#18,989
While the above graphic from the USDA's National Milk Testing Strategy (NMTS) website hasn't been updated to show it yet, late yesterday the USDA announced that Wisconsin - the second-largest milk producer in the U.S. - has at least one herd that has tested positive for HPAI H5N1.
First, the USDA's announcement, after which I'll have a bit more.
USDA Confirms Highly Pathogenic Avian Influenza in a Dairy Herd in Wisconsin
Contact: aphispress@usda.gov
Milk Supply Safe; Considered Low Risk to Human Health and Safety
WASHINGTON, DC- December 14, 2025 – Today, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) National Veterinary Services Laboratories (NVSL) confirmed via PCR (polymerase chain reaction) and ELISA (Enzyme-Linked Immunosorbent Assay) assay a detection of highly pathogenic avian influenza (HPAI) H5 clade 2.3.4.4b in a dairy cattle herd in Wisconsin. APHIS will complete genetic sequencing and announce final results as soon as they are available. This confirmation was a result of routine National Milk Testing Strategy testing, not pre-movement surveillance.
This marks the first known case of HPAI in cattle in Wisconsin. While dairy cattle in a total of 18 states have been infected since the start of the outbreak in March 2024, APHIS has seen cases in only a small number of states this year. APHIS is working closely with the Wisconsin Department of Agriculture, Trade, and Consumer Protection to conduct additional on-farm investigations, diagnostic testing, and epidemiological data collection to better understand the detection and prevent further disease 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. 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.
This detection does not pose a risk to consumer health or affect the safety of the commercial milk supply. The U.S. Food and Drug Administration is confident that pasteurization is effective at inactivating HPAI virus, and that the commercial, pasteurized milk supply is safe. Dairies are required to send only milk from healthy animals into processing for human consumption; milk from impacted animals is being diverted from the commercial milk tank or destroyed so that it does not enter the human food supply.
According to the U.S. Centers for Disease Control and Prevention (CDC), HPAI viruses circulating in birds and U.S. dairy cattle pose a low risk to the general public in the United States. However, people who have job-related or recreational exposures to infected birds or mammals are at higher risk of infection and should take appropriate precautions outlined in CDC guidance.
While reports of infected dairy herds have dwindled markedly during the second half of 2025, the USDA does not publish data on reinfected herds, as noted below by the California Department of Food & Agriculture website, and it isn't entirely clear what percentage of U.S. herds are currently tested on a regular basis.
National Detections
This nationwide outbreak of H5N1 Bird Flu began in poultry in 2022 and was first detected in US dairy cattle in March 2024. All national detections in cattle can be found on the USDA website at: HPAI Confirmed Cases in Livestock | Animal and Plant Health Inspection Service (usda.gov). All national detections in poultry can be found on the USDA website at: Confirmations of Highly Pathogenic Avian Influenza in Commercial and Backyard Flocks | Animal and Plant Health Inspection Service (usda.gov)
Note: The USDA website reports new (first time detections) in dairies; it does not capture when a herd is cleared, ongoing cases, or reinfections on premises that had previous detections.
It will be of considerable interest to learn which genotype of HPAI H5N1 has been detected. During all of 2024, only genotypes B3.13 was detected in cattle, but in early 2025 genotype D1.1 was reported in at least 2 states.
For more information on the USDA's National Milk Testing Strategy you may wish to visit:
