Molecular Characterization of a very Virulent Infectious Bursal Disease Virus from Iran Demonstrates its Similarity with Recent Isolates from the Middle East

Infectious bursal disease (IBD) is an acute, very contagious disease of juvenile chickens. High mortality following its acute clinical form on the one hand, and immunosuppressive effects resulting from subclinical infections, on the other hand, made IBD an economically important disease. In Iran, despite regular vaccination, cases of IBD are still diagnosed clinically, with limited information on their molecular epidemiology. The present study was conducted to characterize IBD viruses responsible for a recent outbreak. Materials and Methods: Samples of the bursa of Fabricius were collected from IBD suspected pullets with up to 40% mortality. The viral RNA was isolated, and an RT-PCR targeting hypervariable region within the VP2 gene was carried out. One positive sample was sequenced and phylogenetically analyzed. Results: The virus detected in this study had the highest homology to a very virulent IBD virus (vvIBDV) identified in 2018 in Iran. It also shared a high level of homologies to vvIBDVs isolated from Kuwait, Iraq, and Turkey. Conclusions: Despite using vaccines, very virulent IBD viruses are circulating in Iran. The close relationships of the detected virus with vvIBD viruses circulating in neighboring countries is an alarming issue announcing the necessity of imposing strict rules on importation and exportation of birds.