When highly pathogenic avian influenza (HPAI) H5N1 jumped from poultry to dairy cattle in 2024, it raised urgent questions about how exactly this respiratory virus found its way into milk. Our guests today, coauthors Rahul Nelli, PhD, MVM, and Todd Bell, DVM, PhD, DACVP, both from the College of Veterinary Medicine at Iowa State University, were at the forefront of understanding that viral load in milk was due to sialic acid receptors in the mammary glands of dairy cows, which act like docking stations for H5N1. Given that the outbreak has spilled over into other species, the team then wondered: Could the mammary tissue of other species also support H5N1 infection, potentially including humans? Their latest research, published in the Journal of Dairy Science and involving multiple institutions, examined mammary glands from pigs, sheep, goats, beef cattle, alpacas, and human breast tissue, finding that all contained high levels of sialic acid receptors susceptible to both avian influenza and seasonal influenza. The two discuss what these findings mean for viral transmission pathways and the human-animal interface, including that there is potential for transmission among these other domestic mammals and humans. With 71 human cases documented in the current outbreak and high viral loads detected in unpasteurized milk from infected animals, understanding these pathways becomes crucial for protecting animals, agricultural workers, and consumers.

Episode Thirty-Seven Show Notes

Learn more about our guests and follow them on LinkedIn: Rahul Nelli and Todd Bell.

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Explore the article discussed in the episode:

Exploring influenza A virus receptor distribution in the lactating mammary gland of domesticated livestock and in human breast tissue, Journal of Dairy Science (February 2026)

Can H5N1 avian influenza in dairy cattle be contained in the US?, Cell (February 2026)

Sialic acid receptor specificity in mammary gland of dairy cattle infected with highly pathogenic avian influenza A (H5N1) virus, Emerging Infectious Diseases (July 2024)