Serologic #Testing for #MERS #Coronavirus and #SARS-CoV-2 Cross-Reactive Immune Responses, the #Netherlands

 

Abstract

Cross-reactive SARS-CoV-2–specific antibodies could compromise the specificity of MERS-CoV serology, potentially leading to misclassification of infection history. SARS-CoV-2 exposure induced MERS-CoV antibodies primarily targeting the conserved S2 domain, with occasional neutralizing capacity. Combining MERS-CoV S1 binding with neutralization, however, limited the influence of SARS-CoV-2–induced cross-reactivity on MERS-CoV serology.

Source: 

Link: https://doi.org/10.3201/eid3211.260690

____

#Evidence of Exposure to Highly Pathogenic Avian #Influenza #H5 Viruses in East #Greenland Polar #Bears

 

Abstract

We detected influenza A virus antibodies in plasma collected from East Greenland polar bears during subsistence hunts in 2024 (3/14 [21%]) and 2025 (6/14 [43%]). Four bears from 2025 had antibodies for the globally emerging highly pathogenic avian influenza virus H5 clade 2.3.4.4b, consistent with survival after exposure.

Source: 

Link: https://doi.org/10.3201/eid3211.261050

____

#Filovirus reactive #antibodies in #wildlife hunting #communities suggest ongoing zoonotic #spillover in forested #Guinea

 

Abstract

Forested Guinea has been the site of multiple high-consequence viral spillover events, including the index case of the 2013-16 West African Ebola epidemic. Deforestation and wildlife hunting rapidly expand the human-animal interface, increasing opportunities for transmission. Here we integrate serologic, spatial and questionnaire data to characterize zoonotic filovirus spillover events and risk factors amongst wildlife hunter communities in Forested Guinea. Hunters and close contacts from 43 villages in 2017 (n = 511) and 2023 (n = 648) were screened using a multiplex microsphere-based immunoassay panel of 9 filoviruses, identifying IgG binding against Ebola virus (EBOV) in 57/1159 individuals (4.9%), as well as species-specific binding against Bundibugyo (BDBV) (49/1159, 4.2%), Taï Forest (TAFV) (13/1159, 1.1%), Reston (4/1159, 0.3%), Měnglà (MLAV) (8/1159, 0.7%), Lloviu (LLOV) (8/1159, 0.7%) and Bombali (BOMV) (1/1159, 0.1%) viruses. Parallel pseudotyped virus neutralization assays identified species-specific neutralization of EBOV, BDBV and TAFV, as well as likely cross-neutralization of BOMV, LLOV and MLAV, suggesting multiple zoonotic virus spillover events. Mixed-effects regression analyses of satellite-derived land-cover data identified environmental risk factors (including forest fragmentation) reflecting potential pathways of exposure. Together, our data suggest multiple ongoing zoonotic filovirus spillover events in wildlife hunting communities and highlight the importance of landscape configuration in driving pathogen spillover.

Source: 

Link: https://doi.org/10.1038/s41467-026-77653-3

____

#Serological and transcriptomic response of African fruit #bats to immune challenge with recombinant #vaccines expressing #Ebola or #Nipah virus #antigens

 

Abstract

Bats are hosts to diverse zoonotic viruses which can cause high case fatality rates in humans. Since detecting viruses in bats is difficult, antibodies are often used for surveillance, though their significance remains unclear in the absence of in vivo immunological studies. To address this knowledge gap, we measured antibody production and gene expression in bats following injection with vaccines encoding either a Nipah virus G glycoprotein or an Ebola virus GP glycoprotein. We selected two African bat species with overlapping ranges, Eidolon helvum (confirmed reservoir of henipaviruses) and Epomophorus gambianus (putative reservoir of filoviruses). Using a Luminex-based multiplex microsphere immunoassay and a pseudotype virus neutralization assay, we observed an increase in antibodies against the Nipah glycoprotein in most bats that received the Nipah vaccine. In contrast, we could only detect anti-Ebola glycoprotein antibodies in one bat species, Ep. gambianus, in response to the Ebola vaccine. Transcriptomic analysis in Ei. helvum revealed that genes involved in ISGylation and T-cell differentiation pathways were differentially expressed in response to the Ebola, but not the Nipah, vaccine. These results demonstrate species-specific differences in responses to antigen exposure, offering insights into bat adaptive immune systems and providing calibration for serological data from wild bats.

Source: 

Link: https://doi.org/10.1098/rsos.252189

____

Epidemiological #investigation of #Shuni virus #infections in #hospitals in two provinces of South Africa (2019–2021) using molecular and serological surveillance

 

Abstract

Shuni Virus (SHUV) is a reemerging zoonotic orthobunyavirus in the Peribunyaviridae family associated with neurological infections and birth defects in humans and animals in Africa and has emerged in the Middle East in the past 10 years. Limited epidemiological data exist in humans, partially due to a lack of clinical awareness and availability of diagnostic assays to determine the incidence of clinical cases and seroprevalence in the population. The goal of this study was to establish serologic and molecular diagnostic assays for SHUV for hospital-based surveillance and to investigate the clinical epidemiology in humans in South Africa. The incidence of SHUV infections was investigated in patients with acute fever of unknown cause with or without neurological signs (AFDUC/N) during the arbovirus season (January-June, 2019–2021). IgM and IgG ELISAs for SHUV were established using baculovirus-expressed glycoproteins and validated against virus-neutralization tests (VNT) positive sera. Orthobunyavirus quantitative RT-PCR (RT-qPCR) and IgM ELISA were used to identify acute infections, and IgG ELISA to define the seroprevalence in patients and healthy control groups in hospitals in Gauteng and Mpumalanga provinces in South Africa. In total, 3/349 (0.84%) AFDUC/N cases tested positive by RT-qPCR and confirmed as SHUV by sequencing. In total, 22/225 (9.7%) AFDUC/N patients had SHUV neutralising antibodies (VNT), of which 11/22 (50.00%) were IgM positive, with an IgM seropositivity of 4.89% (11/225 (4.89%)). Of the RT-PCR and double IgM + VNT+ patients, 60% presented with seizures and 40% with meningitis, of which 36.36% were children and 63.63% were adults, respectively. In total, 9/112 (8%) of the healthy control group tested positive on the IgG ELISA assay. These findings suggest that SHUV is a missed cause of acute neurological infections in hospitalized children and adults in South Africa and should be investigated in humans in Africa and other regions.

Source: 

Link: https://doi.org/10.1371/journal.pntd.0014738

____

Divergent #antibody-mediated population #immunity to #H5, #H7 and #H9 subtype potential #pandemic #influenza viruses

 

Abstract

Influenza continues to cause significant mortality globally and possesses substantial pandemic potential. Assessing pandemic risk requires a clear understanding of existing population immunity. Leveraging a unique large-scale cohort of human sera, we evaluated total and neutralising antibody-mediated immunity to multiple haemagglutinin (HA) proteins, including those from subtypes with high pandemic potential. Our analysis reveals that population immunity is heterogeneous, with distinct age-dependent differences in responses to H5, H7, and H9 avian influenza subtypes. These shifts align with historical circulation patterns of seasonal H1N1 and H3N2 human viruses. Notably, H7 viruses are primarily neutralised through head domain epitopes, while H5 viruses are targeted mainly via stem epitopes, although in both instances some neutralisation occurred via receptor binding site-adjacent epitopes. Furthermore, H7 responses were dominated by non-glycan-targeted IgG2 antibodies, whereas H5 responses were primarily IgG1-mediated. These findings highlight varying levels of susceptibility to influenza across the population, supporting vaccination approaches informed by exposure history.

Competing Interest Statement

CPT has received lecture fees from Moderna.

Source: 

Link: https://www.medrxiv.org/content/10.1101/2025.09.08.25335309v2

____

#Bundibugyo virus #glycoprotein seroreactivity following recombinant VSV–Zaire #Ebola virus glycoprotein #vaccination in outbreak-affected populations of #DRC: a longitudinal cohort study

 

Summary

Background

There are currently no licensed vaccines for disease caused by Bundibugyo virus (BDBV). The recombinant vesicular stomatitis virus–Zaire Ebola virus glycoprotein (rVSVΔG-ZEBOV-GP) vaccine has been widely deployed during Ebola virus disease outbreaks caused by Ebola virus (EBOV). Human studies have shown cross-reactive BDBV antibody responses following licensed Ebola virus disease vaccine administration, but the durability and longitudinal kinetics of these responses in populations vaccinated during outbreaks remain unknown. We aimed to evaluate BDBV glycoprotein seroreactivity following rVSVΔG-ZEBOV-GP vaccination in two longitudinal cohorts from regions of the Democratic Republic of the Congo affected by Ebola virus disease outbreaks.

Methods

This longitudinal cohort study was done in Mbandaka, Equateur Province, and Beni, North Kivu Province. Individuals aged 1 year and older who received the rVSVΔG-ZEBOV-GP vaccine under the WHO ring-vaccination protocol were eligible for enrolment. These populations were defined as: people with confirmed Ebola virus disease, contacts of people with Ebola virus disease or contacts-of-contacts, and health-care or front-line workers in areas affected by Ebola virus disease. Participants were enrolled from June 2 to July 3, 2018, in Mbandaka and from Aug 15 to 29, 2018, in Beni. Serum samples were collected from vaccine recipients and antibody reactivity was assessed using a multiplex pan-filovirus immunoassay. Both cohorts were followed up over 5 years, with seven data collection periods in each province. We evaluated longitudinal trends in EBOV and BDBV glycoprotein seroreactivity using a pan-filovirus multiplex immunoassay across follow-up visits.

Findings

We analysed 5849 serum samples from 1081 participants. 715 (66%) of 1081 participants were male and 366 (34%) were female. BDBV glycoprotein seroreactivity differed substantially between study sites. At baseline, 16 (3%) of 482 participants in Mbandaka and 62 (10%) of 599 in Beni were seroreactive to BDBV glycoprotein. In Mbandaka, BDBV glycoprotein antibody reactivity remained stable through to 6 months after initial vaccination before increasing from a mean median fluorescent intensity (MFI) of 1238 (SD 1599) at 2·5 years, with 16 (5%) of 355 seroreactive, to 4845 (5881) at 3·5 years and 116 (35%) of 329 seroreactive (p<0·0001), followed by waning at later visits. In Beni, BDBV glycoprotein antibody reactivity increased rapidly after the initial vaccination, with seroreactivity peaking at 21 days to a mean MFI of 6678 (SD 6997) with 283 (52%) of 541 participants seroreactive and at 6 months to an MFI of 6852 (6560) with 270 (54%) of 501 seroreactive. Although antibody levels decreased after 6 months, EBOV glycoprotein and BDBV glycoprotein antibody reactivity remained above baseline through to 5 years after vaccination.

Interpretation

The differing patterns of BDBV glycoprotein seroreactivity observed between Beni and Mbandaka warrant further investigation into the epidemiological and immunological factors associated with this seroreactivity, including the epidemiological significance of baseline seroreactivity observed before vaccination. To our knowledge, these findings provide the first longitudinal human data describing BDBV glycoprotein seroreactivity following licensed Ebola virus disease vaccination in populations living in regions now affected by the current outbreak of disease caused by BDBV. They add to the growing body of human evidence describing cross-reactive antibody responses following licensed Ebola virus disease vaccination and support rigorous clinical evaluation of rVSVΔG-ZEBOV-GP during the ongoing outbreak while BDBV-specific vaccines continue to be developed.

Funding

The US Food and Drug Administration, the Gates Foundation, and the US Defense Advanced Research Projects Agency.

Source: 

Link: https://www.sciencedirect.com/science/article/pii/S0140673626016089?dgcid=rss_sd_all

_____

Identification of #Contacts With High Rates of Missed and #Asymptomatic Infection Following an #Outbreak of #Ebola Virus Disease: A Seroepidemiological Study in Likati Health Zone, #DRC

 

Abstract

Background

Ebola virus disease (EVD) is often regarded as severe and highly fatal, but growing evidence suggests that subclinical or minimally symptomatic infections occur and frequently go undetected. During the 2017 outbreak in Likati Health Zone, only 8 cases were confirmed despite many reported exposures. We evaluated the extent of asymptomatic or unrecognized Ebola virus infection and associated factors among contacts of reported cases.

Methods

In November 2017, we conducted a cross-sectional community-based serosurvey among contacts originally identified through Ministry of Health records and newly identified through additional post-outbreak investigations. Participants provided blood samples and completed questionnaires on demographics, exposures, and symptoms within 4 weeks of symptom onset of the EVD case with whom contact was reported. Sera were tested for anti-EBOV nucleoprotein IgG by ELISA. Seropositive individuals were classified as asymptomatic (no symptoms) or unrecognized (≥1 symptom). Secondary attack rate (SAR) was estimated, and logistic regression assessed associations with sociodemographic factors, exposure level, and symptoms.

Results

Among 180 participants (79 originally identified; 101 newly identified), 33 (18.3%) were seropositive. Of these, 19 (58%) reported symptoms, and 14 (42%) were asymptomatic. Any EVD-related symptom was associated with higher odds of seropositivity (OR 2.48, P = .021), though no specific symptom was significant. Asymptomatic individuals had higher antibody titers than symptomatic seropositive contacts (P = .009). The overall SAR was 19.1% (95% CI: 15.9–23.0). High exposure level strongly predicted seropositivity (OR 11.2, 95% CI: 3.8–33.3).

Conclusions

Asymptomatic infections occurred, including among contacts missed during the response, highlighting the need for exposure-based serologic assessments in EVD investigations and raising questions about immune responses and the true disease burden in outbreak-affected settings.

Source: 

Link: https://academic.oup.com/ofid/article/13/7/ofag397/8725922

____

Occupationally Exposed and General #Population #Antibody #Profiles to #Influenza A Viruses Circulating in #Swine as Indication of Zoonotic #Risk

 

Abstract

Persons with occupational exposure to swine might be at disproportionate risk for zoonotic swine influenza A virus. To evaluate human antibody responses, we tested serum or plasma from swine veterinarian, farm employee, and general population cohorts by hemagglutination inhibition assays against representative swine and human seasonal influenza vaccine strains. We analyzed hemagglutination inhibition data by antigenic cartography to assess strain relationships and reproduction number modeling to evaluate pandemic potential using age-stratified immunity profiles. Occupationally exposed groups had lower human seasonal vaccine uptake (45.5% vs. 70%) and lower odds of seropositivity to several H1 and H3 strains from swine than did general population cohorts. One swine strain exhibited significant antigenic drift (3.62 antigenic units) from its nearest vaccine strain. Multiple strains required lower reproduction number thresholds for pandemic spread (1.09–1.35) than recorded pandemic strains (1.46–1.80), demonstrating that population immunity gaps heighten zoonotic risk to circulating swine H1 and H3 strains.

Source: 

Link: https://wwwnc.cdc.gov/eid/article/32/8/25-1995_article

____

Clade 2.3.4.4b #H5N1 #influenza virus and #SARS-CoV-2 #seroprevalence among owned and feral #cats in #Philadelphia and surrounding communities

 

Abstract

Clade 2.3.4.4b H5NX influenza viruses have spread widely in birds since 2020. In addition to causing disease in birds, these viruses have infected a variety of mammals, including humans. Clade 2.3.4.4b H5N1 viruses are currently causing an outbreak among dairy cattle in the United States, and it is important to determine if other mammals have been exposed to H5NX viruses. Cats, specifically outdoor and feral cats, frequently predate wild birds. Recent studies have shown that cats living on dairy cattle farms can be infected with H5N1. Here, we completed serological studies to determine if owned and feral cats living in an urban environment in the United States have evidence of past H5N1 exposures. We used multianalyte bead-based assays to measure clade 2.3.4.4b hemagglutinin (HA) antibody levels in serum samples collected in July 2023 to June 2025 from 417 feral and 228 owned cats from the greater Philadelphia area. We also measured antibody levels against a panel of HAs from other human and non-human influenza viruses, and the receptor binding domain (RBD) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We completed additional H5N1 and SARS-CoV-2 neutralization assays using samples that had detectable antibodies in the multianalyte bead-based assays. One cat (0.16%) was positive for H5 antibodies and twenty cats (3.1%) were positive for SARS-CoV-2 antibodies in both binding and neutralization assays. These data suggest that cats in the Philadelphia area have not been routinely exposed to clade 2.3.4.4b H5N1 viruses but have been more commonly exposed to SARS-CoV-2.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.07.03.736283v1

____

Detection of #antibodies against avian #influenza in #European dairy #cattle, the #Netherlands, January 2026

 

Abstract

In December 2025, highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b genotype DI.2.1 virus was detected in a cat living on a dairy cattle farm. Milk and serum samples from the dairy cattle were tested for avian influenza virus. No viral RNA was detected; however, H5N1-specific antibodies were identified in serum samples from 34 (47.2%) of 72 lactating dairy cows and 24 (63.2%) of 38 youngstock. These demonstrate expansion of the mammalian host range of HPAI H5N1 in Europe.

Source: 

Link: https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2026.31.25.2600464#abstract_content

____

Epidemiological and Virological Characteristics of #H9N2 Avian #Influenza Virus in #Jiangsu Province, #China, 2024

 

Abstract

H9N2 avian influenza viruses inherently carry cross-species transmission potential, making continuous surveillance critical for pandemic prevention. This study focused on monitoring the 2024 H9N2 epidemic in Jiangsu Province’s external environment, analyzing its molecular evolution and receptor binding properties, assessing cross-species transmission and pandemic risks, and investigating serological antibody levels across different human populations. Environmental samples were collected from live poultry markets, farms, slaughterhouses, and bird habitats across Jiangsu, screened via quantitative PCR (qPCR), with positive samples used for virus isolation and whole-genome sequencing. Receptor binding properties were tested by hemagglutination assay, and H9N2 antibody levels were measured in 370 occupationally exposed individuals and 240 non-exposed individuals using hemagglutination inhibition (HI) assays. Among the 5779 collected samples, 6.89% tested H9N2-positive, and 12 strains belonging to the Eurasian lineage Y280-like clade G57 genotype were successfully isolated. All strains carried the HA-Q226L mutation, with 11 showing preferential binding to human α-2,6 receptors and one strain possessing dual receptor binding capability. Internal genes harbored mammalian adaptation mutations, and M2 proteins contained mutations conferring complete resistance to amantadine-class antiviral drugs. Serological tests revealed antibody positive rates of 4.05% in exposed populations and 2.5% in non-exposed populations, with no statistically significant difference between groups. These findings confirm that Jiangsu’s circulating H9N2 viruses have acquired human receptor preference and mammalian adaptation, posing silent infection and pandemic risks. Enhanced surveillance and the development of candidate vaccine stockpiles are strongly recommended.

Source: 

Link: https://www.mdpi.com/1999-4915/18/6/687

____

Cross-reactive #Bundibugyo #antibody responses after licensed #Ebola #vaccines

 

Abstract

Background 

The ongoing Bundibugyo virus disease (BDBV) outbreak in Central Africa highlights the absence of approved vaccines specifically targeting BDBV. Whether licensed Zaire ebolavirus (EBOV) vaccines induce cross-reactive immunity against BDBV remains largely unknown.

Methods 

We performed an immunogenicity analysis using serum samples from participants enrolled in the PREVAC randomized clinical trial evaluating licensed Ebola vaccine strategies in West Africa. Samples collected at day 28 (D28) and month 3 (M3) following vaccination with rVSVΔG-ZEBOV-GP or Ad26.ZEBOV/MVA-BN-Filo were assessed using a multiplex Luminex assay against glycoproteins from multiple filoviruses, including EBOV Kikwit, EBOV Mayinga, BDBV, Sudan virus, Reston virus, and Marburg virus.

Results 

A total of 179 samples were analysed. Detectable cross-reactive antibody responses against BDBV were observed across vaccine groups, timepoints, and age categories. However, BDBV responses remained substantially lower than homologous EBOV responses. In rVSV recipients, median BDBV responses (net MFI) reached 282 (IQR 164–644) at D28 compared with 1788 (832–3311) against the homologous Kikwit antigen. Similar patterns were observed following rVSV booster vaccination and Ad26.ZEBOV/MVA-BN-Filo vaccination. The heterologous Ad26/MVA regimen demonstrated increasing BDBV responses between D28 and M3.

Conclusions 

Licensed EBOV vaccines induced detectable but quantitatively reduced cross-reactive antibody responses against BDBV. Although no direct assessment of vaccine efficacy against BDBV disease was possible, these findings support the plausibility of partial heterologous immunity following EBOV vaccination. In the absence of approved BDBV-specific vaccines, these data support the urgent evaluation of currently available Ebola vaccines during BDBV outbreaks and reinforce the importance of developing broadly protective pan-filovirus vaccines.

Competing Interest Statement

The authors have declared no competing interest.

Clinical Trial

NCT02876328

Source: 

Link: https://www.medrxiv.org/content/10.64898/2026.05.27.26354223v1

____

Detection of Anti- #H5 #Antibodies in People with Exposure to Wild #Birds in Northern #Canada

 

Abstract

Using a commercially available H5 serology assay, we identified a 7.4% (n=5/68) anti-H5 seroreactivity rate among hunters in Northern Canada. All participants reported close contact with wild birds.

Competing Interest Statement

This study was performed outside of JK's duties and responsibilities with the Public Health Agency of Canada.

Source: 

Link: https://www.medrxiv.org/content/10.64898/2026.05.24.26353994v1

____

#Coronavirus #diversity and #SARS-CoV-2 #exposure at the #wildlife – #human interface in Northern #Italy

 

Abstract

Background

Members of the Coronaviridae family infect humans as well as domestic and wild animals. Over the past three decades, three members of this family, all with zoonotic origins, have caused significant epidemics or pandemics (SARS, MERS, and COVID-19). Despite the spread of SARS-CoV-2 being primarily driven by human-to-human transmission, various animal species are susceptible to infection and may contribute to viral circulation. Aim of this work was to monitor coronavirus (CoV) infections in wild mammals in the Emilia-Romagna region (RER), Italy, using a combined approach of molecular screening for viral RNA detection and serological testing for anti-SARS-CoV-2 antibodies.

Methods

Respiratory and gastrointestinal tissue samples were collected from wild animal carcasses between 2022 and 2024. Samples were tested for SARS-CoV-2 using two RT-qPCR assays targeting the E and N genes, and for other CoVs using a nested pan-coronavirus RT-PCR followed by Sanger sequencing of positive samples. Additionally, serum samples obtained from blood, cardiac clot, or thoracic exudate were screened for antibodies against the SARS-CoV-2 nucleocapsid (N) protein, with positive samples subsequently confirmed by an ELISA targeting antibodies to the receptor-binding domain (RBD) of the Spike (S) protein, focused on variants circulating during the study period.

Results

Molecular analyses were performed on 2,238 animals, all of which tested negative for SARS-CoV-2, while 90 (79% hedgehogs) tested positive for CoVs. Among these, most sequences were consistent with coronaviruses typically reported in the respective host species. However, some exceptions – such as Betacoronavirus erinacei in fox, porcupine, hare, and roe deer, and EmbeCoV-related sequences in a porcupine – warrant further attention. Suitable serum samples were available from 1,751 animals. Overall, 65 animals tested positive for anti-N antibodies, 31 of which (22 foxes, 4 badgers, 2 hedgehogs, 1 roe deer, 1 wolf, 1 rat) were subsequently confirmed by an anti-RBD ELISA.

Conclusions

This study provides an overview of CoVs circulation among wild mammals in RER, supporting the role of hedgehogs as reservoirs and identifying some species with evidence of exposure to SARS-CoV-2. Certain unexpected findings highlight the need for further investigations to clarify the potential for cross-species transmission.

Source: 

Link: https://link.springer.com/article/10.1186/s12985-026-03193-3

____

Pre-existing systemic and #nasal #antibodies against avian #H5 #influenza A viruses vary according to #childhood imprinting

 

Abstract

Avian influenza A viruses (IAV) pose a constant pandemic threat, with the recent 2.3.4.4b clade of the H5 subtype causing high pathogenicity and spreading across animal species and geographic locations. Understanding human pre-existing immunity to avian H5 IAV can inform on population susceptibility, a critical aspect of pandemic preparedness. To that end, we analysed the IAV HA-specific antibodies across individuals born between 1928-1999 with different early life exposures to IAV subtypes. Individuals born prior to 1957 had the highest pre-existing serum antibodies to group 1 HA antigens, including the 2.3.4.4b H5 and a group 1 HA stem antigen. These birth-year-specific patterns were not reflected in the limited pre-existing serum neutralising antibodies detectable against a 2.3.4.4b H5 IAV or in H5-specific memory B cell populations. They were however evident in pre-existing nasal IgG and IgA titres to H5, which were greater in individuals born prior to 1957. Our findings demonstrate that the immunological biases afforded by early life exposure extend to antibodies detected in the nasal mucosa, the site of IAV replication.

Source: 

Link: https://www.biorxiv.org/content/10.64898/2026.05.08.723737v1

____

Cross-reactive #human #antibody responses to #H5N1 #influenza virus #neuraminidase are shaped by immune history

 

Abstract

H5N1 highly pathogenic avian influenza viruses have spread globally and pose a pandemic risk. Prior studies suggest that early life exposures to group 1 influenza viruses (H1N1 and H2N2) prime antibodies that cross-react to the hemagglutinin of H5N1, which is also a group 1 virus. However, less is known about how immune history affects antibody responses against the H5N1 neuraminidase (NA). We measured NA inhibition antibodies against multiple H5N1 viruses using sera from 155 individuals born between 1927 and 2016. Individuals likely primed in childhood with H1N1 viruses possessed higher levels of antibodies that cross-react with the NA of H5N1 viruses compared to those primed with H2N2 or H3N2 viruses. While young children rarely possessed cross-reactive N1 antibodies, childhood infections with contemporary H1N1, but not H3N2, viruses elicited them. We also measured antibodies against an H5N5 virus (A6 genotype) that recently caused a fatal infection in the United States. Consistent with the lack of circulation of N5 viruses in humans, we found low levels of antibodies against the N5 NA. Our data suggest that immune history greatly impacts the generation of cross-reactive NA antibodies, and that reassortment with other NAs may increase the risk of H5 infection of humans.

Source: 

Link: https://www.nature.com/articles/s41467-026-72941-4

____

#Genetic and #biological characterization of #H9N2 avian #influenza viruses isolated from #swine in #China

 

Abstract

Background

H9N2 avian influenza virus (AIV) has been circulating in poultry in China for decades and are undergoing adaptation to mammals, posing potential pandemic risks. To investigate the prevalence of H9N2 AIVs in swine, we conducted surveillance in Shandong Province from 2021 to 2023.

Results

Two H9N2 influenza virus strains, A/swine/Shandong/417/2021(Sw/SD/417/21) and A/swine/Shandong/662/2022 (Sw/SD/662/22), were successfully isolated from swine and genetically characterized. Phylogenetic analyses showed that both isolates were reassortants containing gene segments from multiple H9N2 AIV lineages and closely related to currently circulating H9N2 AIV. Key molecular marker analysis revealed that both isolates carried mammalian-adaptive residues in the HA receptor-binding sites (183 N, 190 V, 226 L), a novel HA cleavage site variant (PSKSSRGL), PB2 mutations (A588V, E627V), and the M2 S31N substitution, suggesting potential adaptation to mammalian hosts and resistance to adamantane antivirals. Mice infection experiments demonstrated efficient viral replication in the respiratory tract, particularly in the lungs, but only mild histopathological changes were observed, with no significant weight loss or mortality, indicating low pathogenicity in mice. Serological surveillance of 3,172 swine serum samples showed a low prevalence of H9N2 influenza virus infection (0.44%), with positive samples sporadically distributed across regions and years.

Conclusion

In summary, although H9N2 AIV infection in swine is rare and generally mild, the presence of mammalian-adaptive markers and reassortant genomes highlights the potential risk of cross-species transmission and subclinical adaptation. Continuous avian–swine–human influenza surveillance is therefore essential to mitigate the potential threat posed by H9N2 AIV.

Source: 

Link: https://link.springer.com/article/10.1186/s12917-026-05501-z

____

Serologic #Evidence of #Influenza #H5N1 Virus #Infection in a #Veterinary Professional Exposed to an Infected #Cat — Los Angeles County, #California, Dec. '24–Jan. '25

 

Summary

-- What is already known about this topic?

- Transmission of influenza A(H5N1) viruses from domestic cats to humans has not been documented.

-- What is added by this report?

- During November 2024–January 2025, a total of 139 persons exposed to 19 A(H5N1)-infected domestic cats that consumed raw animal products were identified in Los Angeles County, California. Among 25 exposed persons who received serologic testing, one asymptomatic veterinary professional had serologic evidence of A(H5N1) infection after occupational exposure to an A(H5N1)-infected cat.

-- What are the implications for public health practice?

- These findings provide evidence of zoonotic transmission of influenza A(H5N1) virus from domestic cats to humans. Pet owners are advised not to feed raw animal products to cats. Veterinary professionals should be aware of infection risks, use appropriate personal protective equipment, and adhere to recommended infection control practices to reduce the risk for zoonotic transmission of influenza A(H5N1).

Abstract

Since 2021, avian influenza A(H5N1) clade 2.3.4.4b viruses have spread widely among wild birds and domesticated poultry in the United States, with sporadic spillover into mammals. During November 2024–January 2025, 19 domestic cats in Los Angeles County, California, became ill after consumption of commercially purchased raw milk, raw meat, or raw pet food; nine cats tested positive for influenza A(H5N1) virus (clade 2.3.4.4b genotype B3.13). Overall, 139 persons were exposed to the 19 infected cats, and all were monitored for symptoms. Although 30 persons reported influenza-like illness symptoms, none received a positive influenza A(H5) reverse transcription–polymerase chain reaction (RT-PCR) test result. In April 2025, the Los Angeles County Department of Public Health and CDC invited all exposed persons to participate in an influenza A(H5N1) serosurvey to determine whether transmission of influenza A(H5N1) virus occurred, including in those without symptoms. Sera from 25 (18%) of the 139 exposed persons were tested. Among these, antibodies specific to A(H5N1) clade 2.3.4.4.b (antigenically similar to the clade 2.3.4.4.b influenza A[H5N1] virus isolated from the infected cats) were detected in serum from one veterinary professional, who was asymptomatic. This person did not use respiratory or eye protection during the exposure, did not report influenza-like illness after the exposure, and reported no other known risk factors for A(H5N1) infection. These findings represent serologic evidence of possible transmission of influenza A(H5N1) clade 2.3.4.4.b virus from a domestic cat to a human, highlighting concerns about potential cat-to-human transmission of influenza A(H5N1) virus and the importance of infection control practices in veterinary settings.

Source: 

Link: https://www.cdc.gov/mmwr/volumes/75/wr/mm7517a1.htm?s_cid=OS_mm7517a1_e&ACSTrackingID=USCDC_921-DM155047&ACSTrackingLabel=Week%20in%20MMWR%3A%20Vol.%2075%2C%20May%207%2C%202026&deliveryName=USCDC_921-DM155047

____

#Surveillance on #California dairy #farms reveals multiple possible sources of #H5N1 #influenza virus #transmission

 

Abstract

Transmission routes of highly pathogenic H5N1 between cows or to humans remain unclear due to limited data from affected dairy farms. We performed air, farm wastewater, and milk sampling on 14 H5N1-positive dairy farms across two different California regions. Infectious virus was detected in the air in milking parlors and in wastewater streams, while viral RNA was found in exhaled breath of cows. Sequence analysis of infectious H5N1 virus from air and wastewater samples on one farm revealed viral variants relevant for potential human susceptibility. Longitudinal analysis of milk from the individual quarters of cows revealed a high prevalence of subclinical H5N1-positive cows. Additionally, a heterogeneous distribution of infected quarters that maintained a consistent pattern over time was observed, inconsistent with shared milking equipment serving as the sole transmission mode. The presence of subclinically infected cows was further supported by detection of antibodies in the milk of animals that exhibited no clinical signs during the H5N1 outbreak on one farm. Our data highlight additional sources and potential modes of H5N1 transmission on dairy farms.

Source: 

Link: https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3003761

____