Surveillance and Whole-Genome Analysis of Low Pathogenic Avian Influenza Viruses from Wild Birds in Mongolia, 2025.

Mongolia lies at the intersection of major migratory flyways, the East Asian-Australasian Flyway (EAAF) and the Central Asian Flyway (CAF), serving as a pivotal region for avian influenza virus (AIV) transmission among wild bird populations across Eurasia. Continued surveillance in this region remains important for understanding AIV evolution and dissemination across migratory flyways. In this study, active surveillance was conducted in wild bird habitats in Mongolia during the summer of 2025 to investigate the genetic diversity of circulating AIVs. A total of 1656 fresh fecal samples were collected, resulting in the isolation of 13 viruses, including H3N8, H4N6, H10N8, and H12N5 subtypes. Whole-genome sequencing and phylogenetic analyses revealed high genetic diversity and extensive reassortment, with gene segments closely related to viruses circulating in East Asia, Southeast Asia, Central Asia, South Asia, Europe, and North Africa. Some isolates contained polymerase or nucleoprotein genes clustering within European lineages, whereas most retained Asian genomic backgrounds. These findings support the role of wild birds in Mongolia in facilitating the evolution and spread of AIVs across Eurasia, highlighting the need for continued genomic surveillance in this region.