Dairy Industry Responds to Bovine Leukemia Virus in Breast Cancer

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What was the response to the revelation that as many as 37 percent of breast cancer cases may be attributed to exposure to bovine leukemia virus (BLV), a cancer-causing cow virus found in the milk of nearly every dairy herd in the United States? I discuss this issue in my video Industry Response to Bovine Leukemia Virus in Breast Cancer. The industry pointed out that some women without breast cancer harbored the virus, too. Indeed, BLV was found in the tissues of 29 percent of women who didn’t have breast cancer, a finding the researchers replied “is not surprising considering the long latency period of breast cancer…” In other words, they may not have breast cancer yet.

It can take decades before a breast tumor can be picked up on mammography. So, even though people may be harboring this virus in their breast and feeling perfectly fine, the cancer may still be on its way. That’s how other cancer-causing deltaretroviruses appear to work. These viruses can make proteins that interfere with our DNA repair mechanisms. Infected cells are then more susceptible to carcinogens and slowly accumulate mutations over time. “Therefore, evidence of BLV in normal breast tissues prior to premalignant and malignant changes would be expected.” This pattern is what we see with cervical cancer, “in which the causative virus (HPV) is found not only in the malignant [cancerous] tissue, but also in premalignant dysplastic areas [the precancerous tissue] and in normal tissue adjacent to the malignant tumor.”

If BLV, a retrovirus, is really causing thousands of cases of breast cancer every year, wouldn’t some of the anti-retroviral therapies like some of the AIDS drugs be able to counter it? Perhaps, but it’s best not to get infected in the first place.

However, the agriculture industry appeared to be more concerned about consumer confidence in U.S. dairy than consumer cancer. Indeed, the “U.S. dairy industry face[d] a brewing public-relations brouhaha,” and it became “concerned about the possibility of eventual mandatory control of these diseases in dairy cattle along with public perception and an impact on the consumption of dairy products.” What would control look like? BLV is a blood-borne virus, but how is it spread? Is Bessie sharing dirty needles? In a sense, yes: “[B]lood (and BLV virus) is readily spread from animal to animal with blood contaminated needles and/or syringes, obstetrical sleeves, saw or gouge dehorners, tattoo pliers, ear taggers, hoof knives, nose tongs,” and other instruments that aren’t disinfected between animals. So, for example, when farmers are gouging or sawing at the cows’ heads during dehorning, “they are likely to drive blood into the next animal during the subsequent dehorning process.” Or, when they’re sticking their arms into cows’ rectums for artificial insemination, it’s not uncommon for there to be rectal bleeding—then they just go from one cow to the next.

More than 20 countries have successfully eradicated BLV from their herds by changing their practices, whereas it remains an epidemic in the United States in part because we’re not cleaning and disinfecting blood-contaminated equipment for things like “supernumerary teat removal,” which is done because “the presence of extra teats detracts from the beauty of the cow.” Supernumerary teats are removed by pulling them from the udder and cutting them off with a pair of scissors. Those scissors had better be clean—otherwise they could spread BLV from calf to calf and ultimately to someone’s breakfast, lunch, or dinner. Of course, we could just not slice off their teats at all, but then how would we “improve udder appearance?”


Up to 37 percent of breast cancer cases are attributable to exposure to bovine leukemia virus? See my video The Role of Bovine Leukemia Virus in Breast Cancer and its prequel, Is Bovine Leukemia Virus in Milk Infectious?.

The meat and dairy industries’ intransigence in the face of a human health threat reminds me of the antibiotics and steroids issues—continuing to place the public at risk to save a few bucks. See, for example, Antibiotics: Agribusinesses’ Pound of Flesh and Zeranol Use in Meat and Breast Cancer.

In health,
Michael Greger, M.D.

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