الفهرس 
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Abstract
The presence of IBD was investigated in Kalyoubia Governorate among commercial broiler and Balady (native) chicken farms . A total of 16 farms suffering out breaks of IBD were examined during 9 months . The obtained data revealed that the age of prevalence of IBD ranged between 15-36 days, average morbidity 30-80%, average mortalities 3-26%, and peak of mortality at 3-5 days p.i., course of the disease 6-9 days . All examined chicken farms used different live IBD vaccines, and the disease has recurred in successive batches and became endemic . Clinical and postmortem findings for the 16 farms were typical for IBD . Clinical signs included whitish, yellowish, greenish and bloody watery diarrhoea, anorexia, 1 remors, severe prostration and death . Gross lesions were hemorrhages in the muscles of the thigh, breast and proventriculus-gizzard junction; kidneys were enlarged with prominent renal tubules and sometimes filled with urates; hyperemic thymus and enlarged hemorrhagic bursae . Detection of 1BDV antigen in collected bursae using AGP-test gave positive precipitation reactions during 24-48 hrs . Virus isolation in chicken embryos from commercial or Balady type breeders by CAM and/or YS inoculation revealed embryonic mortalities and gross lesions typical for IBD Trials of isolation of IBDV using CET monolayers failed after three blind passages. Histopathological examination of certain organs from affected birds showed that the predominant lesions were seen in the BF and were characterized by pelical, serosal, muscular edema; lymphoid tissue changes in the form of degeneration, necrosis, depletion, multifocal hemorrhages, heterophilic infiltration and cystic formation . Spleens showed edema, hemorrhages and lymphoid depletion . Kidneys showed edema, hemorrhages and degeneration . The pathogenicity of an IBDV field isolate was tested in 43 days old white LSL cockerels from which maternal antibody has waned, by intraocular inoculation of 100 gl /bird of bursal homogenate . Maternally derived precipitating antibodies could not more be detcted at 28 days of age, neutralizing antibodies reached a mean titer of 8 at 31,35,38 and 42 days age, and ELISA absorbance was 180 at 42 days. Clinical signs after experimental exposure included whitish, yellowish, greenish and bloody diarrhea, anorexia, tremors, severe prostration and death of 85% of infected birds . Gross lesions included hemorrhages in the muscles of the thigh, breast, skin, and proventriculus-gizzard junction. Kidneys were enlarged with prominent renal tubules, sometimes filled with urates. The bursae were edematous, enlarged, and revealed periburstis in the 1st 2-3 days, p.i.; in later stages (4,5 and 6 days p.i.) the bursae diminished in sizes with caseated plugs in the lumen. The thymus 2 and 3 days p.i. revealed enlargement with pinkish coloration, and later on it was slightly diminished in size . Unclotted blood was seen in all examined dead birds during 2-6 days p.i. Histopathological changes in the in bursae on the 1st day p.i. were limited to slight pelical edema . The bursal lesions increased on the 2nd day p.i. and 3rd day p.i., where severe bursal inflammation and hemorrhages occurred, characterized by heterophil infiltration with more pronounced lymphocytic depletion and necrosis . The severity of lesions continued to 4 and 5 days p.i. with well marked central cyst formation . In thymus lesions were mild to multifocal cortical lymphoid depletion and necrosis on the 1st day, and moderate cortical atrophy on the 2nd day; recovery was noted on the 5th day . In harderian gland there was a decreased number of plasma cells and degenerative changes in the acini and excretory ducts . Necrosis of the ellipsoidal and lymphoid follicles were the main lesions in the spleen, and edema and degenerative. tubules were found in the kidneys . Body weight of the infected cockerels decreased by approx.41% during 6 days p.i. compared with controls . Spleen index decreased during 1st 3 days then returned to normal 4 days later . Bursal index increased in the 1st 3 days p.i., then decreased during the next 3 days . Thymic index decreased permanently p.i.
IBDV antigen could be detected by AGP-test in bursal homogenate pools taken from experimentally infected cockerels sacrificed at 12, 16, 18, and 22 lirs p.i. as well as from dead cockerels 2-3 days p.1. Experimental vaccination of 56 cockerels free from maternal antibodies (43 days old) with live IBD vaccine using full field dose by eye DROP route . 10 birds were inoculated by field isolate; 5 at 7 days and the other 5 at 14 days P.V sereded that the vaccine was safe, as it did not produce clinical signs minor bursal damage and 100% protection after challange; while there were 85% deaths in unvaccinated birds (control group) . The remainder 46 birds (vaccinated unchallenged) gave adequate serological response when tested weekly; 4 times; toward agar gel precipitation, neutralization and ELBA tests .