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.

The ongoing bird flu outbreak has led to wild bird deaths, slaughtered livestock, and hazardous conditions for dairy industry workers.

Highly pathogenic avian influenza (HPAI) readily infected cells from milk-producing organs in dairy cows, but beef cells held it off, and virus behaviour was different depending on if it spread through a bird or another mammal.