Molecular epidemiological study of a strangles outbreak in Texas

Strangles (Streptococcus equi subspecies equi) is an infectious disease of horses with worldwide distribution, but there are limited data available regarding strain variation assessed using whole genome sequencing among and within outbreaks in the United States (US), and regarding how US isolates compare with S. equi isolated globally. To address this knowledge-gap, we collected, characterized using whole genome sequencing, and compared 54 S. equi isolates from Texas and Kentucky. We also compared the genomes of these 54 isolates with those of 230 publicly available S. equi isolates collected from other countries. Our results, show that variability within individual S. equi outbreaks was minimal, but some mutations within individual isolates within an outbreak do occur. It appeared that some S. equi strains from the US are closely related to S. equi isolates from other countries, likely reflecting international dissemination of isolates. Collectively, these data will help better understanding of how isolates from the US contribute to the ongoing epidemiology of this host-specific infection.