Marek’s disease: time to review the emerging threat in Indian poultry

Simultaneous detection and differentiation of three oncogenic viral diseases of chicken by use of multiplex PCR

Avian oncogenic or tumor diseases are common in poultry industry causing significant economic loss. Marek's disease (MD), avian leukosis (AL) and Reticuloendotheliosis (RE) are the three major viral oncogenic infections that are difficult to differentiate with gross lesions. Multiplex PCR for simultaneous detection and differentiation of these three viruses was developed and validated. The primers targeting the genes of pp38, pol and LTR for MDV, ALV and REV were designed to yield 206, 429, and 128 bp, respectively. The sensitivity of the PCR primers was checked with serial dilution of positive template DNA for each virus and found to be in the range of 10^-5 to 10^-7 of 1 µg/µl of initial template DNA. Out of 114 suspected tumor samples screened, 8 samples were positive for MDV, 13 samples were positive for ALV and 31 samples positive for REV. Five samples were positive for both MD and ALV; 3 samples were positive for MD and REV and 25 samples were positive for ALV and REV. Eight samples were positive for all three viruses. Multiplex PCR demonstrated to be a useful technique for simultaneous, rapid detection and differentiation of major tumor causing and immunosuppressive viral diseases of chicken.

Quantitative profiling of Marek's Disease Virus in vaccinated layer chicken

The present study was undertaken to quantify the Marek's Disease Virus (MDV) serotypes in vaccinated commercial layer flocks at 7, 14, 21, 28, 35 and 60-90 days post vaccination (dpv) and to correlate the pathogenic Gallid herpesvirus 2 (GaHV-2, MDV1) load with vaccine viral load of Gallid herpesvirus 3 (GaHV-3, MDV2) and Meleagridis herpesvirus 1 (MeHV-1, MDV3). A total of 25 commercial layer flocks were selected in and around Namakkal district of Tamil nadu, India and the feather pulp (FP) and blood samples were collected. Out of 25 flocks, 14 were revaccinated with bivalent vaccine, six were revaccinated with monovalent vaccine apart from the initial bivalent vaccination done at hatchery and five flocks were not revaccinated. SYBR green based real time PCR was used for absolute quantification of MDV serotypes. The pathogenic MDV1 load had shown an increasing trend until 21 dpv followed by a dip and again had shown a constant uptick between 60 and 90 dpv in the flocks that went on to develop MD outbreak. The flocks which had not encountered any Marek's Disease outbreak had shown increasing trend of MDV2 and 3 load until 21 dpv followed by a slight decrease but maintained a higher load when compared to MDV 1 which had marked a sharp decline between 60 and 90 dpv. Outbreak of MD was observed in seven (28%) out of 25 flocks between 18 and 27 weeks of age. It includes, two out of fourteen farms (14%) revaccinated with bivalent vaccine, two out of six farms (33%) revaccinated with MDV3 vaccine and three out of five farms (60%) without revaccination. The overall mean of vaccine viral load at various stages of dpv was constantly low where as pathogenic MDV 1 load was constantly high between 60 and 90 dpv in the flocks that went on to develop Marek's Disease during later part of life.

Molecular detection and phylogenetic analysis of Marek's disease virus virulence-associated genes from vaccinated flocks in southern India reveals circulation of virulent MDV genotype

Marek's disease (MD) is a re-emerging viral disease of chickens and a serious economic threat to the poultry industry worldwide. Continuous surveillance with molecular investigation is essential to monitor the emergence of virulent Marek's disease virus (MDV) strains and to devise any appropriate vaccination strategy and implement bio-security programmes. In the present study, we investigated the cases of MD outbreaks in vaccinated poultry flocks. The MD outbreak was confirmed through necropsy (mainly visceral tumours), histopathology and viral gene specific PCR. The pathotypes of the field MDV strains were assessed by molecular analysis of three virulence-associated genes, meq, pp38 and vIL-8. The Meq sequence of the field strains analyzed in this study lacked the 59 aa unique to mild strains, indicating that they are potentially virulent strains. Mutation at position 71 and the presence of five proline rich repeats in the transactivation domain, both associated with virulence were observed in these strains; however, the signature sequences specific to very virulent plus strains were absent. Phylogenetic analysis of meq oncogene sequences revealed clustering of the field strains with North Indian strains and with a very virulent plus ATE 2539 strain from Hungary. Analyses of pp38 protein at positions 107 and 109 and vIL-8 protein at positions 4 and 31 showed signatures of virulence. Sequence and phylogenetic analysis of oncogene and virulence-associated genes of field MDVs from vaccinated flock indicated that these strains possessed molecular features of virulent strains.

Role of microRNA and long non-coding RNA in Marek's disease tumorigenesis in chicken

Marek's disease virus (MDV), the causative agent of Marek's disease (MD), results in highly infectious phymatosis, lymphatic tissue hyperplasia, and neoplasia. MD is associated with high morbidity and mortality rate. Non-coding RNAs (ncRNAs) entails long non-coding RNA (lncRNA) and microRNA (miRNA). Numerous studies have reported that specific miRNAs and lncRNAs participate in multiple cellular processes, such as proliferation, migration, and tumor cell invasion. Specialized miRNAs and lncRNAs militate a similar role in MD tumor oncogenesis. Despite its growing popularity, only a few reviews are available on ncRNA in MDV tumor oncogenes. Herein, we summarized the role of the miRNAs and lncRNAs in MD tumorigenesis. Altogether, we brought forth the research issues, such as MD prevention, screening, regulatory network formation, novel miRNAs, and lncRNAs analysis in MD that needs to be explored further. This review provides a theoretical platform for the further analysis of miRNAs and lncRNAs functions and the prevention and control of MD and malignancies in domestic animals.