Characterisation of an Indonesian very virulent strain of infectious bursal disease virus

An Indonesian very virulent (vv) strain of infectious bursal disease virus (IBDV), designated Tasik94, was characterised both in vivo and at the molecular level. Inoculation of Tasik94 into 5-week-old specific-pathogen-free (SPF) chickens resulted in 100% morbidity and 45% mortality. The complete nucleotide and predicted amino acid sequences of genomic segments A and B were determined. Across each of the three deduced open reading frames (ORFs), Tasik94 shared the greatest nucleotide homology to Dutch vv strain D6948. Phylogenetic analyses were performed using 15 full-length polyprotein sequences and a total of 105 VP2 hypervariable region sequences from geographically and pathogenically diverse strains. In each case, Tasik94 grouped closely with vv strains, particularly those from Europe. The deduced VP1, VP2, VP3, VP4 and VP5 protein sequences of Tasik94 were aligned with those from published strains and putative virulence determinants were identified in VP2, VP3 and VP4. Alignment of additional protein sequences across the VP2 hypervariable region confirmed that residues Ile[242], Ile[256] and Ile[294] were highly-conserved amongst vv strains, and may account for their enhanced virulence.