Rescue of infectious bursal disease virus from mosaic full-length clones composed of serotype I and II cDNA

Infectious Bursal Disease Virus (IBDV) is the causative agent of one of the most important and wide-spread infectious diseases among commercial chicke n flocks. IBDV causes a depletion of B-lymphoid cells in the bursa of Fabri cius, inducing immunosuppression, morbidity, or even acute mortality. Becau se currently used live IBDV vaccines are derivatives from field isolates no serologic discrimination between field isolates and live vaccines can be m ade. The recently developed reverse genetics techniques for IBDV allows one to generate genetically modified IBDVs which might have altered biological and antigenic properties. Here, we describe the rescue of mosaic serotype I IBDVs, of which the polyprotein encoding region was partly replaced by th e corresponding region of a serotype II strain. A mosaic virus, containing the C-terminal part of serotype II VP3 showed only a slightly delayed relea se of progeny virus compared to unmodified serotype I virus, while maximum viral titers at 25 h post infection were equal. Since serotype, specific ep itope(s) are present in the C-terminal part of VP3, we were able to discrim inate this rescued virus from serotype I and II IBDV strains. These finding s make the use of a chimeric VP3 a promising approach to develop an IBDV ma rker vaccine.