Mapping Reported Modes of #Transmission of Highly Pathogenic Avian #Influenza #H5N1 to #Humans: A Scoping Review

 

Abstract

Background

Highly Pathogenic Avian Influenza A (subtype H5N1) poses a threat to human health, and its pandemic potential emphasizes the need to better understand detailed reported transmission pathways to humans. Existing literature is outdated or lacks detailed, comprehensive analysis of the range of transmission routes and how the virus may enter the human body.

Objective

To comprehensively map all reported H5N1 transmission pathways to humans, as well as viral entry routes.

Methods

CINAHL, Embase, MEDLINE, Scopus, PubMed, grey literature, and reference lists (of included studies) were searched up to October 29th, 2025, with no language restrictions. Observational studies and grey literature reporting H5N1 transmission evidence to humans were included. Two reviewers conducted duplicate screening independently (two of three reviewers per record). One reviewer completed data extraction, which was cross-verified for accuracy by a second. Findings were summarized narratively.

Results

120 sources met inclusion criteria (70 studies, 50 grey literature). Reported H5N1 transmission pathways were classified into animal-to-human (109 of 120 sources, 90.8%; including poultry-to-human in 100 sources [83.3%] and cattle-to-human in nine sources [7.5%]), environment-to-human (32 of 120 sources, 26.7%), and human-to-human (14 of 120 sources, 11.7%). Reported transmission pathways were further classified as direct or indirect contact, synthesized, and linked to suspected routes of human entry, including mucosal entry (eyes, nose, mouth), inhalation of aerosols or droplets, ingestion, and percutaneous exposure. Entry routes are biologically plausible and do not imply relative likelihood or causal attribution.

Conclusions

There are multiple reported pathways of H5N1 exposure, and a single pathway may involve multiple ways to infect humans. Further research is needed to determine causal mechanisms, identify specific risk factors and measures of association, and strengthen evidence-based prevention strategies.

Source: 

Link: https://www.sciencedirect.com/science/article/pii/S235277142600176X?via%3Dihub

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#USA, #Wastewater Data for Avian #Influenza #H5 (CDC, July 24 '26)

 

{Excerpt}

(...)

A(H5) detections in the past week

Time Period: July 12, 2026 - July 18, 2026

    ° A(H5) Detection: 10 site(s) (2.4%)

    ° No Detection: 414 site(s) (97.6%)

    ° No samples: 89 site(s)

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(...)

Source: 

Link: https://www.cdc.gov/wastewater/emerging-viruses/h5.html?

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Seasonal #surveillance in #humans in 2026 for #WNV (West Nile Virus) (ECDC, July 24 '26): 81 confirmed cases so far of which 46 in #Italy

 

{Excerpt}

Week 30, 2026 | Produced on 23 July 2026 at 09:45, based on data submitted up until and including 22 July 2026.

Current situation

    ° Since the beginning of the 2026 transmission season, and as at 22 July, 35 areas affected by West Nile virus (WNV) have been identified in six countries across Europe.

    ° These areas are located in: 

        § Italy (20), 

        § Greece (six), 

        § Romania (four), 

        § North Macedonia (two), 

        § Spain (two) and 

        § France (one).

    ° The six countries have reported 81 locally acquired human cases of WNV infection: 

        § Italy has reported 46, 

        § Greece 21, 

        § North Macedonia five, 

        § Romania five, 

        § Spain three and 

        § France one case.

    ° This week, nine areas are reported as affected for the first time this season. The affected areas identified as at 22 July 2026 are listed in Table 1 and shown in Map 1 below.

(...)

Table 1. Areas affected by West Nile virus during the 2026 transmission season at 22 July, by country and NUTS3 or GAUL1 area

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(...)

Source: 

Link: https://www.ecdc.europa.eu/en/west-nile-fever/surveillance-and-disease-data/disease-data-ecdc

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#Ecuador - #Influenza A #H5N1 viruses of high pathogenicity (Inf. with) (non-poultry including wild birds) (2017-) - Immediate notification [FINAL]

 

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By Manuel González Olaechea y Franco - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=12026471

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These occurrences were detected through passive surveillance conducted by the Ministry of Environment and Energy along the entire coast of mainland Ecuador.

{Peruvian Pelican} Wild bird population in situ in Guayas Province (bird morbidity history). Out of eight birds, one tested positive.

Source: 

Link: https://wahis.woah.org/#/in-review/7717

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#Oseltamivir #Resistance in #Human #Influenza #H5N1 and #H7N9 Infections: A Mini Review

 

Abstract

Avian influenza viruses (AIVs) have been reported to cause infections in humans following avian-to-human transmission, resulting in a range of clinical outcomes. A(H5N1) and A(H7N9) infections, which constitute the majority of human AIV cases, are responsible for severe infections leading to high mortality. The neuraminidase inhibitor oseltamivir is expected to play a major role for the control of AIV infections in humans. However, the emergence of resistance may compromise the impact of antiviral therapy. The objective of this article is to review human cases of A(H5N1) and A(H7N9) infections for which mutations of oseltamivir resistance were detected. Neuraminidase mutations rapidly occurred in a subtype-specific manner, with H274Y and N294S substitutions predominating in A(H5N1) cases and the R292K substitution in A(H7N9) cases. Serious clinical outcomes and mortality were seen in most A(H5N1) and A(H7N9) cases despite oseltamivir therapy, thus highlighting the need for improving antiviral strategies against these AIVs.

Source: 

Link: https://academic.oup.com/ofid/article/13/7/ofag393/8722865

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Evolving #dynamics of #H5Nx avian #influenza in #China revealed by long-term wild bird #surveillance

 

Abstract

H5Nx highly pathogenic avian influenza viruses pose persistent threats to poultry, wildlife, and public health. Over the past two decades, their geographic and host ranges have expanded across migratory networks whose epidemiological connectivity has become increasingly apparent through recent surveillance and genomic analyses. To elucidate these dynamics, we conduct long-term nationwide wild-bird surveillance in China, integrating active and passive monitoring. Our analyses reveal the maintenance, reassortment, and transmission of H5Nx viruses in wild birds, highlighting the value of sustained surveillance in capturing viral evolution. We identify distinct ecological patterns among major clades, with 2.3.4.4b showing the widest distribution and acting as the main lineage mediating intercontinental spread. Since 2020, most 2.3.4.4b viruses detected in wild birds in China have clustered with lineages originating outside China, consistent with repeated reintroduction rather than sustained local circulation. This shift underscores the growing role of migratory connectivity in shaping global viral exchange and the need for coordinated international active surveillance.

Source: 

Link: https://www.nature.com/articles/s41467-026-76039-9

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Identifying the viral and #epidemiological factors behind the apparent global #extinction of #influenza B/Yamagata

 

Abstract

Until 2020, two lineages of the influenza B virus had co-circulated globally. Measures to control the COVID-19 pandemic led to a near-absence of influenza infections. While B/Victoria reemerged in late 2021, there have been no reports of B/Yamagata since the pandemic. To investigate which epidemiological and immunological factors were primarily responsible for the extinction of B/Yamagata, we developed a global model for the two influenza B lineages. To mimic the transmission impacts of the pandemic, we implemented a transient reduction in contacts and identified parameter values that recapitulated viral coexistence dynamic before the pandemic and the qualitative post-pandemic outcomes of B/Victoria (reemergence in late 2021) and B/Yamagata (extinction). Our results suggest that, rather than immunological or evolutionary mechanisms, the extinction of B/Yamagata was mainly driven by its lower basic reproduction number making the virus particularly vulnerable during the early phase of the pandemic. Stochastic simulations of our best-fitting model suggest that B/Victoria was also close to extinction during this period. We investigate the model to assess the feasibility of B/Victoria eradication through vaccination and the potential for a sustained re-emergence of B/Yamagata in the 2026-27 flu season, thus highlighting important considerations for biosafety.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.medrxiv.org/content/10.64898/2026.07.22.26358639v1

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Characterization and evolutionary history of novel #SARS-CoV-2-related viruses in #bats from #Cambodia

 

Abstract

Circulating bat coronaviruses present a significant pandemic threat, yet our understanding of their genetic diversity and evolutionary dynamics remains limited. Over 3 years, we sampled 1,462 bats in Cambodia’s Steung Treng province, identifying extensive and diverse coronaviruses co-circulation. Using metatranscriptomic and amplicon sequencing, we generated 33 complete sarbecovirus genomes sequences, revealing novel lineages that cluster into four distinct groups, each associated with different Rhinolophus bat species. Our analysis highlights rapid migration and recombination of sarbecovirus lineages over short distances and timescales. Of note, the receptor-binding domains of two novel viral groups exhibit high similarity to SARS-CoV-2, and pseudovirus assays confirmed the ability of this spike protein to mediate entry into cells expressing human ACE2, suggesting a potential zoonotic risk. The observed genetic diversity underscores the urgent need for continuous surveillance to identify high-risk animal-to-human interfaces and inform pandemic preparedness.

Source: 

Link: https://www.nature.com/articles/s41467-026-75954-1

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#Mexico - #Influenza A #H7N3 viruses of high pathogenicity (Inf. with) (non-poultry including wild birds) (2017-) - Immediate notification

 

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By Chuck Homler d/b/a FocusOnwWildlife - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=150451071

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    ° As a result of efforts to promote reporting, an outbreak of HPAI H7N3 was detected in a wild bird in the State of Chiapas. 

    ° Active epidemiological surveillance continues nationwide in commercial poultry farms, backyard flocks, and slaughterhouses, as well as monitoring of wild birds.

    ° A wild bird {a Plain chachalaca} that was not part of the zoo's collection, found in the vicinity of the zoo.

Source: 

Link: https://wahis.woah.org/#/in-review/7716

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#SARS-CoV-2 BA.3.2.2 is more evasive of #neutralisation by #plasma from young #children

 

{Excerpt}

(...)

These findings suggest that susceptibility to emerging SARS-CoV-2 variants could diverge across age groups with different exposure histories. Adults in the USA and other countries have accumulated broader immunity through repeated infection and vaccination across antigenically distinct lineages, starting with the ancestral strain, whereas younger children and infants possess narrower exposure histories that are largely shaped by recent variants. The continued surveillance of SARS-CoV-2 variants should consider age-stratified differences in immunity, to anticipate or explain disproportionate burden of infections in some populations. Furthermore, studies of potential age-specific vaccine formulations targeting different variants are warranted, to investigate whether age-specific target selection could lead to broader protection across subpopulations with known differences in their exposure histories and susceptibility to co-circulating variants.

(...)

Source: 

Link: https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(26)00349-X/fulltext?rss=yes

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#Geographic Concentration of #Genomic #Surveillance for Highly Pathogenic Avian #Influenza #H5, South #Asia, 2015-2025

 

Abstract

Early detection of mammalian adaptation in highly pathogenic avian influenza A(H5) depends on genomic surveillance, yet its distribution across high-burden regions is poorly characterized. We quantified open-access (GenBank/INSDC) H5 genomic coverage relative to reported outbreak burden across nine South Asian countries during 2015-2025, linking isolates to FAO EMPRES-i/WOAH events. Of 919 H5 isolates, 814 (89%) came from one country (Bangladesh); the other eight contributed 105. India, with the largest burden (322 events), yielded only 42 isolates (13 per 100); Nepal, 2 of 78; Afghanistan, none of 5. Concentration was extreme (Gini 0.83) and unchanged by adding restricted GISAID records (1,297 combined isolates; Bangladesh 89%) or by normalizing to poultry or human population. Because reported outbreaks track reporting effort, these coverage ratios are directional, not rates. This single-country dependency, deepest where burden is highest, is a regional early-warning vulnerability.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.medrxiv.org/content/10.64898/2026.07.20.26358505v1

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Within- and between-host #dynamics of highly pathogenic avian #influenza in domestic #birds from #Pennsylvania #farms and live bird #markets

 

Abstract

Since late 2021, highly pathogenic avian influenza viruses (HPAI) of the H5 subtype clade 2.3.4.4b have spread across the Americas, devastating wildlife, agricultural animals, and resulting in dozens of human spillovers. National surveillance strategies generally provide only a single representative sequence per poultry outbreak, precluding fine-scale geographic transmission inference or studies of within-outbreak evolution. We produced high-quality deep sequence data from 46 infected Galliformes and Anseriformes sampled from commercial farm and live bird market (LBM) outbreaks in Pennsylvania from 2023-2025. We found that H5N1 viruses were introduced into Pennsylvania at least 68 independent times. We recover independent origins of live bird market outbreaks within the same county 3 weeks apart, and transmission between Pennsylvania LBM and New York commercial birds, suggesting high transmission risk within the Northeast live bird market distribution system. Analyses of within-farm variant populations show frequent variant sharing between samples from the same outbreak, suggesting that variants are propagated among epidemiologically linked infections. We identified 9 known adaptive mutations in these samples, including one instance of PB2 D701N in a LBM chicken sample, suggesting that while rare, concerning mammalian adaptive mutations can be present within these domestic outbreaks. Our data suggest that domestic bird outbreaks support high circulating diversity and wide transmission bottlenecks, increasing the risk of minority variants arising and propagating between infections. These data can help inform targeted biosecurity measures and better quantify the risk of viral adaptation during agricultural outbreaks.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

NIAID, NIH 75N93021C00015

Pew Charitable Trusts

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.07.17.739193v1

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A lethal #human #H5N5 #influenza virus isolate exhibits low #pandemic #risk traits

 

Abstract

In fall of 2025, a fatal infection of highly pathogenic avian influenza (HPAI) virus H5N5 occurred. To define the risk of this emerging virus to humans, we performed a comprehensive analysis based on our established triage. Serological analysis revealed that humans across all birth years had no detectable neutralizing antibodies to this H5N5 isolate. Further characterization revealed a lack of phenotypic signatures associated with epidemiologically successful influenza viruses in humans, including reduced replication in human airway cells and an avian-like pH of inactivation. Additionally, assessment of H5N5 in ferrets revealed a lack of direct contact transmission and moderate disease severity. H5N5 infection in ferrets with prior immunity against the 2009 H1N1 pandemic strain resulted in fewer clinical signs and reduced viral shedding. Together our data suggest that the current H5N5 HPAI lineage poses a low pandemic risk.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.07.20.739507v1

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#Bundibugyo Virus Disease #Outbreak, #DRC & #Uganda (Africa CDC, data as of 18July 2026): 2344 cases and 930 deaths in DRC

 

{Excerpt}

(...)

    ° TOTAL CONFIRMED CASES: 2,364

        § DRC 2,344

        § Uganda 20

    ° TOTAL DEATHS: 932

    ° CFR: 39.4%

        § DRC 930

        § UG 2

    ° TOTAL RECOVERIES: 484

        § DRC 466

        § Uganda 18

    ° CONTACTS FOLLOWED: 85.8%

    ° HCW INFECTIONS: 123

        § DRC 119 

        § Uganda 4

    ° HCW DEATHS: 36

        § DRC 36 

        § Uganda 0

EPIDEMIOLOGICAL STATUS

    ° The outbreak remains concentrated in the DRC, accounting for 99% (2,344/2,364) of confirmed cases and deaths (930/932) —within the country, Ituriis the epicentre, while Nord-Kivu (230) is the main second hotspot

    ° The overall case-fatality ratio (39.4%) remains high, reflecting late presentation and constrained access to care.

    ° Uganda remains in the 42-day countdown to outbreak closure following the discharge of last case on 16 July

EPIDEMIOLOGICAL RISK

    ° A high rate of community deaths is the clearest warning sign in an Ebolavirus response, indicating that transmission chains are detected late or not at all, and that safe-burial and case-finding systems are not yet adequate. Each community death involves multiple high-risk exposures during the deathbed and funeral.

(...)

Source: 

Link: https://reliefweb.int/report/democratic-republic-congo/bundibugyo-virus-disease-outbreak-situation-report-issue-no-62-july-18-2026

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Elicitation of #stem-directed #antibodies in rhesus #macaques by a conventional #hemagglutinin immunogen

 

Abstract

Because they can bind many strains of influenza, antibodies targeting the hemagglutinin (HA) stem have been attractive targets for vaccine development. Many monoclonal antibodies (mAbs) directed at the HA stem have been isolated from humans, and these mAbs have mediated broad protection in animal models. We describe here HA stem-directed mAbs isolated from rhesus macaques immunized with an "ordinary" H1 HA trimer. All immunized rhesus macaques developed high serum titers with broad reactivity to diverse H1N1 and H5N1 viruses, and 7 isolated mAbs strongly blocked canonical stem antibody CR6261 binding to H1. MAb DH726.1 robustly protected mice from lethal challenge with H1N1 and H5N1 viruses, and cryo-EM showed the binding footprint overlapped that of some human mAbs. These findings suggest that vaccination with the standard, trimeric HA immunogens may be sufficient to elicit stem antibodies at titers adequate to protect against zoonotic H5N1 influenza.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

NIH NIAID, Division of Microbiology and Infectious Diseases, P01-AI089618

NIH NIAID Division of AIDS, Center for HIV/AIDS Vaccine Immunology, U19-AI067854

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.07.16.738984v1

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#UK, Precautionary #medical #evacuation following a potential healthcare related #exposure to #Ebola (UKHSA, July 21 '26)

 

    Medical evacuation has been arranged as a highly precautionary measure following a potential healthcare related exposure to Ebola. 

    UKHSA works with international partners to ensure that any British residents who may be at risk can be safely returned home and given the treatment and care required. 

    The individual is a UK resident who has been working with a humanitarian organisation in DRC supporting the Ebola outbreak response.

    The individual is not currently displaying any symptoms and remains well, but as a precautionary measure they have been evacuated on a flight chartered solely for the evacuation. 

    They are now being assessed and monitored in isolation by infectious disease specialists at a London hospital. 

    The incubation period of Ebola ranges from 2 to 21 days and the individual will be closely monitored and required to isolate throughout this period.

    There are currently no confirmed cases of Ebola in the UK and the risk to the general public remains low. UKHSA will provide further updates if there is any change to the current situation.

    Richard Pebody, Director, Epidemic and Emerging Infections at UKHSA, said:

        ''The risk to the general public remains low. This individual has been transferred out of an abundance of caution, and we’re pleased they remain well.''

Source: 

Link: https://www.gov.uk/government/news/precautionary-medical-evacuation-following-a-potential-healthcare-related-exposure-to-ebola

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Avian #Influenza #Report: July 12 - 18 '26 (Wk 29) (HK CHP, July 21 '26): 1 New #Human Case of Infection with #H5 virus in #Bangladesh

 

{Excerpt}

(...)

    ° Avian influenza A(H5): 

        § Bangladesh: 

            - Sylhet Division: A child with onset on May 17, 2026. 

(...)

Source: 

Link: https://www.chp.gov.hk/files/pdf/2026_avian_influenza_report_vol22_wk29.pdf

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#Togo - High pathogenicity avian #influenza #H5N1 viruses (Inf. with) (#poultry) - Immediate notification

 

Poultry farms in the Maritime Region.

Source: 

Link: https://wahis.woah.org/#/in-review/7714

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Loss of #hemagglutination ability by #H3N2 #influenza A virus, subclade K.

 

Abstract

Seasonal human H3N2 influenza viruses, subclade K (J.2.4.1), have been the predominant influenza A viruses in the Northern hemisphere influenza season of 2025/2026. Since 2024, the vaccine virus A/Darwin/6/21 has emerged in different antigenic variants. Antigenic changes are frequently caused by amino acid substitutions near the hemagglutinin (HA) receptor-binding pocket, which can also affect receptor binding properties, such as hemagglutination. Hemagglutination is crucial for assessing antigenicity using the hemagglutination inhibition (HAI) assay, and a loss of binding to turkey erythrocytes could significantly hamper this process. In this study, we explored how substitutions in or around the HA receptor-binding site affect binding to glycans at the molecular level. We employed ELISA, glycan array, flow cytometry, hemagglutination assays, and tissue staining. Substitutions at positions 140, 192, and 223 establish clade J viruses that emerged in 2024. Computational analysis of HA in complex with an elongated glycan reveals that mutation F192 forms a CH-Pi interaction to stabilize the binding. Based on this background, substitutions in antigenic sites A and B within subclade K viruses exhibit a binding preference for elongated glycans, which are not displayed on turkey erythrocytes. Conversely, our previously established glyco-remodeled erythrocytes are efficiently bound by these subclade K H3N2 viruses and could support influenza surveillance and vaccine development.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

CSC fellowship, (202209120001)

National Institute of Allergy and Infectious Diseases, R01 AI165692

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.07.20.739523v1

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Highly Pathogenic Avian #Influenza #H5N5 in a Polar #Bear and Atlantic #Walrus, #Svalbard, 2026, with Widespread Seroconversion in Polar Bears

 

Abstract

Highly pathogenic avian influenza virus (HPAIV) subtype H5N5 was detected in a one-year-old polar bear (Ursus maritimus) and an adjacent adult Atlantic walrus (Odobenus rosmarus rosmarus), both found deceased in Raudfjorden, Svalbard. This represents the first confirmed case of HPAI in a European polar bear and the second in an Atlantic walrus. Viral genomes were nearly identical and harbored PB2-E627V, a marker associated with mammalian adaptation. Several polar bears, including the deceased individual, had previously been observed feeding on the walrus carcass. Antibodies against H5 were detected in 75% of polar bears in 2023 (n=36) and 97% in 2024-2025 (n=65), suggesting extensive circulation of HPAIV in the population following the first detections in birds in Svalbard in 2022, whereas no antibodies were detected in samples from 2014-2022 (n=243).

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

Project OH4Surveillance, funded by the European Union, Grant Agreement No 101132473

Morris Animal Foundation, Grant ID# D25ZO-430; KJB

Norwegian Veterinary Institute, 12311 SvalVilt

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.07.20.739480v1

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