In early 2024, a new wave of H5N1 bird flu appeared in U.S. dairy cows. Veterinarians were surprised because the virus did not affect the lungs as it usually does. Instead, it caused painful infections in the udders.
What Happened to the Cows?
The first cases showed up in the Texas Panhandle. Cows developed a severe form of mastitis, a swelling and damage of the milk‑producing glands. The disease spread quickly from one herd to another, and the virus was found in the milk of infected animals.
Researchers warned that drinking raw milk could spread the virus to people and pets. Pasteurizing milk destroys the virus, making it safe to drink.
Finding the Reason Behind the Odd Symptoms
Dr. Kuchipudi, an expert on flu viruses, studied how the virus attaches to cells. Flu viruses need a special “key” – a sugar molecule called a glycan – to lock onto a cell and start infection.
Earlier studies showed that cows have these sugar keys in their noses and lungs, so scientists expected a lung infection. But the cows were getting sick in their udders, not their airways. This mismatch meant something else was going on.
What the Scientists Discovered
Working with glycomics specialist Dr. Lauren Pepi, the team used lab tests, staining, and ultra‑high‑resolution images to map the virus’s favorite spots. They found that H5N1 only binds well to a type of glycan called N‑linked sialic acid.
These N‑linked receptors are abundant in cow udder tissue but are almost absent in the respiratory tract. Because the udder offers many entry points, the virus turned the mammary glands into a perfect breeding ground.
Why This Matters
The study gives a clear reason why bird flu caused mastitis in dairy cows. It also shows a way to check other animals for hidden risks. By testing different species and their tissues, scientists can predict whether H5N1 would cause lung disease, mastitis, or even brain problems.
Knowing the exact receptors a virus likes helps farmers and health officials act faster, protect workers, and keep milk safe.
Funding for this work came from the University of Pittsburgh School of Public Health and the U.S. Department of Agriculture.