Tufts University How the H5N1 virus is affecting the nation’s cattle, according to an expert at Cummings School of Veterinary Medicine. In March 2024, for the first time in the United States, the highly pathogenic avian influenza (HPAI) H5N1 virus was recognized as having crossed over from birds into cattle. Experts believe the virus was transmitted a month or two beforehand from birds to dairy cows in the Texas panhandle, and then spread as the cows were moved to dairy farms in other parts of the country.
To date, dairy cows in 17 states have tested positive for HPAI, with more than 970 herds affected, according to the Centers for Disease Control and Prevention (CDC). In addition to the confirmed crossover event in Texas, two additional crossover events were confirmed in Colorado and Arizona.