ETIDIOH - NEW

Abstract Prior to the discovery of bat influenza A virus (IAV) subtypes H17N10 and H18N11 , all IAVs were thought to bind sialic acid residues via hemagglutinin (HA) to mediate attachment and subsequent viral entry. However, H17 and H18 engage a proteinaceous receptor : the major histocompatibility complex class II (MHCII). The mechanistic details of this hitherto unknown protein-mediated entry are not understood. Given that conventional IAVs rely on multivalent binding to sialylated glycans , we hypothesized that bat HA similarly interacts with multiple MHCII molecules. Using photoactivated localization microscopy (PALM) on fixed and live cells, we demonstrate that bat IAV particles attach to pre-existing MHCII clusters and induce a further increase in cluster size upon binding. To measure the impact of viral attachment on the dynamics of MHCII, we employ an “inverse attachment” approach, immobilizing viral particles on coverslips before seeding live MHCII-expressing cells on top. Sin...

Abstract Highly pathogenic H5Nx influenza A viruses are causing unprecedented, season-independent outbreaks across avian and mammalian species, including dairy cattle, a novel reservoir. The sialoside-binding properties of influenza A hemagglutinin (HA) are strongly related to its ability to infect and transmit between hosts. Mucin-like O-glycans , omnipresent in respiratory tracts, have been understudied as viral receptors due to their complexity. To address this, we synthesized 25 O-linked glycans with diverse sialosides, including modifications by fucosides and sulfates. Our findings reveal that H5Nx 2.3.4.4b viruses uniquely bind core 3 sialyl-Lewisx and Sia-Gal-β3GalNAc, glycans not recognized by classical H5 or other avian viruses. By determining its crystal structure, we resolved the structural features of both structures in an H5 hemagglutinin (HA) from a 2016 2.3.4.4b virus. While these viruses do not bind human-type receptors , their promiscuous receptor specificity enhances ...

Abstract Lassa mammarenavirus (LASV), a member of the family Arenaviridae , is a highly pathogenic virus capable of causing severe systemic infections in humans . The primary host reservoir is the Natal multimammate mouse (Mastomys natalensis), with human infections typically occurring through mucosal exposure to virus-containing aerosols from rodent excretions . To better understand the molecular mechanisms underlying LASV replication in the respiratory tract, we utilized differentiated primary human airway epithelial cells (HAECs) grown under air–liquid interface conditions, closely mimicking the bronchial epithelium in vivo. Our findings demonstrate that HAECs are permissive to LASV infection and support productive virus replication . While LASV entry into polarized HAECs occurred through both apical and basolateral surfaces , progeny virus particles were predominantly released from the apical surface , consistent with an intrinsic apical localization of the envelope glycoprotein GP...

Abstract   Background :  The current avian influenza A(H5N1) epizootic poses a significant threat to public health , with sporadic infections in humans raising concerns about potential adaptation for efficient human transmission . Laboratory studies have provided evidence that the polymerase basic protein 2 (PB2) E627K mutation facilitates more efficient replication in mammals and humans. This mutation has been detected in Canadian poultry, wild birds and mammals .  Objective :  Our objective was to summarize the current state of evidence on the impact of the avian influenza PB2 E627K mutation on human adaptation, transmission, epidemiology and clinical outcomes in natural human infections.  Methods :  We employed a search strategy across MEDLINE, Embase, Scopus, Global Health and CAB Abstracts for articles published from each database’s inception until mid-May 2023.  Results :  We identified nine eligible articles for review that addressed human ...

{Excerpt} Highly pathogenic H5N1 avian influenza (HPAI) viruses started circulating in lactating dairy cattle in the USA at the end of 2023 (ref. 1) and these viruses are now rapidly spreading between cows2. Eisfeld et al.3 found that a clade 2.3.4.4b H5N1 virus from this cattle outbreak can bind to α2,6-linked sialyl-glycopolymers on microtitre plates . Here we show that the haemagglutinin from a clade 2.3.4.4b H5N1 virus binds poorly to glycans that terminate with α2-6 sialic acids. This is an important finding, as α2,6 sialic acid is abundant in the upper respiratory tract of humans , and acquisition of α2,6 sialic acid receptor specificity is believed to be required for efficient transmission of influenza virus in humans and is considered a risk factor for the emergence of a new pandemic virus4. (...) Source: Nature,  https://www.nature.com/articles/s41586-025-08821-6 ____

Significance We explored how H5Nx influenza viruses , which can infect many different birds and mammals, could adapt to infect humans by altering the hemagglutinin (HA). HA must change to bind human-type receptors for transmission between people. We compared two strains from viruses isolated in 2016 and found that one ( 2.3.4.4e ) can switch to human receptor binding with a single mutation , while another ( 2.3.4.4b ) might require more complex changes to bind simple human-type receptors. These findings highlight the potential for specific strains to evolve and become a pandemic threat, underscoring the importance of monitoring mutations that could lead to human-type receptor adaptation. Abstract H5Nx viruses continue to wreak havoc in avian and mammalian species worldwide . The virus distinguishes itself by the ability to replicate to high titers and transmit efficiently in a wide variety of hosts in diverse climatic environments. Fortunately, transmission to and between humans is sca...

Abstract Rationale and Objectives :  Iron availability and metabolism are important in the pathogenesis of bacterial infections . More recently, links have been reported between iron and the severity of viral infections . In this study, we characterize a crucial relationship between iron metabolism and IAV infection and disease.  Methods :  Iron-related gene expression was assessed in human airway epithelial cells (AEC) infected with IAV. AECs were cultured with ferric iron, iron-loaded transferrin, or iron chelator, deferoxamine (DFO), prior to infection with IAV. Mice were placed on a high iron diet for 8 weeks prior to infection with IAV or treated with anti-transferrin receptor-1 (TFR1) antibody during IAV infection. The effects of iron modulation and depletion of TFR1-mediated responses on IAV infection were assessed.  Measurements and main results :  Iron-related gene expression and metabolism are altered systemically and in lung tissues and AECs during IA...

Abstract High pathogenicity (HP) avian influenza viruses (AIV) generally evolve from low pathogenicity (LP) precursors after transmission from wild birds to chickens (Gallus gallus domesticus) and turkeys (Meleagris gallopavo), causing severe economic losses worldwide. Turkeys are more susceptible to AIV infection than chickens and are considered potential bridging hosts that facilitate the emergence of HPAIV . Beyond the polybasic cleavage site (pCS) in hemagglutinin (HA), little is known about other virulence determinants of HPAIV in these species. In 2015, HPAIV H7N7 and its LP ancestor were isolated from the same chicken farm, which differed by 16 nonsynonymous mutations across all eight gene segments, in addition to the pCS. Here we identify the genetic determinants, including the pCS, that contributed to the HPAIV H7N7 virulence, transmission, replication, and tissue distribution in chickens and turkeys. Notably, the non-structural (NS1) or matrix (M) proteins ’ encoding segments...

Abstract The current outbreak of highly pathogenic avian influenza (HPAI) viruses of the H5N1 subtype clade 2.3.4.4b in dairy cattle in the United States has affected nearly 900 dairy farms and resulted in at least 39 human infections, putting health authorities and the scientific community on high alert. Here we characterize the virus growth properties and host-pathogen interactions of an isolate obtained from a sick dairy cow in Texas in vitro and in vivo and compare it to an older HPAI isolate. Despite so far being associated with mild disease in human patients, the cattle H5N1 virus showed superior growth capability and rapid replication kinetics in a panel of human lung cell lines in vitro . In vivo, cattle H5N1 exhibited more intense pathogenicity in mice , with rapid lung pathology and high virus titers in the brain , accompanied by high mortality after challenge via different inoculation routes. Additionally, the cattle H5N1 demonstrated efficient antagonism of overexpressed RI...

Abstract The novel H10N3 avian influenza virus (AIV) has infected four individuals since 2021 and caused severe respiratory damage , posing a significant threat to public health . However, its pathogenic mechanisms remain poorly understood. Our findings revealed that H10N3 infection induces severe lung damage and causes death in mice , even at low doses. The elevated levels of multiple pro-inflammatory factors in the bronchoalveolar lavage fluid were significantly increased during infection, displaying hallmarks of a cytokine storm . Transcriptome sequencing further revealed systematic activation of inflammation-related pathways, predicting that viral infection induces multiple forms of programmed cell death , including apoptosis, pyroptosis, and necroptosis . Protein-level validation showed that the activation of key cell death markers, including Caspase-3, GSDMD, and MLKL , significantly increased as the infection progressed, with their dynamic changes correlating strongly with the e...

Significance Middle East respiratory syndrome coronavirus (MERS-CoV) is a highly pathogenic coronavirus that continues to cause periodic outbreaks in humans with a case-fatality rate of approximately 35%. MERS-CoV generally transmits poorly, but superspreading events are well documented. Efficient human-to-human transmission of respiratory viruses generally correlates with a tropism for the upper respiratory tract, but this tropism for MERS-CoV remains poorly understood. Characterizing the MERS-CoV tropism in the human upper respiratory tract is of critical importance to understand its epidemiology and pandemic potential of future MERS-CoV variants and other dipeptidyl peptidase 4 (DPP4)-utilizing coronaviruses present in animal reservoirs. Abstract Transmissibility of respiratory viruses is a complex viral trait that is intricately linked to tropism. Several highly transmissible viruses, including severe acute respiratory syndrome coronavirus 2 and Influenza viruses, specifically targ...

Abstract Highly pathogenic avian influenza viruses (HPAIV) pose a serious public health concern . In March 2024, a first-time outbreak of HPAIV H5N1 in dairy cattle herds was reported in the United States (US). Since then, the virus has continued to spread in cattle herds and spilt over into humans . We recently showed that the first human isolate reported in the US in Texas (HPhTX) from a dairy worker in an affected cattle farm has enhanced replication kinetics and pathogenicity in mice compared to a closely related bovine isolate (HPbTX). However, the molecular determinants of differential pathogenicity have not yet been identified. Herein, we show that HPhTX has enhanced polymerase activity , compared with HPbTX, in human cells and that the polymerase basic 2 (PB2) protein is the main factor responsible for this difference. Through single and combined site-directed mutagenesis and swapping the three amino acids different between HPhTX and HPbTX, we found that PB2 mutation E627K is t...

Abstract Influenza A virus (IAV) non-canonical replication products can be bound by host pathogen sensors , such as retinoic acid-inducible gene I (RIG-I). However, innate immune activation is infrequent in cell culture infection, in particular by adapted strains. Moreover, it is not understood why non-canonical IAV RNAs activate RIG-I in a sequence- or RNA structure-dependent manner. We therefore hypothesized that multiple errors need to occur before influenza virus RNA synthesis activates innate immune signaling . To test this idea, we investigated whether RIG-I activation is stimulated by the non-canonical or aberrant transcription of mini viral RNAs (mvRNA), a <125 nt long RNA that is overexpressed in pandemic and highly pathogenic IAV infections . Using mvRNA sequences identified in tissue culture and ferret infections , we find that mvRNAs can cause non-canonical transcription termination through a truncated 5ʹ polyadenylation signal or a 5ʹ transient RNA structure that interr...

ABSTRACT Influenza A viruses with fewer amino acids in the neuraminidase (NA) stalk domain are primarily isolated from chickens rather than wild ducks , indicating that a shortened NA stalk is considered an adaptation marker of avian influenza viruses (AIVs) to chickens. Experimental passages of an H7N7 nonpathogenic AIV (rgVac2-P0) in chickens resulted in a highly pathogenic variant (Vac2-P3L4) with a 34-amino-acid deletion in the NA stalk , encompassing five potential N-glycosylation sites. To investigate how amino acid truncation and deglycosylation in the NA stalk contribute to increased pathogenicity, a virus with glycosylation-deficient mutations at these sites (rgVac2-P3L4/P0NAΔGlyco) was constructed. Contrary to expectations, chickens inoculated with rgVac2-P3L4/P0NAΔGlyco exhibited variable clinical outcomes, attributed to the genetic instability of the virus. A single mutation stabilized the virus, and the mutant (rgVac2-P3L4/P0NAΔGlyco-Y65H) resulted in higher pathogenicity ...

Summary Highly pathogenic avian influenza has spilled into many mammals, most notably cows and poultry, with several dozen human breakthrough infections. Zoonotic crossovers , with hemagglutinins mutated to enhance viral ability to use human α2-6-linked sialic acid receptors versus avian α2-3-linked ones, highlight the pandemic risk . To gain insight into these crossovers, we determined the cryoelectron microscopy (cryo-EM) structure of the hemagglutinin from the zoonotic H5N1 A/Texas/37/2024 strain (clade 2.3.4.4b) in complex with a previously reported neutralizing antibody . Surprisingly, we found that the receptor-binding site of this H5N1 hemagglutinin was already occupied by an α2-3-linked sialic acid and that this glycan emanated from asparagine N169 of a neighboring protomer on hemagglutinin itself. This structure thus highlights recognition by influenza hemagglutinin of an “auto”-α2-3-linked sialic acid from N169, an N-linked glycan conserved in 95% of H5 strains, and adds “aut...

ABSTRACT The evolution of SARS-CoV-2 pathogenicity has been a major focus of attention. However, the determinants of pathogenicity are still unclear. Various hypotheses have attempted to elucidate the mechanisms underlying the evolution of viral pathogenicity , but a definitive conclusion has yet to be reached. Here, we review the potential impact of all proteins in SARS-CoV-2 on the viral pathogenic process and analyze the effects of their mutations on pathogenicity evolution. We aim to summarize which virus-encoded proteins are crucial in influencing viral pathogenicity, defined as disease severity following infection. Mutations in these key proteins, which are the virulence factors in SARS-CoV-2, may be the driving forces behind the evolution of viral pathogenicity. Mutations in the S protein can impact viral entry and fusogenicity . Mutations in proteins such as NSP2, NSP5, NSP14, and ORF7a can alter the virus’s ability to suppress host protein synthesis and innate immunity . Mutat...

Summary The ongoing circulation of highly pathogenic avian influenza (HPAI) A (H5N1) viruses , particularly clade 2.3.4.4b strains , poses a significant threat to animal and public health . Recent outbreaks in cattle highlight concerns about cross-species transmission and zoonotic spillover . Here, we found that the hemagglutinin (HA) protein from a cattle-infecting H5N1 virus has acquired slight binding to human-like α2-6-linked receptors while still exhibiting a strong preference for avian-like α2-3-linked sialic acid receptors. Immunohistochemical staining revealed HA binding to bovine pulmonary and mammary tissues , aligning with clinical observations. HA also binds effectively to human conjunctival, tracheal, and mammary tissues , indicating a risk for human transmission , notably in cases of conjunctivitis . High-resolution cryo-electron microscopy (cryo-EM) structures of this H5 HA in complex with either α2-3 or α2-6 receptors elucidate the molecular mechanisms underlying its re...

ABSTRACT The host range of HPAIV H5N1 was recently expanded to include ruminants , particularly dairy cattle in the United States (US). Shortly after, human H5N1 infection was reported in a dairy worker in Texas following exposure to infected cattle. Herein, we rescued the cattle-origin influenza A/bovine/Texas/24-029328-02/2024(H5N1, rHPbTX) and A/Texas/37/2024(H5N1, rHPhTX) viruses, identified in dairy cattle and human, respectively, and their low pathogenic forms , rLPbTX and rLPhTX, with monobasic HA cleavage sites . Intriguingly, rHPhTX replicated more efficiently than rHPbTX in mammalian and avian cells . Still, variations in the PA and NA proteins didn’t affect their antiviral susceptibility to PA and NA inhibitors. Unlike rHPbTX and rLPbTX, both rHPhTX and rLPhTX exhibited higher pathogenicity and efficient replication in infected C57BL/6J mice . The lungs of rHPhTX-infected mice produced higher inflammatory cytokines/chemokines than rHPbTX-infected mice. Our results highlight ...

Abstract H5Nx viruses continue to wreak havoc in avian and mammalian species worldwide. The virus distinguishes itself by the ability to replicate to high titers and transmit efficiently in a wide variety of hosts in diverse climatic environments. Fortunately, transmission to and between humans is scarce . Yet, if such an event were to occur, it could spark a pandemic as humans are immunologically naive to H5 viruses. A significant determinant of transmission to and between humans is the ability of the influenza A virus hemagglutinin (HA) protein to shift from an avian-type to a human-type receptor specificity . Here, we demonstrate that a 2016 2.3.4.4e virus HA can convert to human-type receptor binding via a single Q226L mutation , in contrast to a cleavage-modified 2016 2.3.4.4b virus HA . Using glycan arrays, x-ray structural analyses, tissue- and direct glycan binding, we show that L133adelta and 227Q are vital for this phenotype. Thus, whereas the 2.3.4.4e virus HA only needs a s...

Abstract We compared virus replication and host responses in human alveolar epithelium infected with highly pathogenic avian influenza (HPAI) A( H5N1 ) viruses. A/Vietnam/1203/2004 replicated most efficiently, followed by A/Texas/37/2024 , then A/bovine/Ohio/B24OSU-342/2024 . Induction of interferon-stimulated genes was lower with A/Texas/37/2024 and A/bovine/Ohio/B24OSU-342/2024, which may indicate a reduced disease severity of those viruses. Source: Emerging Infectious Diseases Journal,  https://wwwnc.cdc.gov/eid/article/31/2/24-1147_article _____