Bovine leukemia virus is a cancer-causing microbe in cattle. Just how many cows have it? The US Department of Agriculture reports that nationwide, 89 percent of herds contain cows with BLV. The most infected region is the Southeast, where 99 percent of herds have the tumor-causing bug. In some herds across the country, almost every single animal is infected. A 1980 study across Canada uncovered a lower but none-too-reassuring rate of 40 percent.
BLV is transmitted through milk. Since the milk from all cows in a herd is mixed before processing, if even a single cow is infected, all milk from that herd will have BLV swimming in it. Citing an article in Science, oncologist Robert Kradjian, MD, warns that 90 to 95 percent of milk starts out tainted. Of course, pasteurization — when done the right way — kills BLV, but the process isn't perfect. And if you drink raw milk, odds are you're gulping down bovine leukemia virus.
Between dairy cows and their cousins that are used for meat (who tend to be infected at lower rates), it appears that a whole lot of BLV is getting inside us. A 2001 study in Breast Cancer Research detected antibodies to the bovine leukemia virus in blood samples from 77 out of 100 volunteers. Furthermore, BLV showed up more often in breast tissue from women with breast cancer than in the tissue from healthy women. Several medical studies have found positive correlations between higher intake of milk/beef and increased incidence of leukemia or lymphoma in humans, although other studies haven't found a correlation.
No hard evidence has yet linked BLV to diseases in humans, but do you feel comfortable knowing that cow cancer cells are in your body? 