Bartonellosis in a Renal Transplant Recipient: Scratching More Than the Surface

Fever of unknown origin (FUO) presents a significant diagnostic challenge in renal transplant recipients due to their immunosuppressed state, which predisposes them to a broad spectrum of potential non-infectious and infectious causes, including atypical pathogens. Among these, <i>Bartonella henselae</i>, the agent of bartonellosis or cat scratch disease (CSD), is a rare but significant pathogen in this population, capable of causing several systemic manifestations, including hepatosplenic involvement. We describe the case of a 60-year-old male renal transplant recipient who presented with FUO, diarrhea, and hepatosplenomegaly six months post transplantation. The absence of classical features of CSD such as regional lymphadenopathy, along with the initial omission of relevant exposure history, delayed diagnosis. A comprehensive diagnostic workup, guided by a thorough review of history that revealed a cat scratch three weeks prior to presentation, positive polymerase chain reaction (PCR) testing for <i>B. henselae</i>, and positron emission tomography-computed tomography (PET-CT) findings of increased splenic uptake with a nodular lesion, corroborated the diagnosis of bartonellosis with splenic involvement. Treatment with azithromycin led to complete resolution of fever and inflammatory markers, and follow-up imaging demonstrated normalization of splenic abnormalities. This case highlights the importance of maintaining a high index of suspicion for zoonotic infections in renal transplant recipients, leveraging advanced diagnostic tools, and tailoring antimicrobial therapy to accommodate immunosuppressive regimens.