NWHC Wildlife Health Bulletin - Avian Influenza Update

USGS National Wildlife Health Center

Wildlife Health Bulletin 2025-01

Summary

• The current HPAI outbreak in North America began in late 2021 and the virus has continued to circulate in North American wild birds (165 species affected) with sporadic spillover infections into North American wild mammals (27 species affected).
• The current outbreak has different transmission patterns than the 2014-2015 outbreak, notably, sustained transmission in wild birds and a broader host range including multiple previously uninfected species of wild birds, wild and domestic mammals, and humans.
• Waterfowl have emerged to be an important reservoir host in this outbreak; apparently healthy birds have regularly tested positive for HPAI virus during live-bird and hunter-harvest sampling.
• Since the current outbreak began in North America, HPAI has been detected in >1,600 poultry facilities in every state and Puerto Rico, nearly 1,000 dairy operations in 17 states, and 70 humans.
• The HPAI H5N1 virus remains avian-adapted, although sporadic mammalian mutations have been detected.