Molecular and antigenic characterization of Bangladeshi isolates of infectious bursal disease virus demonstrate their similarities with recent European, Asian and African very virulent strains

Three isolates of infectious bursal disease virus (IBDV), obtained from chi ckens in Bangladesh in 1999 and designated as BD 1/99, BD 2/99 and BD 3/99, were characterized. In an antigen capture-enzyme-linked immunosorbent assa y using a panel of VP2-specific neutralizing monoclonal antibodies (mAb), a ll three isolates showed a mAb-binding profile similar to that of very viru lent IBDV (vvIBDV) strains. In contrast to the classical virulent strains, they did not react with mAb 3 and mAb 4. Molecular characterization nas per formed by direct sequencing of a 677-base pair cDNA corresponding to the VP 2 variable domain of the polyprotein gene, synthesized by a reverse transcr iption-polymerase chain reaction. In comparison to the classical virulent s trains, the Bangladeshi isolates were found to have five amino acid substit utions in this region. Four of these changes, Pro222Ala, Val256Ile, Leu294I le and Asn299Ser, were also observed in other vvIBDV strains. The fifth sub stitution, Glu300Ala, was similar to that in some African strains of IBDV. The results support the observation that antigenically and genetically simi lar vvIBDV strains, first observed in Europe in the late 1980s, have spread to most parts of the world in a short period of time.