Abstract :
Avian infectious bronchitis virus (IBV) is one of the major problems in Egypt due to frequent emergence of new variants. In present study, tissue samples and serum of 32 broiler chicken flocks in El-Behera and Alexandria governorates suffering from respiratory symptoms and pathological changes in kidney associated with high mortality rate during 2013. 19 IBV antigen detected in CAMs of specific pathogen free (SPF) embryos was carried out after studies three blind successive passages of 32 broiler flocks by the AGPT against reference IBV Beaudette antiserum at a percentage of 59.3%. IBV virus. 19 positive AGPT CAMs samples were examined by by real time RT-PCR at a percentage of 100% with threshold cycle between 16 and 35. The hypervariable region of spike protein1 (SP1) of selected six IBV isolates was amplified by RT-PCR and sequenced to study the genetic diversity between the isolated viruses compared with other IBV strains. Phylogenetic analysis of the obtained sequences of glycoprotein gene of six isolates revealed that they all formed a distinct phylogenetic group with the Ck/Eg/BSU-2/2011 and Ck/Eg/ BSU-3/2011 (Variant 2). Also, The Phylogenetic analysis indicated that the six selected Egyptian isolates are far from vaccine strains that present in Egypt. The HI GMT readings of the serum samples for the selected six IBV flocks that their tissues were previously sequenced showed that the six flocks did not match any one of the four IBV HI (M41, D274, QX, 4/91) antigens but they were more related to 4/91 and D274 which the R.value ranged from 77.7% to 97.2 and 77.7% to 90.27%, respectively. So it is difficult to use HI test as serotyping technique in Egypt due to emergence of new variants other than the four used HI antigens (M41, D274, QX, 4/91) and lack of standardization (presence of reference strain and antiserum) of these new variants. This study demonstrates a constant evolution of IBV in Egypt that necessitates continuous monitoring to control the spread of infections, and the development and use of vaccines based on indigenous viruses.
