Iowa State University's H5N1 study highlights need for broader livestock surveillance

An ongoing outbreak of highly pathogenic avian influenza has affected more than 184 million domestic poultry since 2022 and, since making the leap to dairy cattle in spring 2024, more than 1,000 milking cow herds.

A new study led by Iowa State University researchers shows that the mammary glands of several other production animals – including pigs, sheep, goats, beef cattle and alpacas – are biologically suitable to harbor avian influenza, due to high levels of sialic acids.

“The main thing we wanted to understand in this study is whether there is potential for transmission among these other domestic mammals and humans, and it looks like there is,” said Rahul Nelli, the study’s lead author and a research assistant professor of veterinary diagnostic and production animal medicine.

Sialic acid, a sugar molecule found on the surface of many types of animal cells, provides an influenza virus the microscopic docking station it needs to infect a host cell, an entry point for attaching and invading. A study by many of the same researchers last year found that dairy cattle udders have high levels of sialic acid, which helped explain why the H5N1 avian influenza outbreak was able to spread rapidly among dairy herds.

In the study published Nov. 27 in the Journal of Dairy Science, a research team that includes scientists from the ISU College of Veterinary Medicine and the U.S. Department of Agriculture’s National Animal Disease Center in Ames also found the same receptors in the mammary glands of the humans.

Only a few sporadic cases of H5N1 infection have been reported in the animals examined in the new study, but those species aren’t being tested on a widespread basis, said Dr. Todd Bell, professor of veterinary pathology and a study co-author.

“If we don’t look, we don’t know,” Bell said.

In dairy herds, H5N1 infections are causing sick cows to produce milk contaminated with the virus, prompting nationwide surveillance testing of raw cow milk samples by the USDA. Pasteurization kills influenza viruses, so store-bought milk is safe. But concerns about raw milk should extend to other mammalian livestock, Nelli said.