How H5N1 Hid in Cows’ Udders

Researchers at the University of Pittsburgh School of Public Health identified the reason. The H5N1 virus binds to a specific type of receptor (N-linked sialic acids), which in cattle are concentrated primarily in udder tissue rather than in the respiratory tract.

Experiments using binding assays, staining, and high-resolution imaging confirmed that the udder became an ideal target for the virus. This explains why the infection spread through milk and why it was so difficult to detect in the early stages.

The discovery is important not only for understanding the current outbreak. It provides a tool for predicting H5N1 behavior in other species. Scientists can now examine the tissues of different animals in advance for the presence of suitable receptors and assess risks — whether the virus is likely to affect the lungs, the udder, the nervous system, or something else.

Sources:

1. University of Pittsburgh. "Scientists finally solved how H5N1 bird flu hid in dairy cows." ScienceDaily (June 23, 2026).
2. Srinivas S. et al. "Receptor basis of unusual tissue tropism of avian influenza H5N1 clade 2.3.4.4b virus in cattle." Science Advances (2026). DOI: 10.1126/sciadv.aea2068.