Little is known on the molecular characteristics of genome segments A and B of the African very virulent (VV) infectious bursal disease (IBD) virus (VV-IBDV) variant strains. In this study, the nucleotide sequence of genome segments A and B encoding VP5, precursor polyprotein (NH₂-VP2-VP4-VP3-COOH) and VP1 for an African very virulent IBDV, KMRG-48 strain, was determined. The VP5, precursor polyprotein and VP1 coding regions of KMRG-48 consisted of 437 nucleotides (145 deduced amino acids), 3036 nucleotides (1012 deduced amino acids) and 2637 nucleotides (879 deduced amino acids), respectively. Comparison of deduced amino acid sequences of serotype 1 IBDVs revealed 6 unique amino acid residues at positions 223 (S), 296 (F), 343 (S), 384 (I), 721 (T) and 960 (D) in precursor polyprotein. KMRG-48 also conserved 18 amino acid residues, which are found only in VV-IBDVs. Of these unique amino acids, 3 were in VP5, 4 were in VP2, 2 were in VP4, 3 were in VP3 and 6 were in VP1. Phylogenetic analysis based on nucleotide sequences of VP5, precursor polyprotein, VP2, VP4, VP3 and VP1 revealed that KMRG-48 belonged to the VV genotype. The tree topologies obtained for the nucleotide sequences of VP5, precursor polyprotein, VP2, VP4 and VP3 were the same while the tree topology for the nucleotide sequence of VP1 was quite different compared with that obtained from nucleotide sequences of VP5, precursor polyprotein, VP2, VP4 and VP3, suggesting a possibility of genetic reassortment to contribute in the emergence of VV-IBDV. Experimental infection of susceptible chickens with KMRG-48 confirmed that the virus is a VV-IBDV exhibiting VV phenotype. Taken together, these findings demonstrate that KMRG-48 is a VV-IBDV whose genome segments A and B are derived from VV-IBDV, and that the conserved unique amino acids could influence its virulence and lethality.