California Department of Food & Agriculture reports H5N1 surge in poultry and significant dairy detections; officials describe surveillance, testing and control

State agricultural officials told the Veterinary Medical Board that the Eurasian strain of avian influenza (H5N1) has produced the largest outbreak in California history and is behaving differently in dairy cattle than in poultry, prompting ongoing surveillance, targeted quarantine and research.

CDFA State Veterinarian staff said the virus first appeared in California dairy herds in late summer 2024 and that, as of their update, hundreds of dairies had tested positive or presumptively positive. Many infected herds are under state quarantine that limits animal movement and requires biosecurity. The department reported that some dairies have cleared quarantine after three consecutive weeks of negative bulk‑tank tests, and others remain in multi‑week testing protocols.

Poultry impacts in recent months were described as dramatic: CDFA presented figures showing more than 10 million commercial poultry (layers, broilers, turkeys and ducks) lost in the current surge and earlier waves combined. The department said the latest wave has produced higher weekly detections than prior waves and that whole‑genome sequencing in some poultry cases suggests spillover from infected cattle herds as well as the usual introductions from wild birds.

Key points officials told the board: - Dairy: CDFA identified a large number of affected dairies (hundreds in the state) and described a testing program that includes weekly or more frequent bulk‑milk PCR surveillance; milk testing and mammary gland tropism make bulk milk an effective surveillance sample. CDFA staff said infected dairies often show high morbidity but relatively low mortality and that their teams are working with USDA and university partners to study disease dynamics and post‑infection outcomes. Many dairies are in the process of clearing quarantine via serial negative milk tests.

- Poultry: The current outbreak wave has outpaced previous ones and involved mandatory movement‑control areas, testing and biosecurity. CDFA reported tens of thousands to millions of birds lost per category in recent outbreaks and said environmental testing of barns is part of the process before restocking is permitted.

- Testing workload and labs: CDFA said weekly submissions to state and federal labs number in the thousands for dairy and poultry combined; workload and turnaround time are significant operational issues. CDFA is using California Animal Health and Food Safety Laboratory (Davis) and accredited out‑of‑state labs.

- Research and response: The department described more than 30 coordinated research streams exploring virus ecology, surveillance optimization and interventions, and a longitudinal field study with university partners (UC Davis and Colorado State) collecting milk, serum and environmental samples to better understand infection dynamics in cattle. Preliminary findings include frequent detection in milk, occasional detection in urine and serum, and low yield from nasal swabs — findings that shape surveillance strategy.

- Public health and occupational safety: CDFA and public‑health partners said the most observed human infections in California have been conjunctivitis in dairy workers with close animal exposure; agencies continue to provide PPE guidance and free PPE stockpiles to farms and animal workers in affected zones.

- Pet and food safety: CDFA emphasized that pasteurization inactivates the virus and that pasteurized dairy products present no food‑safety risk. The department said raw‑milk products present a different risk profile and announced increased testing/diversion-to‑pasteurization policies for raw‑milk dairies in higher‑risk zones. CDFA also said it is coordinating with public‑health and wildlife agencies on cases in companion animals and wildlife.

Why this matters: The H5N1 outbreak touches multiple parts of the animal health system — commercial dairy, backyard poultry, wildlife and public health — with direct effects on agricultural production, animal welfare and supply chains. CDFA told the board that its work is as much research and epidemiology as emergency response, and that the virus’s behavior in cattle requires new policy and operational responses.

What the board asked and next steps: Board members asked about lab capacity, staff surge and funding; CDFA said it is tapping USDA surge capacity, is reallocating state staff where possible and is discussing longer‑term gaps with budget authorities. CDFA said it will continue to brief the board as surveillance and research produce new guidance and will coordinate on outreach efforts to veterinarians, pet owners and producers.

Board members and staff urged clear public messaging on pasteurization, raw‑milk risks and reporting channels for suspect flocks or sick animals. CDFA also recommended that veterinarians report suspect cases and that practitioners follow PPE and biosecurity guidance published by public‑health and agricultural authorities.