Histoplasmosis
Histoplasma capsulatum is an endemic dimorphic fungus, acquired by inhalation of conidia in the Mississippi and Ohio River valleys and other endemic regions, that most often causes asymptomatic or mild pulmonary infection but can disseminate in immunosuppressed hosts; diagnosis rests on the Histoplasma urinary antigen assay and treatment is itraconazole for mild to moderate disease or liposomal amphotericin B followed by itraconazole for severe or disseminated infection.
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What this article covers
- Overview
Histoplasma capsulatum is one of the most common endemic mycoses in the world, a dimorphic fungus acquired by inhalation of aerosolized conidia, most often from soil contaminated with bird or bat droppings.
- Epidemiology
Endemic along the Mississippi River Valley in the United States (Ohio, Missouri, Indiana, Mississippi), with additional endemic foci in Central and South America, the Caribbean, and regions of Africa, Australia, and India.
- Risk factors
Residence in or travel to an endemic river-valley region with an exposure activity that disturbs contaminated soil (caving, demolition, farming, chicken coops).
- Pathophysiology
Inhalation of aerosolized conidia deposits the fungus in the alveoli, where it converts to the yeast form at body temperature and is engulfed by alveolar macrophages.
- Clinical features
Acute pulmonary histoplasmosis presents with nonproductive cough, chest pain or discomfort, and fever, the most common clinical manifestation when disease is symptomatic at all.
- Differential diagnosis
Coccidioidomycosis: pulmonary infection after travel to or residence in the endemic southwestern United States (Southern California, Arizona, New Mexico, Texas) rather than a river-valley region…
- Diagnosis
Histoplasmosis is confirmed by identification of the organism: the Histoplasma urinary antigen assay is the fastest confirmatory test, with sensitivity and specificity greater than 85% in acute and…
- Management
Asymptomatic and mild pulmonary histoplasmosis in an immunocompetent host typically resolves without treatment; antifungal therapy is reserved for severe or disseminated disease, and for symptomatic infection warranting treatment.
- Complications
Septic shock in disseminated disease, with mortality as high as 90% if not diagnosed and treated early, the most serious complication and the reason for urgent diagnosis and treatment initiation in a compatible presentation.
- Prognosis
Immunocompetent patients with asymptomatic or mild pulmonary disease have an excellent prognosis without treatment.
- Prevention
No vaccine exists against Histoplasma; prevention centers on exposure avoidance and prompt recognition and treatment in at-risk hosts.
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