Comparative sequence analysis of Meq oncogene of Marek’s disease virus field isolates detected in Marek’s disease affected birds from vaccinated poultry flocks

Serotype 1 of Marek’s disease virus (MDV-1) is the potent causative agent of Marek’s Disease (MD), which is an economically important viral disease of chickens characterised by lymphoproliferative and neuropathic syndromes. The Meq gene is the principal oncogenic gene of MDV-1, which is responsible for neoplastic lesions in birds. In spite of vaccination, MD is still a potent threat to the poultry industry. The study aimed to detect the circulating MDV in the field, which is responsible for MD in vaccinated poultry flocks. The MDVs were detected using primers to amplify the MDV-1 Bam H1-H 132 bp tandem repeat, which distinguishes the field MDV strain from the vaccine strain. PCR was done to amplify the Meq oncogene. The full-length Meq gene (1020 bp) PCR-amplified products were purified and sequenced to analyse the sequence diversity. The local MDV’s Meq gene sequences revealed 98.5-99.9% nucleotide sequence homology with that of 30 reference strains. Analysis of the Meq gene sequences revealed distinct diversity and point mutations in the Meq sequence. Meq proteins showed the presence of four proline-rich repeats, indicating their virulence character. The present study indicated that virulent oncogenic MDV-1 is circulating in Punjab, and the point mutation that was observed in the Meq gene might be one of the factors responsible for increasing the virulence of MDV and thereby causing the failure of commercial vaccines to provide protection against MD.