Author(s):

P Suresh, J Johnson Rajeswar, K Sukumar, TJ Harikrishnan and P Srinivasan

Abstract: This study was undertaken to characterize the oncogenicity associated pp38 gene at molecular level for three serotype 1 Marek’s Disease Virus (MDV) field isolates recovered from vaccinated poultry flocks which had encountered the outbreak of Marek’s Disease (MD) in southern part of India. The prime aim is to generate nucleotide sequence data for important oncogenicity associated pp38 gene of MDV1 which is very much lacking in India. Eighty six blood samples were collected from 15 commercial layer and broiler breeder farms. The virus was isolated in duck embryo fibroblasts (DEF) by co - cultivation of lymphocyte and DEF cells. The Isolates were named as Ind/TN/11/01, Ind/KA/12/02 and Ind/ TN/12/03. The oncogenicity associated pp38 gene was amplified by PCR and sequenced. The isolates were shown to have a homology of 99.3-99.8 per cent within themselves and 79.9-98.4 per cent between MDVs isolated in this study and other isolates of this area reported by earlier workers for pp38 gene. The isolates were shown to have a homology of 97.3-98.3 per cent with various isolates of China and 98.4 – 100 per cent with other isolates of Europe and USA. Alignment analysis of the nucleotide sequences had shown nucleotide mutations when MS 53 strain of China was used as reference strain. The nucleotide mutation in the pp38 gene of MDVs displayed regularity at two positions, including 477 and 640 in the entire field MDV isolates of this study. The mutation at position 477 was unique and coincides with very virulent strains of China and USA including XJ 03, TQ20 and Md5. At position 96 all the isolates are matching with US strains and local isolates of this area reported by earlier workers and differ from MS 53 (G to C). There is a single nucleotide mutation at position 172 (G to C) in the isolate Ind/KA/12/02. There is a single nucleotide mutation at position 548 (G to A) in the isolate Ind/TN/11/01.Phylogenetic analysis on the pp38 sequence of three isolates and other 10 reference strains showed that the analyzed 13 MDVs could be separated three groups (cluster 1, cluster 2 and cluster 3) The study implies that the field isolates of serotype 1 MDVs circulating in vaccinated flocks had been shown to have consistent mutations in different positions in pp38 gene. It would be of use to correlate the pp38 gene sequence results of this study along with other critical oncogenes viz Meq and vIL8 select a better vaccine candidate.

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