Avian flu first made the jump from birds into dairy cows on farms in a number of US states in spring 2024. Until now, all such cases of the H5N1 virus have been ascribed to a genotype called B3.13, but the US Department of Agriculture (USDA) has just announced the detection of a second genotype,

The new H5N1 version, known as D1.1, was found in dairy cattle in Nevada and is different than the B3.13 type that has spread to more than 950 herds in 16 states over the past year, starting in Texas. The D1.1 infection was discovered by testing raw milk under a USDA dairy surveillance project launched last year.

U.S. dairy cattle tested positive for a strain of bird flu that previously had not been seen in cows, the U.S. Department of Agriculture said on Wednesday, ramping up concerns about the persistent spread of the virus.