Molecular characterization of Brazilian infectious bursal disease viruses

A reverse transcriptase-polymerase chain reaction (RT-PCR) procedure was used to amplify a VP2 gene fragment (248 bp) from infectious bursal disease virus (IBDV). The procedure allowed the detection of known IBDV strains from the United States, along with field isolates and commercial vaccines produced in Brazil. Amplified VP2 fragments were further characterized by restriction fragment length polymorphism (RFLP) analysis. From 55 Brazilian commercial flocks, 48 field samples were IBDV positive by RT-TCR. Vaccine RFLP patterns were found in 12 flocks, a pattern compatible with classic IBDV in one flock, four new patterns in 31 flocks, and a pattern compatible with very virulent (vv) IBDV in four flocks. Sequence analysis showed that the vvIBDV RFLP patterns were closely related to the vvIBDVs described in Europe and Asia. Phylogenetic analysis of the four new RFLP patterns showed that they were closely related to but distinct from other classic, variant, and vvIBDVs, suggesting a high prevalence of different IBDV strains in Brazilian commercial flocks.