The genetic diversity of the hypervariable region I of S1 gene (HVR I) of infectious bronchitis (IB) vaccine strains H120, Ma5 and 4/91 was compared to that of 26 infectious bronchitis virus (IBV) strains isolated from the field in Guangxi province of China during the years 1985-2008, and the field isolates were classified into five major genotypes. Monovalent antisera against three vaccine strains and seven field isolates of different genotypes were prepared by immunizing rabbits with mineral oil adjuvant preparations containing viruses propagated in chicken embryos. Virus neutralization (VN) tests were performed in tracheal organ cultures (TOCs) using these 10 strains with the antisera, and a one-way VN test was then used to compare the relationship of 10 monovalent antisera to the other 19 field isolates. As a result, seven different serotypes were classified based on the results of VN tests with the 26 isolates plus the three vaccine strains. We found that different serotypes were prevalent during different time periods, that more new serotypes have been prevalent in more recent years, and the prevalence of the original dominant serotype has been in constant decline since 2004. In addition, the concordance rate of the 26 field isolates between the S1 genotypes and serotypes was 57.7%.

Sixty field strains of avian infectious bronchitis virus (IBV) were isolated from chicken flocks in different regions of Guangxi from 1985 to 2012. Phylogenetic analysis of S1 subunit glycoprotein genes revealed that field isolates from 2009-2011 mostly belonged to the LX4 type, while those from 1985-2008 belonged to the HN08 type, and a few others belonged to the 4/91 type, the TW type and the Mass type. In addition, it is noteworthy that no obvious regional differences were found among these 60 strains isolated from six regions in Guangxi, while there was a high degree of sequence identity among the isolates in the same period of time.

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ABSTRACT. Infectious bronchitis virus (IBV) can multiply effectively in chick embryo kidney (CEK) cells after adapting to the chick embryo. To investigate the dynamic changes in IBV load in the supernatant of primary CEK cells, we developed an SYBR Green I-based real-time polymerase chain reaction assay to quantify nucleic copy numbers of the IBV-Sczy3 strain. The 20, 54, and 87th generations of CEK-adapted IBV-Sczy3 strains were used to infect CEK cells, and then nucleic copy numbers in the samples of supernatant collected at 12, 24, 36, 48, 60, and 72 h were detected. The results showed that the rapid growth period of the virus load of all the 3 generations was approximately 12-36 h post- (2015) infection; the peak of the virus load appeared at 36 h post-infection and then decreased gradually in the order of 20th > 54th > 87th for the 3 generations of CEK-adapted strains; the dynamic change curve of the IBV load in the supernatant of primary CEK cells showed a single peak. The results of this study provide a useful reference for CEK-adapted IBV field strains and the production of CEK-attenuated IBV vaccine.