Bird Flu Detected in US Dairy Cows for First Time
The U.S. Department of Agriculture has confirmed the presence of D1.1 bird flu in dairy cows, following previous detections only in wild birds and poultry. The findings raise concerns about potential human risks, though public health experts maintain the overall threat remains low.
A second type of bird flu has been found in U.S. dairy cows for the first time, the U.S. Department of Agriculture (USDA) announced on Wednesday.
Until recently, all dairy herd detections in the U.S. had been infected with a form of bird flu, or avian influenza, known as B3.13.
This version of bird flu, known as D1.1, has only ever previously been detected in wild birds and poultry, indicating that it has now spilled over into cows.
The detection, found in dairy cattle in Nevada, was a result of the USDA's national milk testing program that launched in early December, according to the agency's Animal and Plant Health Inspection Service.
"USDA APHIS continues to work with the Nevada Department of Agriculture by conducting additional on-farm investigations, testing, and gathering additional epidemiological information to better understand this detection and limit further disease spread," the agency said in a statement on its website.
There has been a total of 957 confirmed cattle infections in 16 states, with 36 new infections in the last 30 days in California and Nevada, the latest USDA data shows.
D1.1 has also been shown to potentially be dangerous to humans. Of the 67 human cases of bird flu detected in the U.S. beginning in April 2024, one of the only patients infected with D1.1 was in Louisiana.
The Louisiana patient died earlier this year, although health officials said the patient was over age 65 and had underlying health conditions.
Additionally, a 13-year-old girl in British Columbia, Canada, was admitted to the intensive care unit with the same strain in November.
The Louisiana patient was exposed to a backyard flock and the British Columbia teenager had an unknown exposure.
The CDC notes that the risk to the general public remains low and that there is no evidence of human-to-human spread.
Late last year, the USDA issued a federal order that all raw milk samples nationwide be collected and shared with the agency in order to test for bird flu.
The USDA order marked the start of the agency's National Milk Testing Strategy, a program intended to boost surveillance of the nation's milk supply and dairy herds and increase understanding of how bird flu is spreading.
The USDA said the D1.1 detection in dairy cows "does not change USDA's [bird flu] eradication strategy and is a testament to the strength of our National Milk Testing Strategy."
APHIS says it plans to publish a technical brief on the findings on its website and post the sequence data on an open-access data bank in the coming week.
