United States 2022 – HPAI H5N1 multi-year epizootic and poultry and dairy depopulations
Enforcement Action
In Effect
February 8, 2022
Summary
On 8 February 2022, USDA Animal and Plant Health Inspection Service (APHIS) announced the first confirmed HPAI A(H5N1) detection in US commercial poultry since 2020, initiating what became the largest avian influenza epizootic in US recorded history. From January 2022 through 4 June 2024, HPAI A(H5)/A(H5N1) was detected in more than 1,140 commercial and backyard flocks affecting more than 96.5 million birds across 48 states, and in more than 9,300 wild bird detections in all 50 states and territories. From 25 March 2024, HPAI H5N1 was confirmed in dairy cattle in Texas and Kansas — the first confirmed detection of H5N1 in US dairy herds — subsequently spreading to 689 dairy herds across 15 states by 2 December 2024. USDA APHIS and state animal health authorities implemented compulsory flock depopulation, farm-level quarantine, and movement controls on live poultry and dairy cattle as standard disease control responses. The epizootic remained ongoing beyond 2024, with continued wild bird, poultry, dairy, and sporadic human detections reported through early 2025.
Background Context
The 2022–2024 H5N1 epizootic was preceded by detection of HPAI H5N1 clade 2.3.4.4b in a great black-backed gull in Canada in late 2021, with subsequent spread into the United States via migratory flyways first detected in December 2021. Viral genomic analysis indicates the virus reassorted with North American avian influenza viruses as it spread across US flyways, generating multiple genotypes. Before January 2022, the last HPAI A(H5) detections in the United States had occurred in 2016. The earlier 2014–2015 US HPAI H5N2 outbreak — documented in a separate Development record — had resulted in expanded biosecurity guidance, indemnity programmes, and response frameworks that formed the operational basis for the 2022–2024 response. From 2022 onward, the virus circulated in wild birds year-round rather than seasonally, maintaining a continuous reservoir capable of repeated introductions into poultry flocks. The dairy emergence in March 2024 was consistent with a single wild-bird-to-cattle introduction event followed by cattle-to-cattle and herd-to-herd spread; this represented a novel cross-species extension of the epizootic not documented in the 2014–2015 outbreak.
System Impact
Direction
Reduces Exploitation
Type
Changes Scale
Significance
High
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
Assigned Reduces Exploitation (impact direction) based on the documented depopulation of more than 96.5 million birds across more than 1,140 flocks — the largest avian influenza depopulation in US recorded history, exceeding the 2014–2015 H5N2 outbreak in scale. The scale change is temporary: the epizootic produced repeated depopulation and restocking cycles across a multi-year period rather than a sustained or structural contraction of the US poultry industry. Each confirmed flock depopulation reduced the number of animals in that production unit during the operative period; restocking followed decontamination and clearance. The dairy cattle dimension — 689 infected herds across 15 states — added documented scale disruption in a second exploitation system, though individual cow mortality and culling figures at herd level are not reported in sources consulted.
Assigned Changes Scale (impact type) because the primary documented mechanism is mass compulsory depopulation of infected flocks and herds directly reducing live animal numbers in affected production units.
Assigned High significance because 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.
Within The System
Key Actors
USDA Animal and Plant Health Inspection Service (APHIS) led federal animal disease surveillance, reporting, and control, publishing flock-level HPAI detections and implementing compulsory depopulation and movement-control protocols. The Centers for Disease Control and Prevention (CDC) provided technical reports, human case tracking, and risk assessments including the June 2024 technical report summarising US detections in birds, mammals, and humans. State animal health authorities and state departments of agriculture implemented local disease response and quarantine in coordination with USDA APHIS; Texas and Kansas were among the first states with confirmed dairy herd infections. USDA APHIS National Veterinary Services Laboratories (NVSL) conducted virus detection, sequencing, and genotyping. The World Organisation for Animal Health (WOAH) received official outbreak notifications; the World Health Organization (WHO) published Disease Outbreak News on the April 2024 human case. The US Poultry & Egg Association produced epidemiologic analyses of the outbreak. Specific commercial poultry and dairy companies are not named in primary surveillance documents.
Editorial Correction Notice
Scale & Prevalence — dairy cattle: The 689 dairy herds confirmed infected by 2 December 2024 is reported at herd level; individual cow mortality and culling figures within affected herds are not reported in sources consulted. Total cattle affected across the dairy dimension of this epizootic requires consultation of USDA APHIS herd-level data or CRS reports providing individual animal counts.
Scale & Prevalence — poultry: The 96.5 million figure covers detections through 4 June 2024. The epizootic continued beyond this date; total poultry depopulated through the full epizootic period to end-2024 and beyond would exceed this figure. Updated USDA APHIS cumulative totals should be consulted before this record moves to Review.
Current status: The epizootic remained ongoing beyond 2024, with continued detections in wild birds, poultry, dairy herds, and sporadic human cases through early 2025. No official endpoint or transition to endemic status has been declared in sources consulted.
Related record: The 2014–2015 HPAI H5N2 outbreak is documented in a separate Development record. That outbreak established the response framework applied in the 2022–2024 epizootic.
Affected animals: Wild bird detections (9,300+ in all states) and wild mammal detections (31 states) are documented in the research but are not included in the affected_animals field because wild bird and wild mammal populations are not Animals CPT records. The epizootic’s wild reservoir dimension is documented in Background Context.
Development type: Classified as Enforcement Action rather than Government Policy because the primary development is the activation of existing USDA APHIS disease control powers against confirmed detections, not the announcement of a new policy instrument. Federal orders affecting dairy cattle movement are Government Policy instruments within the broader Enforcement Action response framework.
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