<em>Streptococcus equi</em> subsp. <em>zooepidemicus</em>: Epidemiological and Genomic Findings of an Emerging Pathogen in Central Italy

Streptococcus equi subsp. zooepidemicus (SEZ) is a significant concern in equine veterinary medicine. Typically, a commensal in horses, SEZ can cause severe diseases including respiratory infections, septicemia, and reproductive tract infections under certain conditions. Recent evidence suggests that SEZ may also cause severe diseases in humans through direct contact with animals or consumption of unpasteurized milk and dairy products. This study investigates SEZ strains isolated from nasal swabs of Equidae in central Italy in 2023 to describe the epidemiology and genomic characteristics of circulating strains. A sampling plan was implemented to randomly collect nasal swabs from equid farms in the Abruzzo and Molise regions. Additionally, a sampling form was designed to gather information on risk factors related to the presence of the bacterium and the potential development of respiratory disease. Relative risk was employed to measure the association between the presence of SEZ in the samples and various variables. The swabs were analyzed using real-time PCR and isolation. To confirm the identification and characterize the strains, the isolates were fully sequenced by next-generation sequencing (NGS) through the Illumina platform (Illumina, San Diego, CA, USA). A total of 478 animals from 99 farms were sampled with 144 animals tested positive for SEZ (79% horses, 20% donkeys, 1% mules). Forty-five percent of the farms examined were found to be positive for SEZ. Monitoring the clonal spread of SEZ is crucial for understanding the ecology of this emerging zoonotic pathogen, assessing the risk, and implementing effective control measures. Furthermore, genomic assessments are recommended to examine the pathogenicity of circulating strains. This study provides a comprehensive understanding of the epidemiology and genomic diversity of SEZ strains isolated in central Italy.