Sequence analysis of the VP1 gene in three very virulent Iranian infectious bursal disease virus strains

Infectious bursal disease (IBD) is a highly contagious disease of chickens caused by the infectious bursal disease virus (IBDV). This study was conducted to characterize three IBDV strains from Iran. A reverse transcriptase-polymerase chain reaction (RT-PCR) procedure was used to amplify a 715-bp fragment of the VP1 gene from IBDV strains. Amplified VP1 fragments of the three Iranian IBDV strains were sequenced and compared with published sequences of IBDV strains from around the world, and their phylogenetic relationships were analyzed. Alignment of IBDV strains revealed 23 nucleotide differences between vvIBDV (except for IL and PT) and other non-vvIBDV strains. Two nucleotide positions, 863G and 1023A, were specific as JRMP07IR and JRMP14IR strains. All vvIBDVs differed (except for IL and PT strains) from non-vvIBDVs at aa (amino acids) positions 242E and 287A. In the three Iranian IBDV strains, aa positions 251R in both JRMP07IR and JRMP14IR, and 360L in JRMP14IR differed from those of other vvIBDVs. In phylogenetic analyses, all three Iranian strains clustered together with vvIBDVs. One Iranian strain, JRMP30IR, was more closely related to two European strains (HOL and UK661) and two south-east Asian strains (OKYM and ZJ2000). However, the other two Iranian strains, JRMP07IR and JRMP14IR, were closer to two Turkish strains (OA/G1 and OE/G2) and a Malaysian strain (UPM94). Further comprehensive investigations will provide researchers a better knowledge on the distribution, variability, and phylogenetic relationships of different IBDVs isolated in Iran and other parts of the world.