Bovine leukemia virus

Bovine leukemia virus (BLV) is a retrovirus that affects cattle. BLV is the causative agent of Enzootic Bovine Leukosis (EBL), a disease characterized by a benign growth of lymphoid tissue that can progress to lymphoma and leukemia in some cases. The virus is part of the Retroviridae family, specifically within the genus Deltaretrovirus. BLV infection is widespread globally, affecting the health and productivity of cattle, and poses a significant economic burden on the dairy industry and beef industry.

Transmission

BLV is primarily transmitted through the transfer of bodily fluids between infected and uninfected animals. The most common routes of transmission include:

• Blood transfer via contaminated needles, dehorning instruments, and other surgical tools.
• Milk and colostrum from infected cows to calves.
• Vertical transmission from an infected cow to her offspring during pregnancy.

In addition, the virus can be spread through close contact, as it is present in various bodily fluids such as saliva, nasal secretions, and semen.

Clinical Signs and Diagnosis

Most cattle infected with BLV are asymptomatic. However, a small percentage may develop persistent lymphocytosis, which is an increase in the number of lymphocytes in the blood. Even fewer may progress to develop EBL, characterized by the development of tumors in various organs, including the heart, abomasum, spleen, and lymph nodes.

Diagnosis of BLV is typically performed through serological tests such as the enzyme-linked immunosorbent assay (ELISA) or the agar gel immunodiffusion test (AGID), which detect antibodies to BLV in the blood. Polymerase chain reaction (PCR) tests can also be used to detect the presence of BLV DNA in blood or tissue samples.

Prevention and Control

There is currently no vaccine available for BLV, so control measures focus on reducing the risk of transmission. These measures include:

• Testing and culling infected animals.
• Using disposable needles and properly sterilizing surgical equipment.
• Avoiding the pooling of milk for feeding calves.
• Implementing good management practices to reduce stress and improve the overall health of the herd.

Economic Impact

The economic impact of BLV on the dairy and beef industries is significant. Infected cattle may suffer from reduced milk production, weight loss, increased susceptibility to other diseases, and decreased fertility. Additionally, the presence of BLV can restrict trade and export opportunities for affected herds.

Public Health Concerns

While BLV is a disease of cattle, there has been some concern about the potential for zoonotic transmission, or the virus spreading from animals to humans. However, to date, there is no conclusive evidence that BLV infects humans or poses a risk to public health.

See Also

• Retrovirus
• Leukemia
• Dairy farming
• Beef farming