Researchers Find Mammary Glands of People, Sheep and Other Livestock Could Harbor Bird Flu

By Rachel Cramer

Millions of wild birds, chickens and turkeys in the U.S. have been affected by the highly pathogenic avian influenza H5N1 virus since 2022. Last year, it spilled over into dairy cows for the first time and has since spread to over 1,000 herds.

Todd Bell, professor of veterinary pathology at Iowa State University, was part of the research team that discovered the “lock-and-key” mechanism allowing H5N1 to infect cells in cow udders.

“Viruses are parasites, and by their nature, they need to attach to a cell, get inside, start to use the cell’s machinery in order to reproduce,” Bell said. “Then they pop back out, go to the next cell, infect that cell or the next animal and continue on their life cycle.”

Proteins topped with sugar molecules dot the outer surface of dairy cow mammary glands, Bell explained. The H5N1 virus fits into some of these “locks” called sialic acid receptors.

Bell and other scientists from ISU's College of Veterinary Medicine, George Mason University and the U.S. Department of Agriculture's National Animal Disease Center in Ames recently found the same receptors in the mammary glands of pigs, sheep, goats, beef cattle, alpacas and humans.

The authors said their results suggest a potential health risk for farm workers and consumers of raw, unpasteurized dairy products beyond cow milk.

But Rahul Nelli, a flu virus receptor expert at Iowa State and lead author of the study, emphasized more research is needed to understand the risks and infection pathways of H5N1 for people and other species.