Histoplasmosis: Epidemiology, Diagnosis, and Clinical Manifestations

Abstract

Purpose of Review This review highlights the epidemiology, diagnosis, and clinical manifestations of histoplasmosis. Recent Findings There is an increasing awareness of histoplasmosis in Central and South America in patients with human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), and deaths from histoplasmosis in this region may outnumber deaths from tuberculosis. Diagnosis in this region is hampered by lack of rapid diagnostic tests. Growth of H. capsulatum in culture is definitive, but takes weeks. In areas in which antigen testing is available, this has become an important rapid diagnostic tool, and methods combining antigen and antibody testing appear to improve diagnostic accuracy for acute pulmonary and central nervous system histoplasmosis. Pulmonary histoplasmosis, although usually self-limited, rarely can lead to life-threatening complications. Uncommon, but serious and sometimes fatal complications of disseminated histoplasmosis include Addison's disease, meningitis, culture-negative endocarditis, and hemophagocytic lymphohistiocytosis. Summary The use of antigen testing has improved our ability to diagnose histoplasmosis, but these tests are not universally available. Complications of both pulmonary and disseminated histoplasmosis remain challenging.

Introductory Chapter: The Global Distribution of Human Histoplasmosis - An Overview

“…Histoplasma inhabits soils enriched with bird and bat excreta, high nitrogen content with a neutral PH [16]. Occupational exposures among excavators and those at construction sites resulting into disruption of soil and inhalation of large inoculum of Histoplasma spores have been described [17].…”

“…Following inhalation of Histoplasma microconidia, it rapidly transforms from the mycelial into the yeast form [17,39]. Innate response involves early migration of the neutrophils toward the yeast; however, they are unable to destroy it.…”

“…Innate response involves early migration of the neutrophils toward the yeast; however, they are unable to destroy it. Alveolar macrophages then engulf the fungi but can't destroy it either, but instead the yeast multiplies inside it [17,39]. In immunocompetent individuals, T-cell-mediated immunity is activated, and the T-cells release pro-inflammatory cytokines which activate mononuclear phagocytes, hence producing tumour necrotic factor α (TNFα) and more cytokines [17,39].…”

“…H. capsulatum may disseminate to other organs but on activation of cellular immunity, it is quickly controlled, and individuals have a quick recovery or develop latency. Therefore, most infections go unnoticed [17,40].…”

“…Patients become symptomatic and may require hospitalisation for antifungal treatment and supportive care occur [5,41]. The most common cause of disseminated progressive disease is reactivation of latent pulmonary infection [17,40].…”