title: Efficacy of various Marek's disease vaccines protocols for prevention of Marek's disease virus-induced immunosuppression.
abstract: Marek's disease virus (MDV) induces tumors and severe immunosuppression in chickens. MDV-induced immunosuppression (MDV-IS) is very complex and difficult to study. In particular, the late MDV-IS (late-MDV-IS) is of great concern since it can occur in the absence of lymphoid organ atrophy or gross tumors. We have recently developed a model to reproduce late-MDV-IS under laboratory conditions. This model measures MDV-IS indirectly by assessing the effect of MDV infection on the efficacy of infectious laryngotracheitis (ILT) vaccination; hence the name late-MDV-IS ILT model. In this study, we have used the late-MDV-IS ILT model to evaluate if MD vaccination can protect against late-MDV-IS. One experiment was conducted to determine whether serotype 1 MD vaccines (CVI988 and Md5ΔMEQ) could induce late-MDV-IS by themselves. Three additional experiments were conducted to evaluate efficacy of different MD vaccines (HVT, HVT+SB-1, CVI988, and Md5ΔMEQ) and different vaccine protocols (day-old vaccination, in ovo vaccination, and double vaccination) against late-MDV-IS. Our results show that none of the currently used vaccine protocols (HVT, HVT+SB-1, or CVI988 administered at day of age, in ovo, or in double vaccination protocols) protected against late-MDV-IS induced by vv+MDV strains 648A and 686. Experimental vaccine Md5ΔMEQ administered subcutaneously at one day of age was the only vaccine protocol that significantly reduced late-MDV-IS induced by vv+MDV strain 686. This study demonstrates that currently used vaccine protocols confer high levels of protection against MDV-induced tumors (protection index=100), but do not protect against late-MDV-IS; thus, commercial poultry flocks could suffer late-MDV-IS even in complete absence of tumors. Our results suggest that MDV-IS might not be related to the development of tumors and novel control methods are needed. Further evaluation of the experimental vaccine Md5ΔMEQ might shed light on protective mechanisms against late-MDV-IS.
authors.affiliation: Department of Population Health and Pathobiology, Veterinary School, North Carolina State University, 1060 William Moore Drive, Raleigh, NC 27607, USA.
authors.forename: Nik M
authors.initials: NM
authors.lastname: Faiz
authors.affiliation: Department of Population Health and Pathobiology, Veterinary School, North Carolina State University, 1060 William Moore Drive, Raleigh, NC 27607, USA.
authors.forename: Aneg L
authors.initials: AL
authors.lastname: Cortes
authors.affiliation: Department of Population Health and Pathobiology, Veterinary School, North Carolina State University, 1060 William Moore Drive, Raleigh, NC 27607, USA.
authors.forename: James S
authors.initials: JS
authors.lastname: Guy
authors.affiliation: Department of Population Health and Pathobiology, Veterinary School, North Carolina State University, 1060 William Moore Drive, Raleigh, NC 27607, USA.
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Fogle
authors.affiliation: Department of Population Health and Pathobiology, Veterinary School, North Carolina State University, 1060 William Moore Drive, Raleigh, NC 27607, USA. Electronic address: imgimeno@ncsu.edu.
authors.forename: Isabel M
authors.initials: IM
authors.lastname: Gimeno
mesh_terms: D000818:Animals; D002645:Chickens; D005260:Female; D007108:Immune Tolerance; D008380:Marek Disease / Q000276:immunology / Q000517:prevention & control*; D022501:Marek Disease Vaccines / Q000008:administration & dosage* / Q000009:adverse effects; D009369:Neoplasms / Q000821:virology; D011201:Poultry Diseases / Q000517:prevention & control*; D014611:Vaccination / Q000379:methods / Q000662:veterinary*
chemical_list: D022501:Marek Disease Vaccines
keywords: Control; ILTV; Immune system; Immunosuppression; MDV; Vaccine