At least 67 people in the U.S. have been infected with bird flu, mostly those who work closely with dairy or cattle, according to the U.S. Centers for Disease Control and Prevention.
USDA officials said they would post genetic sequences and other information about the new form of the virus to a public repository later this week. Scientists said that would be key to understanding whether the spillover was a recent event or whether the virus has been circulating, perhaps widely, for longer.
"If this turns out to have been something that crossed into cattle a couple months ago, a couple months is a long time not to detect it," said Michael Worobey, an evolutionary biologist at the University of Arizona who has studied the H5N1 virus in cattle.