Search Results (524)

Avian influenza viruses (AIVs), including H5N1 and H7N9, from the Orthomyxoviridae family present substantial public health concerns. The predominant circulating clade 2.3.4.4b has demonstrated enhanced capacity for mammalian adaptation, raising concerns about potential reassortment with human seasonal influenza viruses. Unlike H7N9’s limited host range, H5N1 infects birds, various mammals, and humans. Recent concerns include widespread H5N1 infection of U.S. dairy cattle across 18 states, affecting over 1000 herds with 71 human infections (70 H5N1 and 1 H5N5). Key observations include cow-to-cow transmission, viral presence in milk, and transmission to humans, mainly through occupational exposure. Evidence of mammal-to-mammal transmission has been documented in European and Canadian foxes and South American marine mammals. Standard pasteurization effectively inactivates the virus in milk. The continuing mammalian adaptations, particularly mutations like PB2-E627K, PB2-D701N, and PB2-M535I, suggest potential for further evolution in new hosts, emphasizing the need for enhanced surveillance to mitigate pandemic risks. Full article

Highly pathogenic avian influenza (HPAI) A(H5N1) clade 2.3.4.4b has recently emerged as a major threat to wildlife, agriculture, and public health due to its expanding host range and the increasing frequency of spillover into mammals. In July–August 2023, the mass death of over 3500 northern fur seals (Callorhinus ursinus) and at least one Steller sea lion (Eumetopias jubatus) was recorded on Tyuleniy Island in the Sea of Okhotsk, Russia. Two HPAI A(H5N1) viruses were isolated from fur seal carcasses and designated A/Northern_fur_seal/Russia_Tyuleniy/74/2023 and A/Northern_fur_seal/Russia_Tyuleniy/75/2023. Both viruses exhibited high pathogenicity in chickens (IVPI 2.7–3.0) and mice (MLD₅₀ 1.9–2.5 log₁₀EID₅₀/mL), with distinct differences in disease progression, histopathology, and organ tropism. Experimental infection of mice revealed that strain A/74/2023 induced more severe pulmonary and neurological lesions than A/75/2023. Whole-genome sequencing and phylogenetic analysis demonstrated close relatedness to HPAI H5N1 strains circulating in the Russian Far East and Japan from 2022 to 2023, with several mutations associated with mammalian adaptation, including NP-N319K and, in one isolate, PB2-E627K. According to our findings, northern fur seals (Callorhinus ursinus) on Tyuleniy Island acted as spillover hosts for the highly pathogenic avian influenza (HPAI) H5N1 virus of clade 2.3.4.4b. Furthermore, the high population density of fur seals and the extensive mortality observed during the outbreak highlight these animals’ potential role as another vessel for the evolution of avian influenza viruses. This study represents the first documented case of HPAI H5N1 in pinnipeds in the North Pacific region and supports previous reports indicating that pinnipeds, including northern fur seals, are highly susceptible to HPAI H5N1 clade 2.3.4.4b viruses. Full article

To investigate the molecular characteristics of H3N2 canine influenza viruses circulating in Jiangsu, China, we isolated a H3N2 strain (A/Canine/Nanjing/CnNj01-2025) from a dog presenting with respiratory signs at the Veterinary Teaching Hospital of Nanjing Agricultural University. All eight gene segments were sequenced and compared with those of two human H3N2 strains and five avian H3N2 strains. Antigenicity and receptor-binding properties were also assessed. Phylogenetic analysis revealed that the canine isolate descended from the avian lineage and formed an independent evolutionary clade, while the human strains were more distantly related to the avian lineage. Glycosylation analysis of the HA protein revealed that the canine strain carried seven N-glycosylation sites, including a unique site at residue 97/81 (HA/H3 numbering), which serves as a molecular signature of the canine strain. Several amino-acid substitutions were identified in major antigenic sites, including D97/81N, A176/160T, N204/188D, V212/196I, and W237/222L. Analysis of internal genes showed that the canine strain harbored PB2 292T and 590S mammalian adaptation mutations, which are also present in human strains. Hemagglutination inhibition (HI) assays of the canine strain indicated moderate serologic cross-reactivity with a human H3N2 antiserum (16-fold reduction), whereas avian strains showed no cross-reactivity. Receptor-binding assays demonstrated that the virus retained predominant α-2,3 sialic acid binding, comparable to that of avian influenza viruses, and gained a modest affinity for human-type α-2,6 sialic acid receptors. Therefore, the canine H3N2 virus has undergone significant antigenic drift, developed partial serological cross-reactivity with human strains, and acquired detectable but limited binding affinity for human-type receptors. Overall, our findings suggest that the current canine H3N2 influenza virus exhibits distinct genetic and antigenic variations from human and avian strains. Continuous molecular and serological surveillance of canine influenza viruses is therefore warranted to monitor their evolutionary trends and assess the potential for cross-species transmission. Full article

The widespread circulation of Eurasian avian-like H1N1 (EA H1N1) swine influenza virus poses significant zoonotic and pandemic risks worldwide. However, current diagnostic methods are difficult to deploy in the field, as they generally require specialized laboratory infrastructure and trained personnel. Here, we present a novel dual-signal detection platform that combines reverse transcription recombinase polymerase amplification (RT-RPA) with CRISPR/Cas12a technology for rapid, on-site EA H1N1 detection. We established an integrated one-tube assay by designing and optimizing RT-RPA primers targeting a conserved region of the hemagglutinin (HA) gene, together with engineered CRISPR/Cas12a guide RNAs exhibiting high specificity. The platform incorporates two complementary readout modes: real-time fluorescence monitoring and visual colorimetric detection using a smartphone. The assay shows excellent analytical specificity, with no cross-reactivity observed against other swine influenza virus subtypes or common swine pathogens, (including CSFV, PRRSV, PEDV, PCV, TGEV, and RV). The detection limit is 2 copies/μL, and the entire procedure can be completed within 30 mins using simple portable equipment. When evaluated on 86 clinical samples, the assay demonstrated 94.18% concordance with RT-qPCR. Compared with conventional diagnostic methods, this RT-RPA–CRISPR/Cas12a assay offers greater convenience and cost-effectiveness. Its strong potential for field-based rapid testing underscores promising application prospects in swine influenza surveillance and control programs. Full article

The continued diversification of the H9N2 avian influenza virus (AIV) into multiple antigenically and phylogenetically distinct lineages is promoting the emergence of strains with pandemic potential. Constant monitoring of the genetic evolution and changes in biological characteristics of the H9N2 viruses is therefore essential. In this study, we analyzed the genetic evolution of the H9N2 viruses isolated from poultry farms between 2022 and 2023 and evaluated their pathogenicity in chickens and mice. The HA genes of all ten isolates belonged to the h9.4.2.5 lineage, which is currently the predominant evolutionary lineage in China. Yet, their HA genes further divided into distinct subbranches within the h9.4.2.5 lineage. The NA genes of these viruses shared high homology with the prevalent H9N2 AIVs in recent years. However, these viruses were located in different evolutionary groups. Notably, the internal genes showed close relationships with those of recent H3, H6, and H9 subtype AIVs, suggesting active reassortment events among co-circulating viruses. Pathogenicity assessment in mice and chickens demonstrated divergent virulence between two representative isolates, FS22 and JM14, which clustered into different h9.4.2.5 subbranches. FS22 exhibited more efficient and prolonged replication in the lungs and turbinates of mice compared to JM14. Both viruses replicated efficiently in the lungs, kidneys, and trachea of chickens at 3 days post-infection (DPI), but differed in their horizontal transmission potential. Particularly, inoculated and contacted chickens all produced high antibody levels from the 5 DPI until the end of the experiment, and peak antibody titers for both viruses occurred at 7 DPI. These findings underscored the continuous evolution ofH9N2 AIV enhanced its genetic and phenotypic diversity, leading it to pose a threat to public health. Thus, continuous surveillance in poultry farms is necessary. Full article

H6 subtype avian influenza viruses (AIVs) have a broader host range and circulate globally in wild birds, domestic ducks, geese, and terrestrial poultry all over the world. Their demonstrated capacity to adapt receptor-binding affinity for mammalian species constitutes a persistent concern for zoonotic transmission and public health. In this study, a novel triple-reassortant H6N8 AIV strain was isolated from a chicken farm in southern China and designated as A/chicken/Guangdong/JM642/2023 (H6N8). The complete genome of the virus was sequenced using Next-Generation Sequencing. Phylogenetic analysis indicated that the HA gene of the isolate clustered into the Group III/HN573-like, which encompasses H6 subtype viruses bearing various NA genes and belonging to the Eurasian gene pool. The NA gene showed the closest genetic relationship with viruses originating from North America. All six internal genes were derived from H9N2 AIVs. The virus possesses several key molecular determinants known to contribute to an expanded host range and increased virulence. Animal infection studies demonstrated that the virus was capable of infecting mice without prior adaptation. It replicated efficiently in the lungs and nasal turbinates, followed by systemic dissemination resulting in lethal outcomes. Inoculated chickens remained asymptomatic; however, the virus replicated efficiently in multiple organs, with high viral loads detected particularly in the lungs and kidneys. Viral shedding occurred via both the respiratory and digestive tracts, and horizontal transmission was observed among chickens. Notably, infected and contacted chickens developed high levels of antibodies from 8 days post-inoculation (DPI) to the end of observation period. This study enhances our understanding of the genetic and biological characteristics of the novel reassortant H6N8 AIVs and underscores their potential risk to public health. Full article

It has been more than 25 years since the avian influenza A virus (IAV) H5N1 subtype emerged in humans in 1997. Since then, this virus has become endemic in poultry and wild birds and has been causing sporadic infections in humans. Furthermore, the H5N1 subtype has undergone numerous reassortment events with other avian IAVs, resulting in the emergence of various H5Nx subtypes. Furthermore, the original H5 hemagglutinin (HA) has evolved genetically and antigenically and diversified into multiple lineages, phylogenetic clades, and subclades. In 2020, clade 2.3.4.4b H5N1 emerged in Europe and spread intercontinentally. Lately, H5N1 has exhibited a resurgence in transmission across the continents in different avian and mammalian species. Importantly, to the surprise of influenza virologists, H5N1 has recently been found to infect a new host, the cow, and has been detected in cow milk. Furthermore, spillover infections of H5N1 have also been detected in dairy farm workers. This review summarizes the recent transmission of clade 2.3.4.4b H5N1 across the globe and its pathogenesis and adaptation in different hosts. Also, this review discusses the susceptibility of the H5N1 subtype to anti-IAV drugs and vaccines and the public health response and measures that are undertaken and can be taken in the future to contain its further spread. Full article

Highly Pathogenic Avian Influenza (HPAI) viruses, particularly IAV (H5N1), continue to pose a major global threat due to their widespread circulation and high mortality rates in birds. Management of HPAI is complicated by challenges in conserving migratory bird populations, sustaining poultry production, and uncertainties in disease dynamics. Structured decision-making frameworks, such as those based on the PrOACT model, are recommended to improve outbreak response and guide critical actions, especially when HPAI virus (HPAIV) detections occur in sensitive areas like wildlife refuges. Surveillance data from late 2024 to early 2025 show persistent HPAI activity, with 743 detections across 22 European countries and beyond, and notable outbreaks in poultry in nations like Hungary, Iceland, and the UK. The proximity of poultry farms to water sources increases environmental contamination risks. Meanwhile, HPAI A(IAV (H5N1)) and other H5Nx viruses have been detected in a wide range of mammalian species globally, raising concerns about mammalian adaptation due to mutations like E627K and D701N in the PB2 protein. Human infections with IAV (H5N1) have also been reported, with recent cases in North America highlighting zoonotic transmission risks. Molecular studies emphasize the importance of monitoring genetic variations associated with increased virulence and antiviral resistance. Preventive strategies focus on biosafety, personal protective measures, and vaccine development for both avian and human populations. Ongoing genetic characterization and vigilant surveillance remain critical to managing the evolving threat posed by HPAI viruses. Full article

H5N1 is a highly pathogenic avian influenza virus of major global concern. Since 2023, it has circulated widely among wild and farmed birds, with increasing spillover into mammals, including minks, seals, and cattle, and sporadic infections in humans in Chile, the UK, and the USA. The risk of a future pandemic is considered high because ongoing viral evolution could enable efficient human-to-human transmission. The hemagglutinin (HA) glycoprotein is the principal determinant of host range, mediating viral attachment and entry through interactions with sialylated glycans and potentially additional host surface proteins. Here, we developed an artificial intelligence (AI)-based pipeline integrating structural modeling, protein–protein interaction prediction, and biological filtering to identify human cell surface proteins with high likelihood of interacting with H5N1 HA. These interactions may contribute to viral entry and tropism and therefore represent promising candidates for experimental validation and therapeutic targeting. Our findings highlight the utility of AI-driven pipelines in accelerating the discovery of host factors relevant to pandemic influenza viruses. Full article

The diseases caused by genotype VII Newcastle disease virus (NDV), H9N2 avian influenza virus (AIV), and fowl adenovirus serotype 4 (FAdV-4) continue to threaten the global poultry industry. However, no broad-spectrum vaccines provide simultaneous protection against these three pathogens. This study employed bioinformatics and immunoinformatics approaches to design a multi-epitope vaccine, named NFAF, which consists of B-cell, cytotoxic T lymphocyte (CTL) epitopes, and helper T lymphocyte (HTL) epitopes derived from hemagglutinin-neuraminidase (HN) and fusion (F) proteins of genotype VII NDV, hemagglutinin (HA) protein of H9N2, and Fiber2 protein of FAdV-4. The vaccine candidate was predicted to have non-allergenic properties, non-toxicity, high antigenicity, and favorable solubility. Each of its constituent antigenic epitopes has a high degree of conservation. Molecular docking demonstrated stable binding between NFAF and chicken Toll-like receptor (TLRs) and major histocompatibility complex (MHC) molecules. NFAF was expressed in soluble form in Escherichia coli and purified. Polyclonal antibodies against all three target viruses showed specific binding to NFAF. In vitro experiments revealed that NFAF effectively stimulated chicken peripheral blood mononuclear cells (PBMCs) and induced Th1, Th2, and pro-inflammatory cytokine production, confirming its immunogenicity, and increased the mRNA expression of the key signaling molecules MyD88 and NF-κB. These results suggested that NFAF could therefore be an efficacious multi-epitope vaccine against genotype VII NDV, H9N2, and FAdV-4 infections. Full article

Highly pathogenic avian influenza A virus (HPAIV) H5N1, clade 2.3.4.4b, has emerged as a significant zoonotic threat. H5N1 is widely circulating in wild birds, and an increasing number of spillover events have been observed in a wide range of mammalian species. These cases are primarily reported in countries on the European and American continents. This review describes the likely transmission routes, lesions, and clinical manifestations of HPAIV H5N1 clade 2.3.4.4b in naturally infected mammals, with a focus on the involvement of the central nervous system (CNS). In the analysis, pathological findings were categorized by organ system and host species, which were further divided into terrestrial mammals, marine mammals, and dairy cattle. The most frequently reported clinical manifestations were neurological and respiratory signs in marine mammals and neurological signs and lethargy in terrestrial mammals. Macroscopic and histological lesions were commonly found in the CNS and lungs of terrestrial and marine mammals, while dairy cattle showed mainly gastrointestinal and mammary gland involvement. Immunohistochemistry and reverse transcriptase real-time PCR analyses confirmed high viral loads in brain tissues, indicating a neurological tropism of H5N1 clade 2.3.4.4b. Routes of CNS invasion remain uncertain, though both hematogenous and olfactory nerve pathways are discussed. Recent evidence suggests mammal-to-mammal and vertical transmission, raising concerns for the zoonotic and pandemic potential of this virus. In conclusion, the findings emphasize an urgent need for enhanced surveillance to effectively disclose changes in viral pathogenicity and transmissibility among mammalian hosts. Full article

The H9N2 avian influenza virus (AIV) is difficult to prevent and control because of its low pathogenicity and frequent mutation. In a previous study, the HA (hemagglutinin) protein of H9N2 was expressed in a rice endosperm reactor and prepared into a subunit vaccine to immunize chickens and mice, both of which exhibited a good immunity effect. The results of the intermediate tests of the transgenic strains (AIV-1 and AIV-3) showed that the HA gene can be stably expressed. Agronomic traits, such as plant height and number of grains, were significantly optimized in the transgenic strains. Moreover, no exogenous HA genes were found in the leaves of the weeds, and it was initially determined that there was no risk of gene drift. This study provides key technical support for the commercialization of plant subunit vaccines for avian influenza viruses. Full article

Influenza A virus (IAV) has a wide range of avian and mammalian hosts, leading to disease outbreaks and increasing the risk of panzootics and pandemics. Subtype H5N1 of clade 2.3.4.4b is causing the current high pathogenicity avian influenza (HPAI) panzootic. Environmental changes are fuelling the spread of HPAI H5N1 in wildlife worldwide, with occasional spillover events from seabirds to cetaceans. Sampling difficulties and limited tests available for diagnosis are a challenge to cetacean virology research. Understanding the risk of HPAI outbreaks in cetaceans requires a comprehensive examination of events of IAV infection. Documented cases relate to IAV subtypes H1N3, H13N2, H13N9, and H5N1 and have been reported in cetaceans sampled in the Pacific, Atlantic, and Arctic Oceans. The number of H5N1 IAV isolated from cetaceans is increasing and affects six host species of the families Delphinidae and Phocoenidae of the suborder Odontoceti. The analysis of 40 molecular markers of viral adaptation to mammals in 21 H5N1 cetacean isolates reveals mutations are present in three viral proteins: hemagglutinin (HA), polymerase basic protein 2 (PB2), and nucleoprotein (NP). Phylogenetic analysis of HA and PB2 sequences isolated from cetaceans and co-occurring cases in seabirds and marine mammals do not support sustained transmission of the virus between cetaceans. IAV H5N1 appears to be reaching cetaceans after spillover from seabirds and other marine mammals. Increasing worldwide surveillance of IAV infection of cetaceans is crucial, as these marine mammals are sentinel species for human pandemic preparedness and key species for marine biodiversity conservation and ecosystem health. Full article

The detection of H5N1 highly pathogenic avian influenza virus (HPAIV) in lactating dairy cattle in the United States, with high viral titers in raw milk, has raised concerns about zoonotic transmission through unpasteurized milk and dairy products. While viral inactivation during pasteurization is documented, data on persistence in raw-milk cheeses remain limited. This study evaluated the survival of avian influenza viruses (AIVs), both low pathogenic (LPAIV, H1N1) and highly pathogenic (HPAIV, H5N1), during the production and ripening of Grana-type hard cheeses from raw cow’s milk. Experimental cheesemaking was carried out with milk artificially contaminated with A/duck/Italy/281904-2/06 (H1N1; 10^7.75 EID₅₀/mL) or A/duck/Italy/326224-2/22 (H5N1 clade 2.3.4.4b; 10^6.75 EID₅₀/mL). Cheeses were manufactured under Parmigiano-Reggiano standards and ripened 30 days at 5–6 °C. Viral detection in finished cheeses was performed using inoculation in specific-pathogen-free embryonated chicken eggs (SPF-ECEs), hemagglutination (HA) assay, and monoclonal antibody-based ELISA. No infectious virus was detected in cheese samples after two blind passages in SPF-ECEs. Both HA and ELISA tests were negative, indicating complete viral inactivation. These results demonstrate that Grana-type cheese processing, including cooking, acidification, and ripening, effectively inactivates LPAIV and HPAIV. Findings support the microbiological safety of raw-milk hard cheeses regarding AIV, contributing to risk assessment and food safety policies. Full article

The H3N8 low pathogenic avian influenza virus (LPAIV) exhibits broad host tropism, infecting diverse avian and mammalian species, raising concerns about its zoonotic potential. Following the emergence of human infections with H3N8 LPAIV in China, including a fatal case, we investigated the epidemiological and virological characteristics of this virus in Guangdong Province. In 2022, a serological survey revealed H3N8 seroprevalence rates of 10.85% in farmed chickens and 7.97% in ducks. We isolated three H3N8 viruses, designated as A/chicken/Qingyuan/22/2022 (H3N8); A/chicken/Qingyuan/31/2022 (H3N8); and A/chicken/Qingyuan/15/2022 (H3N8), and found that these chicken isolates, like the human isolate A/Changsha/1000/2022, share the same E190 residue. This residue can synergize with sites such as Q226 and G228 to enhance binding affinity for SAα-2,6-Gal. Additionally, they harbor the three amino acid residues N193, W222, and S227. Among these, N193 has the potential to form hydrogen bonds with α2-6-linked glycans, while W222 and S227 may alter the conformational flexibility of the 220-loop. These two effects collectively endow the H3N8 isolates with dual receptor-binding properties. These findings suggest a shift in receptor specificity, potentially facilitating viral adaptation to mammalian hosts. Characterization of viral genome detection dynamics, and histopathology in animal models further elucidated the viral infection dynamics. Our study provides critical insights into the evolutionary trajectory and zoonotic potential of the H3N8 LPAIV. Full article