Emergence and #Evolution of Triple #Reassortant Highly Pathogenic Avian #Influenza #H5N1 Virus, #Argentina, 2025

 

Abstract

The H5N1 subtype of highly pathogenic avian influenza (HPAI) poses a major zoonotic threat due to its high fatality rate and capacity for cross species transmission. In early 2025, Argentina detected a novel triple reassortant A(H5N1) virus in Chaco Province, combining Eurasian, North American, and South American lineage segments. Genomic analyses of subsequent outbreaks in Buenos Aires and Entre Ríos confirmed persistence of this reassortant and additional HA substitutions (T204K, P251S) potentially linked to increased mammalian receptor affinity. Although PB2 sequences lacked canonical mammalian-adaptive markers (E627K, Q591K, D701N), all contained I292M, a mutation associated with human adaptation. Phylogenetic analyses revealed distinct genotypes and increasing divergence. These findings indicate ongoing viral evolution and adaptation within Argentina, emphasizing the urgent need for sustained genomic surveillance, timely data sharing, and integrated One Health strategies to mitigate zoonotic and socioeconomic risks associated with H5N1 spread in South America.

Source: 

Link: https://www.mdpi.com/1999-4915/18/5/525

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An #NS1-F161L #Substitution Determines #Host-Driven #Virulence Enhancement of #H5N6 Avian #Influenza Virus in #Ducks

 

Abstract

H5 subtype avian influenza virus (AIV) can infect both chickens and ducks, leading to substantial economic losses. Nevertheless, certain strains cause silent infections in ducks. In this study, a goose-origin clade 2.3.4.4h H5N6 AIV was isolated, which caused high mortality in mixed-gender white leghorn chickens but no deaths in mixed-gender mallard ducks. After independent serial in vitro passage in duck embryo fibroblasts (DEFs) and in vivo passage in specific-pathogen-free (SPF) ducks, the DEF-passage 10 (P10) virus induced markedly higher mortality rates and viral loads in SPF ducks compared to the DEF-P1 virus and the original parental virus prior to passage. Similarly, the in vivo-passaged P3 and P4 viruses exhibited significantly higher mortality rates than the P1 virus in SPF ducks, with 100% mortality and markedly increased viral titers in the organs. A whole-genome SNP analysis identified seven high-frequency mutations in the M1, NA and NS1 proteins. The NS1-F161L substitution virus exhibited significantly increased mortality rates, viral loads in multiple tissues, and a robustly induced innate immune response in ducks. Furthermore, dynamic evolutionary variations in the NS1 protein among global H5 avian influenza viruses revealed that the NS1-F161L substitution became dominant in clade 2.3.4.4b viruses in 2021 and subsequent years. Collectively, our findings demonstrate that host-driven adaptation can rapidly increase the pathogenicity of H5N6 AIVs in ducks and identify NS1-F161L as a critical virulence marker. These results offer novel insights relevant to the molecular surveillance, virulence prediction, and risk assessment of circulating H5 AIVs in waterfowl.

Source: 

Link: https://www.mdpi.com/1999-4915/18/5/488

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A natural five-amino-acid insert at the S2’ #cleavage site of #MERS-CoV #spike enhances viral membrane fusion

 

Highlights

• A novel 5-aa insert, TSGVF, is present at the S2’ cleavage site of the spike protein of MERS-CoV from dromedary camels.

• Pseudovirus-based entry assays showed that the TSGVF insert increases viral entry efficiency in different human cells.

• Pseudovirus with TSGVF insert at the S2’ cleavage site showed strong resistance to TMPRSS2 inhibitor.

• The natural occurrence of TSGVF insert at the spike S2’ cleavage site enhances viral membrane fusion and syncytia formation.

Source: 

Link: https://www.sciencedirect.com/science/article/pii/S1995820X26000611?via%3Dihub

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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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#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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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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Predicting the #antigenic #evolution of seasonal #influenza viruses using phylogenetic #convergence

 

Abstract

The antigenic evolution of human seasonal influenza viruses is primarily driven by single amino acid substitutions immediately adjacent to the receptor binding site in the hemagglutinin (HA) protein. The ability to predict these substitutions would allow vaccine strains to be selected with an understanding of likely future antigenic variation. Here, we estimate the effect of HA substitutions on viral fitness using measurements of convergent evolution in a large phylogeny. We show that the substitutions which have historically caused major antigenic changes in H3N2 influenza viruses were nearly always one of few substitutions near the HA receptor binding site estimated to be under positive selection in sequences collected before the antigenic transition, based on convergent acquisition of the substitution in multiple independent lineages. Furthermore, this signal predates the establishment of the major clade containing the antigenic substitution by more than one year, so is highly informative for prospective prediction.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

National Institute of Allergy and Infectious Diseases, https://ror.org/043z4tv69, 75N93021C00014

National Institutes of Health, https://ror.org/01cwqze88, R01AI165818

Medical Research Council, https://ror.org/03x94j517, MR/Y004337/1

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.04.10.717627v1

____

#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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Genetic characterization of a novel triple - #reassortant #influenza #H1N2 virus from #pigs, #China, 2021

 

Abstract

Swine influenza virus (SIV) is a highly contagious respiratory pathogen in pigs, with bidirectional transmission posing a potential threat to human health. In this study, nasal swab samples were collected from pigs in Shandong Province, China, and yielded an H1N2 SIV strain, designated A/swine/Shandong/QD726/2021 (H1N2). Whole-genome sequencing was performed for Sw/SD/QD726/2021, and phylogenetic analysis was conducted together with 156 Chinese H1N2 reference sequences obtained from the Global Initiative on Sharing All Influenza Data (GISAID) database and the National Center for Biotechnology Information (NCBI) Influenza Virus Resource database. The results indicated that Sw/QD726/2021 represents a novel reassortant genotype (G21), with the HA gene derived from Eurasian avian-like H1N1 (EA H1N1), the NA and NS genes from triple-reassortant H1N2 (TR H1N2), and the remaining internal genes (PB2, PB1, PA, NP, M) from the 2009 pandemic H1N1 (pdm/09 H1N1). Key amino acid analysis revealed N31 in M2, responsible for adamantane resistance, and S42 in NS1, which influences viral virulence in mouse models. BALB/c mouse experiments demonstrated efficient viral replication in the lungs and nasal turbinates, accompanied by moderate body weight loss and lung lesions, indicating only moderate pathogenicity. These findings underscore the ongoing evolution of H1N2 SIV in pigs and emphasize the importance of enhanced surveillance and preventive strategies to mitigate public health risks.

Source: 

Link: https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2026.1779293/full

____

#Genetic and #biological characterization of a #duck-origin clade 2.3.4.4b #H5N6 avian #influenza virus reveals partial #mammalian #adaptation

 

Highlights

• Duck-origin H5N6 virus A/Duck/Jiangsu/628/2022 shares high homology with the human strain A/Yangzhou/125/2022.

• The 628 strain shows mammalian adaptation markers: HA mutations enhance human receptors affinity and NA mutations reduce sensitivity to neuraminidase inhibitors.

• Limited airborne transmission but detectable droplet-mediated spread suggests increased mammalian transmission risk.

Abstract

Clade 2.3.4.4b H5Nx highly pathogenic avian influenza viruses (HPAIVs) have caused extensive outbreaks in poultry worldwide. H5 HPAIVs have caused sporadic but severe human infections in China, representing a persistent zoonotic threat. Here, we identified a duck-origin H5N6 HPAIV (A/Duck/Jiangsu/628/2022) through routine surveillance and assessed its biological characteristics and mammalian pathogenesis. Phylogenetic analysis revealed > 98% nucleotide identity between strain 628 and the concurrent human H5N6 strain A/Yangzhou/125/2022. Molecular characterization identified multiple mammalian adaptation markers: hemagglutinin substitutions (S137A, T160A, T192I) associated with enhanced human receptor binding; neuraminidase mutations (I117T, D198N) linked to reduced neuraminidase inhibitor susceptibility; and polymerase complex changes (PB1-D622G, PA-K142Q) conferring increased mammalian cell replication. In vitro studies demonstrated that 628 virus replicated more efficiently in mammalian than in avian cells and exhibited dual receptor-binding specificity. Mouse pathogenicity assays revealed moderate virulence with progressive lung pathology. Critically, transmission experiments confirmed both direct contact and airborne transmission capabilities of 628 in guinea pigs. These findings demonstrate that circulating H5N6 viruses have acquired partial mammalian adaptation while retaining avian fitness, significantly elevating pandemic potential. Enhanced surveillance of wild bird populations, poultry farms, and live poultry markets is urgently needed to develop effective prevention and control strategies.

Source: 

Link: https://www.sciencedirect.com/science/article/abs/pii/S037811352600146X?via%3Dihub

____

#Genomic analysis of high pathogenicity avian #influenza viruses from #Antarctica reveals multiple introductions from South #America

 

Abstract

The spread of high pathogenic avian influenza virus (HPAIV) H5N1 clade 2.3.4.4b into Antarctica poses a major threat to polar wildlife. We report the detection of H5N1 in carcasses of eight species during the 2023-2024 and 2024-2025 austral summers in the South Shetland Islands: Antarctic shag, Antarctic tern, kelp gull, pintado petrel, Antarctic petrel, skuas, Antarctic fur seal, and southern elephant seal. Whole-genome sequencing, mutational profiling, and phylogenetic reconstruction revealed that the viruses detected in these hosts descended from distinct introduction events. One group of strains including complete and partial viral genomes from a gull, skuas, fur seals, an Antarctic tern, and a southern elephant seal clustered with H5N1 strains previously detected in marine mammals in South America and formed a polyphyletic lineage consistent with at least two independent introductions into Antarctica. A second group of strains including complete and partial viral genomes from petrels, shags, and skuas clustered with H5N1 strains previously detected in seabirds and marine mammals in South Georgia and with a previously reported HPAIV detection from Torgersen Island, Antarctic Peninsula. These findings reveal extensive epidemiological connectivity between South America and Antarctica, with South Georgia serving as a “stepping stone” for virus spread in the region.

Source: 

Link: https://www.nature.com/articles/s41467-026-71544-3

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Q1020R in the #spike proteins of #MERS-CoV from Arabian #camels confers resistance against soluble #human #DPP4

 

ABSTRACT

The Middle East respiratory syndrome coronavirus (MERS-CoV) is a pre-pandemic coronavirus that is transmitted from camels, the natural reservoir, to humans and can cause severe disease. MERS cases have been documented in Arabia but not Africa, although the virus is circulating in both Arabian and African camels. Further, evidence has been provided that viruses in African camels might have a reduced capacity to cause disease. However, the underlying determinants are incompletely understood. Here, employing pseudotyped particles as model systems for MERS-CoV entry into cells, we compared cell entry of viruses from African and Arabian camels and its inhibition. We show that viruses found in Arabian camels and recent human cases are less susceptible to inhibition by human soluble DPP4 (sDPP4) than viruses from African camels, although both enter human cells efficiently and are comparably sensitive to inhibition by interferon-induced transmembrane (IFITM) proteins and neutralizing antibodies. Furthermore, relative resistance to sDPP4 was linked to mutation Q1020R, present in the spike proteins of recent Arabian but not African viruses. Finally, indirect evidence was obtained that sDPP4 in human plasma can inhibit MERS-CoV cell entry. These results support the concept that soluble DPP4 might constitute a natural barrier against human infection that is more efficiently overcome by viruses currently circulating in Arabian camels than those in African camels.

Source: 

Link: https://journals.asm.org/doi/10.1128/jvi.00282-26

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#Bovine #H5N1 #influenza viruses have adapted to more efficiently use #receptors abundant in #cattle

 

Abstract

Sustained mammal-to-mammal transmission of high pathogenicity H5N1avian influenza viruses is reshaping the host range of these pathogens. One of the longest-running mammalian transmission chains involves the B3.13 genotype circulating in U.S. dairy cattle which was detected early in 2024. Genomic analysis revealed selection and rapid fixation of haemagglutinin mutations D104G and V147M. We demonstate, via glycomic profiling, that bovine tissues, including the mammary gland, are enriched in N- and O-linked glycans capped with N-glycolylneuraminic acid (NeuGc), a sialic acid absent in humans and birds, which instead express only N-acetylneuraminic acid (NeuAc). Early cattle H5 viruses poorly recognized NeuGc, but D104G and V147M enabled efficient engagement of both NeuAc- and NeuGc-containing receptors. These mutations enhanced replication in bovine mammary tissue without major attenuation of replication in human lung and primary nasal epithelial cells. NeuGc-driven receptor adaptation therefore promotes viral fitness in cattle while potentially limiting immediate zoonotic risk. Deep mutational scanning further identifies alternative haemagglutinin substitutions that confer NeuGc usage and represent surveillance markers for emerging cattle H5 lineages.

Competing Interest Statement

JDB and BD are inventors on Fred Hutch licensed patents related to deep mutational scanning. JDB consults for Pfizer, GSK, Apriori Bio, and Invivyd.

Funder Information Declared

Medical Research Council, MR/Y03368X/1, MR/R010757/1, MC_UU_0034/2, MC_UU_0034/3

BBSRC, BB/Y007298/1, BB/X006123/1, BB/X006166/1, BBS/E/PI/230002A, BBS/E/PI/230002B

BBSRC, BBS/E/PI/23NB0004, BBS/E/PI/23NB0003, UKRI2253, BB/V004697/1

Defra, SE2227

Royal Society, https://ror.org/03wnrjx87, RGS\R2\242118

Houghton Trust, HT/SPRG/23/04

Flanders, G005323N, G051322N, G010326N

CEIRR, 75N93021C00045

The Rockefeller Foundation, PC-2022-POP-005

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.04.02.715584v1

____

The emergence and molecular #evolution of #H5N1 #influenza viruses in #USA dairy #cattle

 

Abstract

Prior to 2024, highly pathogenic avian influenza H5N1 clade 2.3.4.4b viruses circulated predominantly in wild birds and poultry. In 2024 and 2025, 2.3.4.4b genotypes B3.13 and D1.1 were detected in United States dairy cattle. Using whole-genome and segment-specific phylodynamic inference, we estimate that B3.13 and D1.1 spilled over from wild birds into dairy cattle in late 2023 and late 2024, respectively. Spillover occurred shortly after the formation of the reassortant genotypes and was followed by months of cryptic transmission prior to detection. We found that both B3.13 and D1.1 evolved at higher rates in cattle relative to birds, primarily due to relaxed purifying selection. Site-specific analyses identified genomic sites under positive selection in cattle relative to birds, indicating adaptation and likely contributing to improved viral fitness after spillover. Intensified genomic surveillance in dairy cattle is essential as population immunity introduces additional selection pressures, with ever-changing risk for human emergence.

Competing Interest Statement

M.A.S. receives contracts from Johnson & Johnson and Gilead Sciences outside the scope of this work. M.U.G.K. received consulting fees from Takeda, Bavaria Nordic, and Google DeepMind for work unrelated to the manuscript.

Funder Information Declared

Fonds voor Wetenschappelijk Onderzoek - Vlaanderen, G051322N, G051323N

UK Medical Research Council/Department for Environment, Food and Rural Affairs (DEFRA) FluTrailMap-One Health consortium, MR/Y03368X/1

Biotechnology and Biological Sciences Research Council (BBSRC)/DEFRA ‘FluTrailMap’ consortium, BB/Y007298/1

Pirbright Institute’s Strategic Program Grants, BBS/E/PI/230002A, BBS/E/PI/230002B

EMBO Installation Grant, 5305

Academy of Medical Sciences Springboard, 1049

Centers of Excellence for Influenza Research and Response, National Institute of Allergy and Infectious Diseases, National Institutes of Health (NIH), Department of Health and Human Services, 75N93021C00015, 75N93021C00014

National Institutes of Health, AI135995, AI153044, AI192139

Rockefeller Foundation, PC-2022-POP-005

Health AI Programme from Google.org

Oxford Martin School Programmes in Pandemic Genomics & Digital Pandemic Preparedness

European Union's Horizon Europe, 874850, 101086640

Wellcome Trust, 303666/Z/23/Z, 226052/Z/22/Z, 228186/Z/23/Z

United Kingdom Research and Innovation, APP8583

Medical Research Foundation, MRF-RG-ICCH-2022-100069

UK International Development, 301542-403

Bill & Melinda Gates Foundation, INV-063472, INV-090281

Novo Nordisk Foundation, NNF24OC0094346

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.03.30.713641v1

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Brown and Lesser #noddies as epidemiological #reservoirs and #sentinels of avian #influenza virus in the South-western Indian #Ocean

 

Abstract

Avian influenza virus (AIV) epidemiology is well documented in temperate regions but remains poorly understood in isolated ecosystems like tropical oceanic islands. On these islands, seabirds nest in dense interspecific colonies where the role of different species as reservoirs and dispersers of AIV may vary greatly. Here, we examine the role of noddies (Anous spp.) as potential reservoirs for low pathogenic AIV and evaluate their potential as sentinel species for highly pathogenic AIV introduction on tropical oceanic islands. We analyzed blood samples from 11 seabird species across eight islands in the southwestern Indian Ocean (2015 to 2020). Noddies exhibited high, stable seroprevalence (30 to 45%), comparable to reservoir host species in temperate regions. The detection of two N7 positive noddies, sampled the same year on two distinct islands, provided direct molecular evidence that AIV actively circulates on these island colonies. While most other species showed low exposure, Bridled Terns (Onychoprion anaethetus) had exceptionally high seroprevalence (80%), though their reservoir status requires further investigation due to limited sampling. Given noddies consistent exposure and regional distribution, we recommend prioritizing islands with large noddy populations for AIV surveillance. Continued investigation of viral dynamics within and among islands is now called for to elucidate the ecological drivers of AIV maintenance and transmission.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.03.31.715511v1

____

Three decades of #discovery: An overview of #Hendra virus, the original #Henipavirus

 

Abstract

Hendra virus (HeV) emerged in Australia in 1994, causing a devastating outbreak among horses in Brisbane with spread to humans, resulting in one death. This nonsegmented, negative-stranded RNA virus belongs to the family Paramyxoviridae and represents the first zoonotic paramyxovirus isolated from bats. Flying foxes (genus Pteropus) serve as the natural reservoir, with all four mainland Australian species carrying antibodies with no apparent disease. HeV initiates infection by binding ephrin-B2 receptors on vascular endothelial cells, driving characteristic pathology involving vasculitis, thrombosis, and neurological complications. Horses are amplifying hosts, shedding virus abundantly in respiratory secretions and posing transmission risks to humans during invasive procedures. To date, seven confirmed human infections have been documented, with a 57% fatality rate, presenting as severe respiratory disease or progressive encephalitis. Two genetic variants are now recognized: the original HeV genotype 1 and the emerging HeV genotype 2, identified in limited equine cases. Recent surveillance of bat roosts revealed substantial viral diversity, with peak shedding occurring during winter—coinciding with equine spillover peaks. Prevention integrates multiple strategies: the licensed equine vaccine Equivac which provides One Health protection for both horses and human contacts; biosecurity measures including proper PPE; and habitat restoration to reduce nutritional stress in bat populations. Emerging therapeutics include monoclonal antibodies, with m102.4 showing cross-protective activity against both HeV and the closely related Nipah virus. No licensed human vaccines currently exist, though candidates are in development. Future prevention strategies increasingly recognize the importance of Indigenous-led conservation approaches alongside biomedical interventions. This review will focus on the history of HeV, virus replication and diversity, epidemiology, clinical manifestations, diagnosis, treatment, prevention, as well as ecological and interdisciplinary countermeasures.

Author summary

Hendra virus (HeV) was first detected in 1994, with two outbreaks occurring within 2 months of that year. One was the index outbreak in the Brisbane suburb of Hendra, and the other was retrospectively diagnosed in the following year. This review examines the discoveries that have been made in the 30 years since its discovery.

Source: 

Link: https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0014138

____

#Evolution and viral properties of the #SARS-CoV-2 #BA32 #subvariant

 

Abstract

The SARS-CoV-2 Omicron subvariant BA.3.2 descends from BA.3. It emerged two years after BA.3 ceased to circulate and differs by 39 spike mutations from BA.3. Similar to BA.2.86, which circulated at low levels before giving rise to JN.1, BA.3.2 shows a low but persistent circulation globally. Here, we characterize the phylogenetic origin, infection in cell culture, and neutralization of BA.3.2 using live virus and blood plasma samples collected in South Africa at different stages of the Covid-19 pandemic. Like the Omicron BA.2.86 subvariant, we find that BA.3.2 likely emerged in Southern Africa. We also find that an 871 bp deletion removed ORF7 and ORF8. In H1299-ACE2 cells, BA.3.2 has lower cytotoxicity measured as plaque area compared to ancestral SARS-CoV-2 but similar to the co-circulating LP.8.1 Omicron subvariant with which it also shares similar replication and infection focus size. BA.3.2 and LP.8.1 exhibit complete escape from neutralization from pre-Omicron collected plasma samples, have low levels of neutralization by plasma collected in 2024, and higher neutralization by plasma collected in 2025, with BA.3.2 showing moderately lower neutralization than LP.8.1. The emergence of long branch subvariants like BA.3.2 without intermediates likely indicates that unmonitored persistent infections continue to drive large evolutionary shifts in this virus.

Source: 

Link: https://academic.oup.com/ve/article/12/1/veag011/8490867

____

Host-specific functional #evolution of #seal #influenza A virus #NS1 protein following #avian-to-seal #transmission

 

ABSTRACT

Marine mammals, particularly seals, are susceptible to both avian and human influenza A viruses (IAVs), making them potential intermediates for zoonotic virus emergence. In recent decades, repeated transmissions of avian influenza viruses (AIVs) from wild aquatic birds, their natural reservoir, have caused significant mortality in seals. Defining the molecular determinants of viral adaptation in marine mammals, and their implications for replication in human cells, is therefore essential. The non-structural protein 1 (NS1) of AIV, a key antagonist of the interferon (IFN) response, plays a central role in host adaptation. Here, we analyzed NS1 proteins from seal influenza viruses (H3, H4, H5, H7, and H10 subtypes) and their closest avian relatives isolated between 1980 and 2023, and evaluated their function in seal, avian, and human cells. Phylogenetic analysis confirmed multiple bird-to-seal transmission events. Seal-derived NS1 proteins generally contained few strain-specific amino acid substitutions and showed comparable expression and IFN antagonism to their avian precursors. A notable exception was the seal H10N7 virus isolated in 2014 in Northeastern Europe, which harbored three previously uncharacterized substitutions at NS1 amino acid residues 94, 104, and 171. These amino acid substitutions markedly altered NS1 properties to enhance protein stability, suppress IFN induction, mediate host transcription shut-off, and increase polymerase activity in human cells, without affecting NS1 expression or reducing virus replication in avian cells. Overall, these results reveal how NS1 undergoes host-specific functional evolution following avian-to-seal transmission and provide mechanistic insight into the adaptation of influenza A viruses to mammalian hosts.

IMPORTANCE

Avian influenza viruses (AIVs) circulate naturally in wild aquatic birds but occasionally infect mammals, including seals, where they can cause severe outbreaks. Seals are of particular concern because they can harbor both avian and human influenza viruses, creating opportunities for reassortment and the emergence of novel zoonotic strains. Understanding how AIVs adapt to mammalian hosts is therefore critical for anticipating and mitigating future influenza threats. Here, we investigated the role of the NS1 protein, a key viral factor that suppresses host immune responses, in seal-derived AIVs. Overall, NS1 expression and function were conserved across different subtypes and host cells. However, we identified unique amino acid substitutions in the NS1 of a seal H10N7 virus that enhanced protein stability, interferon antagonism, and viral adaptation in human cells. These findings illustrate how minor changes in NS1 protein can drive host adaptation and underscore the need for continued surveillance of AIVs in seals.

Source: 

Link: https://journals.asm.org/doi/full/10.1128/jvi.01650-25?af=R

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On the brink of emergence: an evolutionary approach to #Influenza A virus #H5N1 isolated from #humans

 

Highlights

• A detailed phylogenetic analysis of H5N1 HPAIV isolated from humans was performed.

• All strains infecting humans have acquired substitutions in several key proteins.

• All strains have gained specific substitutions to better adapt to the human host.

• Substitutions in key proteins involved in replication and immune evasion were found.

• A significant degree of polymorphic sites was found in the polymerase complex.

• Substitutions in hemagglutinins and neuraminidases from different clades were found.

Abstract

Avian Influenza Viruses (AIVs) pose today a very significant risk to global health given the widespread circulation of H5N1 highly pathogenic avian influenza viruses (HPAIV). After decimating the avian population all over the world, these viruses spill over to many different mammal species, causing also fatal outbreaks. As the virus continues to evolve increasing human cases of H5N1 HPAIV have been reported, causing concern that these viruses may adapt to the human host and became a pandemic new virus. In order to gain insight into this matter, a detailed phylogenetic analysis of H5N1 HPAIV isolated from humans was performed. A significant number of substitutions have been found in the hemagglutinins (HA) and neuraminidases (NA) among the three H5N1 clades already detected in human cases. Some of these substitutions were found to produce changes in the 3D structure of these proteins. Substitutions providing an evolutionary advantage to replicate or evade the immune response in mammals have been found in several non-structural proteins of strains infecting humans, including regulatory proteins, like PA-X or PB1-F2. A significant degree of polymorphic sites was observed in the proteins of the polymerase complex. The results of these studies are discussed in terms of the evolution of H5N1 HPAIV infecting humans and future work to be done to address the pandemic potential of these viruses.

Source: 

Link: https://www.sciencedirect.com/science/article/pii/S0168170226000353?via%3Dihub

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