Phylodynamic and phylogeographic reconstruction of IBV lineages: diverse paths and determinants, one goal for control.

Infectious bronchitis virus (IBV) is a genetically diverse avian coronavirus that significantly impacts global poultry production. While IBV evolution and spread have been widely studied, most analyses lack global scope and statistical evaluation of dispersal drivers. This study investigates the population dynamics, spatiotemporal diffusion, and determinants of spread for three major IBV lineages-GI-16, GI-19, and GI-23-using a phylodynamic framework integrated with a generalized linear model (GLM). All lineages likely originated between the 1960s and 1980s, circulating at low levels before expanding under favorable conditions, often linked to introduction into naïve or poorly managed poultry systems. Temporal trends suggested lineage competition and modulation by vaccination strategies. Phylogeographic analyses showed that local and regional circulation prevailed over long-distance migration. No statistical support was found for a role of migratory birds. Instead, chicken population size, agricultural investment and trade, were significant drivers. Interestingly, agricultural investment was negatively associated with viral migration in Europe-likely due to the protective effect of improved biosecurity and vaccination-yet positively associated with GI-23, reflecting rapid poultry sector expansion in some emerging economies, which was not matched by adequate animal health management. These findings highlight the complex and lineage-specific nature of IBV spread and the importance of science-based, coordinated control strategies, backed by international surveillance.