Dairy cattle in Nevada have been infected with a new type of bird flu that’s different from the version that has spread in U.S. herds since last year, Agriculture Department officials said Wednesday.
The detection indicates that distinct forms of the virus known as Type A H5N1 have spilled over from wild birds into cattle at least twice. Experts said it raises new questions about wider spread and the difficulty of controlling infections in animals and the people who work closely with them.
“I always thought one bird-to-cow transmission was a very rare event. Seems that may not be the case,” said Richard Webby, an influenza expert at St. Jude Children’s Research Hospital.
A version of the H5N1 bird flu virus known as B3.13 was confirmed in March after being introduced to cattle in late 2023, scientists said. It has infected more than 950 herds in 16 states. The new version, known as D1.1, was confirmed in Nevada cattle on Friday, according to USDA. It was detected in milk collected as part of a surveillance program launched in December.
“Now we know why it’s really important to test and continue testing,” said Angela Rasmussen, a virus expert at the University of Saskatchewan in Canada, who helped identify the first spillover.