Infectious Bursal Disease (IBD) is also known as Gumboro disease, where the illness was initially identified. It is an extremely transmissible immune suppressor virus that has a significant financial impact on the poultry sector around the world resulting in increased vulnerability to various infections, adding to its negative effects on the efficacy of vaccines. The very virulent infectious bursal disease (vvIBDV) strains that are extremely virulent and cause a large amount of fatality in hens have emerged in recent years. The present study used reverse transcription polymerase chain reaction (RT-PCR) followed by sequencing to detect and molecularly characterize the VP1 and VP2 genes of IBDV. A phylogenetic study of the partial VP2 gene revealed that three field isolates belonged to Genogroup 3 and clustering Poland, Hong Kong, and Iran, with the highest identities of 98.32% and 98%, respectively. Based on an analysis of the amino acid sequence deduced from the VP2 gene at positions 242I, 253Q, 256I, 272I, 279D, 284A, 294I, 299S, and 330S, three IBDVs were shown to be very virulent strains, however, amino acid analysis of the VP1 in these two isolates showed that one of them had the distinctive vvIBDV TDN amino acid triplet, while the other isolates had a non-vIBDV HEG amino acid triplet at positions 145/146/147, respectively. The VP2 protein sequence of the circulatory vvIBDV genotype showed heterogeneity of a few amino acid substitutions within the hypervariable region with the vaccine strains ((Bursin, Cevac, and D78) that are commonly used in the vaccination program in Iraq. Conclusion: The current investigation might document the detection of highly virulent IBD virus from local farms during the outbreaks that emerged in the Sulaimani province. These data suggest that the current vaccination failure may be related to differences in the VP2 protein at HVR of the regionally circulating IBDV strain.
The VP2 protein sequence of circulatory vvIBDV genotype showed heterogeneity of few amino acid substitutions within the hyper variable region with the vaccine strains ((Bursin, Cevac, and D78) that are commonly used in the vaccination program in Iraq. The current investigation might document the detection of highly virulent IBD virus from local farms during the outbreaks emerged in the Sulaimani province.