Isolation and Molecular Characterization of Vp2 Gene of Infectious Bursal Disease: Demonstrated No Predominant New Strains Circulating in Bangladesh

The present study was conducted for molecular characterization of Bangladeshi isolates of Infectious Bursal Disease virus to establish genetic diversity with other European and Asian strains. A total of 129 bursa of Fabricius were collected after post mortem from IBD infected chicken. Only 30 samples were confirmed for IBDV by amplification of a 729-bp fragment of the VP2 gene hyper variable region using RT-PCR. The hyper variable region (aa 184-426) of amplified VP2 fragments of the 30 IBDV isolates were sequenced and compared with 10 strains published in Gene Bank and their phylogenic relationship were analyzed. Amino acid sequences analysis of the hyper variable region of the VP2 gene revealed that 27 isolates were 99% identical with European and Asian vvIBDV strains and 3 isolates showed close relationship with classical strains of IBDV. Twenty seven Bangladeshi vvIBDV isolates encode amino acids 222A, 2421, 2561, 294I, and 299S, which are conserved among other vvIBDV strains. The 3 Classical isolates showed amino acid substitutions at 222A→P, 256I→V, and 299 S→N positions. All isolates had the same heptapeptide 279D, S-W-S-A-S-G-S (326→332), and 284A. Phylogenetic analysis based on the nucleotide sequence revealed that the Bangladeshi isolates were closely related to European and Asian vvIBDV. Taken together, there was no predominant new strain circulating in Bangladesh during June 2009-May 2011. Moreover, in order to protect birds from the sudden emergence of new predominant strains, continuing surveillance of IBDV strains circulating in the field is of utmost importance.