Avian influenza, or bird flu, is a viral disease that primarily affects birds, especially wild waterfowl and poultry. Highly Pathogenic Avian Influenza (HPAI) refers to virus strains that spread rapidly and cause high mortality. Some strains, like H5N1 and H7N9, can infect mammals, including humans, through contact with infected birds and contaminated surfaces, or inhalation of viral particles. Minimizing its spread is critical as HPAI continues to mutate, potentially increasing its ability to infect new hosts. In January 2025, the first U.S. human death from H5N1 was reported.

The recent outbreak of Highly Pathogenic Avian Influenza (HPAI) H5N1 began in North America during late 2021, spreading globally through major migratory flyways connecting the continent with regions in South America, Europe, and Asia.

Large-scale die-offs have been reported, and the culling of millions of domestic poultry has caused significant disruptions in global food production and rising market prices. Additionally, more than 48 mammal species have contracted the HPAI H5N1 virus during this outbreak, with marine mammals, primarily seals and sea lions, experiencing mass die-offs.

The USDA collaborates with state, Tribal, and other federal agencies to monitor HPAI cases in the U.S. in wild  birds, poultry, mammals, and livestock, while the CDC monitors human HPAI cases.