A Fatal Case of Disseminated Histoplasmosis by Histoplasma capsulatum var. capsulatum Misdiagnosed as Visceral Leishmaniasis—Molecular Diagnosis and Identification

Histoplasmosis is an endemic mycosis in the Americas. However, its diagnosis is challenging due to the complexity and limited availability of conventional laboratory techniques—antigen tests, culture, and staining. Microscopic preparations often confuse with other pathogens, such as Leishmania spp. The genus Histoplasma capsulatum comprises three varieties: var. capsulatum, var. duboissi, and var. farciminosum, which cannot be distinguished using conventional techniques. An infant from a tropical region of Ecuador was hospitalized for fever, bloody diarrhea, and anemia persisting for two months. Upon admission, he received antibiotics and immunosuppressants. Histopathological examination of the lymph nodes, intestines, and bone marrow aspirate reported the presence of Leishmania-like amastigotes, and treatment was initiated with meglumine antimoniate and conventional amphotericin B. However, subsequent analysis of samples using PCR and DNA sequencing identified H. capsulatum var. capsulatum but not Leishmania. Despite fluconazole and amphotericin B, the infant succumbed to the disease. The delay in clinical and laboratory diagnosis of histoplasmosis and the use of nonspecific and ineffective drugs such as fluconazole led to disease dissemination and, ultimately, death. Implementing molecular diagnosis and antigen tests in laboratories located in endemic regions and reference hospitals is crucial.