Scientists at the University of Pittsburgh, in a team led by Suresh Kuchipudi, reported in Science Advances on 20 June that H5N1 avian influenza thrives in dairy cattle because it binds N-linked sialic acid receptors, the molecular docking points the virus needs to enter a cell, which are abundant in cow udder tissue but almost absent in the airways1. H5N1 is a highly pathogenic bird-flu subtype that has been infecting US dairy herds since 2024; the University of Pittsburgh is a public research university in Pennsylvania.
The receptor mismatch explains a two-year blind spot. Because the virus settles in the mammary gland, it presents as mastitis, an udder inflammation, rather than as influenza. A dairy vet seeing inflamed udders reaches for antibiotics, not a flu test, so the herd reads as a routine bovine illness while H5N1 multiplies and spreads. Surveillance keyed to respiratory signals was watching the wrong tissue.
Two consequences follow. Infected cows shed high viral loads in their milk, which puts the hazard on the people doing the milking; pasteurisation destroys the virus, but raw milk does not. The receptor map also gives researchers a way to predict which tissues a flu virus will favour in which species before the next spillover, rather than reconstructing it afterwards. The finding lands while the CDC reports H5N1 in roughly 1,053 dairy herds across 17 states, and after the agency shifted its bird-flu reporting from weekly to monthly, thinning the very surveillance the paper shows was already looking in the wrong place.
