A new study conducted at the University of California, Berkeley, has established a link between bovine leukemia virus and human breast cancer, Nature World Report reports.

This is the first time that researchers have established such a link. The researchers examined the breast tissue from 239 women for the study. The study is published this month in the journal PLOS ONE.

Bovine leukemia virus that infects the blood cells and mammary tissue of dairy and beef cattle is present in much of beef and dairy products. The retrovirus is transmitted among cattle through infected blood and milk. However, it only causes disease in fewer than five per cent of infected animals.

It has been seen that the incidence of breast cancer is greatest in countries with high consumption of bovine food items.

Previous studies on the subject have shown that the presence of antibodies to BLV envelope glycoprotein (gp51) and capsid protein (p24) in humans suggests that humans might possibly be infected with BLV.

Mathilde Bonnet stated, "Our results demonstrated the presence of the EBV genome in a large subset of breat cancers. The virus was restricted to tumor cells and was more frequently associated with the most aggressive tumors. EBV may be a cofactor in the development of some breast cancers."

Last year, it was confirmed in a study led by 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 that the bovine virus could be found in humans.

The study was published last year in Emerging Infectious Diseases.

Buehring said, "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. We still need to confirm that the infection with the virus happened before, not after, breast cancer developed, and if so, how."

 "If BLV were proven to be a cause of breast cancer, it could change the way we currently look at breast cancer control," he added.

Buehring said that this study does not identify how the virus infected the breast tissue samples in their study.