Avian leucosis complex (ALC)
The disease in poultry is caused by an RNA virus classified under avian type C Retrovirus group under the family Retroviridae.
Epidemiology: Avian leucosis viruses are endemic in virtually all flocks of chickens. The clinical manifestation is sporadic in birds over 14 weeks of age with an incidence rate of around 3%. However, in some lines of birds the incidence rate may reach up to 20%.
Symptoms: The clinical sings in affected birds show pale comb, shriveled, cyanotic and enlarged abdomen. On autopsy, tumors occur in liver, spleen, bursa and in a few other internal organs. Microscopically the lesions reveal multicentric aggregates of lymphoblasts.
Diagnosis: ALC is diagnosed by complement fixation test (CFT), radioimmunoassay (RIA) and ELISA for group specific antigens. Tests for reverse transcriptase, immunohistochemical tests; virus isolation methods etc. are available for laboratory confirmation of the disease. There is no effective vaccine available to control this disease.
Treatment and control: It is controlled through
(i) establishing leucosis - free breeding flocks by a routine screening and breeding programme
(ii) strict hygienic conditions on the premises to ward off lateral transmission of the virus
(iii) encouraging breeds derived from ALC- resistant flocks.