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Models of host-microbe dynamics typically assume a single-host population infected by a single pathogen. In reality, many hosts form multi-species aggregations and may be infected with an assemblage of pathogens. We used a meta-transcriptomic approach to characterize the viromes of nine avian species in the Anseriformes (ducks) and Charadriiformes (shorebirds). This revealed the presence of 27 viral species, of which 24 were novel, including double-stranded RNA viruses ( Picobirnaviridae and Reoviridae ), single-stranded RNA viruses ( Astroviridae , Caliciviridae , Picornaviridae ), a retro-transcribing DNA virus ( Hepadnaviridae ), and a single-stranded DNA virus ( Parvoviridae ). These viruses comprise multi-host generalist viruses and those that are host-specific, indicative of both virome connectivity (host sharing) and heterogeneity (host specificity). Virome connectivity was apparent in two well described multi-host virus species -avian coronavirus and influenza A virus- and a novel Rotavirus species that were shared among some Anseriform species, while virome heterogeneity was reflected in the absence of viruses shared between Anseriformes and Charadriiformes, as well as differences in viral abundance and alpha diversity among species. Overall, we demonstrate complex virome structures across host species that co-exist in multi-species aggregations.

The highly pathogenic H5N1 influenza virus has become endemic in poultry in southeast Asia since 2003 and constitutes a major pandemic threat to humans. Here we describe cases of disease caused by H5N1 and transmission of the virus among migratory geese populations in western China. This outbreak may help to spread the virus over and beyond the Himalayas and has important implications for developing control strategies.

The UK and Europe have seen successive outbreaks of highly pathogenic avian influenza across the 2020/21 and 2021/22 autumn/winter seasons. Understanding both the epidemiology and transmission of these viruses in different species is critical to aid mitigating measures where outbreaks cause extensive mortalities in both land- and waterfowl. Infection of different species can result in mild or asymptomatic outcomes, or acute infections that result in high morbidity and mortality levels. Definition of disease outcome in different species is of great importance to understanding the role different species play in the maintenance and transmission of these pathogens. Further, the infection of species that have conservation value is also important to recognise and characterise to understand the impact on what might be limited wild populations. Highly pathogenic avian influenza virus H5N1 clade 2.3.4.4b has been detected in great skuas (Stercorarius skua) across different colonies on islands off the shore of Scotland, Great Britain during summer 2021. A large number of great skuas were observed as developing severe clinical disease and dying during the epizootic and mortalities were estimated to be high where monitored. Of eight skuas submitted for post-mortem examination, seven were confirmed as being infected with this virus using a range of diagnostic assays. Here we overview the outbreak event that occurred in this species, listed as species of conservation concern in Great Britain and outline the importance of this finding with respect to virus transmission and maintenance.

Seabirds are at high risk of extinction, and the emergence of highly pathogenic avian influenza virus (HPAIV) represents an additional threat. In 2024, HPAIV A/H5 clade 2.3.4.4b was detected for the first time in the Antarctic Continent in a dead Brown Skua (Stercorarius antarcticus), and further evidence suggests that not all species have been equally affected. We conducted a survey of HPAIV-related mortalities across 16 seabird nesting sites along the western Antarctic Peninsula (WAP) during the 2024–2025 breeding season. We report a mortality of 35 adult skuas along the WAP and beyond the Antarctic Polar Circle. Eleven skuas from six different geographic areas were sampled and all were positive to HPAIV A/H5 clade 2.3.4.4b. Phylogenetic analyses revealed that these sequences are closely related to the initial HPAIV A/H5 clade 2.3.4.4b reported in Antarctica, and post-mortem findings suggest that the viral infection was likely the cause of death. No other suspected HPAIV-related mortalities were observed in sympatric species. Our findings represent the southernmost record of skua mortality in Antarctica related to HPAIV A/H5 infection to date, demonstrating the dissemination of 2.3.4.4b clade across several localities. The virus is differentially affecting sympatric seabird species and the skuas may act as sentinel species for influenza surveillance.

High pathogenicity avian influenza virus H5N1 subtype (H5N1 HPAIV), clade 2.3.4.4b, is expanding its host and geographical range, and invaded Antarctica in 2023. Although mortality in Antarctic wildlife from H5N1 HPAIV has been suspected, mainly based on virological analysis of swabs collected from dead animals, it has not been unequivocally diagnosed. Here we show that H5N1 HPAIV caused high mortality in a breeding colony of skuas at one of ten sites in Antarctica we visited in March 2024. By combined virological, bacteriological and pathological analyses, we found that H5N1 HPAIV caused multi-organ necrosis and rapid death in skuas, but not in other species examined. Taken together with recent data, skuas in Antarctica are at risk of continued mortality from H5N1 HPAIV infection, threatening their already small populations. Conversely, because of their wide distribution and ecological relevance, skuas may play a substantial role in the spread of the virus across Antarctica. Transdisciplinary surveillance is needed in coming years to monitor the impact of this poultry-origin disease on Antarctica’s unique wildlife.

The black-headed gull is the most common nesting gull species in Hungary. Based on the lifestyle and feeding habits of the black-headed gull, which is highly adapted to the human environment, they can be carriers and spreaders of potential human and other animal pathogens. Between 2014 and 2018 within the framework of the “Life Bird Ringing program” a total of 7 faecal samples were collected from gulls and one sample (MR04) was randomly selected for viral metagenomics and mass sequencing. 95.4% and 4% of the reads were classified into family Seadornaviridae and Astroviridae , respectively, and then were verified by RT-PCR method. In this study, the complete genome of a potential interspecies reassortant rotavirus (RV) strain gull/MR04_RV/HUN/2014 (PP239049-PP239059) and the partial ORF1ab, complete ORF2 of a novel avian nephritis virus strain gull/MR04_AAstV/HUN/2014 (PP239060) was discussed. The strain gull/MR04_RV/HUN/2014 was closely related to rotavirus G (RVG) viruses based on the proteins VP1–VP3, VP6, NSP2, NSP3, and NSP5, but it was more related to the human rotavirus B (RVB) strain Bang373 based on the NSP1, NSP4 and VP7, VP4 proteins, which is assumed to be the result of reassortment between different RVG-RVB rotavirus species. The strain gull/MR04_AAstV/HUN/2014 belonged to the genus Avastrovirus species avastrovirus 2 (AAstV-2) and is related to members of group 6 of avian nephritis viruses (ANVs), but based on the genetic distances it may be the first representative of a separate group. Additional gull samples were found to be negative by RT-PCR. Gulls, which are well adapted to the human environment, could potentially spread enterically transmitted viral pathogens like interspecies reassortant rotaviruses (RVG/RVB), but further molecular surveillance is needed to explore more deeply the viral communities of gulls or other related species adapted to human environments.

Although low pathogenic avian influenza virus (LPAIV) is traditionally considered to have adapted to its wild waterbird host to become avirulent, recent studies have suggested that LPAIV infection might after all have clinical effects. Therefore, I reviewed the literature on LPAIV infections in wild waterbirds. The virulence of LPAIV was assessed in 17 studies on experimental infections and nine studies on natural infections. Reported evidence for virulence were reductions in return rate, feeding rate, body weight, long-range movement and reproductive success, as well as pathological changes in infected organs. However, major caveats in studies of experimental infections were unnatural route of LPAIV inoculation, animal husbandry not simulating natural stressors and low sensitivity of clinical assessment. Major caveats in studies of natural infections were incomplete measurement of LPAIV infection burden, quasi-experimental design and potential misclassification of birds. After taking these caveats into account, the only remaining evidence for virulence was that presence and intensity of LPAIV infection were negatively correlated with body weight. Based on this correlation, together with the demonstrated LPAIV tropism for the intestinal tract, I hypothesize that LPAIV reduces digestive tract function, and suggest how future studies could be directed to test this hypothesis.

Emerging infectious diseases are of major concern to animal and human health. Recent emergence of high pathogenicity avian influenza virus (HPAIV) (H5N1 clade 2.3.4.4b) led to substantial global mortality across a range of host species. Co-occurring species showed marked differences in mortality, generating an urgent need for better epidemiological understanding within affected populations. We therefore tested for antibodies, indicative of previous exposure and recovery, and for active viral infection in apparently healthy individuals (n = 350) across five co-occurring seabird species on the Isle of May, Scotland, during 2023, following H5N1 HPAIV associated mortality in the preceding summer. Antibody prevalence to AIV subtypes varied substantially between species, ranging from 1.1% in European shags ( Gulosus aristotelis ) (to H5) to 78.7% in black-legged kittiwakes ( Rissa tridactyla ) (to H16 or both H13 and H16), and between 31 and 41% for three auk species (H5, H16 or both). At least 20.4% of auks had antibodies to an as yet unidentified subtype, suggesting further subtypes circulating in the population. We found low levels of active, but asymptomatic, AIV infection in individuals (1.6–4.5%), but excluded this as H5N1. Our results emphasise the importance of testing healthy individuals to understand the prevalence of co-circulating AIV subtypes in wild populations, and the potential for future reassortment events which could alter virus behaviour and impact.

Western Alaska is a potential point-of-entry for foreign-origin influenza A viruses (IAVs) into North America via migratory birds. We sampled waterfowl and gulls for IAVs at Izembek National Wildlife Refuge (NWR) in western Alaska, USA, during late summer and autumn months of 2011-2015, to evaluate the abundance and diversity of viruses at this site. We collected 4842 samples across five years from 25 species of wild birds resulting in the recovery, isolation, and sequencing of 172 IAVs. With the intent of optimizing sampling efficiencies, we used information derived from this multi-year effort to: 1) evaluate from which species we consistently recover viruses, 2) describe viral subtypes of isolates by host species and year, 3) characterize viral gene segment sequence diversity with respect to host species, and assess potential differences in the viral lineages among the host groups, and 4) examine how evidence of intercontinental exchange of IAVs relates to host species. We consistently recovered viruses from dabbling ducks (Anas spp.), emperor geese (Chen canagica) and glaucous-winged gulls (Larus glaucescens). There was little evidence for differences in viral subtypes and diversity from different waterfowl hosts, however subtypes and viral diversity varied between waterfowl host groups and glaucous-winged gulls. Furthermore, higher proportions of viral sequences from northern pintails (Anas acuta), emperor geese and glaucous-winged gulls were grouped in phylogenetic clades that included IAV sequences originating from wild birds sampled in Asia as compared to non-pintail dabbling ducks, a difference that may be related to intercontinental migratory tendencies of host species. Our summary of research and surveillance efforts at Izembek NWR will assist in future prioritization of which hosts to sample and swab types to collect in Alaska and elsewhere in order to maximize isolate recovery, subtype and sequence diversity for resultant viruses, and detection of evidence for intercontinental viral exchange.

The migratory bird orders Anseriformes and Charadriiformes are natural reservoirs of avian influenza virus (AIV) and key contributors to its global dissemination. Stopover and wintering areas used by these species are critical hotspots for virus transmission, underscoring the need for routine surveillance. The Pantanal biome in central South America—an extensive floodplain crossed by two major intercontinental migratory routes—hosts numerous species of migratory birds. Given the ecological relevance of this biome and the health risks associated with AIV, this study aimed to investigate AIV circulation in the region. A total of 1,108 orotracheal and cloacal swab samples from 157 bird species were analyzed using RT-qPCR targeting the matrix gene of AIV. Influenza A virus RNA was detected in Charadrius collaris . Subsequent sequencing of the HA and NA genes revealed 94% similarity with H5N2 strains previously identified in Colombian Anatidae in 2011. Additional gene segments (NP;NS;PA;M;PB1;PB2) showed similarity to strains from America and Asia continents. This is the first report of an AIV-infected bird in the Brazilian Pantanal and confirms the presence of a low-pathogenic H5N2 subtype. The findings highlight the role of migratory birds in viral dissemination inland and the potential role of resident species as local reservoirs.