A recent discovery by the Arizona Department of Agriculture has found the H5N1 bird flu virus in milk from a herd of cows in Maricopa County, making it the 17th state where affected cows have been detected. This is the first detection of H5N1 in dairy cows in Arizona.
The US Department of Agriculture’s National Milk Testing Strategy, which samples bulk milk for the presence of H5N1 viruses, led to the discovery. Similar detections were previously reported in Nevada and other states, indicating that the virus has been spreading among herds.
Recent studies have shown that the D1.1 genotype of H5N1 is responsible for severe infections, including a recent case in British Columbia, Canada, and a death in Louisiana, USA. The Arizona detected virus belongs to the same clade but appears to be a different version of the D1.1 genotype.
The detection is consistent with the D1.1 genotype, which does not pose an increased risk to humans. However, experts warn that the prevalence of H5N1 in wild birds across the country increases the likelihood of spillover into cows.
This discovery comes as a surprise, given the recent Nevada detection. The US has only previously detected one human H5N1 infection in 2022, but over the past year, there have been 69 confirmed cases, mostly among people with direct contact with dairy cows or poultry flocks.
Source: https://www.statnews.com/2025/02/14/arizona-bird-flu-h5n1-dairy-cows-spillover