Brucellosis presenting as prolonged fever of unknown origin in a two-year-old child: a diagnostic challenge

Brucellosis is a zoonotic disease with diverse clinical manifestations and is an uncommon but important cause of prolonged fever in children. Diagnosis may be delayed due to nonspecific symptoms, limited exposure history, and variable serologic findings. This report describes a two-year-old patient who experienced 17 days of recurrent fever associated with fatigue, myalgia, and diarrhea following a horse-related injury two months earlier. Extensive evaluation demonstrated elevated inflammatory markers, thrombocytosis, cervical lymphadenopathy, and hepatic lesions, but the etiology was unrevealing. A thorough exposure history prompted targeted zoonotic testing, which identified Brucella-positive IgM in the absence of detectable IgG, consistent with an acute Brucella infection in the appropriate clinical context. This case highlights the importance of detailed exposure history and consideration of brucellosis in the differential diagnosis of pediatric fever of unknown origin (FUO), even in the absence of classic presentation.