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To examine the epidemiology and evolutionary characteristics of avian infectious bronchitis virus (IBV) in mainland China, the S1 gene of 63 IBVs isolated after 1993 was amplified by reverse transcription (RT) -polymerase chain reaction (PCR) and sequenced. Our results showed that the sequence length of 63 IBV strains ranged from 1.608 to 1.635 nucleotide (nt). Compared to the published representative strains, the homology of S1 nt sequences and their deduced amino acid (aa) residues between these isolates and reference strains ranged from 74.6% to 99.9% and 71.7% to 100%, respectively. Analysis of S proteins demonstrated that 63 isolates had eight kinds of cleavage sites (RRFRR, RRIRR, RRSKR, RRTGR, RRHRR, HRRRR, RRSRR and RRLRR), and the amount of RRFRR and HRRRR reached 46. Furthermore, the study showed that there was no direct relation between cleavage sites and genotypes, and cleavage sites were unable to decide the pathology types. Compared to vaccine strain H120, S1 nt sequences of 63 isolates had four sites deleted or inserted frequently, and the S1 proteins had three hypervariable regions. A comprehensive study was also carried out to study the S1 nt sequences of 63 isolates, 210 published reference strains and 10 vaccine strains; the investigation showed that all these stains could be divided into two types including 11 kinds of genotypes by the phylogenetic analysis. However, 63 isolates belonged to Mass, American, LX4, LHLJ/95 I, LDT3/03, J, BJ and LDL/97 I genotypes, and the LX4 genotype was co-circulated dominantly in chicken flocks over an 18-year period. It indicated that there were several IBV genotypes with new changes circulating in China, emphasizing the importance of continued IBV surveillance. [ABSTRACT FROM AUTHOR]

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