Bovine Leukemia Virus

By Barry Whitworth

Bovine Leukemia Virus (BLV) is a retrovirus capable of causing cancer in cattle. The disease that is caused by the virus may be referred to as Enzootic Bovine Leukosis (EBL), malignant lymphoma or lymphosarcoma.

In the United States, it is estimated that 44 percent of dairy cows and 10 percent of beef cows are infected with the virus. Most cattle that are infected with the virus are asymptomatic or show no clinical signs of the disease. However, BLV is responsible for production losses due to increase veterinary cost, reproduction inefficiency, decrease milk production and deaths. The number one reason for USDA condemnation of a carcass at slaughter is lymphosarcoma. Another source of lost income is non-export of live cattle, semen and embryos to foreign counties that have control programs in place.

Cattle are infected with the virus when blood is transferred between animals. Lymphocytes, a particular white blood cell, are the specific cells that are infected with the virus. Transfer of blood may occur through contaminated needles, instruments used for castration or dehorning, tattoo instruments, palpation sleeves, or fly taggers. Calves may be infected in the uterus or during the birthing process. Calves can also be infected from colostrum, but this appears to be rare. Biting insects may play a part in transferring the virus, but the evidence is lacking. Many animals have been experimentally infected with the virus but only cattle, water buffaloes and capybaras are infected naturally.

To learn more about BLV, pick up the latest issue of OKFR!