The present study aimed to determine the molecular characteristics of circulating infectious bronchitis virus (IBV) strains in vaccinated broiler flocks in the Giza and Fayoum governorates. Thirty-four isolates were collected, and egg propagation revealed their ability to induce typical IBV lesions after three to five successive passages. Three selected isolates were identified as IBV using a real-time reverse transcriptase-PCR assay targeted the nucleocapsid (N) gene and further characterized by partial spike (S) gene sequence analysis. Phylogenetic analysis revealed their clustering into two variant groups. Group I consisted of one variant (VSVRI_F3), which had 99.1% nucleotide sequence identity to the Q1 reference strain. Group II consisted of variants VSVRI_G4 and VSVRI_G9, which showed 92.8%-94.3% nucleotide identity with the Egyptian variants Eg/12120S/2012, Eg/12197B/2012, and Eg/1265B/2012. Regarding the deduced amino acid sequence, the three variants had 77.1%-85.2% similarity with the vaccine strains currently used in Egypt. These findings highlight the importance of monitoring the prevalence of IBV variants in vaccinated broiler flocks as well as adopting an appropriate vaccination strategy.
Keywords: Egypt; S1 gene; infectious bronchitis virus; phylogenetic analysis; variants.