Clade 2.3.4.4b H5N1 highly pathogenic avian influenza detected in wild bird feces, Eastern Mongolia, 2024.

IMPORTANCE

Despite ongoing intercontinental spread of clade 2.3.4.4b H5N1 highly pathogenic avian influenza (HPAI), surveillance data from Mongolia -- a critical junction between Central and East Asian migratory flyways -- remain scarce, leaving a gap in understanding how viruses move between northern breeding areas and southern wintering grounds.

OBJECTIVE

We aimed to detect and genetically characterize HPAI viruses in wild bird populations in Mongolia and assess their relationship with viruses circulating in East Asia.

METHODS

Active surveillance was conducted at Ganga Lake, Mongolia, in October 2024. A total of 352 wild bird fecal samples were collected and tested for AIVs. Viral isolates were subtyped, whole-genome sequenced, and phylogenetically analyzed. Host species was identified using c oxidase I barcoding.

RESULTS

Sixteen AIVs were isolated, including one clade 2.3.4.4b H5N1 HPAI virus (M9-3) from whooper swan feces. Genomic analysis revealed M9-3 had > 99% similarity with Korean and Japanese H5N1 isolates reported in late 2024 and undergone recent reassortment and disseminated through migratory flyways.

CONCLUSIONS AND RELEVANCE: This is the first detection of clade 2.3.4.4b H5N1 in Eastern Mongolia in a fecal sample during late autumn. These findings underscore Mongolia's importance as a sentinel location for interregional HPAI dissemination.