الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
In this study from twenty samples representing twenty broiler chicken flocks suspected to be infected with infectious bronchitis virus (IBV) were examined for viral respiratory diseases(IBV, H5N1, H9N2 and NDV) by RT-PCR to know the degree of co infection between IBV and other respiratory diseases and the results revealed that co infection of IBV with NDV is the most common, then the RT-PCR product of five positive samples for IBV were sequenced and further phylogeneticaly analysis, the results showed that four of five isolates were highly related to previously isolated Egyptian variant-2 IBV isolates as (Ck/Eg/BSU-2/2011 and Ck/Eg/BSU-3/2011) and only one isolate from five isolates was highly related to previously isolated Egyptian variant-1 IBV isolates as(IBV/CK/Cairo-Egypt/USC-1/2013).
Due to increase of co-infection of IBV and NDV incidence high percentage of co-infection between IBV and NDV we make an experiment to know the role of each virus IBV and/or NDV in the appearance of clinical signs, mortality percentage and P.M.
from our study we founded that the group which was vaccinated with NDV vaccines (live and dead) and challenged with IBV was apparently normal and mortality percent was (0%) and histopathological lesions were slight, but the group vaccinated with IBV vaccines (live vaccines) and challenged with NDV and the group not vaccinated and challenged with IBV and NDV have very sever clinical signs and very high mortality percent reached to 100%.these all result give indication that IBV alone make small effects and the very serious effects take place from the co circulating factors.