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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: GENETIC AND BIOLOGICAL DETERMINANTS OF AVIAN TUMOR VIRUS PATHOGENICITY, TRANSMISSION, AND EVOLUTION

Location: Avian Disease and Oncology Research

2013 Annual Report


1a. Objectives (from AD-416):
Objective 1: Identify host and/or viral genetic determinants that control pathogenicity, transmission, and drive the evolution of new strains of avian tumor viruses. Subobjective 1.2: Identify the genetic determinants in the MDV genome that account for vitro attenuation. Subobjective 1.3: Factors that influence the development of spontaneous ALV-like tumors. Subobjective 1.4: Confirming an association between MDV replication rate and pathotype. Objective 2: Develop diagnostics for detecting new strains of avian tumor viruses. Subobjective 2.1: Evaluation of MDV BAC clones as standardized reagents for MDV research. Subobjective 2.2: Surveillance for virulent strains of avian tumor viruses in field flocks and develop improved diagnostics for new strains. Subobjective 2.3: Development of reliable techniques for immunohistochemistry (IHC) using paraffin-fixed sections. Objective 3: Elucidate the genetic determinants that modulate MDV interactions with the avian immune system. Subobjective 3.1: Identification and characterization of host/viral genes that mediate production of cell-free enveloped infectious virus particles in the FFE Subobjective 3.2: Role of NK cells in vaccine-induced immunity against MD. Subobjective 3.3: Role of macrophages and T cells in viral transport to lymphoid organs and FFE. Objective 4: Discover safe and highly effective vaccine platforms that convey protection against emerging MDV strains. Subobjective 4.3: Determine protective ability of high passage levels of a BAC clone of strain Md5 of MDV containing LTR from REV. Subobjective 4.4: Evaluation of vaccine competition using HVT strains.


1b. Approach (from AD-416):
Avian tumor viruses of economic importance include: 1) Marek’s disease virus (MDV), a herpesvirus that induces a lymphoproliferative disease of chickens that, in the absence of effective control measures, is capable of causing devastating losses in commercial layer and broiler flocks; and 2) avian retroviruses, namely avian leukosis virus (ALV) and reticuloendotheliosis virus (REV), both are associated with neoplastic diseases and other production problems in poultry. Also, both ALV and REV are potential contaminants of live-virus vaccines of poultry. Critical needs are: 1) better MDV vaccines to protect against the current and next generation of virulent field strains of MDV; 2) a long-term strategy designed to reduce the ongoing emergence of new virulent MDV through multiple barriers or reduction in viral load and shedding; and 3) better procedures to detect and control new ALV recombinants. The primary emphasis will be on molecular approaches to better understand which viral genes are important for immunopathogenesis and shedding of MDV. Parallel studies will monitor the virulence of field strains of MDV and avian retroviruses, primarily ALV. Studies are also aimed at characterization of new virus isolates and on improving assays for their detection; additional efforts will be devoted to better understand MDV immunity and role of MDV vaccines in enhancement of spontaneous non ALV-induced tumors. The four objectives are highly interrelated and interface in a manner that should not only identify new basic knowledge but also translate this knowledge to practical use in control programs. The end product will be a better understanding of viral gene function, virus-host interactions and the development of materials and improved methodology for diagnosis and control of avian tumor viruses.


3. Progress Report:
Substantial progress was made on all objectives of the project. Sequence variants that are associated with in vitro attenuation of Marek’s disease viruses (MDVs) were tested in recombinant MDVs. Of the 5 viruses tested, a single base change in a single gene resulted in almost complete loss of virulence, suggesting that such approach could be used in preparation of next generation MD vaccines. Our studies to determine the correlation between MDV replication and virulence indicated that the lowest virulent strains had significantly lower virus replication compared to viruses in the two higher virulence pathotype groups, but viruses in the higher two groups were unable to be distinguished. Results from evaluating interference between HVT-vectored vaccines suggested that insertion of another viruses’ gene into the HVT vaccine reduces the ability of the virus to replicate in birds. We also characterized several highly virulent MDV strains from current outbreaks; we plan to sequence these isolates in hopes of identifying correlations between DNA sequence and virulence as an alternative to slower and more costly evaluations in birds. Two experiments were conducted to test the protective efficacy of an experimental recombinant MDV vaccine that contains LTR from reticuloendotheliosis virus (REV) termed rMd5/REV LTR BAC. Results from both experiments indicate that this recombinant MDV was as effective as Rispens vaccine, the most effective currently available commercial MDV vaccine. Data obtained from our studies to understand the role of subgroup E avian leukosis virus (ALV-E) and serotype 2 MDV vaccine in enhancement of spontaneous ALV-like tumors, suggest that ALV-E and serotype 2 MDV plays an important role in the enhancement of spontaneous ALV-like tumors in certain lines of chickens. This year, our studies to determine the role of macrophages (MQ) in MD revealed that depletion or partial reduction of MQ population was inversely correlated with number of virus particles and infected cells; also reduction in MQ population had an adverse effect on the expression pattern of cytokines/chemokines in the MDV-infected tissues. Also, our investigations to study role of natural killer (NK) cells in MD vaccinal immunity suggested that vaccination arms NK cells by increasing the production of cytotoxic granule proteins (granzyme and perforin) and interferon gamma, and that a functional marker for NK cell degranulation (called CD107a) was significantly increased in expression at seven days post vaccination.


4. Accomplishments


Review Publications
Pandiri, A.R., Gimeno, I.M., Mays, J.K., Reed, W.M., Fadly, A.M. 2012. Reversion to subgroup J avian leukosis virus viremia in seroconverted adult meat-type chickens exposed to chronic stress by adrenocorticotrophin treatment. Avian Diseases. 56:578-582.

Xu, M., Fitzgerald, S.D., Zhang, H., Karcher, D.M., Heidari, M. 2012. Very virulent plus strains of MDV induce acute form of transient paralysis in both susceptible and resistant chicken lines. Viral Immunology. 25(4):306-323.

Dunn, J.R., Silva, R.F. 2012. Ability of MEQ-deleted MDV vaccine candidates to adversely affect lymphoid organs and chicken weight gain. Avian Diseases. 56:494-500.

Plotnikov, V.A., Grebennikova, T.V., Yuzhakov, A.G., Dudnikova, E.K., Norkina, S.N., Zaberezhny, A.D., Aliper, T.I., Fadly, A.M. 2012. Molecular-genetic analysis of field isolates of Avian Leucosis Viruses in the Russian Federation. Problems of Virology. 57(5):39-43.

Lee, L.F., Heidari, M., Sun, A., Zhang, H., Lupiani, B., Reddy, S.M. 2013. Identification and in vitro characterization of a Marek’s disease virus encoded ribonucleotide reductase. Avian Diseases. 57:178-187.

Lee, L.F., Kreager, K., Heidari, M., Zhang, H., Lupiani, B., Reddy, S.M., Fadly, A.M. 2013. Properties of a meq-deleted rMd5 Marek’s disease vaccine: protection against virulent MDV challenge and induction of lymphoid organ atrophy are simultaneously attenuated by serial passage in vitro. Avian Diseases. 57(2):491-497.

Dunn, J.R., Gimeno, I.M. 2013. Current status of Marek’s disease in the United States & worldwide based on a questionnaire survey. Avian Diseases. 57(2):483-490.

Lupiani, B., Lee, L.F., Kreager, K.S., Witter, R.L., Reddy, S.M. 2013. Insertion of reticuloendotheliosis virus long terminal repeat into the genome of CVI988 strain of Marek’s disease virus results in enhanced growth and protection. Avian Diseases. 57(2):427-431.

Reddy, S.M., Sun, A., Khan, O.K., Lee, L.F., Lupiani, B. 2013. Cloning of a very virulent plus, 686 strain of Marek’s disease virus as a bacterial artificial chromosome. Avian Diseases. 57(2):469-473.

Sun, A., Lee, L.F., Khan, O., Heidari, M., Zhang, H., Lupiani, B., Reddy, S. 2013. Deletion of Marek’s disease virus large subunit of ribonucleotide reductase (RR) impairs virus growth in vitro and in vivo. Avian Diseases. 57(2):464-468.

Last Modified: 10/19/2017
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