On February 11, 2025, the Arizona Department of Agriculture (AZDA), in collaboration with the United States Department of Agriculture (USDA), confirmed the first detection of H5N1 avian influenza in milk from a dairy herd in Maricopa County. As a precautionary measure, the facility is currently under quarantine. Unlike other detections involving the B3.13 genotype, this case involves the D1.1 genotype, and the affected cattle have not yet exhibited signs of illness. Should symptoms emerge, the animals will be isolated from the main herd.
This marks the second detection of H5N1 avian influenza in dairy cows within a little over a week, following recent national milk testing efforts that identified the virus in another herd in Nevada. The findings highlight the continued risk of H5N1 spillover into dairy cattle.
Developments in Oregon and Washington
Agricultural officials in Oregon and Washington have issued warnings about the potential risks associated with raw pet food. Testing of sick domestic cats from separate households in Multnomah County revealed that their infections were linked to contaminated pet food from the same company.
H5N1 Surveillance and Biosecurity Measures
On February 14, AZDA and the USDA Animal and Plant Health Inspection Service (APHIS) confirmed the H5N1 detection in Arizona’s dairy milk samples. The virus belongs to the D1.1 genotype, which is widely circulating in North American wild birds and has been responsible for a surge in poultry outbreaks. Unlike the B3.13 genotype implicated in previous dairy cow infections, this detection represents a separate introduction of the virus into dairy cattle, marking the third such event.
APHIS emphasized that the presence of the D1.1 genotype is not unexpected due to its widespread circulation in wild birds. Officials have urged dairy farmers to strengthen biosecurity measures and promptly report any signs of illness in cattle or unusual deaths in wildlife.
In its latest report, APHIS confirmed five additional detections of H5N1 in dairy cattle, including the Arizona herd and four others from California. These confirmations have increased the national total to 972 cases, with 747 reported in California alone.
Public Health and Dairy Industry Response
The detection of H5N1 in Arizona’s dairy herd stems from the AZDA’s National Milk Testing Strategy, implemented in January to enhance surveillance through farm-level bulk tank sampling. Despite the positive detection, all tested Arizona dairies have returned negative results except for this single case. Additionally, the identified D1.1 genotype does not exhibit any known mutations that would increase the risk of human infection.
Pasteurized milk and dairy products remain safe for consumption, as the pasteurization process effectively eliminates the virus.
Ensuring the health and safety of dairy workers and the public remains AZDA’s priority. The agency is coordinating with the Arizona Department of Health Services and Maricopa County Department of Public Health to provide guidance for worker safety, monitor personnel at the affected facility, and prevent further spread among livestock. Although the overall risk to the general public remains low, individuals in close contact with dairy cattle may be at a higher risk and are advised to take appropriate precautions.
