ABSTRAC ARTICLE INFO Infectious bronchitis (IB), Newcastle disease (ND) and Avian influenza (AI) are highly contagious and the most economically important diseases of the poultry affecting the respiratory tract and causing economic losses in the poultry industry throughout the world. In the present study, 180 broiler flocks were sampled from 6 different Egyptian provinces (Giza, Qaluobia, Sharqia, Menofia, Al Behira and Fayoum) during 2014 to 2015. The birds showed respiratory illness and they

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... ere examined for 4 respiratory viral diseases; avian influenza (AI subtype H5 and H9), vNDV and IBV. All farms were vaccinated against IBV, ND and AI and were investigated using RT-PCR. The results showed that 41 out of 180 broiler farms were positive for either IBV or vND or AI-H5 and AI-H9 as a single infection as follows: 24, 10, 5 and 2 farms respectively. There were 62 farms detected as mixed infection, the highest incidence was shown in 40 farms co-infected with IBV and AI (H9) and 11 with IBV and vNDV, rRT-PCR results for each governorate separately go more or less parallel to that of all governorates collectively, There was no clear geographical preferences in positive viruses among governorates. ,Mortality rate and clinical signs incidence showed the highest percentage for birds reared in winter and Autumn compared with the other seasons. The results revealed that IBV as a single or a mixed infection had a major role in the respiratory problem in the field.