The accurate identification of Taylorella equigenitalis strains is essential to improve worldwide prevention and control strategies for contagious equine metritis (CEM). This study compared 367 worldwide equine strains using multilocus sequence typing according to the geographical origin, isolation year and equine breed. The strains were divided into 49 sequence types (STs), including 10 described for the first time. Three major and three minor clonal complexes (CCs), and 11 singletons, were identified. The genetic heterogeneity was low (0.13 STs/strain) despite the wide diversity of geographical origins (n = 16), isolation years (1977-2018) and equine breeds (n = 18). It was highest outside Europe and in the 1977-1997 period; current major STs and CCs already existed before 1998. Previous data associated the major CC1 with the first CEM outbreaks in 1977-1978 in the United Kingdom, Australia and the United States, and revealed its circulation in France. Our study confirms its circulation in France over a longer period of time (1992-2018) and its distribution in Spain and Germany but not throughout Europe. In addition to CC1, relationships between non-European and European countries were observed only through ST4, ST17 and ST30. Within Europe, several STs emerged with cross-border circulation, in particular ST16 and ST46 from the major complexes CC2 and CC8. These results constitute a baseline for monitoring the spread of CEM outbreaks. A retrospective analysis of a higher number of strains isolated worldwide between 1977 and the early 2000s would be helpful to obtain an exhaustive picture of the original CEM situation.

Alte Bernstrasse 5 Detligen Switzerland

ANSES Laboratory for Animal Health Physiopathology and Epidemiology of Equine Diseases Unit Goustranville France

Central Veterinary Research Laboratory Dubai United Arab Emirates

Diagnostic Bacteriology and Pathology Laboratory National Veterinary Services Laboratories USDA Ames United States

Friedrich Loeffler Institut Institute of Bacterial Infections and Zoonoses Jena Germany

Institute of Veterinary Bacteriology University of Bern Längassstrasse 122 Bern Switzerland

Laboratorio Central de Veterinaria Sanidad Animal Algete Madrid Spain

National Veterinary Research Institute Department of Microbiology Pulawy Poland

State Veterinary Institute Prague Prague Czech Republic

TRAGSATEC Tecnologías y servicios agrarios SA Madrid Spain

Veterinary and Agrochemical Research Center Bacterial Zoonoses of Livestock Unit Operational Direction Bacterial Diseases Brussels Belgium

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Whole genome sequences of nine Taylorella equigenitalis strains isolated in the Czech Republic between 1982-2021: Molecular dating suggests a common ancestor at the time of Roman Empire