H5N1 bird flu can remain infectious in raw milk for at least an hour, study finds

Bird flu is infecting cows across the U.S. Now, scientists have discovered that the virus from infected dairy cows can remain infectious in unpasteurized milk and on the surface of milking equipment for at least an hour. 

This means that dairy workers potentially face an increased risk of infection during the milking process. While the risk of drinking unpasteurized, or raw, milk was not the focus of this study, the research does confirm that live viruses can persist in raw milk. 

Avian iNFLuenza A(H5N1) primarily infects birds but can sometimes jump across to maMMAls. Scientists first detected the virus in cows in the U.S. in March, and it has since been found in more than 60 cattle herds across the country.

Since then, three people in the U.S. have contracted the H5N1 virus following exposure to infected dairy cows. Two developed eye infections and one had some mild respiratory symptoms. However, scientists are still unsure exactly how the disease is being transmitted from cow to cow and from cow to human.

Related: H5N1: What to know about the bird flu cases in cows, goats and people

In addition, "how [H5N1] got into the cows in the first place is a question that is a little bit mind-boggling to scientists," study lead author Valerie Le Sage, a microbiologist at the University of Pittsburgh, told Live Science. The researchers published their findings June 24 in the journal Emerging Infectious Diseases. 

Researchers already knew that H5N1-infected cows could shed the virus in their milk. Earlier this year, the Food and Drug Administration (FDA) reported that about 1 in 5 retail milk products in a sample had tested positive for H5N1 genetic material. However, none of the viruses detected in these products were "live," or infectious, because the products were pasteurized. Pasteurization kills most viruses and microbes.