04 March 2026
A comprehensive international report has documented the ongoing and expanding panzootic of highly pathogenic avian influenza (HPAI) H5 clade 2.3.4.4b affecting a wide range of wild bird and mammal species across multiple continents between October 2020 and September 2024. The virus, a member of the Goose/Guangdong lineage, has demonstrated unprecedented geographic expansion and an increasingly broad host range since acquiring enhanced transmission efficiency among wild birds during 2020–2021.
Outbreaks have frequently been associated with high mortality rates, posing additional conservation threats to vulnerable wildlife populations already facing numerous environmental pressures. During the reporting period, the virus was detected across Asia, the Middle East, Europe, and Africa. HPAI H5 was first identified in North America in late 2021, subsequently spread to South America by late 2022, and reached the Subantarctic and Antarctic regions by October 2023. As of September 2024, no cases had been reported in Oceania.
Seasonal peaks of infection were observed in the Northern Hemisphere, largely coinciding with waterfowl migration and seabird breeding cycles. These outbreaks have resulted in substantial mortality events among waterfowl, seabirds, raptors, and pinniped species. Molecular analyses of viral genomes have clarified patterns of spread and viral genotypes, confirming ongoing viral evolution largely constrained to avian-adapted phenotypes.
The report highlights significant gaps in current wildlife surveillance systems, which primarily rely on sampling sick or dead animals and therefore underrepresent apparently healthy populations. This limitation restricts a comprehensive understanding of viral circulation and its ecological impact.
Key recommendations include developing coordinated, flyway-based surveillance programs targeting both wild birds and mammals; improving reporting and estimation of wildlife mortality events in international databases such as the World Animal Health Information System (WAHIS); strengthening data sharing and long-term monitoring of populations severely affected by HPAI; implementing policies to reduce recurrent outbreaks in poultry and farmed mammals in order to minimize spillover into wildlife; and reinforcing One Health approaches to better protect wildlife populations while addressing zoonotic risks.
