#Ocular findings in Northern #Gannets following an #outbreak of high pathogenicity avian #influenza #H5N1

 

Abstract

During 2021-2022, high pathogenicity avian influenza (HPAI) caused mass mortality in wild birds across Europe, with Northern Gannets (Morus bassanus) among the most affected. Following the outbreak, unusual alterations in the species' characteristic pale iris were observed in some individuals. Opportunistically captured gannets on Bass Rock (n=52), selected to represent a range of iris pigmentation, were examined. Slit-lamp biomicroscopy, indirect ophthalmoscopy, rebound tonometry and photography were performed. Iris pigmentation was classified as normal, mottled or black. Eleven birds underwent avian influenza virus (AIV) serology. Histopathology was performed on two eyes. Abnormal iris pigmentation was found in 74% of adult and immature gannets, with 61% affected bilaterally. Additional signs consistent with uveitis were present in 77% of affected birds. Iris pigmentation abnormalities were positively associated with AIV H5 seropositivity (Fishers exact test, P=0.018). Histopathology from affected eyes showed increased melanin deposition and disorganisation, including loss of a distinct anterior layer of melanocytic cells and hypertrophy of melanocytes within the iris stroma. Field conditions limited uniform lighting and concurrent serology. Iris pigmentation changes were associated with prior HPAI exposure and frequently accompanied by signs of uveitis, suggesting iris alterations may indicate past infection and potential chronic sequelae.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.04.15.718625v1

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Frequent seasonal #reassortment between high and low path #viruses drives the diversification of #influenza #H5N1

 

Abstract

Since 2021, highly pathogenic (HPAI) H5N1 viruses have spread across the Americas, diversifying via reassortment into new genotypes that have spilled into humans and livestock, raising fears of a new influenza pandemic. Pandemic lineages are typically associated with reassortment, but we currently have limited understanding of where and when reassortment is expected to occur, which limits our ability to assess pandemic risks. Using a dataset of 9,052 full-genome sequences, we show that reassortment and novel genotype formation are associated with seasonal variation in low pathogenicity avian influenza (LPAI) cases and with the spatial and host distributions of viral transmission. We pinpoint ducks, geese, and the Central flyway as frequent sources of new genotypes, and show that reassortment rates vary seasonally, driven by mixing between high- and low-pathogenicity viruses. Cattle spillover genotypes (B3.13 and D1.1) evolved during periods of high reassortment, implicating reassortment as a common occurrence in lineages evolving during particular time periods. Together, these findings reframe reassortment as a predictable ecological process, with direct implications for how surveillance and pandemic risk assessment should be designed.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

US Centers for Disease Control Insight Net, CDC-RFA-FT-23-0069

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.04.17.719307v1

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#USA, #Wastewater Data for Avian #Influenza #H5 (#CDC, April 17 '26)

 

{Excerpt}

(...)

Time Period: April 05, 2026 - April 11, 2026

-- A(H5) Detection: 6 site(s) (1.3%)

-- No Detection: 454 site(s) (98.7%)

-- No samples: 103 site(s)

(...)

Source: 

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

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

 

A poultry farm in the Lubelskie Region.

Source: 

Link: https://wahis.woah.org/#/in-review/7451

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

 

A poultry farm in the Chhattisgarh Region.

Source: 

Link: https://wahis.woah.org/#/in-review/7453

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

Wild Anatidae (unidentified) in the Yevrey Region.

Source: 

Link: https://wahis.woah.org/#/in-review/7426

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

 

A poultry farm in Araucanía Region.

Source: 

Link: https://wahis.woah.org/#/in-review/7456

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

 

-- In accordance with the WOAH Terrestrial Animal Health Code, Article 10.4.1, point 4, this outbreak does not change the disease-free status of Sweden as these are wild birds or birds kept in a single household, and therefore do not fall within the WOAH definition of poultry.

__

-- Tjörn: 

- A Whooper swan was found dead. It was sent to the Swedish Veterinary Agency for laboratory analysis as part of the national surveillance program for avian influenza.

-- Varberg: 

- A Eurasian Buzzard was found dead. It was sent to the Swedish Veterinary Agency for laboratory analysis as part of the national surveillance program for avian influenza.

- A Peregrin falcon was found dead. It was sent to the Swedish Veterinary Agency for laboratory analysis as part of the national surveillance program for avian influenza.

-- Nyköping: 

- An Eurasian buzzard was found dead. It was sent to the Swedish Veterinary Agency for laboratory analysis as part of the national surveillance program for avian influenza.

-- Södertälje: 

- A Eurasian jackdaw was found dead. It was sent to the Swedish Veterinary Agency for laboratory analysis as part of the national surveillance program for avian influenza.

-- Hallstahammar: 

- A Eurasian jackdaw was found dead. It was sent to the Swedish Veterinary Agency for laboratory analysis as part of the national surveillance program for avian influenza.

-- Växjö: 

- A Canada goose and a Greylag goose were found dead and sent to the Swedish Veterinary Agency for laboratory analysis as part of the national surveillance program for avian influenza.

Source: 

Link: https://wahis.woah.org/#/in-review/7452

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#Infection of the #bovine mammary #gland by avian #H5N1 subclade 2.3.4.4b #influenza viruses

 

Abstract

The emergence of the panzootic clade of highly pathogenic avian influenza H5N1 (2.3.4.4b) in 2020 marked a major expansion in the host range of influenza A viruses (IAVs), raising concerns about further cross‑species transmission events and zoonotic spillover. Introduction of 2.3.4.4b viruses into U.S. dairy herds has resulted in widespread circulation, accompanied by reduced milk yield, mastitis, and high viral loads in milk. Notably, virus circulation in dairy cattle represents a novel route for mammalian adaptation and transmission that has already led to more than 40 human cases in the U.S. since 2024. Here, we investigated whether avian clade 2.3.4.4b viruses could infect mammary tissue from Aberdeen Angus, Holstein Friesian, and Limousin cattle, three breeds commonly farmed in Europe, the Americas, and Oceania. Using mammary gland explants, we inoculated tissues with attenuated reassortant viruses expressing the haemagglutinin and neuraminidase glycoproteins of three 2.3.4.4b viruses that predated the emergence of H5N1 in US cattle: A/chicken/England/053052/2021 (AIV07), A/chicken/Scotland/054477/2021 (AIV09), and A/chicken/England/085598/2022 (AIV48). Infected epithelial cells were identified using immunohistochemistry in explants from both the teat and gland cistern for all three breeds following infection with AIV09 and AIV48, indicating that mammary tissue from each of the three tested cattle breeds cattle is permissive to H5N1 infection. Lectin staining showed expression of both α2,3‑linked and α2,6‑linked sialic acids in the mammary tissue of all donors showing that all three breeds have the potential to support infection with both avian-adapted and mammalian adapted IAVs. Together, these findings demonstrate that mammary glands from both beef and dairy cattle breeds are permissive to infection with avian‑adapted and mammalian-adapted H5N1 viruses and highlight the potential for this tissue to act as a mixing vessel for IAV reassortment, underscoring the need to include cattle in ongoing H5N1 surveillance and risk‑assessment frameworks.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

Medical Research Council, https://ror.org/03x94j517, MR/Y03368X/1, MR/Y03368X/1, MC_UU_0034/2, MC_UU_0034/3, MC_UU_0034/1

Biotechnology and Biological Sciences Research Council, https://ror.org/00cwqg982, BB/V004697/1

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.04.16.718897v1

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Acquisition of specific #human respiratory tract binding of 2.3.4.4b #H5N1 #hemagglutinins requires multiple #mutations

 

Abstract

It has been suggested that the hemagglutinin of the human-infecting cattle-derived 2.3.4.4b virus A/Texas/34 (H5TX) requires only one mutation, namely Q226L, to switch from binding avian-type to human-type receptor preference. In this study, we examined the binding of H5TX Q226L, along with other key mutations, to sections of human trachea. We conclude that, while H5TX Q226L can bind human-type receptors, more than a single mutation is required for this protein to bind to human respiratory tract tissue. We also report changes in receptor-binding specificity of another 2.3.4.4b HA mutant, H5FR Q226L, associated with the presence of a multibasic cleavage site. This study offers insight into the determinants of evolution towards human-type receptor binding in currently circulating H5Nx viruses. It also emphasizes the importance of testing individual strains using additional methods, including tissue-based approaches, alongside synthetic glycans.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

NWO, OCENW.M20.106

Horizon, 862605

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.04.16.718875v1

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

{England, Lincoln Region} A commercial flock of 3,800 laying ducks. Samples taken were positive for HPAI H5N1. Birds presented clinical signs prior to testing.

Source: 

Link: https://wahis.woah.org/#/in-review/7440

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

 

A poultry farm in Zanzan Region.

Source: 

Link: https://wahis.woah.org/#/in-review/7446

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Cross - #protection against highly pathogenic avian #influenza #H5N1 virus from seasonal influenza #vaccines: a systematic review and meta-analysis of #ferret studies

 

ABSTRACT

The recent surge in spillover events of highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b to humans and mammals in North America has raised urgent pandemic concerns. Human H5N1 vaccines are unavailable in most countries. We synthesized data from ferret challenge trials to evaluate whether widely available seasonal influenza vaccines confer cross-protection against lethal H5N1 infection. We systematically searched PubMed, Embase, and Web of Science for ferret studies of lethal H5N1 challenge published up to 5 July 2025 (PROSPERO #CRD42024520346). Random-effects meta-analyses were conducted to compare vaccine efficacy (VE) of seasonal influenza vaccines and H5N1 vaccines against H5N1-related mortality. Seroprotection was defined as a neutralizing antibody titre of ≥1:40. We identified 35 studies (157 trials). Seasonal influenza vaccines without N1 did not confer significant cross-protection (five trials; VE 14.8%, 95% CI –3.6 to 30.0). In contrast, VE was 73% for N1-containing seasonal influenza vaccines (19 trials; 95% CI 54–84) and 77% for H5N1 vaccines overall (133 trials; 95% CI 72–82) (p = 0.52). The VE of N1-containing seasonal influenza vaccines was modestly lower than that of H5N1 vaccines with seroprotection (88%; 66 trials; 95% CI 84–91; p = 0.009), but comparable to H5N1 vaccines that did not achieve seroprotection (63%; 67 trials; 95% CI 52–71; p = 0.29). The VE of seasonal influenza vaccines against H5N1 was robust across sensitivity analyses, with no evidence of publication bias (p = 0.99). Seasonal influenza vaccines significantly reduce H5N1-associated mortality in ferret trials, suggesting the cross-protection potential of currently available vaccines. Human studies are warranted.

Source: 

Link: https://www.tandfonline.com/doi/full/10.1080/22221751.2026.2654278

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Highly Pathogenic Avian #Influenza #H5N1 Virus #RNA in #Bovine #Semen, #California, #USA, 2024

 

Abstract

Since March 2024, highly pathogenic avian influenza (HPAI) A(H5N1) virus has infected dairy cattle in the United States, prompting concern about novel transmission routes. During an outbreak in California, HPAI H5N1 RNA was detected in an asymptomatic bull’s semen. Although infectious virus was not isolated, semen-associated transmission risks and biosecurity practices remain a concern.

Source: 

Link: https://wwwnc.cdc.gov/eid/article/32/5/25-1639_article

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

 

A wild Whooper Swan in Kastoria Region.

Source: 

Link: https://wahis.woah.org/#/in-review/7433

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#Population #immunity to clade 2.3.4.4b #H5N1 is dominated by anti - #neuraminidase #antibodies

 

ABSTRACT

Clade 2.3.4.4b highly pathogenic avian influenza A(H5N1) viruses continue to expand geographically and across mammalian hosts, raising concern about pandemic potential. The degree and specificity of pre-existing immunity in humans are key determinants of this risk. We analyzed hemagglutinin (HA)- and neuraminidase (NA)-specific antibody responses in 300 sera collected from adults in New York City. While HA directed binding antibodies to clade 2.3.4.4b H5 were low and hemagglutination-inhibiting antibodies were absent, we detected widespread binding and functional NA antibodies against N1 neuraminidases from clade 2.3.4.4b H5N1 viruses. Neuraminidase inhibition (NI) titers were highest against North American D1.1 genotype N1 viruses and correlated strongly with neutralizing activity, whereas HA-binding antibodies did not. An additional N-linked glycosylation site, as found in the NA of a human D1.1 isolate from British Columbia, reduced susceptibility to NI antibodies. Antibodies titer to N5 from H5N5 were low to minimal. These findings indicate that population-level immunity to clade 2.3.4.4b H5 viruses is dominated by NA-directed antibodies, with important implications for pandemic risk assessment.

IMPORTANCE

Understanding how pre-existing human immunity shapes susceptibility to emerging influenza viruses is central to pandemic preparedness. Here, we determined that human sera contain widespread, functional antibodies targeting H5N1 neuraminidase, which correlate with virus neutralization, whereas HA-directed responses are limited. We further show that acquisition of an NA glycosylation site reduces antibody inhibition, highlighting a potential pathway for immune evasion. These results identify neuraminidase-specific immunity as a major immunological barrier to severe H5N1 disease in humans and emphasize the need to incorporate NA antigenicity into influenza surveillance, risk assessment, and next-generation vaccine design.

Source: 

Link: https://journals.asm.org/doi/10.1128/mbio.00445-26

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Historical #Pandemic and Contemporary #Influenza A Viruses Reveal #PB2 M631L as a Convergent #Adaptation to #Human ANP32

 

Abstract

Understanding the genetic changes that allow avian influenza A viruses (IAVs) to switch their natural hosts and establish productive infection in humans is important for pandemic risk assessment. Adaptations in the IAV polymerase are required to overcome species-specific restrictions imposed by host ANP32 proteins. Notably, avian virus polymerase is generally only poorly supported by human ANP32 proteins due to species-specific differences. Consequently, efficient polymerase adaptation to the binding interface of human ANP32 requires distinct amino acid changes, such as PB2 E627K. A separate adaptation, PB2 M631L, has recently been reported in mammalian-adapted IAV; however, its functional role across divergent viral lineages and its relationship to host ANP32-dependent adaptation remain incompletely defined. Here, we examine PB2 M631L in the polymerases of a 1918 pandemic strain, a recombinant contemporary H1N1pdm09, and a recent clade 2.3.4.4b H5N1 virus. Using polymerase activity and protein-interaction assays, we show that PB2 M631L enhances polymerase activity and ANP32 binding in human—but not avian—contexts, and that this effect is conserved across multiple viral backgrounds. In H1N1pdm09, PB2 M631L also increased virus replication in mammalian cells. These findings indicate that PB2 M631L contributes to enhanced polymerase compatibility with human ANP32 proteins and are consistent with a role in adaptation across multiple influenza virus lineages. Our results highlight how analysis of historical pandemic strains can inform risk assessment for future emerging viruses.

Source: 

Link: https://www.mdpi.com/2076-2607/14/4/859

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Respirable #Aerosol #Production and Reduction of Avian #Influenza #Transmission #Risk during #Chicken Processing, #Bangladesh

 

Abstract

In Bangladesh, influenza A(H5N1) viruses are endemic in poultry. Processing infected chickens can aerosolize viruses, increasing the risk for human infections. We evaluated particulate matter (PM2.5) mass concentration during slaughtering and defeathering methods used in live bird markets in Bangladesh to identify solutions to reduce aerosol exposure. We slaughtered 675 chickens using cones and barrels with 3 lid types and defeathered 45 chickens using a defeathering machine with 5 lid types. We interviewed 3 slaughterers to understand method preference. For slaughtering, barrels with a solid or star-cut lid reduced PM2.5 mass concentrations by 65%–73% compared with uncovered barrels. For defeathering, machines fully covered by a solid lid or lid with a hole and pivot door reduced PM2.5 mass concentrations by 50% compared with machines with no lid. Slaughterers preferred barrels covered with solid lids and defeathering machines covered with solid or hinged lids. Those methods might reduce aerosol exposure during poultry processing.

Source: 

Link: https://wwwnc.cdc.gov/eid/article/32/4/25-1878_article

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#USA, #Wastewater Data for Avian #Influenza #H5 (#CDC, April 10 '26, summary)

 

{Excerpt}

(...)

Time Period: March 29, 2026 - April 04, 2026

-- A(H5) Detection: 7 site(s) (1.6%)

-- No Detection: 430 site(s) (98.4%)

-- No samples: 125 site(s)

(...)

Source: 

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

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#Investigation and #impact of mammalian #adaptation markers on #H5N8 high pathogenicity avian #influenza #polymerase activity

 

Abstract

Highly pathogenic H5Nx viruses of clade 2.3.4.4b have spread worldwide, causing major economic losses and increased human exposure. Since 2020, multiple mammalian infections have been reported, raising concerns about further adaptation to mammalian hosts. We analyzed influenza A virus sequences from the Influenza Virus Database at the National Center for Biotechnology Information to identify new mammalian adaptation markers in the polymerase complex and nucleoprotein, using recursive partitioning. These markers were grouped into “proteotypes” to assess their co-occurrence and association with host origin. This analysis revealed distinct groups of proteotypes linked to mammalian adaptation, including those seen in historical and pandemic human strains. Identified mutations were introduced alone or in combination into a 2.3.4.4b H5N8 virus to evaluate their impact on polymerase activity in mammalian cells using a minigenome assay. PB1 V336I and PB2 K702R increased polymerase activity in human cells, particularly with PB2 E627K, supporting enhanced surveillance of 2.3.4.4b H5Nx viruses. These findings highlight mutation combinations relevant for enhanced surveillance of 2.3.4.4b H5Nx viruses.

Source: 

Link: https://www.nature.com/articles/s44298-026-00188-3

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