Scientists explain why H5N1 bird flu hides in dairy cows' udders, not their lungs
Bird flu has spread through U.S. dairy herds since 2024, often going unrecognized for weeks. University of Pittsburgh researchers report in Science Advances that H5N1 binds to N-linked sialic acid receptors that are abundant in cow udders but nearly absent in the airways, explain
When H5N1 first reached U.S. dairy cattle in early 2024, it went unrecognized for weeks because the infection looked nothing like typical bird flu. Instead of attacking the lungs, as it does in most mammals, the virus caused severe infection in the cows' udders. Researchers at the University of Pittsburgh School of Public Health, writing in Science Advances, traced this to the receptors the virus uses to enter cells. H5N1 binds to a specific subtype called N-linked sialic acid receptors, which are abundant in mammary tissue but nearly absent in the respiratory tract, making the udder an ideal site for the virus. The team says the mechanism offers a faster way to anticipate where the virus might jump next, and notes the same receptor pattern is relevant for understanding risk to other species, including humans. Larger studies will show how this shapes future outbreak surveillance.