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SPECIFIC FUNGAL INFECTIONS

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HISTOPLASMOSIS

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  • Histoplasmosis is caused by inhalation of dust-borne microconidia of the dimorphic fungus Histoplasma capsulatum. In the United States, most disease is localized along the Ohio and Mississippi river valleys.

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Clinical Presentation and Diagnosis
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  • In the vast majority of patients, low-inoculum exposure to H. capsulatum results in mild or asymptomatic pulmonary histoplasmosis. The course of disease is generally benign, and symptoms usually abate within a few weeks of onset. Patients exposed to a higher inoculum during a primary infection or reinfection may experience an acute, self-limited illness with flu-like pulmonary symptoms, including fever, chills, headache, myalgia, and nonproductive cough.

  • Chronic pulmonary histoplasmosis generally presents as an opportunistic infection imposed on a preexisting structural abnormality, such as lesions resulting from emphysema. Patients demonstrate chronic pulmonary symptoms and apical lung lesions that progress with inflammation, calcified granulomas, and fibrosis. Progression of disease over a period of years, seen in 25% to 30% of patients, is associated with cavitation, bronchopleural fistulas, extension to the other lung, pulmonary insufficiency, and often death.

  • In patients exposed to a large inoculum and in immunocompromised hosts, progressive illness, disseminated histoplasmosis, occurs. The clinical severity of the diverse forms of disseminated histoplasmosis (Table 38–1) generally parallels the degree of macrophage parasitization observed.

  • Acute (infantile) disseminated histoplasmosis is seen in infants and young children and (rarely) in adults with Hodgkin disease or other lymphoproliferative disorders. It is characterized by unrelenting fever; anemia; leukopenia or thrombocytopenia; enlargement of the liver, spleen, and visceral lymph nodes; and GI symptoms, particularly nausea, vomiting, and diarrhea. Untreated disease is uniformly fatal in 1 to 2 months

  • Most adults with disseminated histoplasmosis demonstrate a mild, chronic form of the disease. Untreated patients are often ill for 10 to 20 years, with long asymptomatic periods interrupted by relapses characterized by weight loss, weakness, and fatigue.

  • Adult patients with acquired immunodeficiency syndrome (AIDS) demonstrate an acute form of disseminated disease that resembles the syndrome seen in infants and children. Progressive disseminated histoplasmosis can occur as the direct result of initial infection or because of reactivation of dormant foci.

  • In most patients, serologic evidence remains the primary method in the diagnosis of histoplasmosis. Results obtained from complement fixation, immunodiffusion, and latex antigen agglutination antibody tests are used alone or in combination. Detection of Histoplasma antigen by enzyme immunoassay (EIA) in the urine, blood, or bronchoalveolar lavage fluid of infected patients provides rapid diagnostic information and is particularly useful in patients who are severely ill.

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Table Graphic Jump Location
TABLE 38–1abcdefClinical Manifestations and Therapy of Histoplasmosis

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