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Ellington C, Cortes AL, Faiz NM, Mays JK, Fadly A, Silva RF, Gimeno IM. Characterization of Md5-BAC-REV-LTR virus as Marek's disease vaccine in commercial meat-type chickens: protection and immunosuppression. Avian Pathol 2021; 50:490-499. [PMID: 34463588 DOI: 10.1080/03079457.2021.1970108] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Md5-BAC-REV-LTR is a recombinant Marek's disease virus (MDV), with an insertion of the long terminal repeat (LTR) of reticuloendotheliosis virus (REV) into the genome of the highly virulent MDV strain rMd5. It has been shown that Md5-BAC-REV-LTR does not induce tumours and confers high protection against challenge with MDV in 15 × 7 chickens. The objective of the present study was to evaluate the protection and safety (in terms of oncogenicity and immunosuppression) of Md5-BAC-REV-LTR in commercial meat-type chickens bearing maternal antibodies against MDV. Our results show that sub-cutaneous administration of Md5-BAC-REV-LTR at 1 day of age conferred high protection (protection index PI = 84.2) against an early challenge (1 day) by contact exposure to shedder birds infected with the vv+ MDV 648A strain. In such stringent challenge conditions, Md5-BAC-REV-LTR was more protective than a commercial CVI988 (PI = 12.4) and similar to the experimental vaccine Md5-BACΔmeq (PI = 92.4). Furthermore, Md5-BAC-REV-LTR did not induce either tumours or immunosuppression in this study. Immunosuppression was evaluated by the relative lymphoid organ weights and also by the ability of the vaccine to induce late-MDV-induced immunosuppression associated with reactivation of the virus. This study shows that Md5-BAC-REV-LTR has the potential to be used as a MD vaccine and is highly protective against early challenge with vv+ MDV. RESEARCH HIGHLIGHTSMd5-BAC-REV-LTR is highly protective against early challenge with vv+ MDV in commercial meat-type chickens.Md5-BAC-REV-LTR does not cause early immunosuppression.Md5-BAC-REV-LTR does not cause late immunosuppression.Unlike other serotype 1 vaccines, Md5-BAC-REV-LTR is not detected in feather pulp at 7 days post vaccination.
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Affiliation(s)
- C Ellington
- Department of Population Health and Pathobiology, Veterinary School, North Carolina State University, Raleigh, NC, USA
| | - A L Cortes
- Department of Population Health and Pathobiology, Veterinary School, North Carolina State University, Raleigh, NC, USA
| | - N M Faiz
- Department of Population Health and Pathobiology, Veterinary School, North Carolina State University, Raleigh, NC, USA.,Department of Veterinary Clinical Studies, Faculty of Veterinary Medicine, Universiti Putra Malaysia, Serdang, Malaysia
| | - J K Mays
- USDA-ARS Avian Disease and Oncology Laboratory, East Lansing, MI, USA
| | - Aly Fadly
- USDA-ARS Avian Disease and Oncology Laboratory, East Lansing, MI, USA
| | - Robert F Silva
- USDA-ARS Avian Disease and Oncology Laboratory, East Lansing, MI, USA
| | - I M Gimeno
- Department of Population Health and Pathobiology, Veterinary School, North Carolina State University, Raleigh, NC, USA
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Abstract
A healthy immune system is a cornerstone for poultry production. Any factor diminishing the immune responses will affect production parameters and increase cost. There are numerous factors, infectious and noninfectious, causing immunosuppression (IS) in chickens. This paper reviews the three viral diseases that most commonly induce IS or subclinical IS in chickens: Marek's disease virus (MDV), chicken infectious anemia virus (CIAV), and infectious bursal disease virus (IBDV), as well as the interactions among them. MDV-induced IS (MDV-IS) affects both humoral and cellular immune responses. It is very complex, poorly understood, and in many cases underdiagnosed. Vaccination protects against some but not all aspects of MDV-IS. CIAV induces apoptosis of the hemocytoblasts resulting in anemia, hemorrhages, and increased susceptibility to bacterial infections. It also causes apoptosis of thymocytes and dividing T lymphocytes, affecting T helper functions, which are essential for antibody production and cytotoxic T lymphocyte (CTL) functions. Control of CIAV is based on vaccination of breeders and maternal antibodies (MAbs). However, subclinical IS can occur after MAbs wane. IBDV infection affects the innate immune responses during virus replication and humoral immune responses as a consequence of the destruction of B-cell populations. Vaccines with various levels of attenuation are used to control IBDV. Interactions with MAbs and residual virulence of the vaccines need to be considered when designing vaccination plans. The interaction between IBDV, CIAV, and MDV is critical although underestimated in many cases. A proper control of IBDV is a must to have proper humoral immune responses needed to control CIAV. Equally, long-term control of MDV is not possible if chickens are coinfected with CIAV, as CIAV jeopardizes CTL functions critical for MDV control.
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Affiliation(s)
- I M Gimeno
- A Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607
| | - K A Schat
- B Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853
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Ahmed H, Mays J, Kiupel M, Dunn JR. Development of reliable techniques for the differential diagnosis of avian tumour viruses by immunohistochemistry and polymerase chain reaction from formalin-fixed paraffin-embedded tissue sections. Avian Pathol 2018. [PMID: 29533078 DOI: 10.1080/03079457.2018.1451620] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
A variety of techniques have been developed as diagnostic tools for the differential diagnosis of tumours produced by Marek's disease virus from those induced by avian leukosis virus and reticuloendotheliosis virus. However, most current techniques are unreliable when used in formalin-fixed paraffin-embedded (FFPE) tissues, which often is the only sample type available for definitive diagnosis. A collection of tumours was generated by the inoculation of different strains of Marek's disease virus, reticuloendotheliosis virus or avian leukosis virus singularly or in combination. FFPE tissue sections from tumour and non-tumour tissues were analysed by optimized immunohistochemistry (IHC) techniques and traditional as well as quantitative polymerase chain reaction (PCR) with newly designed primers ideal for DNA fragmented by fixation. IHC and PCR results were highly sensitive and specific in tissues from single-infected birds. Virus quantity was higher in tumours compared to non-tumour spleens from Marek's disease (MD) virus-infected birds. Thus, using FFPE sections alone may be sufficient for the diagnosis of MD by demonstration of high quantities of viral antigens or genome in tumour cells, along with the absence of other tumour viruses by traditional PCR, and if standard criteria are met based on clinical history and histology. IHC furthermore allowed detection of the specific cells that were infected with different viruses in tumours from birds that had been inoculated simultaneously with multiple viruses. Following validation with field samples, these new protocols can be applied for both diagnostic and research purposes to help accurately identify avian tumour viruses in routine FFPE tissue sections.
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Affiliation(s)
- Husnain Ahmed
- a Avian Disease and Oncology Laboratory, US National Poultry Research Center, US Department of Agriculture , Agricultural Research Service , East Lansing , MI , USA.,b Department of Comparative Medicine and Integrative Biology , College of Veterinary Medicine, Michigan State University , East Lansing , MI , USA
| | - Jody Mays
- a Avian Disease and Oncology Laboratory, US National Poultry Research Center, US Department of Agriculture , Agricultural Research Service , East Lansing , MI , USA
| | - Matti Kiupel
- c Veterinary Diagnostic Laboratory , Michigan State University , Lansing , MI , USA
| | - John R Dunn
- a Avian Disease and Oncology Laboratory, US National Poultry Research Center, US Department of Agriculture , Agricultural Research Service , East Lansing , MI , USA
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4
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Sun P, Cui N, Su S, Chen Z, Li Y, Ding J, Cui Z. Influence of avian leukosis virus long terminal repeat on biological activities of Marek's disease virus. Avian Pathol 2016; 44:278-86. [PMID: 26274570 DOI: 10.1080/03079457.2015.1042835] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
GX0101 was the first reported field strain of recombinant Marek's disease virus (MDV) that contained a long terminal repeat (LTR) from the reticuloendotheliosis virus (REV). It is a very virulent MDV strain, with relatively high horizontal transmission ability. The REV LTR in GX0101 genome was proved to decrease the pathogenicity but increase the potential for horizontal transmission of the virus. Here we constructed a recombinant MDV GX0101-ALV-LTR to study stability of avian leukosis virus (ALV) LTR at the REV LTR insertion site in GX0101 genome and its influence on biological activities of the recombinant virus. The results showed that GX0101-ALV-LTR was able to replicate stably both in vitro and in vivo. ALV LTR remained stable in chickens infected either by inoculation with the recombinant virus GX0101-ALV-LTR or by horizontal transmission, as well as in cell culture. The pathogenic properties of GX0101-ALV-LTR virus were evaluated in infected specific-pathogen-free chickens. The present study demonstrated that the GX0101-ALV-LTR virus had a weaker inhibitory effect on the growth rates of the infected chickens and induced weaker immunosuppressive effects. Horizontal transmission ability of the GX0101-ALV-LTR virus appeared to be similar with its parental virus GX0101. In short, ALV LTR was stable in GX0101 after replacing REV LTR, and the recombinant virus showed similar horizontal transmission ability but decreased pathogenicity.
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Affiliation(s)
- Peng Sun
- a College of Veterinary Medicine , Shandong Agricultural University , Tai'an , Shandong , P.R. China
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Marek's disease vaccines: Current status, and strategies for improvement and development of vector vaccines. Vet Microbiol 2016; 206:113-120. [PMID: 28038868 DOI: 10.1016/j.vetmic.2016.11.024] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Revised: 11/19/2016] [Accepted: 11/23/2016] [Indexed: 11/24/2022]
Abstract
Marek's disease (MD) is a lymphoproliferative viral disease of chickens, which has been controlled through vaccination since 1969. MD vaccines protect against tumors but do not provide sterilizing immunity, and thus it is generally believed that their use has contributed to increase virulence of field strains with the ability to cause MD in vaccinated chickens. Traditional methods of developing vaccines, like cell culture attenuation, have proved unsuccessful for the development of improved vaccines to protect against highly virulent MD virus (MDV) field strains. With the advent of recombinant DNA technology, it is now possible to study MDV gene function and develop rational vaccines that protect against highly pathogenic strains. In addition, the long term protection conferred by MD vaccines, their excellent safety profile, their efficacy when administered early (at hatch or in ovo), and their ability to overcome maternal antibodies, has made MDV an excellent candidate vector to protect not only against MD but also against other important viral poultry diseases. In this review we will discuss the current status of MD vaccines and their use as vector vaccines to control important viral poultry diseases.
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Mays JK, Black-Pyrkosz A, Spatz S, Fadly AM, Dunn JR. Protective efficacy of a recombinant bacterial artificial chromosome clone of a very virulent Marek's disease virus containing a reticuloendotheliosis virus long terminal repeat. Avian Pathol 2016; 45:657-666. [PMID: 27258614 DOI: 10.1080/03079457.2016.1197376] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Marek's disease virus (MDV), an alphaherpesvirus, causes Marek's disease (MD), a lymphoproliferative disease in poultry characterized by T-cell lymphomas, nerve lesions, and mortality. Vaccination is used worldwide to control MD, but increasingly virulent field strains can overcome this protection, driving a need to create new vaccines. Previous studies revealed that insertion of reticuloendotheliosis virus (REV) long terminal repeat (LTR) into a bacterial artificial chromosome (BAC) clone of a very virulent strain of MDV, Md5, rendered the resultant recombinant virus, rMd5 REV-LTR BAC, fully attenuated in maternal antibody positive (Mab+) chickens at passage 40. In the current study, the protective efficacy of rMd5 REV-LTR BAC was evaluated. First, passage 70 was identified as being fully attenuated in maternal antibody negative chickens and chosen as the optimal passage level for use in protective efficacy studies. Second, three protective efficacy trials were conducted comparing the rMd5 REV-LTR p70 BAC to the CVI988/Rispens vaccine. Groups of Mab+ and Mab- 15I5 × 71 chickens were vaccinated in ovo at 18 days of embryonation or intra-abdominally at day of hatch, and challenged at 5 days post-hatch with the vv+MDV strain 686. Vaccination at day of hatch and in ovo with rMd5 REV-LTR p70 BAC protected chickens against MDV-induced bursa and thymic atrophy, but did not provide the same level of protection against MD tumours as that afforded by the commercial vaccine, CVI988/Rispens.
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Affiliation(s)
- Jody K Mays
- a Avian Disease and Oncology Laboratory, United States Department of Agriculture , Agricultural Research Service , East Lansing , MI , USA
| | - Alexis Black-Pyrkosz
- a Avian Disease and Oncology Laboratory, United States Department of Agriculture , Agricultural Research Service , East Lansing , MI , USA
| | - Stephen Spatz
- b US National Poultry Research Center, United States Department of Agriculture , Agricultural Research Service , Athens , GA , USA
| | - Aly M Fadly
- a Avian Disease and Oncology Laboratory, United States Department of Agriculture , Agricultural Research Service , East Lansing , MI , USA
| | - John R Dunn
- a Avian Disease and Oncology Laboratory, United States Department of Agriculture , Agricultural Research Service , East Lansing , MI , USA
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Bao KY, Zhang YP, Zheng HW, Lv HC, Gao YL, Wang JF, Gao HL, Qi XL, Cui HY, Wang YQ, Ren XG, Wang XM, Liu CJ. Isolation and full-genome sequence of two reticuloendotheliosis virus strains from mixed infections with Marek's disease virus in China. Virus Genes 2015; 50:418-24. [PMID: 25850423 DOI: 10.1007/s11262-015-1191-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Accepted: 03/13/2015] [Indexed: 10/23/2022]
Abstract
Reticuloendotheliosis virus (REV), classified as a gammaretrovirus, has a variety of hosts, including chickens, ducks, geese, turkeys, and wild birds. REV causes a series of pathological syndromes, especially the immunosuppression of the host, which may lead to an increased susceptibility to other pathogens, thus greatly damaging the poultry industry. Mixed infections of REV and Marek's disease virus (MDV) have been reported in many countries, including China. Previous reports revealed that MDV vaccines were not efficacious, and even less-virulent MDV strains would cause some losses due to mixed infections with REV. Additionally, contaminants in the MDV vaccine might be the main source of REV. In this study, two clinical samples were collected from two flocks of chickens that were diagnosed with MDV. Subsequently, two REV isolates were obtained from the clinical samples. The isolates, named CY1111 and SY1209, were further confirmed through an indirect immunofluorescence assay and electron microscopy. Complete genome sequences of the two REV strains were determined to test the relationship between them and other REV strains. Phylogenetic trees showed that the two REV strains were closely related to most REV strains that were isolated from a variety of hosts. Therefore, REVs might spread freely among these hosts under natural conditions. Additionally, most REV strains in China were in the same clade. The present work offers some information regarding REV in China.
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Affiliation(s)
- Ke-yan Bao
- Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, 150001, People's Republic of China
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A recombinant field strain of Marek's disease (MD) virus with reticuloendotheliosis virus long terminal repeat insert lacking the meq gene as a vaccine against MD. Vaccine 2015; 33:596-603. [DOI: 10.1016/j.vaccine.2014.12.057] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Revised: 12/11/2014] [Accepted: 12/17/2014] [Indexed: 11/19/2022]
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Cao W, Mays J, Dunn J, Fulton R, Silva R, Fadly A. Use of Polymerase Chain Reaction in Detection of Marek's Disease and Reticuloendotheliosis Viruses in Formalin-Fixed, Paraffin-Embedded Tumorous Tissues. Avian Dis 2013; 57:785-9. [DOI: 10.1637/10542-032713-resnote.1] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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10
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Sequence analysis of the whole genome of a recombinant Marek's disease virus strain, GX0101, with a reticuloendotheliosis virus LTR insert. Arch Virol 2013; 158:2007-14. [PMID: 23553452 DOI: 10.1007/s00705-013-1671-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Accepted: 02/08/2013] [Indexed: 10/27/2022]
Abstract
Marek's disease virus Chinese strain GX0101, isolated in 2001, is the first reported recombinant gallid herpesvirus type 2 (GaHV-2) field strain with one reticuloendotheliosis virus (REV) long terminal repeat (LTR) insert. We constructed an infectious bacterial artificial chromosome (BAC) clone of GX0101, which showed characteristics very similar to those of the parental virus in replication and pathogenicity. Using the GX0101 BAC clone, the complete genome of GX0101 was sequenced and analyzed. The length of the GX0101 genome is 178,101 bp, and it contains only one REV-LTR insert at a site 267 bp upstream of the sorf2 gene.
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Gimeno IM, Witter RL, Cortes AL, Reddy SM, Pandiri AR. Standardization of a model to study revaccination against Marek's disease under laboratory conditions. Avian Pathol 2012; 41:59-68. [PMID: 22845322 DOI: 10.1080/03079457.2011.635636] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Revaccination, the practice of administering Marek's disease (MD) vaccine a second time, has been used in commercial poultry flocks for many years. The rationale is largely anecdotal as the few published reports have failed to provide support for the value of the practice. In the present work, we have standardized a model to study MD revaccination under laboratory conditions. Nine bird experiments were conducted to evaluate homologous revaccination (same vaccine administered twice) and heterologous revaccination (administration of two different vaccines) with various challenge models. Our results demonstrated that heterologous revaccination (with a second vaccine more protective than the first vaccine) but not homologous revaccination provided a beneficial increase in protection. Administration of the first vaccine at 18 days of embryonation followed by a more protective second vaccine at hatch reproduced systematically the benefits of revaccination. In addition, our results show that revaccination protocols might aid in solving major drawbacks associated with various highly protective experimental MD vaccines; that is, lymphoid organ atrophy and residual virulence. Strain RM1 is one of the most protective vaccines against early challenge with highly virulent MD virus but it induces severe lymphoid atrophy in chickens lacking maternal antibodies against MD virus. In this study, strain RM1 did not induce lymphoid organ atrophy when administered as second vaccine in a revaccination protocol. Similarly, strain 648A100/BP5 maintains residual virulence in chickens lacking maternal antibodies against MD virus but did not induce any lesions when used as a second vaccine. Until now, arbitrary revaccination protocols have been occasionally proven useful to the poultry industry. The model developed in this study will allow for a better understanding of this phenomenon and its optimization. A more rational use of this practice will be of great help to control MD outbreaks until better vaccines are available.
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Affiliation(s)
- Isabel M Gimeno
- Population Health and Pathobiology Department, College of Veterinary Medicine, North Carolina State University, Raleigh, USA.
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12
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Mays JK, Silva RF, Kim T, Fadly A. Insertion of reticuloendotheliosis virus long terminal repeat into a bacterial artificial chromosome clone of a very virulent Marek's disease virus alters its pathogenicity. Avian Pathol 2012; 41:259-65. [PMID: 22702453 DOI: 10.1080/03079457.2012.675428] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Co-cultivation of the JM/102W strain of Marek's disease virus (MDV) with reticuloendotheliosis virus (REV) resulted in the generation of a recombinant MDV containing the REV long terminal repeat (LTR) named the RM1 strain of MDV, a strain that was highly attenuated for oncogenicity but induced severe bursal and thymic atrophy. We hypothesize that the phenotypic changes were solely due to the LTR insertion. Furthermore, we hypothesize that insertion of REV LTR into an analogous location in a different MDV would result in a similar phenotypic change. To test these hypotheses, we inserted the REV LTR into a bacterial artificial chromosome (BAC) clone of a very virulent strain of MDV, Md5, and designated the virus rMd5-RM1-LTR. The rMd5-RM1-LTR virus and the rMd5 virus were passaged in duck embryo fibroblast cells for up to 40 passages before pathogenicity studies. Susceptible chickens were inoculated intra-abdominally at hatch with the viruses rMd5-RM1-LTR, rMd5 BAC parental virus, wild-type strain Md5, or strain RM1 of MDV. The rMd5-RM1-LTR virus was attenuated at cell culture passage 40, whereas the rMd5 BAC without RM1 LTR retained its pathogenicity at cell culture passage 40. Using polymerase chain analysis, the RM1 LTR insert was detected in MDV isolated from buffy coat cells collected from chickens inoculated with rMd5-RM1-LTR, but only at 1 week post inoculation. The data suggest that the presence of the RM1 LTR insert within MDV genome for 1 week post inoculation with virus at hatch is sufficient to cause a reduction in pathogenicity of strain Md5 of MDV.
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Affiliation(s)
- Jody K Mays
- Avian Disease and Oncology Laboratory, US Department of Agriculture, Agricultural Research Service, East Lansing, MI 48823, USA
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Gimeno IM, Witter RL, Cortes AL, Reed WM. Replication ability of three highly protective Marek's disease vaccines: implications in lymphoid organ atrophy and protection. Avian Pathol 2012; 40:573-9. [PMID: 22107091 DOI: 10.1080/03079457.2011.617725] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
Abstract
The present work is a chronological study of the pathogenesis of three attenuated serotype 1 Marek's disease (MD) virus strains (RM1, CVI988 and 648A80) that provide high protection against MD but have been attenuated by different procedures and induce different degrees of lymphoid organ atrophy. All studied strains replicated in the lymphoid organs (bursa,x thymus and spleen) and a peak of replication was detected at 6 days post inoculation (d.p.i.). Differences, however, were observed among vaccine strains. RM1 strain replicates more in all lymphoid organs compared with CVI988 and 648A80 strains. In addition, replication of RM1 in the thymus did not decrease after 6 d.p.i. but continued at high levels at 14 d.p.i. and until the thymus was completely destroyed. Lung infection occurred very early after infection with all of the three vaccines and the level of replication was similar to that found in the lymphoid organs. Infected cells were very large and appeared scattered in the lung parenchyma and in the parabronchial lining. The study of the target cells for the early infection in cell suspensions of blood and spleen showed that both non-adherent cell populations (enriched in lymphoid cells) and adherent cells (enriched in monocytes/macrophages) supported MD virus infection. Infection in adherent cells was especially high at very early stages of the infection (3 to 6 d.p.i.). Atrophy of lymphoid organs is a major drawback in the production of highly protective vaccines against MD. A better understanding of the mechanisms associated with lymphoid organ atrophy will aid in overcoming this problem.
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Affiliation(s)
- Isabel M Gimeno
- Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, USA.
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