Estimating the #infection #fatality #ratio of zoonotic avian #influenza viruses with #pandemic potential using an evolutionary epidemiological model

 

Abstract

The risk of zoonotic avian influenza (AIV) infection to humans is challenging to estimate as many human avian influenza virus infections are undetected because infections may be asymptomatic, symptomatic but not tested, and difficult to identify through contact tracing, as human-to-human transmission is rare. We derive equations that consider the evolutionary mechanisms that give rise to pandemics and are parameterized to be consistent with records of past pandemics. We estimate that thousands of human infections with AIVs possessing pandemic potential occur worldwide in an average year. Combining these estimates with H5N1 fatality data, we estimate a historical average infection fatality ratio of 32 (95% uncertainty interval: 9.6-75) deaths per 10,000 infections. This estimate is comparable to SARS-CoV-2 during the recent pandemic and higher than seasonal human influenza. We estimate that preventing animal-to-human influenza spillovers would delay pandemic emergence by several years. Preventing human infections with AIVs is necessary given the high risk of severe outcomes to individuals and to reduce the risk of pandemics occurring in the future.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.medrxiv.org/content/10.64898/2026.01.21.26344526v3

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

 

Abstract

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

Competing Interest Statement

The authors have declared no competing interest.

Source: 

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

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Case - #Fatality #Risk of #Norovirus, #England, 2022–2025

 

Abstract

Norovirus incidence increased in England during 2022–2025, when GII.17 replaced GII.4 as the dominant genotype. By using nationally linked norovirus testing and fatality data, we found age and care setting, but not genotype, were associated with case-fatality risk. Increased incidence might reflect changes in transmissibility or population immunity.

Source: 

Link: https://wwwnc.cdc.gov/eid/article/32/8/26-0091_article

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Pan-continental #spillover #risk: integrated spatiotemporal, transmissibility and #surveillance analysis of avian #influenza #H5N1 in #Africa

 

Abstract

Background: 

The HPAI H5N1 panzootic represents a critical threat to human health in Africa, where traditional poultry systems and dense human-animal interfaces facilitate frequent zoonotic spillover. While sporadic human cases raise pandemic concerns, continent-wide integration of spatial dynamics, transmissibility indicators, and surveillance performance has been lacking. This study quantifies avian influenza transmission over two decades across Africa, identifies geographical hotspots, and evaluates the responsiveness of current surveillance systems.

Methods: 

We analysed 8,037 avian influenza outbreak events and 369 laboratory-confirmed human cases, predominantly caused by HPAI H5N1 (2004–2025), using harmonised data from FAO (EMPRES-i+), WHO, and WOAH. A Bayesian Besag-York-Mollié (BYM) spatiotemporal model estimated residual transmission risks and Incidence Rate Ratios (IRR) by subtype. The basic reproduction number (R₀) was derived via an exponential growth model applied to human outbreak phases across infectious durations of 7–30 days. Surveillance responsiveness was assessed by quantifying notification delays between clinical observation and official reporting.

Results: 

Risk of infection in animals: HPAI H5N1 was the dominant strain, representing 87.8% of animal cases, with Egypt acting as the primary epidemiological epicentre (66% of total records). The spatiotemporal model revealed that H5N1 is associated with a significantly higher risk of animal infection (IRR = 8.37; 95% CI: 6.65–10.53). Although 71% of outbreaks were reported within 5 days of detection, significant delays (≥15 days) occurred in 12% of cases, with notable regional disparities. Risk of infection in human: H5N1 was associated with a 67-fold increase in the incidence of human cases compared to other subtypes (IRR = 66.78; 95% CI: 25.29–176.37). Sensitivity analyses yielded R0 estimates ranging from 1.05 (95% CI: 0.91–1.31) to 1.23 (95% CI: 0.60–2.33), indicating localised epidemic potential.

Conclusion: 

Our findings highlight a persistent and geographically heterogeneous H5N1 reservoir in Africa with high zoonotic affinity. Although sustained human-to-human transmission remains limited, the identification of dual poultry-human hotspots and localised R0 peaks underscores the urgent need for geographically targeted One Health interventions. Strengthening real-time reporting systems and improving biosecurity in high-risk poultry value chains are critical to mitigating future pandemic threats on the continent.

Source: 

Link: https://www.frontiersin.org/journals/epidemiology/articles/10.3389/fepid.2026.1813211/full

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A systematic #review of #Nipah virus disease epidemiological #parameters, #outbreaks, and mathematical #models

 

Summary

Our systematic review, based on PRISMA guidelines (PROSPERO CRD42023393345), characterised the epidemiology, outbreaks, and mathematical models of Nipah virus, an important public health threat in south and southeast Asia. We searched PubMed and Web of Science from database inception to March 14, 2025, and extracted 243 parameters, 89 risk factors, 39 models, and 23 distinct outbreaks from 119 papers. IgG seroprevalence estimates in the general population ranged from 0% to 12·5%. Nipah virus causes severe disease, with pooled case–fatality ratio estimates ranging widely from 9·1% (95% CI 0·2–41·3) in Singapore to 81·9% (95% CI 71·9–88·9) in Bangladesh. The infection timeline and clinical course of Nipah virus remain poorly characterised; we estimated a median incubation period of 8·77 days (165, 95% CI 7·53–10·02) from eight estimates in seven articles with sufficient information. Transmission parameter estimates were scarce, and all but one of five central estimates of the basic reproduction number were less than one. Nipah virus mathematical models (39) were rarely fitted to data (eight). All extracted information is accessible via our R package, epireview.

Source: 

Link: https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(26)00239-2/abstract?rss=yes

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Inter-population #connectivity of southern elephant #seals and the likely intra-species #transmission #pathways of high pathogenicity avian #influenza

 

Abstract

High Pathogenicity Avian Influenza (HPAI) H5N1 clade 2.3.4.4b has spread beyond birds to affect seals across the Southern Ocean and sub-Antarctic region, with southern elephant seals (Mirounga leonina) particularly devastated. The virus, likely introduced via spillover from infected migratory birds, has killed tens of thousands of adult seals and pups throughout most of their range, though Macquarie Island remains unaffected so far. We used twenty years of elephant seal movement data from the southern Indian and Pacific oceans to assess whether seal-to-seal transmission could spread HPAI H5N1 between breeding colonies, despite the vast distances separating them (Marion Island, Iles Crozet, Iles Kerguelen, and Macquarie Island). There was substantial overlap in seals' at-sea distributions during their winter post-moult trips, when seals travel for weeks at average speeds of 3.5 km/h. Two transmission pathways were examined: (1) terrestrial "stepping stone" routes, where infected seals could pass the virus between colonies during short intervals to remain infectious were feasible from Marion Island to Kerguelen but not from Kerguelen to Macquarie Island; and (2) at-sea encounters between seals, which occurred frequently enough to enable transmission. The findings suggest that once established at Macquarie Island, the virus could potentially spread further to New Zealand's sub-Antarctic islands and mainland New Zealand. While seal-to-seal transmission appears possible, we conclude this is unlikely. Nonetheless, understanding at-sea contact rates enhances knowledge of H5N1 epidemiology and demonstrates the value of combining long-term population monitoring with movement data to understand wildlife disease dynamics.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

Integrated Marine Observing System, https://ror.org/010x3gp67

CNRS

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.07.07.737127v1

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Systemic #atopy and upper - #airway disease define susceptibility to incident #asthma after #COVID19 in #Korea

 

Abstract

Incident asthma is an important respiratory sequela after COVID-19, but it is unclear which allergic phenotypes amplify risk. Using a linked nationwide Korean database of 3,987,182 individuals with confirmed severe acute respiratory syndrome coronavirus 2 infection, we compare claims-based incident asthma in those with pre-existing systemic atopy and/or upper-airway disease (allergic rhinitis, chronic rhinosinusitis, atopic dermatitis or food allergy) versus those without after 1:1 propensity score matching. During follow-up to 31 December 2022, participants with pre-existing disease have higher asthma incidence than matched controls (3.55 vs 2.13 per 1,000 person-years), with a hazard ratio of 1.66 (95% confidence interval 1.58–1.75). Asthma risk is elevated for each condition and increases with greater disease burden. These findings show that pre-existing allergic and upper-airway phenotypes stratify post-COVID incident asthma risk on a national scale, supporting targeted surveillance in high-risk subgroups.

Source: 

Link: https://www.nature.com/articles/s41467-026-74860-w

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Size of the 2026 #Ebola #outbreak and #risk of cross-border #spillover from #Bundibugyo virus in Ituri Province, #DRC, and its implications for #preparedness: a recalibrated stochastic modelling study

 

Summary

Background

On May 15, 2026, WHO declared a Bundibugyo virus (BDBV) outbreak in Ituri Province, DR Congo with an estimated index case on April 1, 2026 (6-week pre-declaration interval). By May 24, DR Congo reported 906 suspected cases (105 confirmed and ten confirmed deaths) across three provinces. Uganda reported seven confirmed cases (three imported; four locally acquired including three health-care workers; case-fatality ratio 14%). WHO declared a Public Health Emergency of International Concern on May 17, 2026; Africa Centres for Disease Control and Prevention declared a Public Health Emergency of Continental Security on May 18, 2026. The study aimed to establish a short-term trajectory of the BDBV outbreak and probability of cross-border spillover into countries with elevated risk of importation to guide preparedness priorities.

Methods

We calibrated a stochastic SEIRD (susceptible, exposed, infectious, recovered, and dead) ensemble model to the laboratory-confirmed case series, anchoring on 598 cumulative confirmed cases on June 8, 2026 (day 68) using simulation filtering (calibration window ±30%; reporting fraction 1·0 for laboratory-confirmed cases). The case-fatality ratio was drawn from a previous value centred on the observed confirmed-case ratio of approximately 19% (115 of 598). A linked daily-hazard spillover model estimated importation probability for Uganda, South Sudan, Rwanda, and Burundi over a 12-week horizon. The early suspected-case series, which peaked at 1077 on May 26, 2026, before being substantially revised downward by laboratory reclassification, is reported for context but was not used for calibration.

Findings

Laboratory-confirmed DR Congo cases rose from 33 on May 18, 2026, to 598 by June 8, 2026. Calibrated to the confirmed-case anchor (598 on June 8, 2026; central basic reproduction number [R0]=1·71), the confirmed-case trajectory is most consistent with the central scenario. Under the central scenario the ensemble projected a median of 990 cumulative confirmed cases by week 12 (June 24, 2026; 90% prediction interval [PI] 709–1293) and 174 deaths; the low scenario projected 870 confirmed cases (90% PI 641–1133) and 160 deaths. The early suspected-case count (peak 1077 on 26 May 2026) was substantially revised by laboratory reclassification and is reported for context only. Cross-border spillover remained material: Uganda 94·2% importation probability (19 confirmed cases as of June 4, 2026, including five health-care worker infections and two deaths); South Sudan 69·3%; Rwanda 8·6%; and Burundi 2·0%. As of June 22, 2026, DR Congo has 1048 confirmed cases and 267 confirmed deaths and Uganda has 20 confirmed cases, two confirmed deaths, and one probable death. These numbers are changing daily and are likely to align with what is predicted in the central scenario.

Interpretation

From the most recent laboratory-confirmed data, the outbreak is closer to what is predicted by the central scenario, even with the intensified response within DR Congo. However, uncertainty remains around reported case numbers due to low rate of contact tracing. Sustained control nonetheless remains the primary determinant of regional risk: importation into Uganda is already established, and South Sudan must continue to reinforce infection prevention and control, rapid response capacity, and cross-border surveillance under International Health Regulations 2005. These projections should be interpreted as exploratory preparedness-oriented estimates derived from a stochastic scenario-based modelling framework, rather than predictions generated from formally fitted epidemiological models using comprehensive parameter estimation and identifiability analyses.

Funding

None.

Translations

For the French and Swahili translations of the abstract see Supplementary Materials section.

Source: 

Link: https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(26)00320-8/fulltext

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#Genomic #epidemiology of two #travel-associated #pediatric #measles viruses within the B3 Lineage

 

Highlights

    • The Children’s Hospital of Philadelphia (CHOP) detected a B3 MeV case in 2023 and in 2025.

    • Whole-genome amplification of the two CHOP B3 MeV isolates was performed.

    • The CHOP genomes were assessed with a global dataset of all 168 National Center for Biotechnology Information B3 MeV near-full length genomes from 2005-2025.

    • The CHOP isolates form a clade with 39 other isolates from four countries, 36 of which cluster with a 15 single nucleotide polymorphism cutoff.

    • The CHOP clade diverged in 2019, contains the most recently emerged B3 nodes, and shares a private mutation in the phosphoprotein at a codon undergoing positive selection.

Abstract

Background

Children’s Hospital of Philadelphia (CHOP) identified a MeV case in late 2023 and also early 2025, both of which were associated with international travel. Of the 24 MeV genotypes, the B3 and D8 lineages have been the most prevalent globally since 2021. Initial genotyping indicated that the two CHOP isolates belong to the B3 lineage.

Objectives

To inform MeV molecular surveillance, we conducted a genomic epidemiology analysis to situate the CHOP strains within the global genetic landscape of past and present MeV B3 cases.

Study design

We performed whole-genome amplification, genome assembly, and phylogenomics of our two MeV cases. These strains were then analyzed alongside all 168 National Center for Biotechnology Information near-full length MeV B3 genomes using population and evolutionary genetic approaches. This dataset includes strains isolated from 13 countries between 2005 and 2025.

Results

The two CHOP strains form a monophyletic group with 39 other isolates from four countries; 36 clade members form a discrete network connected by a 15 single nucleotide polymorphism (SNP) cutoff. The CHOP clade shares a Q45H phosphoprotein mutation at a codon undergoing diversifying selection, as with a H593R hemagglutinin mutation carried by the 2025 CHOP strain. The CHOP clade likely diverged in 2019 and has a median root-to-tip distance of 0.020 compared to 0.017 for the other B3 strains, consistent with this clade encompassing the most recently divergent nodes.

Conclusions

Our work places the CHOP MeV cases within a diversifying and emergent global clade of the dominating B3 lineage that is a future risk due to ongoing B3 MeV transmission.

Source: 

Link: https://www.sciencedirect.com/science/article/abs/pii/S1386653226000557?dgcid=rss_sd_all

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The #risk of #global #Ebola virus #spread is low: #epidemiology of Ebola disease cases outside Africa, 1976 to May 2026

 

Abstract

Following the Bundibugyo virus disease outbreak reported in the Democratic Republic of the Congo in May 2026, we reviewed all known Ebola disease cases outside Africa and found that intercontinental transmission risk remains low. We identified 28 confirmed epidemic-linked cases outside Africa; only four involved travellers with latent infection whose symptoms were detected after border screening. Excluding medically evacuated cases, the crude overall risk since 2000 was 0.17 Ebola disease cases outside Africa per 1,000 reported cases in Africa.

Source: 

Link: https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2026.31.24.2600508?emailalert=true#abstract_content

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#Overview of available modelling #evidence to inform the scale and potential spread of #Bundibugyo virus in the current #Ebola disease #outbreak (ECDC, June 17 '26, summary)

 

ASSESSMENT | 17 June 2026

Key findings 

    • So far in the current outbreak of Ebola disease caused by Bundibugyo virus, international modelling efforts have focused on estimating the outbreak size and near-term trajectories, as well as the risk of regional and international spread.  

    • Multiple modelling groups suggest that the true size of the outbreak is larger than reported. 

        - One model estimated that cumulative infections as of 13 June were between 3.0 and 10.2 times the reported number of cases (90% credible interval). 

    • Epistorm estimated the relative risk of importation to be highest for Rwanda, Tanzania and Kenya, which together account for approximately 54% of the relative risk. 

        - ECDC has estimated the risk of importation into the EU/EEA to be low. 

    • The United States Centers for Disease Control and Prevention published scenario modelling analysis results that estimated a 65% probability that the outbreak will exceed 20 000 cases within three months under a scenario where 20% of individuals with Bundibugyo virus infection were isolated and no other interventions were implemented. 

    • Current modelling estimates are highly uncertain due to data limitations. 

        - Multiple epidemic trajectories remain compatible with the available surveillance data, limiting confidence in estimates of outbreak size and future trends. 

(...)

Suggested citation: European Centre for Disease Prevention and Control. Overview of available modelling evidence to inform the scale and potential spread of Bundibugyo virus in the current Ebola disease outbreak. ECDC: Stockholm; 2026.   ISBN 978-92-9498-899-7; doi: 10.2900/3614787; Catalogue number TQ-01-26-044-EN-N 

© European Centre for Disease Prevention and Control, Stockholm, 2026

(...)

Source: 

Link: https://www.ecdc.europa.eu/en/publications-data/overview-available-modelling-evidence-inform-scale-and-potential-spread

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Seasonal #influenza versus #COVID19 #hospitalisation #risk during the 2025–26 influenza season

 

{Excerpt}

(...)

Contemporary surveillance data have shown higher population rates of influenza infections and hospitalisations during the 2025–26 influenza season; however, these aggregate metrics cannot disentangle infection frequency from disease severity. This analysis extends that evidence by comparing outcomes on a per-infection basis among patients with multiplex-based, laboratory-confirmed infection, showing that seasonal influenza was associated with a 43% higher risk of hospitalisation than COVID-19, corresponding to approximately 48 additional hospitalisations per 1000 infected individuals. The higher severity associated with seasonal influenza during this season likely reflects a combination of factors, including the increased virulence of circulating influenza strains, mismatch between vaccine composition and dominant circulating influenza variants, and the continued attenuation of SARS-CoV-2 severity over successive waves.

(...)

Source: 

Link: https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(26)00289-6/fulltext?rss=yes

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Regional #Signals Preceding the 2026 #Bundibugyo Virus Disease #Outbreak

 

Highlights

    • Bundibugyo virus circulated undetected for months prior to outbreak declaration.

    • Four earlier regional hemorrhagic fever clusters flagged by open surveillance are unresolved.

    • These clusters warrant urgent reanalysis due to concern for regional spread.

Abstract

Background

The May 2026 Bundibugyo virus disease (BVD) outbreak in the Democratic Republic of the Congo was declared a Public Health Emergency of International Concern after substantial undetected community transmission. We describe regional surveillance signals detected by the Biothreats Emergence, Analysis, and Communications Network (BEACON), our open access event based surveillance program, in the weeks preceding outbreak declaration.

Methods

We reviewed BEACON reports of VHF-compatible illness clusters detected in the transboundary DRC-Uganda-Burundi-South Sudan region during March–April 2026, prior to the May 15 laboratory confirmation of BDBV.

Results

BEACON detected four temporally proximal VHF-compatible illness signals: (1) March 9, North Kivu Province—suspected Ebola case under investigation with unresolved laboratory results; (2) March 10, Kasaï Province—fatal hemorrhagic illness with secondary cases and negative Ebola PCR; (3) March 30, Burundi—35-case undiagnosed cluster near the DRC border with 5 deaths, negative testing for major filoviruses and >200 pathogens, pending metagenomic sequencing; (4) April 22, South Sudan—three suspected VHF cases with negative initial testing. All four signals shared a similar diagnostic phenotype: VHF-compatible presentation, mobilization of investigation teams, negative initial testing, and no publicly reported confirmed etiology. None were formally reported to have been resolved.

Conclusions

Our detection of four unresolved VHF signals preceding the confirmed BDBV outbreak highlights gaps in formal follow-up mechanisms for negative cases and fragmented regional diagnostic coordination. In light of confirmed BDBV circulation and Africa CDC's identification of 10 countries at high risk for spread, these preceding signals warrant urgent retrospective investigation and laboratory.

Source: 

Link: https://www.ijidonline.com/article/S1201-9712(26)00497-2/fulltext

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#Scenario #analysis for potential #community spread of #Andes virus (ANDV)

 

Abstract

We simulated the potential community spread of Andes virus (ANDV) following the introduction of a single infectious individual in a generic population, based on epidemiological parameters derived from a human-to-human historical outbreak. Under current available evidence, our analyses suggest that, within 4 months from the index case’s symptom onset, the expected outbreak size is unlikely to exceed 50 cases, with a high probability of epidemic extinction, particularly when > 50% cases are effectively isolated from the start of the outbreak.

Source: 

Link: https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2026.31.22.2600425#abstract_content

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Breeding #pig #transport drives the dispersal of #swine #influenza A virus across #Europe

 

Abstract

Pigs serve as reservoirs of former human influenza A virus (IAV) H1N1 and H3N2 lineages and act as mixing vessels for diverse strains, facilitating the emergence of novel IAVs. Understanding the spread and evolution of swine IAVs (swIAVs) is therefore crucial to assess the risk of strains with zoonotic potential emerging. This study uses a phylogeographic framework to investigate the predictors of swIAV dispersal across Europe. All publicly available swIAV genomic sequences were retrieved and subsampled for the ten largest European pig-producing countries. Discrete phylogeographic reconstructions were conducted for H1, H3, N1, N2 encoding genes and all internal gene segments. Our analyses indicate that viral dispersal predominantly occurred from north-western to southern and eastern Europe, with frequent long-distance transitions between non-adjacent countries. We also extended the discrete phylogeographical analyses with generalized linear models to test the association between viral movement and potential predictors, such as live pig trade, pork trade, pig densities, farm sizes, or the geographic distance between key pig production zones. We find that breeding pig trade is the only consistently well-supported predictor of between-country transition events, whereas pork trade and geographic distance were not supported. This highlights that farms importing breeding pigs from multiple countries could act as hotspots for reassortment of diverse swIAV strains. Strengthening external biosecurity on farms with emphasis on quarantining breeding pigs, limiting long-distance transport, and implementing a One Health surveillance system for earlier detection of emerging strains, could help curb the rapid spread and evolution of swIAV in Europe.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.06.01.729471v1

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Increased burden of #influenza #H1N1pdm09 in older adults following the #COVID19 #pandemic

 

Abstract

Of the two influenza A virus (IAV) subtypes circulating endemically in humans, A/H3N2 and A/H1N1pdm09, A/H3N2 has historically been the dominant driver of disease burden in older adults. Based on an analysis of publicly available global surveillance data from 2015 to 2025 (>300,000 subtyped, age-stratified infections), we report a substantially increased contribution of A/H1N1pdm09 to influenza morbidity in older adults since approximately 2022. Birth cohort-stratified analyses suggest elevated A/H1N1pdm09 burden among individuals born before 1955-1959, consistent with erosion of pre-existing immunity originally generated by exposure to historical A/H1N1 strains. Pooled estimates across datasets and analytical approaches indicate the increase in A/H1N1pdm09 burden rises with earlier birth year, ranging from 1.22-fold (95% CI 1.08-1.37) for the 1955-1959 birth cohort to 3.10-fold (95% CI 2.58-3.72) for the 1930-1934 cohort. These findings point to a substantial rise in the overall influenza burden among the most vulnerable age groups, with implications for vaccine policy, clinical management, and public health planning.

Competing Interest Statement

C.A.R. has received consulting fees from CSL Seqirus, Moderna, Pfizer, GSK, and Sanofi for advisory services unrelated to this work.

Source: 

Link: https://www.medrxiv.org/content/10.64898/2026.05.20.26353664v1

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Two #epidemics, one #genotype, different outcomes: evolutionary #changes of Avian #Influenza #H5N1, genotype EA-2024-DI

 

Abstract

Since 2020, high pathogenicity avian influenza H5Nx viruses of clade 2.3.4.4b have become enzootic in Europe, causing recurrent epidemic waves characterized by extensive reassortment events. Here, we describe the emergence of a single high-fitness genotype (EA-2024-DI) that has driven two consecutive waves, evolving into distinct sub-lineages. While its circulation is ongoing, during the 2025-2026 wave it caused an unprecedented number of cases in wild birds. Using phylodynamic analyses of a large dataset of genomic sequences, we compared the spatial diffusion and host transmission pattern of the EA-2024-DI sub-lineages across the three most recent epidemic waves (2023-2024, 2024-2025 and 2025-2026). We show that the genotype has persisted over time and has spread primarily through wild Anseriformes, but with a marked change in the transmission patterns between the different waves and a shift in the epicenter from Eastern to Central Europe, the latter having emerged as an important hub for virus diffusion throughout Europe. Our results reveal a recent increase in the frequency of viruses from wild and domestic mammals carrying mutations enhancing virus replication in mammalian hosts, highlighting the importance of proactive monitoring of this group of hosts to better understand its role in the virus ecology and evolution.

Competing Interest Statement

The authors have declared no competing interest.

Funder Information Declared

Funded by the European Union under grant agreement (101084171) - (Kappa-Flu). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or REA. Neither the European Union nor the granting authority can be held responsible for them

Support for this work was provided by the European Union within the framework of the activities foreseen by the European Union Reference Laboratory for Avian Influenza and Newcastle Disease under grant agreement 101201937

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.05.25.727580v1

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Spatiotemporal #Dynamics of Highly Pathogenic Avian #Influenza #H5 Virus Introductions and Regional Spread in the Republic of #Korea

 

Abstract

Highly pathogenic avian influenza (HPAI) viruses from clade 2.3.4.4 have caused recurrent outbreaks in poultry since 2014. In the Republic of Korea, clade 2.3.4.4b viruses have driven five epidemic waves, yet the factors underlying HPAI introduction and farm-to-farm spread remain poorly understood. We compiled hemagglutinin gene sequences of clade 2.3.4.4b viruses from wild birds and poultry in the Republic of Korea (October 2016–March 2024) and reconstructed dispersal dynamics using Bayesian phylogeography. Dispersal patterns suggest that domestic duck farms in the western provinces likely form a key interface for spillover from wild birds into poultry. Mixed-effects generalized linear models showed that both wild-to-poultry and farm-to-farm transition rates were positively associated with the number of poultry farms in the destination province, while wild-to-poultry rates were further associated with higher avian influenza virus infection probability among wild birds. Wild-to-poultry transition rates were lower in 2020–2024 than in 2016–2018, which may reflect strengthened interventions. These findings suggest that poultry farm abundance and introduction pressure from wild birds jointly shape the spatial dynamics of HPAI introduction and spread. More broadly, these factors may provide operational indicators to guide risk-based surveillance and control strategies.

Competing Interest Statement

The authors have declared no competing interest.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.05.21.726857v1

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Computational Structural Analysis Predicts #Host-Range Promiscuity and #Antiviral #Resistance in North #American #H5N1 Lineages

 

Abstract

Influenza A virus has been circulating in birds in Eurasia for more than 146 years, but human infection has been sporadic. H5N1 (clade 2.3.4.4b) has recently infected hundreds of species of wild and domestic birds and mammals in North America. Infections include 71 people in the United States. There have been 2 human fatalities (United States and Mexico). We have integrated time-series analysis, molecular phylogenetics, and structural biology to understand how H5N1 is circulating in North America and adapting to new hosts. Our time-series analysis reveals that the circulation of H5N1 follows a distinct seasonal pattern, with cases in the United States increasing November to April. We also document an increase in the number of cases reported since 2021. We show that H5N1 spreads in North America as 2 distinct lineages. These viral lineages have achieved a vast host range by efficiently binding the viral surface protein hemagglutinin to both mammalian and avian cell surface receptors. This novel host-range promiscuity is concomitant with the strengthening of the viral polymerase basic 2 protein binding for mammalian and avian immune proteins. Once bound, the immune proteins have diminished ability to fight the virus, thus allowing for efficient replication. Our analyses predict that while most antivirals remain effective, a fatal human isolate showed reduced binding to multiple drugs from different classes. The H5N1 virus is causing an animal pandemic through promiscuity of host range and strengthening ability to evade the innate immune systems of both mammalian and avian cells.

Source: 

Link: https://spj.science.org/doi/10.34133/csbj.0066

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Epidemiological study of #hantavirus in Southern #Brazil, 2009-2019

 

ABSTRACT

Brazil has the highest number of hantavirus cardiopulmonary syndrome cases on the American continent, with Santa Catarina being the state with the most notifications. This retrospective longitudinal study aimed to describe the epidemiological profile of 177 hantavirus cases reported in Santa Catarina from 2009 to 2019, using data from the Notifiable Diseases Information System (SINAN). Statistical analyses of socio-demographic, clinical, and epidemiological data revealed that the typical patient was a male of working age with low educational attainment, living in a rural area. The highest incidence occurred in the Santa Catarina West, Midwest, and Mountain regions, strongly associated with agricultural activities. The case fatality rate (CFR) was highest among the 15-19-year age group. Clinical risk factors for death included respiratory signs, increased hematocrit, and the need for mechanical ventilation. Patients who sought early care had a higher CFR, possibly due to the initial difficulty of differentiating hantavirus from other viral diseases. Conversely, regions with higher notification rates showed lower CFRs, suggesting better surveillance. This study highlights critical areas for public health intervention and the key characteristics of hantavirus patients (males in rural areas and adolescents aged 15-19 years in regions with low notification rates) and areas for public health intervention. Training for medical professionals in regions with low notification rates should aim to reduce lethality, especially in regions with low reported cases (Itajai river delta and South), where underreporting may be occurring. Furthermore, the high lethality in adolescents and in patients with non-specific initial symptoms requires greater awareness. This study shows the utility of a governmental database in identifying epidemiological patterns and creating public health strategies tailored to regional specificities.

Source: 

Link: https://www.scielo.br/j/rimtsp/a/VB7LM8DjmVJ9yJBwYzSjzMh/?lang=en

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