Histoplasmosis is a fungal infection caused by Histoplasma capsulatum. This disease may also be called Ohio Valley, Central Mississippi Valley, Appalachian Mountain, or Darling’s disease. In the United States, it occurs in three forms: primary acute histoplasmosis, progressive disseminated histoplasmosis (acute disseminated or chronic disseminated disease), and chronic pulmonary (cavitary) histoplasmosis, which produces cavitations in the lung similar to those in pulmonary tuberculosis.
A fourth form, African histoplasmosis, occurs only in Africa and is caused by the fungus Histoplasma capsulatum duboisii.
The prognosis varies with each form. The primary acute disease is benign; the progressive disseminated disease is fatal in approximately 90% of patients; and, without proper chemotherapy, chronic pulmonary histoplasmosis is fatal in 50% of patients within 5 years.
H. capsulatum is found in the feces of birds and bats or in soil contaminated by their feces, such as that near roosts, chicken coops, barns, caves, or underneath bridges. Transmission occurs through inhalation of H. capsulatum or H. duboisii spores or through the invasion of spores after minor skin trauma. Possibly, oral ingestion of spores may cause the disease.
The incubation period is from 5 to 18 days, although chronic pulmonary histoplasmosis may progress slowly for many years. Probably because of occupational exposure, histoplasmosis is more common in adult males. Fatal disseminated disease, however, is more common in infants and elderly men.
Histoplasmosis occurs worldwide, especially in the temperate areas of Asia, Africa, Europe, and North and South America. In the United States, it's most prevalent in the central and eastern states, especially in the Mississippi and Ohio River valleys.
Symptoms vary with each form of this disease. Primary acute histoplasmosis may be asymptomatic or may cause symptoms of a mild respiratory illness similar to a severe cold or influenza. Typical clinical effects may include fever, malaise, headache, myalgia, anorexia, cough, chest pain, anemia, leukopenia, thrombocytopenia, and oro-pharyngeal ulcers.
Progressive disseminated histoplasmosis causes hepatosplenomegaly, general lymphadenopathy, anorexia, weight loss, fever and, possibly, ulceration of the tongue, palate, epiglottis, and larynx, with resulting pain, hoarseness, and dysphagia. It may also cause endocarditis, meningitis, pericarditis, and adrenal insufficiency.
Chronic pulmonary histoplasmosis mimics pulmonary tuberculosis and causes a productive cough, dyspnea, and occasional hemoptysis. Eventually, it produces weight loss, extreme weakness, breathlessness, and cyanosis.
African histoplasmosis produces cutaneous nodules, papules, and ulcers; lesions of the skull and long bones; lymphadenopathy; and visceral involvement without pulmonary lesions.
A history of exposure to contaminated soil in an endemic area, miliary calcification in the lung or spleen, a positive histoplasmin skin test or urine antigen test indicate exposure to histoplasmosis. Rising complement fixation and agglutination titers (more than 1:32) strongly suggest histoplasmosis. A histoplasmosis antigen assay test can help in diagnosis.
CONFIRMING DIAGNOSIS The diagnosis of histoplasmosis requires a morphologic examination of tissue biopsy and culture of H. capsulatum from sputum in acute primary and chronic pulmonary histoplasmosis and from bone marrow, lymph node, blood, and infection sites in disseminated histoplasmosis. However, cultures take several weeks to grow these organisms. Faster diagnosis is possible with stained biopsies. Also available is a deoxyribonucleic acid probe for histoplasma that can be used for difficult isolates.
Findings must rule out tuberculosis and other diseases that produce similar symptoms. The diagnosis of histoplasmosis caused by H. duboisii necessitates examination of tissue biopsy and culture of the affected site.
Treatment consists of antifungal therapy, surgery, and supportive care. Antifungal therapy is most important. Except for asymptomatic primary acute histoplasmosis (which resolves spontaneously) and the African form, histoplasmosis requires high-dose or long-term (10-week) therapy with amphotericin B, fluconazole, ketoconazole, or itraconazole. For a patient who also has acquired immunodeficiency syndrome, lifelong therapy with fluconazole is indicated.
Supportive care usually includes oxygen for respiratory distress, glucocorticoids for adrenal insufficiency, and parenteral fluids for dysphagia due to oral or laryngeal ulcerations. Histoplasmosis doesn't require isolation.
Patient care is primarily supportive.
❑Give medications as ordered, and teach patients about possible adverse effects. Because amphotericin B may cause chills, fever, nausea, and vomiting, give appropriate antipyretics and antiemetics, as ordered.
❑Patients with chronic pulmonary or disseminated histoplasmosis also need psychological support because of long-term hospitalization. As needed, refer the patient to a social worker or occupational therapist. Help the parents of children with this disease arrange for a visiting teacher.
❑To help prevent histoplasmosis, teach people in endemic areas to watch for early signs and to seek treatment promptly. Instruct those who risk occupational exposure to contaminated soil to wear face masks.
Review other book chapters online related to Histoplasmosis:
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Professional Guide to Diseases (Eighth Edition) Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2005 ISBN: 1-58255-370-X 
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