This study was conducted to estimate the prevalence of IBD in broiler farms from different localities in different Governorates; AlQalubia, AlGharbia, AlMenofia and ALBehera and also to make further characterization of the obtained strains through nucleotide sequencing then evaluate the pathogenicity of the strain in SPF ECE and commercial broiler chicks. Fifteen out of total 32 (46.87%) bursal samples showed 620 bp amplicon size of HVR of VP2 when tested with RT-PCR. The nucleotide sequencing classified 2 strains as vvIBDV and one was similar to classical attenuated vaccines. The vvIBDV strain resulted in 100 % mortality of inoculated embryos with moderate to severe congestion of the body, cranial hemorrhage, congested and greenish liver with necrotic foci. The CAMs showed thickening with petechial hemorrhage. The experimental infection with (IBDV_ EGY 2018/N23) isolate was assessed in vaccinated groups with hot, intermediate and hot + intermediate vaccines and unvaccinated 25 days old Cobb broiler chicks; the c+ve group showed a significant difference in RWBF and cumulative bursal lesion in comparison with c–ve group. It recorded higher MSI than c–ve. All vaccinated groups showed significant increase in Abs titer when compared with non-vaccinated one and the hot vac. group recorded the highest titer. They also showed non-significant difference in RWBF and cumulative bursal lesion score in comparison to c-ve one at 10 dPI and lower MSI than c+ve but the hot + intermediate vac. group recorded the lowest lesion score and MSI. This study concluded the reemergence and circulation of vvIBDV in spite of the intensive vaccination strategies |
