Incidence of avian leukosis virus infection in commercial broiler chicken

Avian leukosis virus (ALV) is an economically important poultry pathogen and its infection may result in low productivity and mortality in chickens. Based on the viral envelope, glycoprotein antigenic structure, host range and mutual interference among different strains, ALVs can be classified as 10 subgroups, A-J. Subgroups A-E and J exist in chickens. ALV-A, B and J are the most common exogenous subgroups that cause chicken tumours, whereas tumours caused by subgroups C, D appear to be rare. Subgroup E is an endogenous leukosis virus, which has low or no pathogenicity to chickens directly, but studies have shown that chickens infected with ALV-E remained viraemic with exogenous virus for longer time and developed neoplasm at a much higher frequency than did the control chickens not infected with ALV-E. Liver samples (35 flocks) were collected from commercial broiler birds which showed liver abnormalities like hepatomegaly, paleness, necrotic spots and haemorrhages. The liver samples were processed and DNA was extracted and polymerase chain reaction PCR amplification of 466 bp glycoprotein gene of ALV subgroup A-E was amplified. Out of 35 flocks, 27 flocks were found positive for ALV and sequence Sequence analysis revealed that 94–96% homology with envelope gene of ALV. Phylogenetic analysis showed that it belonged to ALV subgroup E. Eradication of ALV from primary breeding stocks is the most effective means to control ALV infection.