Streptococcus equi Subspecies zooepidemicus Infective Endocarditis: A Case Report of a Rare Bacterium and Review of the Literature

Infective endocarditis (IE) is a dreaded disease with a high mortality rate. In Denmark, IE is most often caused by <i>Staphylococcus aureus</i> or <i>Streptococcus</i> species. We present a rare case of a 50-year-old woman with a history of a dual-chamber pacemaker due to third-degree atrioventricular block and a mechanical mitral valve inserted due to mitral stenosis. The patient was admitted to the hospital after she was found lying on the floor in her home. The patient was diagnosed with <i>Streptococcus equi</i>subspecies <i>zooepidemicus</i> (<i>S. zooepidemicus</i>) prosthetic heart valve IE, which was complicated with meningitis, myocardial infarction, and an increasing vegetation load despite antibiotic treatment. The patient underwent heart valve surgery with insertion of a biological mitral valve, and <i>S. zooepidemicus</i> was identified in the excised valve tissue. <i>S</i>. <i>zooepidemicus</i> is a rare zoonotic pathogen in humans. The bacterium is most often found on the skin and mucous membranes of horses and may cause opportunistic infections in horses and other animals. Our literature review found 11 studies reporting 13 cases with <i>S. zooepidemicus</i> IE in humans.