AIM: To characterize the circulating infectious bronchitis virus(IBV) strains in Egypt depending on the sequence of the spike-1(S1) gene [hypervariable region-3(HVR-3)] and to study the pathotypic features of these strains.METHODS: In this work, twenty flocks were sampled for IBV detection using RRT-PCR and isolation of IBV in specific pathogen free(SPF) chicks during the period from 2010 to 2015. Partial sequencing and phylogenetic analysis of 400 bp representing the HVR-3 of the S1 gene was conducted. Pathotypic characterization of one selected virus from each group(Egy/Var-Ⅰ, Egy/Var-Ⅱ and classic) was evaluated in one day old SPF chicks. The chicks were divided into 4 groups 10 birds each including the negative control group. Birds were inoculated at one day by intranasal instillation of 105EID50/100 μL of IBV viruses [IBV-EG/1212B-2012(Egy/Var-Ⅱ), IBV/EG/IBV1-2011(Egy/Var-Ⅰ) and IBV-EG/11539F-2011(classic)], while the remaining negative control group was kept uninfected. The birds were observed for clinical signs, gross lesions and virus pathogenicity. The real-time rR TPCR test was performed for virus detection in the tissues. Histopathological examinations were evaluated in both trachea and kidneys.RESULTS: The results revealed that these viruses were separated into two distinct groups; variant(GI-23) and classic(GI-1), where 16 viruses belonged to a variant group, including 2 subdivisions [Egy/Var-Ⅰ(6 isolates) and Egy/Var-Ⅱ(10 isolates)] and 4 viruses clustered to the classic group(Mass-like). IBV isolates in the variant group were grouped with other IBV strains from the Middle East. The variant subgroup(Egy/Var-Ⅰ) was likely resembling the original Egyptian variant strain(Egypt/Beni-Suif/01) and the Israeli strain(IS/1494/2006). The second subgroup(Egy/Var-Ⅱ) included the viruses circulating in the Middle East(Ck/EG/BSU-2 and Ck/EG/BSU-3/2011) and the Israeli strain(IS/885/00). The two variant subgroups(Egy/Var-Ⅰ and Egy/Var-Ⅱ) found to be highly pathogenic to SPF chicks with mortalities up to 50% than those of the classic group which was of low virulence(10% mortality). Pathogenicity indices were 25(Egy/Var-Ⅱ), 24(Egy/Var-Ⅰ) and 8(classic); with clinical scores 3, 2 and 1 respectively.CONCLUSION: These findings indicated that the recent circulating Egyptian IBVs have multiple heterogeneous origins in marked diversifying nature of their spread, with high pathotype in specific pathogen free chicks. AIM: To characterize the newly infected IBV strain in Egypt depending on the sequence of the spike-1 (S1) gene [hypervariable region-3 (HVR-3)] and to study the pathotypic features of these strains. METHODS : In this work, twenty flocks were sampled for IBV detection using RRT-PCR and isolation of IBV in specific pathogen free (SPF) chicks during the period from 2010 to 2015. Partial sequencing and phylogenetic analysis of 400 bp representing the HVR-3 of the S1 gene was conducted. One chick was splashed into 4 groups 10 birds each including the negative control group. Birds were inoculated at one day by intranasal instillation of 105EID50 / 100 μL of IBV viruses [IBV-EG / 1212B-2012 (Egy / Var- II), IBV / EG / IBV1-2011 (Egy / Var- I) and IBV-EG / 11539F-2011 (classic)], while the remaining negative control group was kept uninfected. The real birds were observed for these viruses were separated variant (GI-23) and classic (GI-1), where 16 viruses belonged to a variant group, including 2 subdivisions [Egy / Var- )] and 4 viruses clustered to the classic group (Mass-like). IBV isolates in the variant group were grouped with other IBV strains from the Middle East. The variant subgroup (Egy / Var-I) was likely to resemble the original Egyptian variant The second subgroup (Egy / Var-II) included the viruses circulating in the Middle East (Ck / EG / BSU-2 and Ck / EG / BSU-3/2011) and the Israeli strain (IS / 885/00). The two variant subgroups (Egy / Var-I and Egy / Var- II) found t o be highly pathogeniPathogenicity indices were 25 (Egy / Var-II), 24 (Egy / Var-I) and 8 classic); with clinical scores 3, 2 and 1 respectively. CONCLUSION: These Results indicated that the recent circulating Egyptian IBVs have multiple heterogeneous origins in marked diversifying nature of their spread, with high pathotype in specific pathogen free chicks.