Analysis of a QX-like avian infectious bronchitis virus genome identified recombination in the region containing the ORF 5a, ORF 5b, and nucleocapsid protein gene sequences.

The complete genome of a QX-like infectious bronchitis virus (IBV) strain Sczy3 isolated recently in Sichuan was sequenced. The genome contains 27,695 nucleotides (nt), and possesses a genomic structure similar to other IBV strains. Sequence comparisons demonstrated that the Sczy3 genome had the highest nt sequence identity with QX-like IBVs and was most dissimilar to the Massachusetts type IBV. Differences in the sequences of genes present in the Sczy3 genome and other IBVs gene sequences were also identified. Phylogenic analysis showed that the entire genome and most of the Sczy3 genes were located in the same cluster as LX4. Recombination analysis showed that Sczy3 is a chimeric strain derived from LX4 (major parental sequence) and H120 (minor parental sequence) suggesting that recombination occurred in a region containing the 3' terminal 5a sequence (83 nt), the 5' terminal 5b sequence (222 nt), and the 5' terminal nucleocapsid protein gene sequence (132 nt). Mutations and intergenic recombination may have played an important role in the evolution of IBVs.