Molecular characterization and phylogenetic analysis of oncogenes from virulent serotype-1 Marek's disease virus in India

Marek's disease (MD) is one of the most important neoplastic diseases of poultry caused by Marek's disease virus (MDV), an oncogenic avian herpes virus, which is responsible for great economic losses to the poultry industry worldwide. Inspite of the usage of HVT and bivalent vaccines in the poultry flocks, MD continues to be a major threat to the poultry industry in India. In the present study, MD outbreaks were reported in poultry farms from different regions of Andhra Pradesh, India. The postmortem examination of dead birds showed presence of lymphomas in different visceral organs suggestive of virulent oncogenic M DVs. Histopathological examination revealed infiltration of pleomorphic lymphoblastoid cells typical of MD. The blood and tissue samples were collected and PCR was standardized targeting a 132 bp tandem repeat region specific for serotype-1 MD viruses. Further, the characterization of the oncogenes i.e. Meq and viral interleukin 8 (vIL-8) was carried out by PCR and nucleotide sequencing. The sequence analysis of Meq gene of different clinical cases from India revealed >99 % homology with RBIB (very virulent) and GA (virulent) strains and that of vIL-8 gene showed >99 % identity with virulent strains LS and LMS. Phylogenetic analysis of oncogenes was carried out with other available sequences in the GenBank. Finally, we conclude that MDV strains obtained in the present outbreaks in India could be designated as virulent or very virulent pathotypes based on nucleotide, amino acid and phylogenetic analysis of the viruses.