Genetic and pathologic characteristics of infectious bursal disease viruses isolated from broiler chickens in Iran during 2014-2015

Infectious bursal disease (IBD) virus causes a highly contagious immunosuppressive disease in chickens. A total number of 12 pooled bursal samples were collected during 2014-2015 from broiler farms in different regions of Iran. Typical macroscopical and histopathological lesions of the bursa of Fabricius were found similar to reports by other researchers. A 474-bp part of hypervariable region of VP2 (hvVP2) was sequenced and analyzed. Ten isolates had the characteristic amino acid residues of very virulent IBD (vvIBD) viruses and the other two were identified as attenuated (vaccine) strains. The vvIBD isolates had a unique G to S mutation at position 254, compared to other Iranian vvIBD isolates. Two attenuated isolates had the mutation 253Q, not found in D78 strain, creating virulent variant of vaccine strains. Degree of similarity among the studied vvIBD isolates was relatively high (97.6-100%), proposing a common ancestor for them. However, they were partly different from previous Iranian and neighbor countries' isolates (96.2-97.3% similarity to Shiraz isolate and 95.7-96.7% to Iraq and Turkey isolates). In phylogenetic analysis, the studied vvIBD isolates classified as a separate subgroup in the group of isolates from Iran and neighbor countries. More studies on genetic and antigenic characteristics of these isolates as well as probable modifications in their pathogenicity are needed to evaluate the significance of the mentioned differences.