In the study by University of California, Berkeley, published this month in the journal PLOS ONE and available online, researchers analysed breast tissue from 239 women, comparing samples from women who had breast cancer with women who had no history of the disease for the presence of bovine leukaemia virus (BLV).
They found that 59% of breast cancer samples had evidence of exposure to BLV, while 29% of the tissue samples from women who never had breast cancer showed exposure to BLV.
“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,” said study lead author Gertrude Buehring, a professor of virology at Berkeley.
“However, this is the most important first step. We still need to confirm that the infection with the virus happened before, not after, breast cancer developed, and if so, how.”
Bovine leukaemia virus infects dairy and beef cattle’s blood cells and mammary tissue. It is easily transmitted but causes disease in fewer than 5% of infected animals.
A 2007 survey by the US department of Agriculture found that milk from 100% of dairy operations with large herds of 500 or more cows tested positive for BLV antibodies. A study last year finally confirmed that the virus could be found in humans.
“Studies done in the 1970s failed to detect evidence of human infection with BLV,” said Buehring. “The tests we have now are more sensitive, but it was still hard to overturn the established dogma that BLV was not transmissible to humans. As a result, there has been little incentive for the cattle industry to set up procedures to contain the spread of the virus.”
Bill Condie is a science journalist based in Adelaide, Australia.
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