Submitted to: American Association of Avian Pathologists
Publication Type: Abstract Only
Publication Acceptance Date: December 21, 2013
Publication Date: July 21, 2013
Citation: Lee, L.F., Heidari, M., Zhang, H., Lupiani, B., Reddy, S.M. 2013. Safety and efficacy of a backpassaged rMd5-delta-Meq vaccine virus in chickens [abstract]. American Association of Avian Pathologists, July 19-23, 2013, Chicago, Illinois. p. 35. Technical Abstract: Marek’s disease virus EcoR1-Q fragment of the viral genome encodes meq (MDV EcoQ) gene. Meq is an unique oncogene, present only in serotype 1 MDV and is consistently expressed in all latent or tumor cells. The meq gene was deleted from the very virulent rMd5 genome and was designated as rMd5-delta-Meq. This virus was shown to be an effective vaccine candidate in both maternal antibody (MAb) positive and negative chickens. However, in MAb- chickens, it induces bursal and thymic atrophy (BTA) similar to that of parental rMd5 virus. BTA in MAb- chickens is considered a safety issue and will undoubtedly interfere with commercialization and licensing of this candidate vaccine. Backpassage virus in chickens is a strategy that is used to improve vaccine efficacy. We have backpassaged rMd5-delta-Meq five times in chickens with 2 weeks intervals. The resultant virus showed improved replication and remained non-pathogenic and as an effective vaccine.