Emergence and rapid propagation of ST4 Mycoplasma bovis subtype in France and Belgium

Mycoplasma (M.) bovis is a major pathogen worldwide involved in bovine respiratory disease with significant economic and welfare impacts. Since the 2000s, the laboratory-based surveillance network Vigimyc has integrated molecular typing of an annual subset of M. bovis isolates collected in France, and more recently in Belgium. This study aimed to characterize the epidemiological situation and evolution of M. bovis in both countries over the 2018-2024 period. A total of 498 M. bovis isolates were characterized using a routine monitoring approach based on polC subtyping. We observed the apparent re-emergence and the rapid spread of polC st1 isolates since 2019 in France and 2020 in Belgium, accompanied by a concurrent and marked decline of the previously dominant polC st2 genotype. To investigate this phenomenon, we performed whole-genome sequencing on 45 polC st1 isolates to explore their genetic diversity and evolutionary relationships between strains. Genome-based analyses highlighted that this population was phylogenetically distinct from the older polC st1 isolates collected before 2000 and belonged to the ST4 according to the updated PubMLST database. The genetic diversity within these isolates was extremely low in comparison to that observed in the other subtypes, thus highlighting the recent and clonal emergence of this new lineage. In the absence of apparent AMR switch associated with this expansion, as previously observed for the emergence of polC st2 population, we identified putative genetic patterns specific to this lineage that may contribute to the fitness and epidemiological success of recent polC st1 isolates.