USDA APHIS and state animal health authorities implemented compulsory depopulation of all poultry in confirmed HPAI-positive flocks as a standard eradication measure. From January 2022 through 4 June 2024, more than 96.5 million birds were depopulated across more than 1,140 commercial and backyard flocks in 48 states. Wild bird surveillance documented more than 9,300 HPAI A(H5N1) detections in all 50 states and territories, confirming year-round nationwide wild reservoir presence. From 25 March 2024, H5N1 was confirmed in dairy cattle herds in Texas and Kansas; by 2 December 2024, 689 dairy herds across 15 states had confirmed infections. Federal orders affecting dairy cattle testing and interstate movement were implemented following the dairy emergence. Two human H5N1 cases were confirmed in the United States during this period — a poultry worker in April 2022 and a dairy worker with symptom onset on 27 March 2024 — with no sustained human-to-human transmission documented. Post-exposure monitoring of persons occupationally exposed to infected birds or dairy cattle was maintained by CDC and state and local public health departments throughout the epizootic.

Anticipated Effects

If USDA APHIS depopulation and movement-control protocols continue to be applied as written when new HPAI detections occur, confirmed poultry flocks would continue to be depopulated and subject to quarantine, with ongoing restocking cycles after decontamination, as long as the epizootic persists.

If federal orders affecting dairy cattle testing and interstate movement remain in force, dairy producers would continue to face testing requirements prior to moving cattle between herds and states, altering how and where dairy operations source and move animals.

If surveillance and biosecurity guidance issued during the outbreak are maintained across poultry and dairy operations, operators would continue to adjust on-farm practices — including access controls, separation from wild birds, and pre-movement testing — to reduce infection risk, without necessarily reducing overall long-term production capacity.

If spread of H5N1 in dairy herds persists and additional genotypic evolution occurs, the risk of further cross-species transmission events — including potential human exposure through occupational contact — would remain elevated above pre-epizootic baseline.

Significance Rationale

The epizootic affected 48 states simultaneously, produced the largest documented poultry depopulation in US history by animal count, extended into dairy cattle in a novel cross-species emergence, and required sustained multi-year, multi-species disease management across the entire US poultry and dairy sectors.