Divergent early host transcriptional responses to H5N8 highly pathogenic avian influenza virus in chickens and ducks.

Highly pathogenic avian influenza viruses (HPAIVs) of the H5N8 subtype have caused severe outbreaks in poultry and wild birds worldwide. Disease outcome differs markedly between avian species: chickens typically develop acute infection with high mortality, whereas ducks often exhibit milder or delayed disease. The molecular basis underlying these species-specific differences in early host responses remains incompletely understood. To characterize early transcriptional responses to HPAIV infection, RNA sequencing (RNA-seq) was performed on lung tissues from chickens and ducks experimentally infected with H5N8 HPAIV at 24 hours post-inoculation (hpi). Differential gene expression analysis and functional enrichment analyses were conducted, and selected host genes were validated by quantitative real-time PCR. At 24 hpi, a comparable number of differentially expressed genes (DEGs) was identified in chickens and ducks; however, the organization of the transcriptional response differed markedly between species. Chickens exhibited a pathway-centered transcriptional profile dominated by innate immune and inflammatory signaling, whereas ducks displayed a more distributed and balanced transcriptional response spanning multiple functional categories. Functional enrichment analyses revealed strong activation of interferon- and cytokine-associated pathways in chickens, while transcriptional changes in ducks were dispersed across processes related to RNA metabolism, antiviral regulation, and cellular homeostasis. Among species-specific differentially expressed genes, MOV10L1 showed opposite regulation in these bird species. These findings demonstrate that early host responses to H5N8 HPAIV infection differ between chickens and ducks not only in gene identity but also in transcriptional organization. The distributed response architecture observed in ducks may contribute to controlled antiviral responses with limited immunopathology. This study provides a comparative transcriptomic framework for understanding species-specific host responses to HPAIV infection in poultry.