#Synergy between HA #cleavage site #sequence and NA-mediated #plasminogen recruitment as a virulence mechanism for low-pathogenic avian #influenza

 

ABSTRACT

An outbreak of H3N1 low-pathogenic avian influenza virus (LPAIV) in Belgium in 2019 caused unexpected levels of mortality and morbidity in poultry. These viruses possess an NA polymorphism associated with plasminogen (PLG) binding, as well as an atypical sequence around the HA cleavage site; accordingly, HA cleavage mediated by NA-driven PLG recruitment has been proposed to underlie their systemic spread and pathogenicity. To test this, we established a reverse genetics system for A/chicken/Belgium/460/2019 and created single mutations in HA (K345R) and NA (S122N) that restored the viruses to normal consensus, as well as an HA/NA double mutant. Confirming previous work, trypsin-independent spread and HA cleavage of wild-type Ck/Belgium were observed in the presence of fetal bovine serum containing PLG in vitro. Dose-dependent HA cleavage and trypsin-independent spread were also observed in the presence of purified chicken PLG. Compared to the wild-type virus, both HA cleavage and virus spread in vitro were reduced by the HA K345R mutation and further blocked by the NA mutation S122N. PLG-mediated HA cleavage was seen in a variety of avian cell lines and chicken organoids, excluding cell type-dependent effects. Furthermore, in ovo tests showed that mutant viruses unable to recruit PLG were less able to replicate systemically in chicken embryos. Bioinformatics analyses revealed other viruses that could potentially recruit PLG, including two independent outbreaks of H6N1 viruses, one of which we confirmed PLG-driven spread in vitro. We conclude that PLG recruitment by NA is a general virulence mechanism of N1 LPAIVs.

Source: 

Link: https://journals.asm.org/doi/full/10.1128/mbio.02466-25?af=R

____

Genomic-based #biosurveillance for avian #influenza: whole genome sequencing from wild #mallards sampled during autumn migration in 2022–23 reveals a high co-infection rate on migration stopover site in #Georgia

 

Abstract

The Caucasus region, including Georgia, is an important intersection for migratory waterbirds, offering potential for avian influenza virus (AIV) transmission between populations from different geographic areas. In 2022 and 2023, wild ducks were sampled during autumn migration events in Georgia to study the genetic relationships and molecular characteristics of influenza strains. Sequencing and phylogenetic analysis were used to compare the sampled strains to reference sequences from Africa, Asia, and Europe, allowing assessment of genetic relationships and virus transmission between migratory birds. Protein language modeling identified potential co-infections. Of 225 duck samples, 128 tested positive for the influenza M gene. 55 influenza-positive samples underwent whole-genome sequencing, revealing significant diversity. Analysis of the hemagglutinin (HA) segment showed notable differences among subtypes. Most samples were H6N1 and H6N6, but co-infections with combinations like H6H3, N8N1, N6H9, N2N6, and H9H6/N1N2 were also identified. These findings demonstrate the high variability of influenza viruses in migratory waterbirds in Georgia, including a notable rate of co-infections. Some samples exhibited uncommon genetic characteristics compared to other strains from the same year, suggesting Georgia’s role as a mixing vessel for influenza viruses. This facilitates reassortment during co-infections and contributes to the genetic diversity observed across flyways.

Source: 

Link: https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2026.1735728/full

____

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

____

Progressive #Adaptation of Subtype #H6N1 Avian #Influenza Virus in #Taiwan Enhances #Mammalian #Infectivity, Pathogenicity, and #Transmissibility

Abstract

The interspecies transmission of avian influenza viruses remains a significant public health concern. H6 viruses have gained attention following the first human infection by a chicken-origin H6N1 virus (A/Taiwan/02/2013, Hu/13), highlighting their zoonotic potential. To understand the evolutionary trajectory and mammalian adaptation of this Taiwan lineage, we compared two avian isolates (A/Chicken/Taiwan/CF19/2009, Ck/09; A/Chicken/Taiwan/2267/2012, Ck/12) and Hu/13 in vitro and in vivo. Hu/13 exhibited enhanced replication in MDCK cells, producing larger plaques and higher viral titers than Ck/09 and Ck/12. In BALB/c mice, Hu/13 demonstrated the highest pathogenicity and mortality, followed by Ck/12, while Ck/09 induced minimal morbidity. Hu/13 and Ck/12 replicated efficiently in respiratory tissues, eliciting robust cytokine responses and severe pulmonary lesions. In ferrets, Hu/13 showed relatively efficient transmission, infecting all direct physical-contact and two out of three airborne-contact ferrets, whereas Ck/09 failed to transmit. Histopathology confirmed escalating lung pathology from Ck/09 to Ck/12 and Hu/13. Whole-genome sequencing identified adaptive mutations in Hu/13 during ferret replication, though no canonical mammalian-adaptive changes (e.g., PB2-E627K or HA-Q226L) were detected. These findings demonstrate progressive mammalian adaptation, replication efficiency, and transmissibility within the Taiwan H6N1 lineage. Enhanced surveillance is crucial to monitor mammalian-adaptive mutations, informing pandemic preparedness and public health strategies.

Source: Viruses, https://www.mdpi.com/1999-4915/17/5/733

____