A Systematic Review of the Molecular Epidemiology, Phylodynamics, Genetic Diversification, and Regional Dissemination of GI-23 Infectious Bronchitis Virus in Iran and the Middle East

Introduction: Infectious bronchitis virus (IBV) remains one of the most challenging viral pathogens impacting the poultry industry worldwide. Among circulating genotypes, GI-23 (Variant 2/IS-1494-like) has become the predominant lineage in Iran and the Middle East. Its ongoing circulation, genetic diversification and variation raises its regional dissemination risks and vaccine ineffectiveness problems.
Methods: This systematic review was conducted according to PRISMA guidelines to evaluate the Relevant studies published between 2015 and 2025 were retrieved from PubMed, Scopus, Web of Science, and Google Scholar. Studies reporting molecular characterization, sequencing, phylogenetic analyses, recombination, or vaccine-related findings of GI-23 IBV in Iran and Middle Eastern countries were included and systematically analyzed.
Results: This review demonstrated that GI-23 considers as a dominant IBV lineage in the Middle East for nearly two decades. In Iran, the prevalence of GI-23 reached nearly 70% among characterized isolates between 2015 and 2017. Partial S1 gene analyses revealed high nucleotide identities (99.31–100%) among Iranian and Middle Eastern GI-23 isolates. Eastern GI-23 isolates, supporting ongoing transboundary circulation. Otherwise, phylogenetic studies identified substantial genetic heterogeneity within the lineage, with approximately 11–13% divergence between major Variant-1 and Variant-2 groups. Iranian isolates were predominantly assigned to the GI-23.2 sublineage and shared 95–97% similarity with previously reported Iranian variants. Molecular evolutionary analyses estimated a substitution rate of approximately 4.3 × 10⁻³ substitutions/site/year. Multiple amino acid substitutions and insertion/deletion events within S1 hypervariable regions were demonstrated, including 7–11 substitutions in HVR3 of Variant-2 strains. Recombination involving GI-23, GI-13, and GI-19 lineages was also reported. Circulating Iranian GI-23 strains showed only 82.64% nucleotide identity with H120 and 4/91 vaccine strains.
Conclusions: High nucleotide identity among Iranian and Middle Eastern GI-23 isolates suggests a close epidemiological and genetic relationship. Continuous molecular surveillance and genotype-matched vaccination strategies is essential for disease control in the Middle East.