This study was conducted to characterize nine infectious bursal disease virus (IBDV) isolates from Iran. A reverse transcriptase–polymerase chain reaction (RT-PCR) procedure was used to amplify a 743-bp fragment of the VP2 gene hypervariable region from IBDV field isolates. Amplified VP2 fragments of the nine IBDV isolates were sequenced and compared with published sequences of IBDV strains from Iran and around the world, and their phylogenetic relationships were analyzed. Three isolates demonstrated close relation to classical attenuated strains of IBDVs, and six isolates showed sequences common in European and Asian strains of very virulent IBDVs (vvIBDVs). Four nucleotide changes—802A, 934A, 940A, and 1366A—were common in all Iranian vvIBDVs except in one isolate. Amino acid sequences of three Iranian vvIBDVs were 100% identical and resembled vvIBDV strains from European (UK661), Asian (HK46, GZ96), and Iranian origins (IR01, SDH1). Some unique amino acid substitutions after major hydrophilic peak A in Iranian vvIBDV field isolates were observed: 231S-L, 231S-P, and 233N-K. Phylogenetic analysis showed that the Iranian vvIBDVs were closely related to European and Asian vvIBDVs. Further comprehensive investigations will provide more information on the distribution, variability, and phylogenetic relationships of different IBDVs isolated in Iran and other parts of the world.

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