Genomic Analysis of Infectious Bursal Disease Virus in Nigeria: Identification of Unique Mutations of Yet Unknown Biological Functions in Both Segments A and B.

Infectious bursal disease (IBD) is a viral poultry disease known worldwide for impacting the economy and food security. The disease is endemic in Nigeria, with reported outbreaks in vaccinated poultry flocks. To gain insight into the dynamics of infectious bursal disease virus (IBDV) evolution in Nigeria, near-complete genomes of four IBDVs were evaluated. Amino acid sequences in the hypervariable region of the VP2 revealed conserved markers (222A, 242I, 256I, 294I and 299S) associated with very virulent (vv) IBDV, including the serine-rich heptapeptide motif (SWSASGS). Based on the newly proposed classification for segments A and B, the IBDVs clustered in the A3B5 group (where A3 are IBDVs with vvIBDV-like segment A, and where B5 are from non-vvIBDV-like segment B) form a monophyletic subcluster. Unique amino acid mutations with yet-to-be-determined biological functions have been observed in both segments. Amino acid sequences of the Nigerian IBDVs showed that they are reassortant viruses. Circulation of reassortant IBDVs may be responsible for the vaccination failures observed in the Nigerian poultry population. Close monitoring of changes in the IBDV genome is recommended to nip deleterious changes in the bud through the identification and introduction of the most appropriate vaccine candidates and advocacy/extension programs for properly implementing disease control.