The U.S. Department of Agriculture has confirmed the first case of highly pathogenic avian influenza (HPAI) in a Wisconsin dairy herd. This is the state’s first detection in cattle since the virus began affecting herds in 2024.
Federal veterinarians found the virus during routine sampling under the National Milk Testing Strategy. The National Veterinary Services Laboratories used PCR and ELISA tests to verify the results. USDA will share full genetic sequencing once it finishes the analysis.
Although 18 states have reported HPAI in dairy cattle since last year, new detections in 2025 have stayed relatively limited. Even so, USDA and the Wisconsin Department of Agriculture, Trade, and Consumer Protection have already begun on-farm investigations. They are collecting diagnostic samples and tracing possible sources to prevent further spread.
Biosecurity Still the Best Defense
USDA stressed that this detection does not change the national plan to contain and remove HPAI from cattle herds. Strong biosecurity remains the most effective way to block the virus. Because of this, producers are encouraged to review and strengthen daily practices, limit animal movement, reduce wildlife exposure, and monitor workers and equipment entering cattle areas.
If cattle show any unusual illness, or if producers notice sick or dead wildlife near barns or water sources, USDA urges them to call their state veterinarian right away.
Commercial Milk Supply Remains Safe
USDA also emphasized that this case does not affect the safety of commercial milk. Pasteurization destroys the virus, and regulations already require processors to accept milk only from healthy cows. As a result, milk from affected animals is diverted or destroyed and never enters the food chain.
Public Health Risk Remains Low
According to the U.S. Centers for Disease Control and Prevention, the risk to the general public remains low. However, people who work directly with infected animals—such as dairy workers, veterinarians, or wildlife staff—should continue to follow CDC protective guidelines. These steps include wearing proper protective equipment and reporting symptoms quickly.
What Dairy Producers Can Do Now
To reduce risk on their farms, producers should:
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Strengthen biosecurity plans and review them with employees
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Limit visitors, vehicles, and wildlife access to cattle areas
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Watch cows closely for sudden drops in production or changes in behaviour
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Report illness immediately to a state veterinarian
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Keep equipment, boots, and tools clean between barns or pens
USDA will release more information as genetic sequencing and trace-out work continue.
