Analysis Of The Genome Of IBV CK/CH/LSD/051 Isolated In China And The Protection Conferred By Attenuated Vaccines

Infectious bronchitis is prevalent in many countries. It has been one of the most infectious diseases that disserve the chicken breedings. Although infectious bronchitis vaccines play an important role in the control of IB all over the world, this disease break out occasionally with unknown the pathogenetic mechanism.According to the published genome sequences of infectious bronchitis virus (IBV) on GenBank, twenty-nine primers were designed and the genome of the isolated CK/CH/LSD/05I strain of IBV was amplified by RT-PCR. All the RT-PCR products were cloned into the pMD18-T vector and sequenced. The genome sequence of CK/CH/LSD/05I strain was 27638 bp in length. The ratio of A+T in the genome was 61.78%. Compared with the genome of Beaudette, Mass41, Cal99, BJ, KQ6, GD/S14/2003, SAIBK, LX4, the similarities were 88.7%, 88.7%, 89.5%, 86.1%, 88.6%, 86.9%, 88.5% and 86.9%, respectively. The 3′UTR and 5′UTR were the most conservative region among the genome. The S gene have the most variations, the similarity was between 66.8% and 83.7%. The phylogenetic analysis results showed that the CK/CH/LSD/05I constituted a distinct branch.CK/CH/LSD/05I was an IBV variant, which was identified by the phylogenic analysis, BLAST searches of the entire S1 gene and the vaccination-challenge test. Virulence studies indicated that there were not obviously kidney pathological changes on chickens, and the rate of recovery of the virus in the kidney and trachea post-inoculation was 20% and 100%, respectively. Thus CK/CH/LSD/05I was unlike the nephropathogenic IBV isolates frequently found in China; however, it exhibited an affinity for the respiratory tract. Additionally, sufficient respiratory protection was not provided by the commercial vaccine H120 and three heterologous strains against CK/CH/LSD/05I challenge. It was shown that CK/CH/LSD/05I might be a variant of IBV.This study fulfilled the biological information database of Coronavirus, and also provided a basis for pathogenesis and variation mechanism of IBV at the molecular lever. The appreciation, on the efficacy of different attenuated IBV strains against the challenge of CK/CH/LSD/05I, provided theoretical evidence for vaccined chickens infecting IB. Furthermore, our study suggested a new idea for controlling IB.