LYMPHOID LEUKOSIS

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Causative Agent(s)

Virally induced clonal malignancy of the bursal-dependent lymphoid system. Caused by certain members of the leucosis/sarcoma group of avian retroviruses. Occurs naturally only in chickens.

Clinical Presentation and Epidemiology

Transmission is by shedding the virus by infected hen into the albumin or yolk (or both). Congenitally infected chickens fail to produce neutralizing antibodies and usually remain viraemic for life. Horizontal infection after hatching also occurs. The earlier the infection, the more likely it is to lead to tolerance, persistent viremia, and tumours. Tumours are more frequent with congenital infection. Tumours are composed almost entirely of B lymphocytes, that often have IgM on the surfaces. Common in liver, spleen, and bursa. Found occasionally in kidneys, gonads, and mesentery.

Diagnostic Consideration

Diagnosis is based on history, clinical signs, gross necropsy, and histopathology. Immunocytology is highly distinguishing with other tumours but may not be easily available. Standard and quantitative PCR, virus isolation and serology are useful in diagnosis.

Management and Treatment

Can be prevented (even up to 5 months of age) by treatments that destroy the bursa.