Event Title First Global Alliance for Research on Avian Diseases (GARAD) Conference
Session Title Unknown
Event Date & Time On Tue, 30 Jun 2015 at 14:00:00 - 14:25:00
Venue Edmond J. Safra Lecture Theatre
Abstract Title Evolution and antigenic diversity of infectious bursal disease virus (IBDV)
Authors Daral Jackwood
Affiliations Food Animal Health Research Program The Ohio State University Ohio Agricultural Research and Development Center Wooster, Ohio, USA.
Abstract Content

Infectious bursal disease, also called Gumboro disease, is caused by infectious bursal disease virus (IBDV). This virus is a member of the family Birnaviridae, genus Avibirnavirus, and contains a bi-segmented double-stranded RNA genome. Two serotypes are recognized but only serotype 1 viruses cause an immunosuppressive disease in chickens. For many years a single antigenic subtype of serotype 1 was thought to exist. In the 1980s, a new antigenic subtype was identified in the US. These viruses were designated antigenic variants and the term classic was used to describe the original antigenic subtype. Today the terms classic and variant are no longer adequate to describe the antigenic variability observed among IBDV strains. Evolutionary forces at work for over half a century have selected for numerous phenotypic changes in these viruses. Several antigenic subtypes have been described within the original classic virus group and antigenic drift is largely responsible for the continued emergence of new antigenic strains of IBDV. Although these new antigenic strains are usually called variant viruses in the literature, they are often unlike the variant viruses first described in the US. The antigenic phenotype of IBDV is determined by the hypervariable sequence region of VP2 (hvVP2). The crystal structure of VP2 identified four loop structures in hvVP2 that were designated PBC, PDE, PFG, and PHI. Studies have shown that several evolutionary forces are responsible for selecting amino acid mutations on these loop structures. Amino acid substitution mutations in the PBC and PDE domains have contributed to antigenic drift among IBDV strains. For example, we examined amino acids 222 and 254 in the hvVP2 region of the Del-E strain and found that single amino acid mutations at both sites affect antigenicity. In addition to antigenic drift, the loop structures on VP2 have mutated through homologous recombination. During co-infections of different IBDV strains in a single host cell, genome segments can break and recombine. We have identified viruses that had amino acids in the PBC and PHI loops that were similar to the Winterfield IBDV strain while the PDE and PFG loop sequences were typical of the Del-E strain.