Federal officials confirm Wisconsin’s first case of bird flu in a dairy cattle herd

Officials have detected highly pathogenic avian influenza (HPAI) H5N1 in a dairy cattle herd in Wisconsin, according to the US Department of Agriculture’s (USDA’s) Animal and Plant Health Inspection Service (APHIS). The detection marks the state’s first known case of H5N1.¹

The case, belonging to the H5 clade 2.3.4.4b, was confirmed via polymerase chain reaction (PCR) and ELISA (Enzyme-Linked Immunosorbent Assay) by the National Veterinary Services Laboratory on December 14, 2025. Officials detected the case through ongoing nationwide surveillance of milk samples as part of the USDA’s National Milk Testing Strategy, a mandatory testing system first established in early December 2024.²

In a news release announcing the H5N1 detection, the USDA said APHIS will finish genetic sequencing and announce the final results as soon as they are available. According to the USDA, federal animal health officials are working with Wisconsin agriculture authorities to conduct further on-farm investigations, expand diagnostic testing, and collect epidemiological data to better understand the detection and limit further spread.

“The detection does not change USDA’s HPAI eradication strategy. Biosecurity is still key to mitigating the risk of disease introduction or spread between premises,” the USDA wrote in an announcement.¹ “APHIS recommends enhanced biosecurity measures for all dairy farms. Producers should immediately report any livestock with clinical signs, or any unusual sick or dead wildlife, to their state veterinarian.”

The detection does not pose a risk to consumers or the commercial milk supply, the USDA said. According to the FDA, pasteurization effectively inactivates the HPAI virus, and milk from affected animals is diverted or destroyed before it can enter the food chain.¹

To date, dairy cattle across 18 states have been infected with H5N1 since the outbreak began in March 2024. This fall, Nebraska also saw its first case of H5N1 in dairy cattle,³ and Iowa and Minnesota experienced an H5N1 outbreak in poultry on commercial farms.⁴ On October 2, 2025, Wisconsin also reported an H5N1 poultry outbreak in a commercial flock in Jefferson County, which housed more than half a million birds.⁴ In September 2025, Wisconsin had another outbreak in poultry that affected more than 3 million commercial poultry.⁴

Although HPAI viruses in birds and US dairy cattle pose a low risk to humans, those who may experience exposure to infected birds or mammals, such as veterinarians and veterinary staff, face a higher risk of infection. To lower exposure, the CDC recommends⁵:

• Understanding that avian influenza viruses can infect humans through the eyes, nose, mouth, or by inhalation.
• Developing and following a workplace health and safety plan designed to reduce exposure risks.
• Participating in site-specific hazard assessments to identify potential exposures and exposure levels tied to specific work tasks and settings.
• Using practical safeguards, including physical controls and workplace practices that limit exposure.
• Wearing personal protective equipment (PPE) when required and using it correctly.
• Following control and PPE recommendations based on whether exposure risk is low, medium, or high.
• Being familiar with and complying with applicable Occupational Safety and Health Administration (OSHA) or state OSHA requirements.

References

1. USDA confirms highly pathogenic avian influenza in a dairy herd in Wisconsin. News release. US Department of Agriculture. December 14, 2025. Accessed December 15, 2025.
2. USDA announces new federal order, begins national milk testing strategy to address H5N1 in dairy herds. News release. US Department of Agriculture. December 6, 2024. Accessed December 15, 2025. https://www.usda.gov/about-usda/news/press-releases/2024/12/06/usda-announces-new-federal-order-begins-national-milk-testing-strategy-address-h5n1-dairy-herds
3. Bautista-Alejandre A. USDA confirms first case of bird flu in Nebraska dairy cattle. dvm360. September 16, 2025. Accessed December 15, 2025. https://www.dvm360.com/view/usda-confirms-first-case-of-bird-flu-in-nebraska-dairy-cattle
4. Bautista-Alejandre A. New bird flu outbreaks reported in poultry across 3 Midwestern states. dvm360. October 6, 2025. Accessed December 15, 2025. https://www.dvm360.com/view/new-bird-flu-outbreaks-reported-in-poultry-across-3-midwestern-states
5. Reducing exposure for workers to avian influenza A viruses. US Centers for Disease Control and Prevention. May 6, 2025. Accessed December 15, 2025. https://www.cdc.gov/bird-flu/worker-safety/index.html