الفهرس 
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Abstract
Re-emergence of highly virulent forms of IBDV has been the cause of significant economic losses. In present study, Fifty-two bursa samples were assayed using reverse transcriptase-polymerase chain reaction (RT-PCR) for IBDV targeting VP2 gene. Out of the tested samples 20 were positives. Eleven IBDV-positive samples were selected for further isolation and characterization. The virus was isolated by inoculating bursa suspension into embryonated specific pathogen-free (SPF) eggs. Chorioallantoic membrane(s) (CAMs) were collected and tested by AGPT confirming the presence of IBDV. The virus was detected by RT-PCR and sequence analysis of PCR products of 11 selected samples was carried out. Nine samples were characterized as very virulent (vvIBDV) and 2 samples were classic attenuated IBDV similar to classic attenuated (vaccine) strains. Histopathological analysis of the bursa revealed necrosis, presence of depleted follicles and some infiltration of heterophils, characteristic to previously reported in IBDV cases. The genotyping of Egyptian vvIBDV indicate continuous evolution of IBDV in Egypt and they were closely related to previous isolated strains from Egypt.