H5N1 avian flu takes a deadly turn in dairy cattle with udder infections

An unusual outbreak of H5N1 avian influenza struck dairy cattle in the Texas Panhandle in early 2024. Instead of the expected respiratory symptoms, the virus caused severe necrotizing mastitis, targeting the udder rather than the lungs. This shift in infection patterns has raised concerns among researchers and farmers alike. Dr. Suresh Kuchipudi and his team at the University of Pittsburgh School of Public Health investigated the outbreak. Their study, published in Science Advances, revealed that the virus had a strong preference for bovine mammary tissue over respiratory organs. This challenged long-standing assumptions about how influenza strains behave in livestock.

The researchers used a multimodal approach to uncover the reason behind this unusual tropism. By combining high-precision receptor mapping with functional binding experiments, they identified a specific subclass of N-linked sialic acid receptors. These receptors are abundant in mammary epithelial cells but rare in bovine airway tissues, allowing H5N1 to infect the udder effectively.

The study also highlighted the risks of viral shedding into milk. Farm workers exposed to raw milk face potential zoonotic transmission, prompting calls for stricter biosecurity measures. The research was a collaborative effort, funded by the U.S. Department of Agriculture and Pitt Public Health, and involved experts from multiple institutions.

Previous observations of feline fatalities from H5N1 had already signalled the need for better surveillance. This new finding underscores the importance of monitoring emergent strains to prevent further spread in agricultural settings. The discovery of viral tropism determinants offers a new tool for early detection of emergent influenza strains. It also provides a clearer understanding of how H5N1 adapts to different hosts. These insights could help shape future surveillance and control strategies in both animal and human health.