In October 2021, a wild bird-origin H3N8 influenza virus-A/Chinese pond heron/Jiangxi 5-1/2021 (H3N8)-was isolated from Chinese pond heron in China. Phylogenetic and molecular analyses were performed to characterize the genetic origin of the H3N8 strain. Phylogenetic analysis revealed that eight gene segments of this avian influenza virus H3N8 belong to Eurasian lineages. HA gene clustered with avian influenza viruses is circulating in poultry in southern China. The NA gene possibly originated from wild ducks in South Korea and has the highest homology (99.3%) with A/Wild duck/South Korea/KNU2020-104/2020 (H3N8), while other internal genes have a complex and wide range of origins. The HA cleavage site is PEKQTR↓GLF with one basic amino acid, Q226 and T228 at HA preferentially bind to the alpha-2,3-linked sialic acid receptor, non-deletion of the stalk region in the NA gene and no mutations at E627K and D701N of the PB2 protein, indicating that isolate A/Chinese pond heron/Jiangxi 5-1/2021 (H3N8) was a typical avian influenza with low pathogenicity. However, there are some mutations that may increase pathogenicity and transmission in mammals, such as N30D, T215A of M1 protein, and P42S of NS1 protein. In animal studies, A/Chinese pond heron/Jiangxi 5-1/2021 (H3N8) replicates inefficiently in the mouse lung and does not adapt well to the mammalian host. Overall, A/Chinese pond heron/Jiangxi 5-1/2021 (H3N8) is a novel wild bird-origin H3N8 influenza virus reassortant from influenza viruses of poultry and wild birds. This wild bird-origin avian influenza virus is associated with wild birds along the East Asian-Australasian flyway. Therefore, surveillance of avian influenza viruses in wild birds should be strengthened to assess their mutation and pandemic risk in advance.

MicroRNAs (miRNAs) are key regulators of gene expression, exerting post-translational control through mRNA silencing or degradation. These molecules play pivotal roles in host–pathogen interactions, particularly in modulating antiviral immune responses. The global public health threat posed by the H5N1 Highly Pathogenic Avian Influenza (HPAI) virus necessitates urgent exploration of novel therapeutic strategies. Our investigation revealed significant dysregulation of miR-18a-5p following influenza virus infection, observed consistently across both in vitro and in vivo models. Experimental evidence demonstrated that miR-18a-5p overexpression effectively inhibits H5N1 virus propagation through multiple mechanisms: (1) in vitro studies using A549 cells transfected with miR-18a-5p mimics showed a substantial reduction in viral replication; (2) animal models (mice and chickens) with elevated miR-18a-5p expression exhibited markedly suppressed AIV replication, reduced pathogenicity, and improved survival rates. The therapeutic potential of miR-18a-5p was particularly evident in its ability to significantly decrease mortality rates in H5N1-infected animals. Furthermore, this miRNA demonstrated robust protective effects against virus-induced lung damage, suggesting its dual role in both preventing and treating H5N1 infections. These findings position miR-18a-5p as a promising candidate for the development of broad-spectrum antiviral interventions, offering a novel strategic approach to combat this serious public health challenge.