Abstract
Infectious bursal disease (IBD) is caused by a virus related to the family Birnaviridae. The virus is a worldwide pathogen and causes immunosuppression and great losses in broiler flocks. In this study, molecular characterization of two Saudi Arabian IBDVs (IBD01/14/SA and IBD02/14/SA) was carried out by reverse transcriptase polymerase chain reaction (RT-PCR) and partial sequence of hypervariable region of VP2 gene. Nucleotide sequences of 740-bp PCR product of the Saudi Arabian isolates were compared with the corresponding nucleotide sequence of 56 reported IBDVs representing different pathotypes from different continents. Phylogenetic analysis showed that the Saudi Arabian isolates were split from the tree to form a distinguished cluster with the Canadian IBDVs and 586/USA field viruses. Deduced amino sequences from both strains were found to share the amino acid substitutions of the standard very virulent (vv) strains. The Saudi Arabian strains showed unique amino acid substitutions 254N and 359K and exhibited a modified antigenic profile. The deduced amino acid sequence and antigenic profile of both wild-type Saudi Arabian strains showed high similarity to the IBDI+ vaccines; hence, the Saudi Arabian strains might be more useful for protecting chickens against overt clinical signs and mortalities.