Evaluation Of Two Strains Of Mareles Disease Virus Serotype 1 For The Development Of Recombinant Vaccines Against Very Virulent Infectious Bursal Disease Virus

Attenuated strains of Marek's disease virus serotype 1 (MDVI), and the closely related herpesvirus of turkeys, are among the most potent vectors for development of recombinant vaccines for poultry. To investigate the effects of MDVI strain characteristics on the protective efficacy of the recombinant vaccines, we developed two recombinant MDVI vaccines for expressing the VP2 gene of infectious bursal disease virus (IBDV) based on two different MDVI strains, the attenuated strain 814 and the Meq gene deleted recombinant MDVI strain rLMS Delta Meq, as the viral vectors. The r814-VP2 virus based on the 814 strain exhibited higher replication efficiency in cell culture while lower viral titers in chickens, compared to rLMS Delta Meq-VP2 derived from the rLMS Delta Meq strain. Further studies indicated that r814-VP2 produced higher levels of VP2 protein in cells and elicited stronger immune responses against IBDV in chickens than rLMS Delta Meq-VP2. After IBDV challenge, rLMS Delta Meq-VP2 provided 50% protection against mortality, and the birds that survived developed bursa] atrophy and gross lesions. In contrast, r814-VP2 conferred complete protection not only against development of clinical signs and mortality, but also against the formation of bursal lesions. The results indicate that different MDVI vector influences the protective efficacy of recombinant MDVI vaccines. The r814-VP2 has the potential to serve as a bivalent vaccine against two important lethal pathogens of chickens.(C) 2016 Elsevier B.V. All rights reserved.