<i>Bartonella henselae</i> tricuspid valve endocarditis presenting as fever of unknown origin

Cat scratch disease (CSD), caused by <i>Bartonella henselae</i>, is an uncommon cause of fever of unknown origin (FUO) and rarely presents with visceral organ involvement. This case report describes a middle-aged woman with 3 months of night sweats and 1 month of fevers. Initial workup showed elevated inflammatory markers, multiple splenic lesions and a pelvic fluid collection. A detailed history noted that she recently adopted a stray kitten, prompting <i>Bartonella</i> serological testing. Given the atypical presentation, a broad infectious evaluation was also pursued, including testing for mycobacterial, fungal and other bacterial pathogens. When <i>B. henselae</i> IgG titre returned strongly positive and transoesophageal echocardiogram (TEE) showed a tricuspid valve vegetation, the diagnosis of culture-negative endocarditis was established. Treatment with doxycycline and rifampin led to rapid symptom resolution.This case highlights the potential for CSD to present as right-sided endocarditis. Clinicians should consider <i>B. henselae</i> infection in patients with FUO and cat exposure, even without classic regional lymphadenopathy. Due to its fastidious nature, <i>B. henselae</i> often evades culture, underscoring the role of serological or molecular testing in diagnosis. This report emphasises the diagnostic challenges of culture-negative endocarditis and the critical importance of detailed exposure history in guiding targeted diagnostic testing and stepwise serological evaluation in atypical disease patterns.