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.

This study was initiated to determine the interaction between two infectious bursal disease virus (IBDV) strains in the early stages of infection by detection and quantification of IBDV RNA in lymphoid and non-lymphoid tissues. SPF chickens were inoculated with single infection or dual infection by the mild strain B87 followed by the pathogenic strain BC6/85 at 0, 1, 2, and 3 days post-inoculation (dpi) with B87. Real-time RT-PCR assays were developed to examine the viral loads of the tissues collected at various time intervals. The results reveal that B87 could delay the time point of positive detection of the BC6/85 strain in the bursa of Fabricius from 1 dpi to 3 dpi, indicating that B87 interfered with the replication of BC6/85. The interference occurred when BC6/85 was inoculated at 2 dpi and 3 dpi with the B87 strain. Moreover, BC6/85 could affect the proliferation and duration of B87 in SPF chickens. The rates of positive detection for B87 decreased significantly during dual infection. The investigation of the interaction between the two strains is important for the implementation of appropriate control measures.

The gut microbiota, often referred to as the “forgotten organ”, plays an indispensable role in maintaining host physiological metabolism, immune function, and nutrient absorption. Moreover, the gut microbiome serves as a critical biological barrier against viral infections and is increasingly recognized as a potential target to augment antiviral therapies. Recent studies have revealed that microbial ligands and metabolites derived from the gut microbiota are pivotal in modulating respiratory immune responses, providing compelling evidence of the complex interaction network between microorganisms and the host, particularly the signaling pathways linking the gut to distal organs such as the lungs. This review examines the communication and regulatory mechanisms between the gut microbiota and pulmonary mucosal surfaces during influenza virus infection, emphasizing how gut microbial communities and probiotics influence host immune responses, promote the production of immune-related molecules, and enhance antiviral defenses. The aim is to provide comprehensive insights into the gut–lung axis and its implications for respiratory health.

Avian influenza, a disease caused by avian influenza virus (AIV), mainly infects birds but can also infect mammals, which poses a serious threat to public health. Therefore, thorough understanding of its pathogenic mechanism and the identification of antiviral targets are essential for the prevention, control, and treatment of AIV. The polymerase acidic protein (PA) is a core component of the viral RNA-dependent RNA polymerase complex and plays a central role in viral transcription through its cap-snatching activity during early infection. We employed a multi-omics approach combining transcriptome analysis with PA interaction proteomics to characterize host responses during AIV infection and explore the PA–host interaction network. Transcriptomics revealed a polarized host response marked by activated translation-related processes, mitochondrial energy metabolism, and innate immune signaling, alongside broad suppression of nuclear transcriptional regulation and cell cycle pathways. Immunoprecipitation–mass spectrometry identified host proteins associated with PA that were enriched in RNA metabolism, ribosome biogenesis, and protein homeostasis. Integrative analysis of transcriptomic and interactome data, along with protein–protein interaction network analysis, prioritized a subset of high-confidence PA-interacting host factors. Among these, ribosomal protein RPS27A was validated to interact with PA and to support viral replication during early infection in this study.