U.S. Farms detect Avian Flu in their Cattle herds
Breaking News: D1.1 Genotype of H5N1 Bird Flu Detected in U.S. Dairy Cows
The U.S. Department of Agriculture (USDA) and the Centers for Disease Control and Prevention (CDC) are actively responding to the detection of the D1.1 genotype of H5N1 bird flu in dairy cows in the United States. This genotype has been associated with more severe human infections than previously circulating genotypes, raising concerns for human health impacts.
The D1.1 genotype was confirmed in dairy cattle in Nevada and Arizona by the USDA's National Veterinary Services Laboratories (NVSL) in early 2025. This marks new spillover events from wild birds to cattle, separate from an earlier B3.13 genotype spillover. The D1.1 genotype has been the most frequently detected H5N1 genotype across North America in 2025, infecting wild birds, poultry, dairy cattle, and mammals.
Between March 2024 and July 2025, over 1000 dairy herds in 17 states tested positive for H5N1, with California alone confirming over 749 infected dairies. These herds are under quarantine and surveillance by state and federal authorities.
To reduce human infection risk, the USDA and CDC recommend using personal protective equipment (PPE) for workers in contact with infected animals or materials, including N95 masks, eye protection, and gloves.
There have been at least two severe human cases linked to the D1.1 genotype: a fatal human case in Louisiana with exposure to sick backyard birds and a severe occupational exposure case in California linked to infected dairy cows. The D1.1 genotype is associated with more severe human disease compared to the B3.13 genotype, which mostly caused mild conjunctivitis in some infected dairy workers and poultry cullers.
Ongoing efforts include surveillance, laboratory testing, quarantine of infected herds, public health monitoring, and worker protection guidelines to control the virus and mitigate human health risks. Michael Osterholm, an epidemiologist at the University of Minnesota, has emphasized the importance of vigilance and proactive measures in combating the persistent threat posed by the virus.
As of now, 36 states are enrolled in the USDA's National Milk Testing Strategy (NMTS), covering a significant portion of the nation's commercial milk supply. The NMTS involves testing raw milk samples from dairy farms to monitor the transmission of bird flu, leveraging pasteurization as a protective measure against the virus. These efforts aim to contain the spread of the virus and safeguard both livestock and public health.
As experts and authorities work to address the emergence of the D1.1 genotype in American cattle, the need for heightened surveillance and swift action remains paramount. The USDA is collaborating with the Nevada Department of Agriculture to conduct thorough assessments on the affected farm. The urgent need for containment measures to prevent further spread has been underscored.
[1] CDC Update: Avian Influenza A(H5N1) in U.S. Dairy Cattle - Nevada, March 2025
[2] USDA Confirms Avian Influenza A(H5N1) in Dairy Cattle in Nevada and Arizona
[3] CDC Avian Influenza A(H5N1) in U.S. Dairy Cattle - Arizona and California, March 2025
- The detection of the D1.1 genotype of H5N1 bird flu in U.S. dairy cows has raised concerns for both animal and human health, as it has been associated with more severe human infections compared to previous genotypes, highlighting the intersection of environmental science, medical-conditions, and health-and-wellness.
- As the USDA and CDC work to respond to this new spillover event, they stress the importance of science and technology in tracking the virus and implementing containment measures, illustrating the crucial role of scientific advancement in maintaining a healthy and safe environment.
- Efforts to combat this outbreak go beyond just animal health and human safety, extending into the realm of cultural practices, as it is imperative that people follow guidelines such as the use of personal protective equipment (PPE) to minimize the risk of human infection.
