Sequence analysis of Meq oncogene among Indian isolates of Marek's disease herpesvirus

Abstract

Marek's disease (MD), caused by Marek's disease virus (MDV), is a highly contagious neoplastic disease of chicken that can be prevented by vaccination. However, in recent years many cases of vaccine failure have been reported worldwide as chickens develop symptoms of MD in spite of proper vaccination. Distinct polymorphism and point mutations in Meq gene of MDV have been reported to be associated with virulence and oncogenicity. The present study was carried out with the objective to isolate and characterize field isolates of MDV on the basis of Meq gene. Twenty five samples of suspected cases of MD were collected and processed for virus isolation in duck embryo fibroblast (DEF) primary culture where 28% (7 of 25) samples showed characteristic cytopathic effects of MDV in the form of plaques and syncytia. Additional evidence of presence of MDV in these samples was confirmed by PCR. To analyze diversity in all seven isolates of MDV, a polymorphism study was carried out by cloning and sequencing of full length of Meq gene (1020 bp). Sequence homology of 7 isolates with 23 reference strains showed 98.10–99.40% similarity in nucleotide and 95.90–98.50% similarity in amino acid sequences. Six isolates revealed 5 repeat sequences of 4 prolines (PPPP) whereas, one isolate revealed only 4 repeats. In phylogenetic analysis, these isolates formed a separate cluster showing close relatedness to the Chinese isolates. The study indicates a high mutation rate in field isolates of MDV that may be probable cause of vaccination failure.

Characterization of Marek’s disease virus and phylogenetic analyses of meq gene from an outbreak in poultry in Meghalaya of Northeast India

“…While meq gene detection indicates the pathogenicity of the virus, the number of repeat sequences of four prolines (PPPP repeats) in the meq gene (overall range 2-8) have been reported to correlate with MDV virulence and oncogenicity [19] with the most pathogenic isolates having the fewest number of repeats [17]. Compared with 30 reference strains, both the isolates have 5 PPPP repeats similar to the six isolates from north India [9] and one each from Hungary and South India indicating the virulence potential. The isolates in cluster II have 2-4 PPPP repeats while the isolates in cluster III have PPPP repeats ranges from 4 to 7 probably indicating the level of pathogenic potential of the isolates in each clusters.…”

Marek's disease viruses circulating in commercial poultry in Italy in the years 2015–2018 are closely related by their meq gene phylogeny

“…At the moment in vivo studies are mandatory for an accurate inclusion of GaHV‐2 strains into one of the known pathotypes. The meq gene polymorphism is also useful to create epidemiological molecular linkages between various GaHV‐2 strains, according to the numerous studies that have been recently published from various countries: China (Tian et al, ; Yu et al, ; Zhang, Liu, Zhang, Shi, & Li, ), Poland (Woźniakowski & Samorek‐Salamonowicz, ), USA (Padhi & Parcell, ), Colombia (Lòpez‐Osorio et al, ), Egypt (Abdallah et al, ; Hassanin, Abdallah, & El‐Araby, ), India (Gupta, Deka, & Ramneek, ; Prathibha, Sreedevi, Vinod Kumar, & Srilatha, ; Suresh, Johnson Rajeswar, Sukumar, Harikrishnan, & Srinivasan, ) and Japan (Abd‐Ellatieff et al, ).…”

Data on meq gene sequence analysis of Ludhiana MDV isolates

“…This data revealed that seven Meq amino acid sequences of Ludhiana isolates had the highest sequence similarity with LSY (LN07I), LCD (SC07II), CVI 988/Rispens vaccine strain and mCU-2 strain. The values of similarity between the sequences are reported in [1] .…”