الفهرس 
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Abstract
A total of 15 broiler chicken flocks belonging to Desouk and Qallin (Kafr el-Sheikh Gov.) as well as to Bassioun (Gharbia Gov.) exhibited rapid increase in mortality rate and respiratory manifestation were thoroughly investigated during the period from December 2013 to January 2015. Rapid field detection of AIV by immuno-chromatography tests revealed detection of AIV antigen in one (6.67 %) broiler chicken flock. Twenty one tissue pool samples collected from the broiler chicken flocks as well as 244 swabs and one brain tissue pool from 127 free living birds- in the vicinity and inside the affected broiler chicken farms- were subjected for isolation and molecular characterization of NDV and AIV subtypes (H5 and H9). In addition, 75 and 60 samples (pooled; liver, heart and spleen) from broiler chickens and free living birds respectively subjected to isolation and characterization of E. coli by using selective media, serotyping, in vitro and in vivo virulence assay. Nineteen (90.48 %) and 2 (9.52 %) out of 21 samples collected from broiler chicken flocks showed positive isolation for NDV and AIV H5 respectively, whereas 25 (10.2 %) and one (0.41%) out of 245 samples from free living birds showed positive isolation for NDV and AIV H5 respectively and no positive results could be obtained for AIV H9N2 from all samples. Molecular characterization by sequencing of F gen fragment and phylogenetic analysis of the selected 13 NDV isolates, revealed two isolates from broiler chicken flocks and 9 isolates from free living birds had possessed the same velogenic genotype motif of 112R-R-Q-K-R-F117, in addition to clustering with published class II genotype VII sub genotype d NDVs and closely related to Israel and China isolates, whereas one isolate from broiler chicken flocks had possessed the lentogenic genotype motif of 112G-R-Q-G-R-L117, in addition to clustering with published class II genotype II NDVs. Molecular characterization of pigeon NDV isolate showed velogenic genotype motif 112K-R-Q-K-R-F117 and clustered with published class II genotype VI. Molecular characterization of two selected AIV H5 isolates (cattle egrets and broiler chickens) by sequencing of HA gen fragment and phylogenetic analysis revealed clustering the isolates in the same subclade 2.2.1/ C. Isolation and identification of E. coli from broiler chicken samples revealed 48/75 (64 %) isolates, whereas free living bird samples revealed 10/60 (16.67%) isolates. In vitro pathogenicity test using Congo red (CR) binding assay showed that out of 48 isolates from broiler chickens 22 (45.8 %) showed CR +ve, whereas out of 10 isolate from free living birds 5 (50 %) showed CR positive. Serotyping was carried out on 5 selected CR positive isolates of broiler chickens and all 10 isolates of free living birds. Three E. coli serogroups belonged to O44, O55 and O157 from broiler chickens and 6 serogroups belonged to O128, (2¬¬) O55, O136, O127 and O164 from free living birds were inoculated in day-old SPF chicks that revealed 100 % mortality with the strain O136 (house sparrow origin), 80 % mortality with the strain O44 (broiler chicken origin), 40 % mortality with strain O55 (dove origin), 20 % with both strains; O157 (chicken origin) and O128 (house sparrow origin), whereas other strains; O55 (chicken origin), O55 (house sparrow origin), O127 (dove origin) and O164 (cattle egret origin) did not caused any mortality in chicks. The study suggested that free living birds can play an important role in prevalence of velogenic NDV genotype VIId which is responsible for recent outbreaks in Egypt and isolation of genotype VI from pigeons may be proposed to be responsible for next Newcastle disease outbreaks, whereas isolation of AIV H5 from cattle egret focuses on the role of this bird as reservoir for HPAIV H5. In addition, these wild birds can play important role in introduction of pathogenic strains of E. coli to broiler chicken farms.