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Question of the Day: What is Bovine Leukosis Virus?

What is Bovine Leukosis Virus?

Bovine leukosis virus is a cancer-causing virus found in dairy and beef cattle herds.  It is spread by white blood cells, so any contaminated equipment from BLV-positive cattle (palpation gloves, body fluid, biting insects, needles, surgical dehorning equipment, etc.) can spread the virus throughout a herd.  When a cow becomes infected, she will remain infected for the rest of her life and acts as a carrier for the virus.  Although most cows will not develop any symptoms caused by the virus, a small percentage (2-3%)  will develop cancer caused by BLV.  There is no vaccine or treatment for this virus.

What are the symptoms of BLV?

Enzootic Bovine Lymphosarcoma is the type of cancer caused by BLV and it impacts the lymph nodes, internal organs, and the spinal cords of infected cattle.  Clinical signs depend on the site of tumor development.  Observable signs include blood in the stool, edema, hind leg paralysis, infertility, and large lymph nodes.  Cattle can be tested using an ELIZA test.

How can BLV be controlled in the herd?

There are several options for minimizing or eliminating BLV from cattle herds.  Purchasing negative animals, culling positive animals, managing positive animals in separate areas, wash surgical equipment, change needles and palpation gloves between every animal, and separate calves from cows before they nurse are some of the basic steps to get started.  Discuss a long term management plan with your veterinarian.

Why is controlling BLV important?

Economic losses due to decrease in milk production, animal production, and premature cull costs add up quickly.  However, a recent study from University of California-Berkeley found that women with breast cancer had a significantly higher rate of BLV in their cancerous tissues.  The association between breast cancer and BLV was very strong, and although many causes of breast cancer are genetic, the authors concluded that 37% of breast cancer cases could be attributed to BLV exposure.  BLV is present in cows’ milk, but the virus is destroyed in the pasteurization process.


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