ISU Study Finds H5N1 Receptors in Mammary Glands of Multiple Species — What It Means for Dairy, Livestock and Humans

A team of researchers at Iowa State University has identified the same sialic acid receptors in the mammary glands of several milk-producing species that the H5N1 avian influenza virus used to attach in infected dairy cattle. The finding raises theoretical concerns about susceptibility across species — from sheep and goats to alpacas, pigs, beef cattle and even humans — though no infections outside dairy cows have been confirmed to date.

What the Researchers Did

Prompted by the detection of H5N1 in cow milk in March 2024, Professor Todd Bell and colleagues, including Rahul Nelli, examined mammary tissues from commonly milked animals and human samples to see whether the glands contained the molecular receptors the virus binds to. They found the same sialic acid molecules in the mammary cells of those species that H5N1 attached to in dairy cattle.

Implications and Limits

The presence of these receptors means, in theory, the virus could attach to and potentially replicate in mammary cells of other species. However, the team stresses that receptor presence alone does not prove infection or transmission. Key unknowns remain: how efficiently H5N1 replicates in those tissues, whether mammary infection can spread to other organs, and whether virus in milk can transmit infection to humans or animals under real-world conditions.

“So far, we haven’t seen any such scenario yet, but that doesn’t mean it may not happen, because viruses always mutate,” said Rahul Nelli, summarizing the cautious outlook of the research team.

Public-Health and Farm Guidance

While the U.S. Centers for Disease Control and Prevention currently rates human risk from H5N1 as low, the ISU team emphasized continued vigilance at human–animal interfaces. The researchers noted that some raw milk samples from infected cows contained very high concentrations of virus, and they reiterated the CDC position that pasteurization inactivates the virus and makes dairy products safe to consume.

Recommendations: avoid raw (unpasteurized) milk, ensure dairy products are pasteurized, monitor livestock for illness, remove or dispose of dead birds promptly, and limit contact between wild birds and farm animals.

Context and Next Steps

The current H5N1 outbreak began in February 2022 and has affected more than 184.2 million commercial and backyard poultry. The virus spread to dairy cattle in 2024 and has been detected in more than 1,000 cows across 18 states. According to USDA APHIS data, detections have continued in some western states, while Iowa had not reported a dairy detection since July 2024.

The ISU study, published Nov. 27 in the Journal of Dairy Science, is intended to inform regulators — including the CDC and USDA — and help farmers by identifying where the virus might appear on farms. Future research at ISU will investigate whether the same receptors exist in respiratory, gastrointestinal and neurological tissues, measure replication efficiency in mammary glands, and assess environmental reservoirs (for example, contaminated water troughs or ground material) that could facilitate transmission between animals.

Bottom line: The study identifies a plausible pathway for H5N1 to interact with multiple milk-producing species, strengthens the case against consuming raw milk from potentially infected animals, and highlights urgent questions for follow-up research to determine real-world risk.