Detection and characterization of endogenous avian leukosis virus obtained from contaminated avian vaccines

In this study the reverse transcriptase polymerase chain reaction (RT- PCR) and the enzyme linked immunosorbent assay (ELISA) were utilized for screening of different live avian viral vaccines to detect biocontamination with avian leukosis virus (ALV). By using ELISA test, the group specific antigen of avian leukosis virus was detected in three batches of Marek’s disease virus (MDV) vaccines as well as in one batch of avian encephalomyelitis virus (AEV) vaccine. To identify the subgroup of the contaminant ALV, contaminated samples were tested by RT – PCR using sets of primers specific to the envelope (env) gene of avian leukosis virus. Virus subgroup was determined by running simultaneously 6 RT- PCR reactions. Results of RT- PCR revealed detection of subgroup E specific product in all four ELISA – positive vaccine batches. No PCR products were detected with primers designed for detection of exogenous virus subgroups A, B, C, D, or J. Trials for isolation of ALV from contaminated vaccines were failed after inoculation and incubation in chicken embryo fibroblast cell cultures for 21 days, indicating inability of the contaminant ALV to replicate in inoculated cultures. Detection sensitivity of RT – PCR was 1000 – fold higher than that of ELISA. Results indicate that both ELISA and RT-PCR are reliable assays for detection of vaccine contamination with ALV, although ELISA is still lacking the ability to differentiate between different ALV subgroups. These disadvantages of ELISA could be overcome by using RT-PCR which is proved as a rapid, specific and sensitive technique for both the detection and characterization of ALV