Abstract
The present study aimed to specify the most important respiratory viral diseases affecting broiler chickens under Egyptian conditions. Forty four broiler chicken flocks were investigated in three governorates (Alexandria, El-Behera and Kafr El-sheikh) that showed high mortality rate with respiratory manifestations and/or diarrhea. The collected samples (trachea and lungs homogenates) were examined for Avian Influenza viruses (AIv) (H5&H9), Newcastle Disease virus (NDv) and Infectious Bronchitis virus (IBv) through isolation in specific pathogen free (SPF) eggs and identification by slide hemagglutination test and Real time reverse transcriptase polymerase chain reaction (RRT-PCR). The results revealed that the highest detection rate was NDv (20/44) with positivity percent (45.46%), 7 flocks out of 44 were positive for AI H9 (15.90%), while 3 flocks (3/44) were positive for AI H5 (6.82%), on the other hand 4 flocks (4/44) were positive for IBv (9.10%). Sequencing and phylogenetic analysis of F gene of selected 8 NDv isolates, they were related to genotype VII, also sequencing for haemagglutinin (HA) gene of selected AIv isolates showed that two isolates belonged to H5N8 highly pathogenic avian influenza (HPAI) (clade 2.3.4.4.b) and one isolate belonged to H5N1 HPAI clade 2.2.1.2, while two selected H9 isolates were related to H9N2 low pathogenic avian influenza (LPAI) group B. on the other hand, sequencing of S1 gene for one selected IBv isolate was related to EGY variant II. So, continuous surveillance of different respiratory diseases that represent a large economic threat for poultry industry should be maintained to facilitate the possible protocols to prevent and control these diseases.

Key words: Broiler chickens, Influenza virus, IB, RRT-PCR, Newcastle disease