Review of the Epizootic and Epidemic Situation regarding Highly Pathogenic Avian Influenza in Russia and Globally in 2025

In 2025, high epizootic activity of highly pathogenic avian influenza virus (HPAIV) persisted globally, as evidenced by more than 7,000 outbreaks reported in poultry and wild birds across 75 countries, resulting in mortality or culling of birds exceeding 98 million specimens. The majority of outbreaks worldwide were associated with HPAIV A(H5N1) clade 2.3.4.4b, which has remained the predominant lineage in global circulation since 2021. In addition to the dominant A(H5N1) clade 2.3.4.4b subtype, circulation of other highly pathogenic subtypes was observed, including A(H5N5), A(H5N2), A(H5N8), and A(H5N9), as well as A(H7), indicating ongoing evolution of avian influenza viruses in natural and anthropogenic ecosystems. In the United States and several other countries, HPAIV A(H5N1) caused numerous infections in wild and domestic mammals as well as in humans. In 2025, the world’s first human case of A(H5N5) influenza was documented in the United States. A total of 74 zoonotic HPAIV human infections were reported globally in 2025, including 32 cases caused by A(H5) viruses of various clades (2.3.4.4b, 2.3.2.1e, 2.3.2.1a), reflecting a continuing increase in interspecies transmission that poses a potential public health threat. In the Russian Federation, high epizootic activity of HPAIV persisted throughout 2025, with outbreaks caused by A(H5N1) clade 2.3.4.4b viruses reported in both wild and domestic birds. Notably, in the Russian Far East, circulation of an A(H5N1) virus carrying mammalian-adaptive mutations associated with increased virulence in mammals was detected. Additionally, amino acid substitutions in antigenic sites were identified in several A(H5N1) isolates. Despite ongoing virus evolution, no substantial alterations in the antigenic properties of HPAIV A(H5N1) strains circulating in the Russian Federation have been observed to date.