Tricuspid valve endocarditis in a horse owner, caused by Streptococcus equi subsp. zooepidemicus

Streptococcus equi subsp. zooepidemicus (SESZ) are zoonotic group C streptococci primarily acquired from contact with horses and other animals, such as llamas. They are unusual causes of infection in humans and rarely cause infective endocarditis.

A 58-year-old woman presented with fever, malaise, and polyarthritis. Clinical evaluation diagnosed native tricuspid valve SESZ endocarditis. The SESZ isolate was genetically closely related to a clone causing an outbreak of post-streptococcal glomerulonephritis linked to the consumption of unpasteurized cheese in Brazil. The patient had no exposure to unpasteurized cheese but rode horses. Her infection course was notable for persistent fever despite combination antibiotic therapy. Resolution of her symptoms ultimately required tricuspid valve and aortic valve replacement and mitral valve repair.

This is the first reported case of native tricuspid valve SESZ endocarditis. The case demonstrates the natural history of this rare disease and illustrates the importance of taking an exposure history.