What is BLV?
Enzootic bovine leukosis is a contagious disease of cattle caused by bovine leukemia virus (BLV). BLV is a retrovirus of cattle and is related to retroviruses of other mammals, including HIV in humans. About 40% of BLV-infected cattle will develop an abnormally large number of lymphocytes – a type of white blood cell that plays an important role in immune function1. This condition is called lymphocytosis. Once cattle develop lymphocytosis from BLV it tends to persist for the remainder of the animal's life – therefore, this is often referred to as persistent lymphocytosis. Lymphocytosis in BLV-infected cattle is an indication that the animal's immune system may be compromised2–4. BLV infection with or without persistent lymphocytosis has been associated with a decrease in milk production and an increased risk of being culled, which are thought to be results of altered immune function5–8. It is estimated that around 5% of infected cattle will eventually develop lymphoma – tumors originating from infected lymphocytes which can occur in many different organs1,9. This is currently the most common type of cancer found in cattle at the time of slaughter in the United States10,11.