Enzootic bovine leukosis (cattle)

Description

Enzootic bovine leukosis (EBL) is caused by the retrovirus, bovine leukaemia virus (BLV), which is transmitted horizontally through contact with body fluids containing infected cells, principally blood and milk. Transmission from dam to calf via ingestion of infected milk is the principal route of infection although it has also been associated with natural breeding and veterinary procedures such as rectal palpation, contaminated needles and de-horning equipment.  Congenital transmission also occurs but is less important.  Like other retroviral infections, once established, is lifelong and characterised by the development of circulating antibody, which is also present throughout life.  Affected animals usually develop antibody within 2-3 months of infection. The virus has been eliminated from dairy herds in Australia, but beef cattle may remain infected at a very low prevalence.

Less than 3% of infected animals develop malignant disease.  The peak incidence of disease is in mature cattle, 6 - 8 years old.  Some infected animals have a fluctuating lymphocytosis of moderate degree.  The most common presentation is an enlarged lymph node due to lymphoma.  Any nodes may be affected, e.g. retrobulbar (causing eye protrusion), or pharyngeal (causing stertorous respiration). Lymphoma can involve almost any organ.

Confirmation of lymphoma alone does not confirm EBL, since cattle may also be affected by sporadic forms of lymphoma, not associated with bovine leukaemia virus. Three sporadic forms of lymphoma are described:  The calf type (usually develops in the first six months of life), the thymic type (in yearlings) and the skin type (most often in two year old cattle).

Diagnosis and tests available

Diagnosis

Diagnosis is usually based on confirmation of both lymphoma and bovine leukaemia virus infection.

Tests available

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Additional Information