September 27, 2015
Researchers at the University of California, Berkeley's School of Public Health have established a new link between the bovine leukemia virus (BLS) and the risk of breast cancer in women.
The study, recently published in the journal PLOS ONE, tested the breast tissue of 240 American women for traces of BLV, which is often found in cattle herds throughout the United States and infects the animals' blood cells and mammary tissues, LiveScience reports.
The researchers found that 59 percent of the samples taken from women with breast cancer contained signs of BLV, while only 29 percent of the samples taken from women without breast cancer carried signs of the virus. Based on their analysis, they concluded that the chances of having breast cancer were three times higher when BLV was present, taking other risk factors into account -- including alcohol consumption, obesity and hormone treatments after menopause.
While the data is eye-opening, researchers have not yet determined how the virus is transmitted to human beings. There is a possibility that dairy products and beef could lead to infection, but it is not clear how the virus reached the human breast tissue samples. According to Gertrude Buehring, the study's lead author, the key question is to figure out whether humans get the virus from cattle or from other humans.
One theory, proposed by Dr. Michael Greger, director of public health and agriculture at the Humane Society of the United States, suggests that something about breast cancer tissue may attract the virus. He said the next step would be to following women who have been exposed to BLV, and those who haven't, to see whether antibody tests show a higher likelihood of developing breast cancer.
Among cows, researchers know that BLV spreads through herds when calves are fed from tanks that contain a mixture of breast milk from several cows. Those calves can contract the virus even if their mother is BLV-negative.
While it's too soon say that there is a causal link between BLV and breast cancer, the study points to a need for more research into the public health implications of industrialized agriculture.