Unmasking Bartonella henselae: A forgotten cause of hepatosplenic and marrow involvement.

Bartonella henselae is an uncommon but important cause of prolonged pyrexia of unknown origin (PUO) and hepatosplenomegaly. Conventional diagnostic tools often fail in disseminated disease, leading to delayed or missed diagnoses. We report a 60-year-old man with PUO, progressive weight loss, and hepatosplenomegaly. Clinical suspicion, guided by significant cat exposure, led to molecular confirmation of B. henselae infection after conventional workup proved inconclusive. Liver biopsy revealed pleomorphic rod-shaped organisms on Warthin-Starry staining, while real-time PCR targeting the rpoB gene and conventional PCR targeting the gltA gene performed on bone marrow aspirate confirmed disseminated bartonellosis. The patient responded well to prolonged doxycycline and rifampicin therapy, achieving near-complete recovery. This case underscores the importance of clinical vigilance, histological clues, and molecular diagnostics in identifying rare but treatable infections.