#Pathology of dose dependent inocula of #H5N8 avian #influenza viruses in experimentally infected #chicken

 

Abstract

In the present study, we assessed the pathogenicity of H5N8 avian influenza viruses belongs to the clade 2.3.4.4b in chicken. Birds of three different dose groups, 10 2 , 10 4 , and 10 6 EID 50 were used in the study. No mortality was observed in 10 2 EID0 group. Percent cumulative mortality of 10 4 and 10 6 EID 50 group was 66.67 and 100 %, respectively. Varying duration of MDT of 3.2 and 2 days was observed in 10 4 and 10 6 EID 50 group, respectively. The CID 50 of virus was found to be 10 4.5 EID 50 . High no. of viral RNA copies were found both in oropharyngeal and cloacal swabs and in various organs of birds infected in 10 4 and 10 6 EID 50 group. Significant gross and histological changes and presence of viral antigen in various organs were observed in 10 4 and 10 6 EID 50 group. So, the study concludes that Indian HPAI, H5N8 isolates are highly pathogenic in nature to chicken by affecting most organs systemically. CID 50 of this H5N8 virus indicates poor adaption in chicken and it implies poor transmission possibility of this virus for host species in field condition. Though this virus are highly pathogenic in nature as that of HPAI, H5N1 viruses, absence of endothelial staining in most organs attributes variation in replication process and pathogenesis from HPAI, H5N1 viruses. Hence, further studies need to be done to elucidate the pathobiology of this virus in various bird species.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

Indian Council of Agricultural Research, https://ror.org/04fw54a43

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.01.27.700741v1

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#Genetic characterization of highly pathogenic avian #influenza #H5N8 virus isolated from commercial #poultry #farms in #Egypt reveals zoonotic potential

 

Abstract

Highly pathogenic avian influenza (HPAI) H5N8 virus, first identified in late 2016 in Egypt, continues to circulate and has replaced the previously dominant HPAI H5N1 virus of clade 2.2.1. In this study, HPAI H5N8 was detected on 23 commercial poultry farms in Egypt. Complete genome sequences of three isolates collected in 2021 were obtained using next-generation sequencing (NGS) and subjected to genetic characterization. Phylogenetic analysis showed these isolates to belong to clade 2.3.4.4b, comprising two genotypes: EA-2021-Q and EA-2020-A. Molecular analysis of the haemagglutinin (HA) protein revealed the presence of T156A and V538A substitutions in the duck isolate and an N183S substitution in the chicken isolate. Several additional nonsynonymous mutations were identified, including 147I and 504V in the PB2 protein, 127V, 672L, and 550L in the PA protein, 64F and 69P in the M2 protein, and 42S in the NS1 protein. Comparative analysis of HA antigenic sites between these isolates and the human vaccine against H5N8 revealed four nonsynonymous mutations: S141P, A154N, D45N, and V174I. Notably, the HA sequences of the studied isolates shared 98.7–99.4% amino acid sequence identity, and the NA sequences shared 96.1–97.1% identity to those of the 2.3.4.4b candidate human H5N8 vaccine strain (CVV) A/Astrakhan/3212/2020-like. These findings underscore the importance of continuous monitoring of the genetic evolution of avian influenza viruses to guide updates of candidate vaccine strains. Furthermore, the high similarity between the detected isolates and a zoonotic Russian H5N8 wild-type strain highlights the potential risk of cross-species transmission and possible human infection.

Source: 

Link: https://link.springer.com/article/10.1007/s00705-025-06479-z

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#Influenza #H5N8 #vaccine induces humoral and cell-mediated #immunity against highly pathogenic avian influenza clade 2.3.4.4b #H5N1 viruses in at-risk individuals

 

Abstract

Finland faced an outbreak of highly pathogenic clade 2.3.4.4b A(H5N1) avian influenza in 2023, which spread from wild birds to fur farms. Vaccinations of at-risk individuals began in June 2024 using the MF59-adjuvanted inactivated A(H5N8) vaccine (Seqirus; A/Astrakhan/3212/2020, clade 2.3.4.4b). Here, in an observational study, we assessed vaccine-induced immune responses in occupational at-risk individuals participating in the phase IV trial, including virus-specific antibody (n = 39 individuals) and T-cell (n = 18 individuals) responses. Vaccination elicited functional antibodies against the vaccine virus and two heterologous clade 2.3.4.4b strains associated with outbreaks on Finnish fur farms and dairy cattle in the United States. Among previously unvaccinated individuals, seroprotection rates against the vaccine virus were 83% (95% CI 70–97%) by microneutralization assay (titre ≥20) and 97% (90–100%) by haemagglutination inhibition assay (titre ≥40). In those previously vaccinated against avian influenza, a single dose induced seroprotection. A(H5N8)-specific memory CD4+ T-cell responses were detectable, with ~5-fold increase in IFNγ secretion after two doses. These results demonstrate that the vaccine probably provides cross-protection against circulating H5 clade 2.3.4.4b viruses. EU Clinical Trial Number 2023-509178-44-00.

Source: 

Link: https://www.nature.com/articles/s41564-025-02183-5

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Active #Surveillance for Emerging #Influenza A Viruses – Findings from a #OneHealth Study in #Vietnam’s Live Bird #Markets

 

Highlights

-- We conducted surveillance for influenza A viruses at live bird markets in northern Vietnam.

-- Six different subtypes of influenza A virus were found co-circulating in the markets.

-- Notable genetic mutations were found across many genes.

-- These markets have great potential to generate new pandemic influenza A virus strains.

Abstract

Objectives

Live bird markets (LBMs) in Asia have often been the source of human infections with avian influenza virus (AIV).

Methods

From July 2021 to August 2023, we employed a One Health approach in conducting periodic surveillance for novel influenza A viruses in five LBMs in northern Vietnam. Specimens were studied with egg culture, molecular assays, Sanger sequencing, and next-generation sequencing.

Results

We studied a total of 688 human, avian, and bioaerosol specimens. Among these, 118 (17.2%) were found to have molecular evidence of AIVs. Next-generation sequencing of 92 isolates revealed multiple AIV subtypes, including H4N6 (n=1), H5N1 (n=3), H5N8 (n=6), H6N2 (n=3), H6N6 (n=18), and H9N2 (n=61) and mix infections (n=7). Our H5Nx sequences belonged to the Eurasian lineage clade 2.3.4.4b, while our H6N2 sequences were of group III, H6N6 of group II, and H9N2 of the BJ94-lineage clade 4.6.14.

Conclusions

The relatively high prevalence of AIV, particularly highly pathogenic H5N1 and H5N8 viruses, along with the subtype diversity, frequent co-infections and notable mutations, highlights the urgent need for continued monitoring and control of AIV in Vietnam’s poultry farms and LBMs.

Source: International Journal of Infectious Diseases, https://www.ijidonline.com/article/S1201-9712(25)00354-6/fulltext

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#Genomic #surveillance and #evolution of co-circulating avian #influenza #H5N1 and #H5N8 viruses in #Egypt, 2022–2024

 

ABSTRACT

For over two decades, avian influenza virus (AIV) has significantly impacted the Egyptian poultry population, with multiple subtypes and genotypes contributing to significant economic and agricultural losses. As part of an ongoing national surveillance effort, this study aimed to monitor and genetically characterize AIV circulation across various poultry sectors in Egypt. Between 2022 and 2024, a total of 446,790 swab samples were collected, representing commercial farms (n = 25,057), backyard flocks (n = 403), and live bird markets “LBM” (n = 1250) to assess the prevalence and genetic diversity of circulating AIV strains. A total of 173 sampling units were found positive for high pathogenicity (HP) AIV H5, including farms (n = 17), backyards (n = 11), and LBMs (n = 145). The HPAIV of H5N8 subtype was dominant (n = 75) over the H5N1 (n = 27) subtypes among all sectors and bird species (chickens, ducks, turkeys). Whole genome sequence analysis of positive H5 samples revealed high similarity with HPAIVs of clade 2.3.4.4b, which has been confirmed phylogenetically. Two distinct subtypes H5N1 (EA-2021-AB genotype) and H5N8 (EA-2020-A genotype) were identified, with two variants detected within the H5N8 viruses. Evolutionary analyses indicate that Egyptian H5N8 viruses are under strong selection pressure and exhibit a higher nucleotide substitution rate compared to the Egyptian H5N1 viruses of clade 2.3.4.4b. With the evolving HPAI H5 virus’s situation in different locations around the globe, including Egypt, this study underlines the importance of active surveillance in the timely detection of emerging AIV genotypes, monitoring virus evolution, and refining risk assessments.

Source: Emerging Microbes and Infections, https://www.tandfonline.com/doi/full/10.1080/22221751.2025.2562046#abstract

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#Influenza A Virus #infection is associated with TDP-43 #pathology and neuronal #damage in the #brain

Abstract

Viral pandemics such as COVID-19 have demonstrated long-term neurological consequences, including memory impairment and depression, emphasizing the importance of understanding virus-brain interactions [1]. Similar concerns have been raised for Influenza A virus (IAV), which has been implicated in neurodegenerative disorders [2, 3]. In this study, we investigated the neuropathological effects of highly pathogenic avian influenza (HPAI) H5N1 and H5N8 strains in a mouse model. Although viral RNA was detected in the brain post-infection, no viral proteins were found, suggesting limited or transient brain replication. Despite this, infected brains showed significant neuronal damage, including axonal loss and nuclear condensation, as evidenced by immunofluorescence and Nissl staining. We also observed pathological changes in TDP-43, including conformational alterations and increased phosphorylation, which required antigen retrieval for detection, features reminiscent of those found in frontotemporal dementia and amyotrophic lateral sclerosis [4, 5]. Transcriptomic analysis further revealed strain-specific host responses, including activation of interferon-related genes and downregulation of microtubule-associated pathways. These findings suggest that IAV infection can trigger hallmarks of neurodegeneration in the absence of persistent viral protein expression, possibly through host-driven mechanisms. Our results underscore the need for further investigation into virus-induced molecular pathways contributing to neurodegenerative disease.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.06.30.662477v1

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Avian #Influenza in #Ireland: A Spatiotemporal, Subtype, and Host-Based Analysis (1983-2024)

Abstract

Avian influenza virus (AIV) is a significant global concern, causing widespread mortality in wild birds, domestic poultry and most recently wild and domestic mammals. This study presents a retrospective analysis of AIV detections in the Republic of Ireland. Data was sourced from official surveillance databases, peer-reviewed literature and grey literature sources. Spatio-temporal, host-specific and subtype patterns were assessed using descriptive statistics, chi-square tests, linear regression and kernel density estimations. A total of 2,888 confirmed AIV detections were recorded from 25 of Ireland's 26 counties. Wild birds accounted for 98.7% of detections, with domestic birds comprising 1.3% and two detections in foxes. H5N1 was the most prevalent subtype (96.7%) followed by H5N8 and H6N1. Spatial clustering was observed in urban areas, particularly Dublin. The highest seasonal peak occurred during summer, contrasting with traditional winter-associated patterns. Several detections occurred in migratory species outside of typical residency periods, suggesting potential climate-related shifts in migration behaviour. This study represents the first review of AIV surveillance data in Ireland to date. The findings highlight evolving patterns in virus distribution, seasonality and host dynamics, with implications for national surveillance strategies. Continued cross-species monitoring and integration of ecological data are essential to inform effective management strategies.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.05.26.656175v1

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Investigating Factors Driving Shifts in Subtype #Dominance within #H5Nx Clade 2.3.4.4b High-Pathogenicity Avian #Influenza viruses

Abstract

H5Nx clade 2.3.4.4b high-pathogenicity avian influenza viruses (HPAIVs) have decimated wild bird and poultry populations globally since the autumn of 2020. In the United Kingdom (UK) and in continental Europe, the H5N8 subtype predominated during the first epizootic wave of 2020/21, with few detections of H5N1. However, during the second (2021/22) and third (2022/23) epizootic waves, H5N1 was the dominant subtype. The rapid shift in dominance from H5N8 to H5N1 was likely driven by a combination of virological, immunological, and/or host-related factors. In this study, we compared viral fitness and immunological responses in ducks, a key reservoir species, using dominant genotypes of H5N1 (genotype AB) and H5N8 (genotype A) from the second wave. While viral shedding dynamics were similar for both viruses, H5N8 was more pathogenic. Antigenic analysis of post-infection duck sera revealed that the haemagglutinin (HA) protein was antigenically similar across clade 2.3.4.4b H5 HPAIVs, but neuraminidase (NA) proteins displayed different patterns of cross-reactivity. We also modelled a scenario where ducks were pre-exposed to H5N1 (genotype C) or H5N8 (genotype A) from the first wave and subsequently challenged with either homologous or heterologous subtypes from the second wave (genotype AB or A). Despite the absence of seroconversion, pre-exposure to different subtypes resulted in varying clinical outcomes following challenge. These findings indicate that both viral and immunological factors likely played significant roles in the emergence and spread of H5Nx HPAIVs in wild bird populations.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.04.23.650244v2

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#Ecology and #environment predict spatially stratified #risk of #H5 highly pathogenic avian #influenza clade 2.3.4.4b in wild #birds across #Europe

Abstract

Highly pathogenic avian influenza (HPAI) represents a threat to animal and human health, with the ongoing H5N1 outbreak within the H5 2.3.4.4b clade being the largest on record. However, it remains unclear what factors have contributed to its intercontinental spread. We use Bayesian additive regression trees, a machine learning method designed for probabilistic modelling of complex nonlinear phenomena, to construct species distribution models (SDMs) for HPAI clade 2.3.4.4b presence. We identify factors driving geospatial patterns of infection and project risk distributions across Europe. Our models are time-stratified to capture both seasonal changes in risk and shifts in epidemiology associated with the succession of H5N6/H5N8 by H5N1 within the clade. While previous studies aimed to model HPAI presence from physical geography, we explicitly consider wild bird ecology by including estimates of bird species richness, abundance of specific taxa, and "abundance indices" describing total abundance of birds with high-risk behavioural traits. Our projections of HPAI clade 2.3.4.4b indicate a shift in persistent, year-round risk towards cold, low-lying regions of northwest Europe associated with H5N1. Methodologically, we demonstrate that while most variation in risk can be explained by climate and physical geography, adding host ecology is a valuable refinement to SDMs of HPAI.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2024.07.17.603912v2

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Investigating #Factors Driving Shifts in #Subtype #Dominance within #H5Nx Clade 2.3.4.4b High-Pathogenicity Avian #Influenza viruses

Abstract

H5Nx clade 2.3.4.4b high-pathogenicity avian influenza viruses (HPAIVs) have decimated wild bird and poultry populations globally since the autumn of 2020. In the United Kingdom (UK) and in continental Europe, the H5N8 subtype predominated during the first epizootic wave of 2020/21, with few detections of H5N1. However, during the second (2021/22) and third (2022/23) epizootic waves, H5N1 was the dominant subtype. The rapid shift in dominance from H5N8 to H5N1 was likely driven by a combination of virological, immunological, and/or host-related factors. In this study, we compared viral fitness and immunological responses in ducks, a key reservoir species, using dominant genotypes of H5N1 (genotype AB) and H5N8 (genotype A) from the second wave. While viral shedding dynamics were similar for both viruses, H5N8 was more pathogenic. Antigenic analysis of post-infection duck sera revealed that the haemagglutinin (HA) protein was antigenically similar across clade 2.3.4.4b H5 HPAIVs, but neuraminidase (NA) proteins displayed different patterns of cross-reactivity. We also modelled a scenario where ducks were pre-exposed to H5N1 (genotype C) or H5N8 (genotype A) from the first wave and subsequently challenged with either homologous or heterologous subtypes from the second wave (genotype AB or A). Despite the absence of seroconversion, pre-exposure to different subtypes resulted in varying clinical outcomes following challenge. These findings indicate that both viral and immunological factors likely played significant roles in the emergence and spread of H5Nx HPAIVs in wild bird populations.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.04.23.650244v1

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Mathematical #modelling of in vitro #replication dynamics for multiple highly pathogenic avian #influenza clade 2.3.4.4 viruses in #chicken and #duck cells

Abstract

The introduction and subsequent detection of highly pathogenic avian influenza (HPAI) in poultry is influenced by the virus replication fitness, transmission fitness, and virulence in poultry. These viral fitness parameters are important for implementing surveillance and control measures for poultry. This study investigates the potential application of an avian in vitro model using primary chicken embryo (CEF) and duck embryo fibroblasts (DEF) to identify the viral fitness for a reference panel of eight dominant HPAI clade 2.3.4.4 virus genotypes: four H5N1 viruses isolated between 2021 and 2024, as well as three H5N8 and one H5N6 virus isolated between 2014 and 2020. Infectious virus titre and cytopathogenicity were measured in the primary cell cultures over time and these data were analysed using a mathematical model which delineates cell populations into susceptible, latent, infectious, and dead compartments. In addition to obtaining traditional virological parameters such as peak virus replication and the time to 50% cell death, eight new parameters, key among those, the infecting time (tinf), generation time (tgen) and basic reproduction number (R0), were estimated using the mathematical model. Collectively, these parameters contribute to virus characterization, enhancing the resolution for comparing genetically similar viruses. This approach can allow for the evaluation of virus virulence, replication fitness, and, ideally, transmissibility fitness across different hosts. This study underscores the potential of integrating avian in vitro models with mathematical modeling and builds towards rapid risk assessments of novel HPAI viruses.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.04.22.649950v1

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#Israel - #Influenza A #H5N8 viruses of high pathogenicity (Inf. with) (non-poultry including wild birds) (2017-) - Immediate notification

 A wild Booted Eagle in HaZafon Region.

Source: WOAH, https://wahis.woah.org/#/in-review/6408

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Research Note: Novel #reassortant avian #influenza A(#H9N2) Viruses in Wild #Birds in #Shanghai, #China, 2020–2023

Abstract

The H9N2 subtype of avian influenza virus poses significant challenges to global poultry and human health. During the active surveillance of avian influenza virus in wild birds in Shanghai from 2020 to 2023, a total of nine H9N2 viruses were identified. To better understand the genetic characteristics of these H9N2 viruses in Shanghai, the whole genome sequences were analyzed. Phylogenetical analysis showed that the nine H9N2 viruses have undergone complicated reassortment with waterfowl viruses along the East Asian-Australasian flyways. The nine H9N2 viruses were classified into seven genotypes, and some of them could contribute internal genes to recently circulating HPAI A(H5N8) and A(H5N1) viruses of clade 2.3.4.4b. These results highlight the importance of active surveillance of AIVs in wild birds to comprehend viral ecology and evaluate potential transmission risk in poultry and humans.

Source: Poultry Sciences, https://www.sciencedirect.com/science/article/pii/S0032579125000975?via%3Dihub

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Characterization of novel highly pathogenic avian #influenza A(#H5N6) clade 2.3.4.4b virus in wild #birds, East #China, 2024

{Excerpt}

Dear Editor,

The highly pathogenic avian influenza viruses (HPAIVs) are important epizootic and zoonotic pathogens that cause significant economic losses to the poultry industry and pose a serious risk to veterinary and public health. Wild birds have been recognized as the primary reservoirs for influenza A virus, and some species show little sign of clinical disease or even can be asymptomatic during long distance carriers of the virus (Lycett et al., 2019). Since it was first discovered in 1959, the H5Nx HPAIVs have spread globally and cause outbreaks in wild birds, poultry and sporadic human and other mammalian infections (Lycett et al., 2019). Due to the reassortant events of diverse strains facilitated by migratory waterfowl, the clade 2.3.4.4 of H5Nx viruses acquiring neuraminidase (NA) gene from other low pathogenicity avian influenza viruses (LPAIVs) emerged in 2014 and gradually became the dominant sub-clade (Lee et al., 2017). The genetic diversity of clade 2.3.4.4 of H5Nx hemagglutinin (HA) has further evolved into eight subclades (2.3.4.4a to 2.3.4.4h) according to a unified nomenclature (Graziosi et al., 2024). H5N6 of clades 2.3.4.4d-h were predominantly identified in China from 2014 to early 2020 until the occurrence of a novel H5N6 derived the clade 2.3.4.4b HA gene of H5N8 in December 2020 (Gu et al., 2022). Subsequently, the preponderant clade of the H5N6 subtype HPAIV in China switched into 2.3.4.4b. Recently, novel H5N6 HPAIVs containing HA gene from clade 2.3.4.4b H5N1 virus entered R. O. Korea, with disease outbreaks in poultry and wild bird mortality events (Cho et al., 2024; Heo et al., 2024).

(...)

Source: Virologica Sinica, https://www.sciencedirect.com/science/article/pii/S1995820X25000021?via%3Dihub

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Exotic and #Zoological #Birds Resident and Imported into #Nigeria harbour Highly Pathogenic Avian #Influenza Virus: #Threat to #Poultry Production, Food security and Public Health.

Abstract

Influenza is a major infectious disease challenge affecting animal and human health globally, and wild birds are historically the primary reservoirs of all the known Influenza A virus subtypes. Here, we detected the Highly Pathogenic Avian Influenza (HPAI) virus in exotic and aquatic birds in three different locations in Nigeria. On the 8th of February 2021, exotic birds: Yellow Golden Pheasant (Chrysolophus pictus), Sultan chicken (Gallus gallus domesticus), Lakenvelder chicken (Gallus gallus domesticus), and Common pheasant (Phasianus calchicus), imported from Libya and transported across the Niger Republic border to Nigeria, were presented to the National Veterinary Research Institute, Vom, for screening. Also, a family in Lagos State bought some exotic aquatic birds from a live bird market in Sokoto State, Nigeria, where sudden death was recorded with the birds showing few clinical signs. Similarly, the sudden death of some aquatic birds was reported in Mandela Parks and Gardens in Asaba, Delta State, few weeks after some captured wild birds were introduced to the Park and Gardens. Oropharyngeal, cloacal, and tissue samples were all collected from the reported cases. Total viral nucleic acid was extracted and screened for Influenza A viruses using real-time RT-PCR. The HPAI viruses H5N1 and H5N8 were detected in the imported aquatic (geese and ducks) and exotic (yellow golden pheasant) birds. The samples tested negative for low-pathogenic Avian Influenza Virus (H9N2) as well as other avian viruses, viz., Avian avulavirus-1 (Newcastle disease Virus) and infectious bronchitis virus. This highlights the role of these resident and imported exotic birds in the local transmission and spread of the HPAI virus to domestic poultry. The findings call for proper biosecurity and quarantine measures for exotic and wild birds to reduce the potential risk to animal and public health in Nigeria.

Source: BioRxIV, https://www.biorxiv.org/content/10.1101/2025.01.22.634354v1

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