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Infectious bursal disease (IBD) is caused by an RNA virus belonging to the Avibirnavirus genus within the Birnaviridae family. The global prevalence of infectious bursal disease virus (IBDV) is a significant concern, affecting birds of all ages. Birds infected with IBDV exhibit symptoms, such as depression, bleeding in the thighs and pectoral muscles, and enlargement of the bursa. This study aimed to identify predominant IBDV serotypes using molecular methods and to gain insights into the resulting pathological conditions in infected chickens. Additionally, the study investigated the viral sequence and the relationship between a local Diyala isolate and reference strains from the Genebank. In the current study, the IBDV was isolated from broiler chickens aged 2-3 weeks from 15 farms in the Diyala Governorate of Iraq. A total of 15 samples, each from a different farm, were collected. Necropsy samples were obtained from various organs of broiler chickens, including the bursa of Fabricius, lungs, liver, and kidneys. Specific primers targeting the VP2 gene were used for reverse transcription-polymerase chain reaction (RT-PCR) analysis. The RT-PCR analysis yielded a 727 bp fragment, confirming the presence of IBDV in 10 out of the 15 samples. One strain was assigned the accession number LC498531 in the NCBI database. Phylogenetic analysis using the neighbor-joining tree program revealed three distinct groups. All examined regional samples (S1) were situated within the constructed tree. Five samples formed a specific group, indicating a close relationship. Histological examination of the tissues showed visible alterations such as degeneration, necrosis, and infiltration of inflammatory cells, particularly heterophils, providing clear evidence of the disease. In conclusion, this study confirmed the presence of IBDV in broiler chickens from multiple farms in Iraq’s Diyala Governorate, highlighting distinct clustering patterns in viral sequences. Moreover, the study confirmed the virus's presence using conventional RT-PCR, with histological examination supporting the findings. Keywords: Broiler chicken, Bursal enlargement, Infectious bursal disease, RT-PCR
Nasser et al. (Mon,) studied this question.