F80
Bovine Leukosis Virus (BLV)

Causative Agent: Bovine leukosis virus (BLV) is a retrovirus infection of dairy and beef cattle that causes a type of cancer called malignant lymphoma. This condition is also called lymphosarcoma or leukemia. In a typical herd, 30-40% of the animals may be infected, but only 1-5% of these animals show any clinical signs.

Clinical Signs: Clinical signs become evident as the tumors invade different tissues and may include weight loss, enlarged lymph nodes, loss of appetite, rear-limb weakness or paralysis, fever, protruding eyeballs, gastrointestinal obstruction, abnormal heartbeat, and increased blood lymphocyte count. Once the clinical signs begin, the disease is most often fatal and there are no drugs to treat the cancer. BLV is not transmissible to humans and no human disease has ever been attributed to BLV.

Disease Transmission: The most common method of spreading the disease is by contact with blood from infected animals. Blood-contaminated milk, urine, and manure can spread the disease. BLV can be spread when needles or other equipment are used on an infected animal and then on a non-infected animal.

Diagnosis: There are very few specific clinical signs. Most cases remain undetected until slaughter. In some cases, however, enlarged lymph nodes in the body can be detected during a rectal palpation. Blood serum tests such as AGID can be used to determine animals with antibodies to BLV. These blood samples should be collected in red top tubes and sent to the appropriate laboratory. Recent advances in testing can detect BLV in a combined milk sample.

Prevention: There are no vaccines available for the prevention of BLV. Following basic management practices is the only effective control:

  1. Identify BLV positive animals in the herd and slaughter clinical animals immediately.
  2. Buy only animals tested BLV negative in the last 30 days.
  3. Raise replacement heifers away from any contact with adult animals.
  4. Use hot irons or dehorning paste for dehorning.
  5. Sterilize intravenous tubes, needles, fetal delivery equipment, and mechanical dehorners with a solution effective against BLV.
  6. When vaccinating or injecting cattle, use needles only once.
  7. Use palpation sleeves only once, particularly if blood is present.
  8. Pasteurize milk or colostrum from infected cows before feeding to young calves.