Raw milk has made headlines recently for widespread samples containing the virus that causes H5N1, or bird flu, with the U.S. Department of Agriculture launching a program in December to track the virus through milk testing. But bird flu is far from the only disease-causing pathogen lurking in raw milk: Unpasteurized milk can contain bacteria such as E. coli and Listeria, for instance.

New Stanford Medicine research has found that another virus affecting both animals and people — Rift Valley fever virus — can remain active in raw milk samples for roughly as long as someone might want to drink it. Rift Valley fever is an acute viral illness spread to people through mosquitoes or the bodily fluids of infected animals. These findings mirror recent Stanford research showing that flu virus can be infectious in refrigerated raw milk for up to five days.

While Rift Valley fever virus mostly impacts sub-Saharan Africa, these findings have important implications for understanding human disease risk from drinking raw milk, said Brian Dawes, MD, PhD. He is an infectious disease fellow and postdoctoral researcher in Stanford Medicine’s LaBeaud Lab and led the research. Desiree LaBeaud, MD, associate dean of global health, was the senior author. Alina De La Mota-Peynado of the USDA was co-lead author.