Characterization of infectious bursal disease virus isolates from Indonesia indicates the existence of very virulent strains with unique genetic changes

Sequencing of the hypervariable region of viral protein VP2 of infectious bursal disease virus (IBDV) isolates obtained from non-vaccinated chickens in Indonesia showed that the majority (16/17) were closely related to published very virulent (vv)IBDV strains. Four isolates contained identical amino acid sequences to Asian and European vvIBDVs, sharing vv-specific amino acid residues 222(Ala), 256(Ile), and 294(Ile). Eight isolates differed by one amino acid at position 222(Ala leads to Ser); however, this change did not alter the pathogenicity or antigenicity of these strains. Two isolates, with amino acid substitutions at positions 272(Ile leads to Thr) and 279(Asp leads to Asn), did not cause clinical disease or mortality, and were therefore considered to be naturally occurring, attenuated mutants of vvIBDV. The results illustrate variability that might occur among vvIBDV strains.