The H5N1 bird flu outbreak in dairy cows in the United States has likely been going on for months longer than was previously realized, and has probably spread more widely across the country than the confirmed outbreaks would imply, according to an analysis of genetic sequences that were released Sunday by the U.S. Department of Agriculture.
The genetic data point to a single spillover event that probably occurred in late 2023, Michael Worobey, an evolutionary virologist at the University of Arizona, told STAT on Tuesday.
“The bad news is it looks like this is well entrenched and has been in cattle for a long time and … probably very, very, very widespread,” said Worobey, who worked on the analysis with a number of scientists in the U.S. and Europe.
He suggested the outbreak needs to be taken more seriously than it has been until now, especially given the amount of exposure humans have with cattle. “We need to just study the hell out of it for starters … and see if we can close the gap on what is happening and what we know.”