UC Berkeley
researchers have linked bovine leukemia virus, a cancer-causing
virus prevalent in
cattle, with human breast cancer.
(September 15, 2015)
A new study by UC Berkeley researchers establishes for the first time a
link between infection with the bovine leukemia virus and human breast cancer.
In the study, published this month in the journal PLOS ONE
and available online, researchers analyzed breast tissue from 239 women for the
presence of bovine leukemia virus (BLV), comparing samples from women who had
breast cancer with women who had no history of the disease. They found that 59
percent of breast cancer samples had evidence of exposure to BLV, as determined
by the presence of viral DNA. By contrast, 29 percent 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 in the Division of Infectious
Diseases and Vaccinology at UC Berkeley’s School of Public Health. “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 leukemia virus infects dairy and beef cattle’s blood
cells and mammary tissue. The retrovirus is easily transmitted among cattle
primarily through infected blood and milk, but it only causes disease in fewer
than 5 percent of infected animals.
A 2007 U.S. Department of Agriculture survey of bulk milk
tanks found that 100 percent of dairy operations with large herds of 500 or
more cows tested positive for BLV antibodies. This may not be surprising since
milk from one infected cow is mixed in with others. Even dairy operations with
small herds of fewer than 100 cows tested positive for BLV 83 percent of the
time.