NATURALLY OCCURRING-NEUTRALIZING MONOCLONAL-ANTIBODY ESCAPE VARIANTS DEFINE THE EPIDEMIOLOGY OF INFECTIOUS BURSAL DISEASE VIRUSES IN THE UNITED-STATES

A panel of two non-neutralizing and six neutralizing monoclonal antibodies (Mabs) were used in antigen-capture enzyme immunoassays (AC-ELISA) to examine the antigenicity of 1301 wild type infectious bursal disease viruses (IBDV) isolated from different poultry flocks througout the United States over a three year period. Analysis of these isolates with protective, neutralizing Mabs directed against the VP 2 structural protein of IBDV showed that four antigenically distinct groups of serotype 1 IBDV could be separated on the basis of the presence or absence of one or more Mab defined, conformation-dependent, multivalent neutralization site. AC-ELISA reactivity patterns of the Mabs with isolates demonstrated that IBDV field populations were relatively antigenically homogeneous per premise isolation. Geographically, various antigenic species were more or less prevalent, or nearly absent. Competition analysis with neutralizing Mabs coupled with AC-ELISA results suggested that neutralization epitopes for IBDV are distinct, spatially arranged, yet closely linked. Of 5 Mab defined neutralization epitopes, shown to be related to protection from virulent challenge by Classic IBDV strains isolated prior to 1985, only two of the epitopes remain unaltered on the most recent emergent variant field strain of IBDV isolated.