Scientists are sounding alarms about a genetic mutation that was recently identified in four dairy cow herds, nearly one year after H5N1 bird flu was first reported in Texas dairy cattle.

The change is one that researchers have dreaded finding because it is associated with increased mammal-to-mammal transmission and disease severity.

"That is the mutation found in the first human case, which was extremely pathogenic in ferrets," said Yoshihiro Kawaoka, an infectious disease expert at the University of Wisconsin, Madison and the University of Tokyo. "Finding the same mutation in cows is significant."

The mutation is called PB2 E627K, and it was seen in a Texas dairy worker last March. It was not seen again until these sequences were uploaded late Tuesday. The data were uploaded by the USDA's National Veterinary Laboratory Services to a public access genetic repository known as GISAID.

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