Why are cattle and humans suitable hosts for bird flu?

A study conducted at Iowa State University (ISU) has identified a possible route of transmission for the highly pathogenic H5N1 avian influenza virus. The study suggests that the mammary glands of cattle and humans may be carriers of the virus.

The results of the study were published in the Journal of Dairy Science.

The research team wondered whether the virus , which appeared in the milk of dairy cows in 2024 , could also live in the mammary glands of other dairy animals and even in humans.

By analyzing the mammary glands of various animal species—sheep, goats, cattle, alpacas, pigs, and humans—the researchers discovered that they all possess the same sialic acids, which act as receptors for the virus in dairy cattle. This suggests that the virus could theoretically attach to these cells and replicate within them, although no cases of infection have been observed in these species to date.

The study highlights that important questions remain unanswered, such as how efficiently the virus replicates in these glands and whether it can spread to other parts of the body. This information will be crucial for the U.S. Department of Agriculture (USDA) and the Centers for Disease Control and Prevention (CDC) to develop more precise measures to contain the spread of the virus, which has already infected more than 184 million birds and over 1,000 cows in the United States.

The researchers also emphasized the importance of pasteurization, as exceptionally high levels of the virus were found in some samples of contaminated raw milk. According to the CDC, pasteurization kills H5N1, so they recommend avoiding raw milk from any animal while research continues.

In conclusion, the research team warns that this virus behaves differently from typical avian influenza strains, which typically primarily infect the respiratory tract. Therefore, they recommend continuing active surveillance on farms, avoiding contact between wild birds and domestic animals, and continuing to investigate other possible transmission routes, such as water, soil, or other body systems.