الفهرس 
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Abstract
This study was attempted to investigate molecular changes of Avian Influenza virus (AIV), Newcastle disease virus (NDV) & Infectious Bronchitis virus (IBV) in some Egyptian governorates. Sixty two samples from 62 farms located in Alexandria, Matrouh, Behira and Kafr El-shikh show respiratory symptoms and diarrhea suspected to be IBV, ND and AI infections and high mortality rate. Samples taken from trachea, bronchi and lung in order to isolate Newcastle disease virus ,avian influenza virus and infectious bronchitis virus in SPF egg for blind passages for (NDV and AIV) and 5 consecutive blind passages for(IBV). The harvested allantoic fluid after serial passages and tested for hemagglutination viruses by HA test result was 50 samples positive HA and 12 negative HA followed by HI test found that 26 samples NDV and 15 samples AIV. The harvested allantoic fluid for detection of NDV, AIV and IBV by RT-PCR. Two positive isolates of NDV were random selected for further genetic analysis by F gene sequences and the results revealed that all isolates had similarity relatedness to Chinese strain by 98% and 99% respectively. Two positive isolates of AIV were random selected for further genetic analysis by M gene sequences and the results revealed that all isolates had similarity relatedness to Egyptian strain from 97% to 100% and similar to American strain by 90%.