CARSON, CITY, Nevada: A new type of bird flu has been found in dairy cows in Nevada, different from the strain that has been spreading in U.S. cattle since last year, according to the U.S. Agriculture Department.

This means that the H5N1 bird flu virus has jumped from wild birds to cows at least twice. Experts worry this could make it harder to control the disease in animals and farm workers.

"I thought bird-to-cow transmission was very rare, but that may not be true," said Richard Webby, a flu expert at St. Jude Children's Research Hospital.

A version of H5N1 called B3.13 was first found in March 2024 and has since infected over 950 herds in 16 states. The new strain, called D1.1, was confirmed in Nevada on Friday after being found in milk samples collected for testing.

Angela Rasmussen, a virus expert from Canada who first helped identify bird flu in cows, said testing is very important to track the spread of the virus.

The D1.1 strain has been connected to severe human illness. In January, a person in Louisiana died from bird flu after contact with wild and backyard birds. In Canada, a teenage girl in British Columbia was hospitalized for months after catching the virus from poultry.

So far, at least 67 people in the U.S. have been infected, mostly farm workers who handle cattle.

The USDA will release genetic data on the new strain later this week, which will help scientists understand how long the virus has been in cattle.

"If this crossed into cows months ago, that is a long time for it to go unnoticed," said Michael Worobey, a biologist at the University of Arizona.

He warned that officials must quickly share information, as this virus could cause a pandemic worse than COVID-19.

"This is critical for national and global security," Worobey said, stressing the need to protect people, animals, and businesses.