A new bird flu genotype, D1.1, has been detected in dairy cows in Nevada, marking the first time this genotype has been identified in cattle. The discovery comes amidst its spread among wild birds and poultry across the United States and Canada. As of mid-January, 36 states have enrolled in a program covering approximately two-thirds of the nation's commercial milk supply, highlighting the widespread impact of this virus.
The Animal and Plant Health Inspection Service (APHIS) confirmed the detection in a statement, noting that this represents the first identification of the D1.1 genotype in dairy cattle.
"This is the first detection of this virus genotype in dairy cattle," – APHIS representatives
The D1.1 genotype has become the predominant strain in the North American flyways over the past fall and winter. It has been identified not only in wild birds and domestic poultry but also in mammals. This broad subtype of bird flu, known as H5N1, has been circulating among U.S. dairy cows since at least 2024, with the first cattle cases reported in March of last year. So far, nearly 960 herds nationwide have been affected by H5N1.
The USDA has taken proactive measures by testing raw milk samples from dairy farms to track the spread of bird flu effectively. The Nevada Department of Agriculture is working closely with the USDA to conduct additional tests on the affected farm and implement measures to prevent further spread.
"This confirmation was a result of State tracing and investigation, following an initial detection on silo testing under the USDA's National Milk Testing Strategy (NMTS) in Nevada." – APHIS representatives
The human impact of the D1.1 genotype has also been felt, with reports of infections among poultry workers in Washington state and a teenager in British Columbia. Tragically, a person in Louisiana contracted a severe case that proved fatal.
"We shouldn't be surprised about a new spillover to cattle, given the very significant activity in waterfowl across much of the United States," – Michael Osterholm
