Disseminated Histoplasmosis and Aortic Valve Infective Endocarditis in a Patient With Recent Aortobifemoral Bypass

BACKGROUND Fungal endocarditis constitutes up to 3% of diagnosed infective endocarditis cases, and Histoplasma spp. cause approximately 10% of fungal endocarditis cases. Histoplasma infection occurs through inhalation of spores typically found in contaminated soil. The clinical forms are variable, ranging from asymptomatic to fatal presentations. Asymptomatic individuals may develop reactivated disease years after the primary exposure. Most cases of histoplasmosis are confined to the pulmonary system. In rare instances, fungal elements disseminate to the heart valves, where destructive injury occurs. CASE REPORT A 59-year-old woman presented with vascular bypass occlusion, 2 months after aortobifemoral bypass for aortoiliac occlusive disease. She reported severe, unrelenting nausea and vomiting; a large aortic valve mass was detected on transthoracic echocardiography. Bacterial endocarditis was initially suspected, but cultures were unrevealing. Follow-up microbial cell-free DNA testing identified Histoplasma capsulatum and low-level Streptococcus mitis/oralis, prompting further evaluation for disseminated histoplasmosis. Bone marrow biopsy showed Histoplasma negativity according to polymerase chain reaction. The patient subsequently underwent aortic valve replacement, and pathology confirmed fungal elements consistent with H. capsulatum. Gram and acid-fast bacilli staining of the aortic valve yielded negative results. CONCLUSIONS Fungal endocarditis carries substantial morbidity and is challenging to diagnose due to its nonspecific presentation over time and the absence of standardized blood culture protocols. Treatment options include surgical valve replacement and targeted antifungal therapy. This case underscores the diagnostic difficulties associated with fungal endocarditis, particularly in the context of negative cultures and a history of travel to endemic areas, when microbial coinfection cannot be definitively excluded.