The U.S. Department of Agriculture (USDA) has confirmed the detection of a second strain of bird flu in dairy cows, marking the first time this particular virus has been identified in cattle.
Previously, all detected cases in U.S. dairy herds were linked to a form of avian influenza known as B3.13. However, the newly identified strain, D1.1, had only been seen in wild birds and poultry until now—suggesting a spillover into livestock.
Discovery and Ongoing Investigation
The discovery of D1.1 in Nevada dairy cattle was made through the USDA’s National Milk Testing Program, which launched in December to enhance virus surveillance.
“USDA APHIS continues to work with the Nevada Department of Agriculture by conducting additional on-farm investigation, testing, and gathering epidemiological data to better understand this detection and limit further disease spread,” the agency stated.
The USDA’s latest data reveals a total of 957 confirmed cattle infections across 16 states, with 36 new cases reported in California and Nevada within the past 30 days.
Potential Human Health Risks
While bird flu in cattle is a growing concern, the Centers for Disease Control and Prevention (CDC) maintains that the risk to the general public remains low, with no evidence of human-to-human transmission.
However, D1.1 has been linked to severe cases in humans. Of the 67 human infections recorded in the U.S. since April 2024, at least one patient in Louisiana tested positive for D1.1. This patient, over the age of 65 with underlying health conditions, later died.
Additionally, a 13-year-old girl in British Columbia, Canada, was hospitalized in intensive care with the same strain in November 2024.
National Surveillance and Response Measures
In response to the ongoing spread, the USDA mandated the collection of raw milk samples nationwide to improve tracking and containment efforts. This initiative is part of the National Milk Testing Strategy, a program designed to:
- Enhance virus surveillance in dairy herds
- Monitor the spread of avian influenza
- Ensure public health safety
Despite the new detection, the USDA maintains that the discovery of D1.1 does not alter its bird flu eradication strategy. The Animal and Plant Health Inspection Service (APHIS) plans to publish a technical brief on its findings, alongside sequencing data, in the coming week.
Looking Ahead
As the situation evolves, federal and state agencies will continue monitoring and researching the spread of avian influenza in dairy cattle. For now, officials emphasize that precautionary measures remain in place to safeguard both livestock and public health.
