Analysis of global whole genome sequence data of Streptococcus equi collected from equines associated with strangles

The equine disease strangles, which is characterised by the formation of abscesses in the lymph nodes of the head and neck, is one of the most frequently diagnosed infectious diseases of horses around the world. The causal agent, Streptococcus equi subspecies equi, establishes a persistent infection in approximately 10% of animals that recover from the acute disease. Such 'carrier' animals appear healthy and are rarely identified during routine veterinary examinations pre-purchase or movement, but can transmit S. equi to naïve animals initiating new episodes of disease. Here we report the analysis and visualisation of phylogenomic and epidemiological data for 670 isolates of S. equi recovered from 19 different countries using a new core genome multilocus sequence typing (cgMLST) web resource. The genetic relationships between different isolates of S. equi were resolved with exquisite detail, highlighting national and international transmission events that drive this endemic disease in horse populations throughout the world. Our data argue for the recognition of the international importance of strangles by the Office International des Épizooties (OIE) to encourage the screening of horses pre-purchase or movement in order to reduce the health, welfare and economic cost of this disease. The Pathogenwatch cgMLST web resource described herein is available for structural genomic surveys of populations of S. equi and its close relative S. zooepidemicus that are recovered from horses and other animals, including humans, throughout the world.