The emergence, evolution and spread of infectious bronchitis virus genotype GI-23

Abstract

Avian infectious bronchitis is a contagious viral disease, caused by avian infectious bronchitis virus (IBV), that leads to severe losses in the poultry industry all over the world. Since the 1950s, IBV has circulated in the Middle East and North Africa, and no tangible evidence has shown any effects of measures taken to control its spread or evolution. Furthermore, new IBV variants are continually discovered. Although several genetic studies on IBV have been conducted, many IBV strains from this region have either been misclassified or remain unclassified. The genotype 23 (GI-23) variant emerged and has prevailed in the Middle East by continuously evolving through inter- and/or intra-genotypic recombination. The GI-23 genotype is currently enzootic throughout Europe and Asia. Although many studies of protection against the circulating strains have been conducted, they have not been standardized according to regulatory requirements. In this review, we provide an overview of the evolution and genetic diversity of IBV genotypes and a genetic classification of IBV strains, with a focus on the GI-23 genotype. The high prevalence of IBV GI-23 strains necessitates the adoption of vaccination schemes using GI-23-based vaccines.

Fig. 1

Phylogenetic analysis of the IBV genetic lineages (200 sequences) (A) and GI-23 sequences (B) from the Middle East based on full-length S1 gene sequences using the maximum-likelihood method and the Tamura-Nei model. There were 1736 positions in the final dataset. Distances between the proposed sublineages and subclades (C) were calculated using MEGA X software.

Fig. 2

Phylogenetic analysis of the IBV genetic lineages (194 sequences) (A) and GI-23 sequences (B) from the Middle East based on HVR3 sequences using the maximum-likelihood method and the Tamura-Nei model. There were 349 positions in the final dataset. Distances between the proposed sublineages and subclades (C) were calculated using MEGA X software.

Fig. 3

Geographical distribution of genetic lineage 23 of IBV in the Middle East, North Africa, Europe, and Asia. Countries that have reported the detection of GI-23-like strains are indicated in red.