Scientists finally solved how H5N1 bird flu hid in dairy cows

When H5N1 bird flu began infecting U.S. dairy cattle in early 2024, veterinarians struggled to identify the cause. The virus was difficult to recognize because it behaved very differently in cows than it does in other mammals. Rather than primarily infecting the lungs, H5N1 caused severe infections in the udders while leaving the respiratory system largely unaffected. Now, researchers at the University of Pittsburgh School of Public Health have uncovered the biological reason behind this unusual pattern. Their findings, published in Science Advances, provide the first detailed explanation for why bird flu took such an unexpected form in cattle. The work could also help scientists better anticipate how H5N1 might behave if it spreads to new animal species in the future.