الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
This study was carried out to isolate and identify strains of infectious bursal disease from field outbreaks in 13 field cases with mortality 1.25-3.92%. Nine were confirmed positive with AGPT followed by molecular identification using RT-PCR and characterization using restriction enzymes where these isolates divided into 4 classical, 3 variant and 2 very virulent. Pathogenicity of this isolate was studied in 14 days age chick with protective maternal antibody and mortality, morbidity, body and organs weight and index, histopathological changes and antibody response were calculated. Some of these isolates were found to have effect on thymus and others on proventriculus. IBD vaccines including D78, 228E, IBD Blen and Bursacvac Plus were studied to explore their immunogenicity. In spite of these vaccines proved to break through maternal antibody, it causes varied destructive effect on bursa, spleen, proventriculus and thymus. from the virus isolates (4) were used (2 variant and 2 very virulent) to study their pathogenicity to 33 days old male chicks having unprotective maternal antibodies where the variant isolates induced no marked clinical signs but induce atrophy of bursa, thymus and spleen with histopathological changes variant 4 showed marked proventriculus lesions than variant 7 isolates. The cross immunogenic activity of the 4 vaccines and IBDV isolates were also studied and proved that these vaccines prevent clinical signs of disease but not prevent effect on chicken performance or histopathological lesions affection on organ weights.