Histoplasmosis

Key Features

Essentials of Diagnosis

• Residence in or travel to an endemic area

• Pneumonia with flulike illness

• If disseminated, hepatosplenomegaly, anemia, leukopenia

• Histoplasmal antigen in urine, blood, bronchoalveolar lavage fluid or CSF

• Detection by staining the organism in smears or tissue, or by culture

General Considerations

• Histoplasma capsulatum is found in the central and eastern United States (Ohio and Mississippi River valleys), Mexico, and most of South America

• Soil contamination is enhanced by the presence of bat or bird feces

• Infections in endemic areas are very common at all ages and are usually asymptomatic

• Over two-thirds of children are infected in these areas

• Human-to-human transmission does not occur

• Congenital infection does not occur

Clinical Findings

Symptoms and Signs

• Asymptomatic in 90% of infections

• Pneumonia

  • Approximately 5% of patients have mild to moderate disease

  • Cause of this illness is usually not recognized as being Histoplasma

  • Acute pulmonary disease may resemble influenza with fever, malaise, myalgia, arthralgia, and cough occurring 1–3 weeks after a heavy exposure (may be longer with less intense exposure)

  • Subacute form resembles infections such as tuberculosis with cough, weight loss, night sweats, and pleurisy

  • Chronic disease is unusual in children

  • Physical examination may be normal or rales may be heard

  • A small number of patients may have immune-mediated signs such as arthritis, pericarditis, and erythema nodosum

• Disseminated infection (5% of infections)

  • Fungemia during primary infection probably occurs in the first 2 weeks of all infections, including those with minimal symptoms

  • Transient hepatosplenomegaly may occur, but resolution is the rule in immunocompetent individuals

  • Heavy exposure, severe underlying pulmonary disease, and immunocompromise are risk factors for progressive infection characterized by

    • Anemia

    • Fever

    • Weight loss

    • Organomegaly

    • Bone marrow involvement

    • Death

  • Dissemination may occur in otherwise immunocompetent children; usually they are younger than age 2 years

• Other forms

  • Ocular involvement consists of multifocal choroiditis

  • Usually occurs in immunocompetent adults who exhibit other evidence of disseminated disease

  • Brain, pericardium, intestine, and skin (oral ulcers and nodules) are other sites that can be involved

  • Adrenal gland involvement is common with systemic disease

Differential Diagnosis

• Pulmonary disease resembles

  • Viral infection

  • Other causes of community-acquired pneumonia

  • Tuberculosis

  • Coccidioidomycosis

  • Blastomycosis

• Systemic disease resembles

  • Disseminated fungal or mycobacterial infection

  • Leukemia

  • Histiocytosis

  • Cancer

Diagnosis

Laboratory Findings

• A positive skin test or serology can detect asymptomatic histoplasmosis

• Routine tests are normal or nonspecific in the benign forms

• Pancytopenia is present in many patients with disseminated disease

• Organisms can be seen on histology or culture

• Tissue yeast forms

  • Small and may be mistaken for artifact

  • Usually found in macrophages, occasionally in peripheral blood leukocytes in severe disease

  • Infrequently found in sputum, urine, or CSF

• Cultures of infected fluids or tissues may yield the organism after 1–4 ...