Evolution of infectious bronchitis virus in China over the past two decades

Abstract

Avian infectious bronchitis is a highly contagious disease caused by infectious bronchitis virus (IBV) that affects poultry production worldwide. The absence of vaccine cross-protection and the frequent emergence of new variant strains complicate control of IBV. Here we designed a study to measure the evolution dynamics of IBV strains in China. One hundered and seven complete sequences and 1022 S1-region sequences of Chinese IBVs isolated between 1994 and 2014 were analysed by using MEGA 5.0 software and the Bayesian analysis sampling trees (BEAST) method, and selection pressure on different proteins was assessed. The phylogenetic dissimilarity of different gene trees in the data set indicated possible recombination. Fourteen isolates were identified as recombinants, possibly generated from vaccines of the Massachusetts serotype in recombination with circulating viruses. The earliest IBV in China was found to have existed in the early 1900s, and continues to evolve at a rate of approximately 10 À5 substitutions per site per year. We found that purifying selection was the main evolutionary pressure in the protein-coding regions, while the S1 gene bears the greatest positive selection pressure. The proportion of QX-like genotype strains increased over time.These results indicate that the genotypes of Chinese IBVs have undergone a remarkable transition during the past 20 years.

Genetic, antigenic, and pathogenic characteristics of avian infectious bronchitis viruses genotypically related to 793/B in China

“…This indicates that it is possible for a GX-YL9-like virus and the 4/91 vaccine strain to co-exist in a certain chicken flock, which is believed to be an important prerequisite for recombination between IBV strains in the field (Cavanagh, 2007). Importantly, the 4/91 vaccine strain is still commonly used in China, and GX-YL-9-like viruses are still circulating in China for a long time (Zhao et al, 2016); hence, more IB cases associated with ck/CH/LGD/ 120723-like viruses might be expected in the future. This was the case in the present study, as seven viruses, which emerged from recombination events between the 4/91 vaccine strain and a GX-YL-9-like virus, were isolated in different regions in different years in China.…”

Impacts of poultry vaccination on viruses of wild bird

“…Selection for viruses that 'escape' vaccineinduced immunity can occur when there is incomplete cross-protection between viral serotypes or antigenic types. This has been reported for a number of poultry viruses, particularly avian influenza virus (AIV) [16 ,17], but also other viruses, including IBV [15 ] and NDV [18]. The viruses that persist in poultry despite (or due to) the use of vaccines can then be transmitted to wild birds, with the viruses detected in wild birds reflecting those that are in local farmed poultry.…”

“…Other than direct impacts that the attenuated vaccine viruses may have on wild birds there is also the potential for the attenuated vaccine viruses to evolve to higher levels of virulence in wild birds, including through the process of recombination. Phylogenetic evidence of recombination is growing and has been reported for both IBV and NDV, including recombination between vaccine and wildtype viruses [14,15 ].…”

Analysis of antigenicity and pathogenicity reveals major differences among QX-like infectious bronchitis viruses and other serotypes

“…The inaccuracy of the coronavirus RNA-dependent RNA polymerase and high frequency of genetic changes in IBV (e.g., gene insertion, mutation, deletion, and reconstruction), promote the emergence of new variant strains, genotypes and serotypes of IBV, and these are continuously reported (Cavanagh et al, 1986;Chen et al, 2017;Yan et al, 2016;Zhao et al, 2016). IBV immunity is serotype-specific, and Mass-type vaccines (H120) can be ineffective against infection with different IBV isolates in China (Chen et al, 2017;Sun et al, 2011;Zhao et al, 2015).…”