Histoplasmosis: An emerging infection

Abstract

Histoplasmosis is commonly found in US and central America; recently cases were diagnosed from Kerala also. The causative organism Histoplasma capsulatum is found abundant in soil mixed with bird or bat guano. Infection occurs by the inhalation of small oval conidia which can enter the terminal bronchioles and then the alveolar spaces. They multiply inside the macrophages and the cellular immune system of the host decides the outcome. Usually it is a self limiting pulmonary infection, but it can vary from mild pneumonitis to severe acute respiratory distress syndrome. If primary manifestation progresses, disseminated histoplasmosis involving liver, spleen, bone marrow, adrenal gland and mucocutaneous membranes result. Skin test antigen is used in epidemiological studies to find the true extent of infection. Rapid diagnosis is possible with histoplasma antigen detection but serology is useful only in certain cases. Histopathology aids the diagnosis a lot. But the fungal culture remains the gold standard for the confirmation. Histoplasmosis is successfully treated with azoles if it is a mild infection and if severe liposomal Amphotericin B is used initially and then switched over to Itraconazole to be continued for several months.