New Avian Influenza Spillover in Wisconsin: What Pest Control Pros Need to Know

The U.S. Department of Agriculture (USDA) recently confirmed a new case of highly pathogenic avian influenza (HPAI) in a Wisconsin dairy herd. This case represents a fresh spillover from wildlife to cattle, unrelated to previous outbreaks.

According to USDA’s Animal and Plant Health Inspection Service (APHIS), this is a separate introduction of the virus, rather than transmission from previously infected herds.

Virus Confirmed Through Advanced Testing

Whole genome sequencing conducted by the National Veterinary Services Laboratories (NVSL) on December 17 identified the virus as H5N1 clade 2.3.4.4b, genotype D1.1. USDA officials emphasized that these advanced diagnostics allowed them to quickly determine the virus strain and its wildlife origin.

How This Case Differs From Past Outbreaks

Previously, most detections of bird flu in U.S. dairy cattle were linked to animal movements from a 2023 spillover in Texas (B3.13 strain). Early in 2025, isolated spillovers involving the D1.1 strain occurred in Nevada and Arizona. The Wisconsin case adds another independent wildlife-to-cattle transmission to the growing list.

What Pest Control Professionals Should Note

Wild birds continue to be a primary vector for HPAI spillover events. For pest control experts serving farms, dairy operations, and commercial facilities, this reinforces the importance of:

• Bird exclusion: Use physical barriers or deterrents to prevent wild birds from accessing feed, storage, and livestock areas.

• Sanitation: Remove spilled feed and water sources that attract birds to limit potential virus transmission.

• Monitoring: Stay alert for unusual bird die-offs or wildlife activity around farms.

Products like Avitrol Medium Corn Chops can help manage pest birds. The medium-ground corn provides a palatable taste for smaller species like sparrows while effectively deterring populations from sensitive areas.

Avitrol Easy Blend

This product is labeled for Pigeons, House Sparrows, Starlings, Blackbirds, Cowbirds, and Grackles. With a permit in the US, it can also be used to treat Crows, Seagulls, Ravens, Magpies, and Vultures. This product is used to permanently discourage flocks of birds from gathering in unwanted places.

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Containment and Safety Updates

The Wisconsin case was detected through USDA’s National Milk Testing Strategy, designed for early infection surveillance. No additional herd infections have been reported, and APHIS indicates the situation appears contained.

Importantly, consumer health and the milk supply remain safe:

• Pasteurization kills the virus

• Milk from affected animals is diverted or destroyed

• Standard food safety protocols remain unchanged

USDA reassures that commercial milk remains safe, and nationwide monitoring continues.

Key Takeaway for Pest Pros: Wildlife, particularly wild birds, remain a key source of disease spillover. Proactive bird control on farms and commercial operations is not just about property protection - it’s a critical step in biosecurity and public health.