Abstract:
Infectious bursal disease virus (IBDV) causes an acute and highly contagious immunosuppressive disease in young chickens aged 3 to 6 weeks. The molecular epidemiology of IBD virus causing severe disease in chickens in Tanzania has not been consistently studied. A cross-sectional study that involved collection of bursal of Fabricius from dead chicken following IBD outbreak(s) in Dar es Salaam was conducted. The laboratory analysis of samples was performed by reverse transcription polymerase chain reaction (RT-PCR), nucleotide sequencing, sequence alignment and phylogeny analysis targeting the VP2-hypervariable region (VP2-HVR). The findings of this study revealed that one out of eight samples (12.5%; n=1) was positive for VP2-HVR by RT-PCR and sequencing. A BLAST search of generated sequence indicated 96% nucleotide identity of the field isolate (TZ/DSM/2018) to the LUSC 47-2016 strain detected in chicken from Lusaka, Zambia. The TZ/DSM/2018 virus had conserved putative virulence marker amino acids at 222(A), 242(I), 256(I), 294(I) and 299(S) positions corresponding to very virulent IBDV feature, with unique amino acids at positions 263S and 338P. On phylogeny analysis, the TZ/DSM/2018 virus clustered in the same clade with the African VV-IBDV genotype. Taken together, this study has revealed the existence of the African VV-IBDV genotype in Dar es Salaam, which is genetically different from the vaccine isolate. Further studies are required to perform the in-depth genetic and antigenic characterization of circulating IBDV strains in Tanzania, so that a rational IBD control method can be recommended in the region.
