Two decades (2005 to 2025) of avian influenza research trends, knowledge gaps and distribution of emerging H5N1 2.3.4.4b clade in South Asia.

Avian influenza virus (AIV) remains a persistent zoonotic and economic threat in South Asia, yet a comprehensive understanding of its research trajectory, outbreak patterns, and viral evolution in the region remains limited. This study integrates bibliometric, epidemiological, metadata, and phylogenetic analyses to assess two decades (2005–2025) of AIV research and H5N1 dynamics in South Asia. Bibliographic records were retrieved from Scopus and analysed using VOSviewer and Biblioshiny, while hemagglutinin (HA) gene sequences of H5N1 clade 2.3.4.4b were obtained from GISAID and analysed using maximum-likelihood phylogenetic tree. A total of 858 documents were identified, exhibiting a strong upward research trend (R²=0.90), with peak outputs between 2021 and 2024; primary research articles dominated (84.9%), and Bangladesh, India, and Pakistan emerged as the most productive countries and institutional hubs. Keyword evolution revealed sustained focus on avian influenza, H5N1, poultry, and Bangladesh, alongside the post-2020 emergence of One Health, zoonoses, and mutation-related themes. Epidemiological synthesis showed 18 confirmed human H5N1 cases reported between 2005 and 2025, predominantly in Bangladesh, indicating low but recurrent spillover events. Phylogenetic analysis of 267 clade 2.3.4.4b HA sequences revealed multiple well-supported country- and time-specific clades, with Bangladesh acting as a major center of viral persistence and evolution, particularly in domestic ducks, while cross-country clustering among Bangladesh, India, Sri Lanka, and the Maldives suggests regional viral movement likely mediated by migratory birds and poultry trade networks. Collectively, these findings highlight an interconnected H5N1 ecosystem shaped by surveillance intensity, host ecology, and transboundary transmission, underscoring the need for strengthening One Health–oriented surveillance, cross-border collaboration, and sustained genomic monitoring in South Asia.