Update on Highly Pathogenic Avian Influenza (HPAI)
Today, the U.S. Department of Agriculture (USDA) announced information on the genetic sequencing of the highly pathogenic avian influenza (HPAI) that was detected in Dodge County, Wisconsin last week. Access USDA's press release here.
On December 17, the National Veterinary Services Laboratories (NVSL) completed whole genome sequencing and confirmed that the virus is H5N1 clade 2.3.4.4b genotype D1.1. Analysis indicates that this detection is a new spillover event from wildlife into dairy cattle, separate from previous events.
Some key points from USDA's news release include:
- Most detections in U.S. dairy herds have resulted from movements linked to the original spillover event that occurred in the Texas Panhandle in late 2023, involving the B3.13 strain.
- In early 2025, through the National Milk Testing Strategy, USDA detected two spillover events in Arizona and Nevada dairy herds. Both were identified early, with limited spread to other farms. These events involved the D1.1 strain.
- The Wisconsin herd, also detected through the National Milk Testing Strategy, represents a new, separate spillover event and involves the D1.1 strain. At this time, no additional dairy herds have been identified as infected in association with this event.
Wisconsin and the National Milk Testing Strategy (NMTS)
With help from industry partners, Wisconsin is sampling milk at the farm level for the mandatory USDA Animal and Plant Health Inspection Service (APHIS) NMTS. When Wisconsin began NMTS testing in May 2025, the goal was to test each farm approximately every month. Wisconsin achieved unaffected Gold Status under the NMTS in September 2025. In October, DATCP reduced its testing frequency to 50%.
Wisconsin will resume NMTS testing at a 100% frequency statewide. DATCP will continue to utilize milk samples that are already collected through existing, routine sampling to streamline the NMTS testing process. The DATCP HPAI in Dairy Cattle webpage will continue to be updated weekly as the testing continues.
Biosecurity and Monitoring
It is important to remain vigilant and utilize enhanced biosecurity measures.
H5N1 Protocol: What to Do if H5N1 is Confirmed on Your Dairy Farm
DATCP created a resource document in case of a detection of H5N1 on a dairy farm. The document is intended to serve as a general reference for industry, but individual needs and response actions may differ for H5N1 detections depending on the operation and specific circumstances. Access the H5N1 Protocol: What to Do if H5N1 is Confirmed on Your Dairy Farm document.
Human Health Precautions
Human cases of H5N1 have been reported following exposure to infected animals. Access the confirmed cases and exposure sources for human infections.
The Wisconsin Department of Health Services (DHS) advises those working with animals to take precautions and wear PPE per CDC guidance. According to the Centers for Disease Control and Prevention (CDC), the public health risk from HPAI detections remains low.
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