Researchers from the University of California at Berkeley have discovered that a significant number of breast cancer cell samples taken from over 200 women had been exposed to bovine leukemia virus, or BLV. According to a report from UPI, the virus affects the blood cells and mammary tissues of cattle used for both dairy and beef, and was long believed to pose little threat to humans.

BLV is actually extremely common – most of the bulk milk tanks at factory farms across the country have traces of the virus, but only 5 percent of cows get sick from it. According to the U.S. Department of Agriculture, new research indicates that BLV can actually make its way from a cow to a human host.

According to Dr. Gertrude Buehring, a virology professor at Berkeley, “The association between BLV infection and breast cancer was surprising to many previous reviewers of the study, but it’s important to note that our results do not prove that the virus causes cancer. However, this is the most important first step.”

Researchers will need to prove that the infection of the virus occurred before the development of breast cancer in order to establish a causal link. So far, they have found that 59 percent of breast cancer cells showed the presence of BLV DNA. In about 29 percent of the samples, BLV was found in women who did not have breast cancer.

While there will need to be more studies done in order to establish a stronger link, the scientists also found that the presence of BLV increased the risk of developing breast cancer by about 3.1 times.