State officials: Detection was routine bulk milk surveillance, not illness, strain not B3.13

MADISON, Wis. — Bird flu in dairy cattle is back in the national headlines after Wisconsin reported its first-ever case of highly pathogenic avian influenza (HPAI) in a dairy herd in Dodge County, which is situated about midway between Madison and Wilwaukee, and also more north.

The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) confirmed the detection on Dec. 14 when samples tested by the Wisconsin Veterinary Diagnostic Laboratory were verified by the National Veterinary Services Laboratories (NVSL).

Both DATCP and the USDA AHPIS said the detection was identified through routine bulk milk surveillance conducted under USDA’s national HPAI monitoring strategy, not through pre-movement testing for interstate cattle transport and not because the herd initially reported any sign of illness.

The affected farm has been quarantined, and any cattle showing signs of illness are being separated for further evaluation and treatment. DATCP is responding in coordination with USDA, FDA, CDC, and state partners.

In an email response to questions asked by Farmshine, a DATCP spokesperson said final strain identification is still pending but confirmed the virus is not the B3.13 strain, which is the strain of concern that has shown cow-to-cow transmission in other states. B3.13 has been associated with more pronounced clinical signs in dairy cattle, including sharp drops in milk production, drops in feed intakes and rumination, fever, and changes in the appearance of milk and manure.

USDA will announce the final strain results once genetic sequencing is complete. Other strains detected in cattle to-date, including D1.1, are believed to result from spillover from infected birds and have not shown sustained cow-to-cow transmission.

Federal and state agencies stressed there is no concern about the safety of the commercial milk supply. Milk sold commercially is pasteurized, and the CDC continues to consider the risk to the general public to be low.

USDA APHIS data show that while HPAI remains widespread in wild birds nationwide, APHIS reports “limited new detections in dairy cattle” in recent weeks with just one other detection in a California dairy herd in the past 30 days (Nov. 25). APHIS is working closely with Wisconsin’s DATCP to conduct additional data collection to better understand the detection and prevent further disease spread.

Cumulatively, since March 2024, HPAI has been detected on 1084 dairies in 19 states.

Importantly, most states have reported that recent dairy detections were identified through surveillance, not widespread illness.

Across the U.S., the response has been largely consistent, guided by USDA APHIS and state veterinarians:

Routine bulk milk surveillance is ongoing as a primary early-detection tool, even on farms without visible clinical signs.

Quarantine and movement controls are placed on affected premises, with restrictions lifted only after follow-up testing and veterinary review.

Enhanced biosecurity guidance is being emphasized, particularly limiting visitors, tightening protocols for service providers, and managing wildlife and birds around feed and water sources.

Producer outreach and education has increased, often through extension, dairy producer organizations.

States continue to remind producers that detections are not strain-specific on public dashboards, and that genetic sequencing results are communicated separately once available.

In a December 16 update, the Pennsylvania Center for Dairy Excellence reminded producers that enhanced biosecurity remains essential, especially in view of dairy proximity to poultry operations in the Commonwealth. CDE continues to offer free biosecurity kits and signage.