replication in chicken cells but not in duck cells and positively affected replication in horse cells. In vivo, the mutations reduced virus virulence and mortality in chickens. Ducks excreted high viral loads longer than chickens, although they appeared clinically healthy. To elucidate why these viruses infected chickens and ducks despite the absence of NeuGc, we re-evaluated the receptor binding of H7 HAs using glycan microarray and flow cytometry studies. This re-evaluation demonstrated that mutated avian H7 HAs also bound to α2,3-linked NeuAc and sialyl-LewisX, which have an additional fucose moiety in their terminal epitope, explaining why infection of ducks and chickens was possible. Interestingly, the α2,3-linked NeuAc and sialyl-LewisX epitopes were only bound when presented on tri-antennary N-glycans, emphasizing the importance of investigating the fine receptor specificities of IAVs. In conclusion, the binding of NeuGc-adapted H7 IAV to tri-antennary N-glycans enables viral replication and shedding by chickens and ducks, potentially facilitating interspecies transmission of equine-adapted H7 IAVs.IMPORTANCEInfluenza A viruses (IAVs) cause millions of deaths and illnesses in birds and mammals each year. The viral surface protein hemagglutinin initiates infection by binding to host cell terminal sialic acids. Hemagglutinin adaptations affect the binding affinity to these sialic acids and the potential host species targeted. While avian and human IAVs tend to bind to N-acetylneuraminic acid (sialic acid), equine H7 viruses prefer binding to N-glycolylneuraminic acid (NeuGc). To better understand the function of NeuGc-specific adaptations in hemagglutinin and to elucidate interspecies transmission potential NeuGc-adapted viruses, we evaluated the effects of NeuGc-specific mutations in avian H7 viruses in chickens and ducks, important economic hosts and reservoir birds, respectively. We also examined the impact on viral replication and found a binding affinity to tri-antennary N-glycans containing different terminal epitopes. These findings are significant as they contribute to the understanding of the role of receptor binding in avian influenza infection.

Phylogeographic Dynamics of H9N2 Avian Influenza Viruses in Tunisia.

Avian influenza virus subtype H9N2 is endemic in commercial poultry in Tunisia. This subtype affects poultry and wild birds in Tunisia and poses a potential zoonotic risk. Tunisian H9N2 strains carry, in their hemagglutinins, the human-like marker 226 L that is most influential in avian-to-human viral transmission. For a better understanding of how ecological aspects of the H9N2 virus and its circulation in poultry, migratory birds and environment shapes the spread of the dissemination of H9N2 in Tunisia, herein, we investigate the epidemiological, evolutionary and zoonotic potential of seven H9N2 poultry isolates and sequence their whole genome. Phylogeographic and phylodymanic analysis were used to examine viral spread within and among wild birds, poultry and environment at geographical scales. Genetic evolution results showed that the eight gene sequences of Tunisian H9N2 AIV were characterized by molecular markers involved with virulence and mammalian infections. The geographical distribution of avian influenza virus appears as a network interconnecting countries in Europe, Asia, North Africa and West Africa. The spatiotemporal dynamics analysis showed that the H9N2 virus was transmitted from Tunisia to neighboring countries notably Libya and Algeria. Interestingly, this study also revealed, for the first time, that there was a virus transmission between Tunisia and Morocco. Bayesian analysis showed exchanges between H9N2 strains of Tunisia and those of the Middle Eastern countries, analysis of host traits showed that duck, wild birds and environment were ancestry related to chicken. The subtypes phylodynamic showed that PB1 segment was under multiple inter-subtype reassortment events with H10N7, H12N5, H5N2 and H6N1 and that PB2 was also a subject of inter-subtype reassortment with H10N4.

Synchrony of Bird Migration with Global Dispersal of Avian Influenza Reveals Exposed Bird Orders.

Highly pathogenic avian influenza virus (HPAIV) A H5, particularly clade 2.3.4.4, has caused worldwide outbreaks in domestic poultry, occasional spillover to humans, and increasing deaths of diverse species of wild birds since 2014. Wild bird migration is currently acknowledged as an important ecological process contributing to the global dispersal of HPAIV H5. However, this mechanism has not been quantified using bird movement data from different species, and the timing and location of exposure of different species is unclear. We sought to explore these questions through phylodynamic analyses based on empirical data of bird movement tracking and virus genome sequences of clade 2.3.4.4 and 2.3.2.1. First, we demonstrate that seasonal bird migration can explain salient features of the global dispersal of clade 2.3.4.4. Second, we detect synchrony between the seasonality of bird annual cycle phases and virus lineage movements. We reveal the differing exposed bird orders at geographical origins and destinations of HPAIV H5 clade 2.3.4.4 lineage movements, including relatively under-discussed orders. Our study provides a phylodynamic framework that links the bird movement ecology and genomic epidemiology of avian influenza; it highlights the importance of integrating bird behavior and life history in avian influenza studies.

Recombinant parainfluenza virus 5 expressing clade 2.3.4.4b H5 hemagglutinin protein confers broad protection against H5Ny influenza viruses.

The global circulation of clade 2.3.4.4b H5Ny highly pathogenic avian influenza viruses (HPAIVs) in poultry and wild birds, increasing mammal infections, continues to pose a public health threat and may even form a pandemic. An efficacious vaccine against H5Ny HPAIVs is crucial for emergency use and pandemic preparedness. In this study, we developed a parainfluenza virus 5 (PIV5)-based vaccine candidate expressing hemagglutinin (HA) protein of clade 2.3.4.4b H5 HPAIV, termed rPIV5-H5, and evaluated its safety and efficacy in mice and ferrets. Our results demonstrated that intranasal immunization with a single dose of rPIV5-H5 could stimulate H5-specific antibody responses, moreover, a prime-boost regimen using rPIV5-H5 stimulated robust humoral, cellular, and mucosal immune responses in mice. Challenge study showed that rPIV5-H5 prime-boost regimen provided sterile immunity against lethal clade 2.3.4.4b H5N1 virus infection in mice and ferrets. Notably, rPIV5-H5 prime-boost regimen provided protection in mice against challenge with lethal doses of heterologous clades 2.2, 2.3.2, and 2.3.4 H5N1, and clade 2.3.4.4h H5N6 viruses. These results revealed that rPIV5-H5 can elicit protective immunity against a diverse clade of highly pathogenic H5Ny virus infection in mammals, highlighting the potential of rPIV5-H5 as a pan-H5 influenza vaccine candidate for emergency use.IMPORTANCEClade 2.3.4.4b H5Ny highly pathogenic avian influenza viruses (HPAIVs) have been widely circulating in wild birds and domestic poultry all over the world, leading to infections in mammals, including humans. Here, we developed a recombinant PIV5-vectored vaccine candidate expressing the HA protein of clade 2.3.4.4b H5 virus. Intranasal immunization with rPIV5-H5 in mice induced airway mucosal IgA responses, high levels of antibodies, and robust T-cell responses. Importantly, rPIV5-H5 conferred complete protection in mice and ferrets against clade 2.3.4.4b H5N1 virus challenge, the protective immunity was extended against heterologous H5Ny viruses. Taken together, our data demonstrate that rPIV5-H5 is a promising vaccine candidate against diverse H5Ny influenza viruses in mammals.

The episodic resurgence of highly pathogenic avian influenza H5 virus.

Highly pathogenic avian influenza (HPAI) H5N1 activity has intensified globally since 2021, increasingly causing mass mortality in wild birds and poultry and incidental infections in mammals1-3. However, the ecological and virological properties that underscore future mitigation strategies still remain unclear. Using epidemiological, spatial and genomic approaches, we demonstrate changes in the origins of resurgent HPAI H5 and reveal significant shifts in virus ecology and evolution. Outbreak data show key resurgent events in 2016-2017 and 2020-2021, contributing to the emergence and panzootic spread of H5N1 in 2021-2022. Genomic analysis reveals that the 2016-2017 epizootics originated in Asia, where HPAI H5 reservoirs are endemic. In 2020-2021, 2.3.4.4b H5N8 viruses emerged in African poultry, featuring mutations altering HA structure and receptor binding. In 2021-2022, a new H5N1 virus evolved through reassortment in wild birds in Europe, undergoing further reassortment with low-pathogenic avian influenza in wild and domestic birds during global dissemination. These results highlight a shift in the HPAI H5 epicentre beyond Asia and indicate that increasing persistence of HPAI H5 in wild birds is facilitating geographic and host range expansion, accelerating dispersion velocity and increasing reassortment potential. As earlier outbreaks of H5N1 and H5N8 were caused by more stable genomic constellations, these recent changes reflect adaptation across the domestic-bird-wild-bird interface. Elimination strategies in domestic birds therefore remain a high priority to limit future epizootics.

Global distribution, receptor binding, and cross-species transmission of H6 influenza viruses: risks and implications for humans.

The H6 subtype of avian influenza virus (AIV) is a pervasive subtype that is ubiquitously found in both wild bird and poultry populations across the globe. Recent investigations have unveiled its capacity to infect mammals, thereby expanding its host range beyond that of other subtypes and potentially facilitating its global transmission. This heightened breadth also endows H6 AIVs with the potential to serve as a genetic reservoir for the emergence of highly pathogenic avian influenza strains through genetic reassortment and adaptive mutations. Furthermore, alterations in key amino acid loci within the H6 AIV genome foster the evolution of viral infection mechanisms, which may enable the virus to surmount interspecies barriers and infect mammals, including humans, thus posing a potential threat to human well-being. In this review, we summarize the origins, dissemination patterns, geographical distribution, cross-species transmission dynamics, and genetic attributes of H6 influenza viruses. This study holds implications for the timely detection and surveillance of H6 AIVs.

LIMITED ACCUMULATION AND PERSISTENCE OF AN INFLUENZA A VIRUS IN TADPOLE SNAILS (PHYSA SPP.).

Waterfowl infected with avian influenza A viruses (IAVs) shed infectious virus into aquatic environments, providing a mechanism for transmission among waterfowl, while also exposing the entire aquatic ecosystem to the virus. Aquatic invertebrates such as freshwater snails are likely exposed to IAVs in the water column and sediment. Freshwater snails comprise a significant portion of some waterfowl species' diets, so this trophic interaction may serve as a novel route of IAV transmission. In these experiments, tadpole snails (Physa spp.) were exposed to a low-pathogenicity IAV (H3N8) to determine whether snails can accumulate the virus and, if so, how long virus persists in snail tissues. Snail tissues were destructively sampled and tested by reverse-transcription quantitative real-time PCR. Our experiments demonstrated that tadpole snails do accumulate IAV RNA in their tissues, although at low titers, for at least 96 h. These results indicate that it may be possible for IAV transmission to occur between waterfowl via ingestion of a natural invertebrate prey item; however, the time frame for transmission may be limited.

Vigilance Urged Against Bird Flu Amid Ongoing Outbreaks in Mammals.

This Medical News article discusses the risk to humans from the currently circulating highly pathogenic avian influenza A(H5N1) virus.

BTN3A3 evasion promotes the zoonotic potential of influenza A viruses.

Spillover events of avian influenza A viruses (IAVs) to humans could represent the first step in a future pandemic1. Several factors that limit the transmission and replication of avian IAVs in mammals have been identified. There are several gaps in our understanding to predict which virus lineages are more likely to cross the species barrier and cause disease in humans1. Here, we identified human BTN3A3 (butyrophilin subfamily 3 member A3)2 as a potent inhibitor of avian IAVs but not human IAVs. We determined that BTN3A3 is expressed in human airways and its antiviral activity evolved in primates. We show that BTN3A3 restriction acts primarily at the early stages of the virus life cycle by inhibiting avian IAV RNA replication. We identified residue 313 in the viral nucleoprotein (NP) as the genetic determinant of BTN3A3 sensitivity (313F or, rarely, 313L in avian viruses) or evasion (313Y or 313V in human viruses). However, avian IAV serotypes, such as H7 and H9, that spilled over into humans also evade BTN3A3 restriction. In these cases, BTN3A3 evasion is due to substitutions (N, H or Q) in NP residue 52 that is adjacent to residue 313 in the NP structure3. Thus, sensitivity or resistance to BTN3A3 is another factor to consider in the risk assessment of the zoonotic potential of avian influenza viruses.