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Enzootic Bovine Leukosis

Enzootic Bovine Leukosis (EBL) also known as Bovine lymphosarcoma, Leukemia and Malignant lymphoma.

Enzootic bovine leukosis (EBL) is a lympho-proliferative disease of cattle. It occurs in all breeds of both sexes.

Etiology

Enzootic Bovine Leukosis is caused by bovine leukemia virus (BLV)-Exogenous C-type oncogenic retrovirus of retroviridae.
The virus infects a subpopulation of B lymphocytes, and proviral DNA is integrated to a number of sites on the cellular DNA.

Iatrogenic transmission occurs through inoculation of small amounts of infected blood (e.g. infected needles, tattooing, dehorning and rectal palpation).
Vertical transmission from the dam to the calf (3–20 % of calves may become infected) and by colostrum or milk (less than 2 %).
Insect transmission is also a possibility; higher rates of infection were reported in the summer.

Bovine leukosis is observed in two forms:
- (a) Sporadic form – rare and occur in cattle below 3 yrs of age.
- (b) Enzootic form- most common and occur in cattle over 3yrs of age.
Infections are usually subclinical; only 30–70% of infected cattle develop persistent lymphocytosis, and 0.1–10% of the infected animals develop tumours.
Signs will depend on the site of the tumours and may include digestive disturbances, inappetence, weight loss, weakness or general debility and sometimes neurological manifestation.

Weight loss.
Laboured breathing due to heart involvement.
Persistent diarrhoea following infiltration of the abomasum wall by neoplastic cells.
Marked enlargement of several superficial lymph nodes.
Edema of the brisket and the intermandibular region.
Paralysis of the hind legs due to tumour compression of the spinal cord.
Protrusion of the eye as a result of tumour invasion of the orbital cavity.
Debilitation or emaciation.
Pale mucosal surface.
Bloated animal.
Swelling of the neck when thymus is involved.
Cutaneous nodules in the terminal stage.

Based on clinical symptoms and lesions.
Virus can be detected in the culture supernatant following in-vitro culture of peripheral blood mononuclear cells (PBMC) from infected animals.
Proviral DNA can also be detected in PBMC or tumours of infected animals by PCR.
Detection of antibody by AGID in serum.
Detection of antibody by ELISA in serum or milk of infected animals.

Lymphadenitis due to tuberculosis and actinobacillosis.
Hyperplastic haemo-lymph nodes.
Congestive heart failure due to traumatic pericarditis.
Enlarged spleen in septicaemic disease.
Compression of spinal cord by tumour is differentiated with dumb form of rabies.

Vaccine are not available for BLV.
Test and slaughter of seropositive animals in the herd.
Screening of antibodies in milk by ELISA.
Use single disposal gloves and needle to avoid transmission of disease through blood.
Cleaning and disinfection of dehorning and tattoo equipment and surgical instruments after use.