Evidence of Avian Leukosis Virus Subgroup E and Endogenous Avian Virus in Marek’s Disease Vaccines Derived from Chicken Embryo Fibroblasts

The aim of this study was to detect and characterize the endogenous ALVs in cell associated MD vaccine. Chicken embryo fibroblast cell associated Marek’s disease vaccine was tested for possible contamination with Avian Leukosis Viruses (ALVs). Initially the vaccine cell lysate was tested for presence of group specific antigen (p27) of ALVs by ELISA and found positive for GSA. Subsequently total DNA and RNA was isolated from vaccine CEFs and analyzed by PCR and RT-PCR using primers specific for ALV subgroups A-E and J. Subgroup specific PCR and RT-PCR revealed that the CEFs were positive for ALV-E and negative for all other exogenous ALV subgroups (ALV-A, B, C, D and J). Envelope gp85 gene sequence alignment and phylogenetic analysis further confirmed that the ALV sequences found in CEFs of MD vaccine were belongs to endogenous ALV-E. Further this sequence has high homology with endogenous loci ev-1, ev-3 and ev-6. Amplification of genomic DNA with endogenous virus locus specific primers revealed that the CEFs of MD vaccine possess ev-1 and ev-6 and negative for ev-3, ev-9 and ev-21. In conclusion, the data in this study clearly demonstrated that the cell associated commercial MD vaccine tested was contaminated with an endogenous subgroup E and also possess ev-loci such as ev1 and ev-6.