Phylodynamic and Recombination Analyses of Avian Infectious Bronchitis GI-23 Reveal a Widespread Recombinant Cluster and New Among-Countries Linkages.

Infectious bronchitis virus GI-23 lineage, although described approximately two decades ago in the Middle East, has recently drawn remarkable attention and is considered an "emerging" lineage due to its current spread to several other regions, including Europe. Despite the relevance, no comprehensive studies are available investigating its epidemiologic and evolutionary pattern. The present phylodynamic study was designed to fill this gap, benefitting from a collection of freely available GI-23 sequences and ad-hoc generated European ones. After a relatively ancient origin in the Middle East, likely in the first half of the previous century, GI-23 circulated largely undetected or underdiagnosed for a long time in this region, likely causing little damage, potentially because of low virulence coupled with limited development of avian industry in the considered years and regions and insufficient diagnostic activity. The following development of the poultry industry and spread to other countries led to a progressive but slow increase of viral population size between the late '90s and 2010. An increase in viral virulence could also be hypothesized. Of note, a big recombinant cluster, likely originating in the Middle East but spreading thereafter, especially to Europe through Turkey, demonstrated a much-marked increase in viral population size compared to previously circulating variants. The extensive available GI-23 sequence datasets allowed to demonstrate several potential epidemiological links among African, Asian, and European countries, not described for other IBV lineages. However, differently from previously investigated IBV lineages, its spread appears to primarily involve neighbouring countries and those with strong economic and political relationships. It could thus be speculated that frequent effective contacts among locations are necessary for efficient strain transmission. Some countries appear to play a major role as a "bridge" among less related locations, being Turkey the most relevant example. The role of vaccination in controlling the viral population was also tentatively evaluated. However, despite some evidence suggesting such an effect, the bias in sequence and data availability and the variability in the applied vaccination protocols prevent robust conclusions and warrant further investigations.

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

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.