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Histoplasmosis, also known as Darling's disease, is a disease caused by the fungus Histoplasma capsulatum. Its symptoms vary greatly, but the disease primarily affects the lungs. Occasionally, other organs are affected—this form of the disease is called disseminated histoplasmosis, and it can be fatal if untreated.
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H. capsulatum is found throughout the world and is endemic in certain areas of the United States, particularly in states bordering the Ohio River valley and the lower Mississippi River. (Positive histoplasmin skin tests occur in as many as 80% of the people living in areas where H. capsulatum is common, such as the eastern and central United States.) H. capsulatum grows in soil and material contaminated with bat or bird droppings. The fungus has been found in poultry house litter, caves, areas harboring bats, and in bird roosts (particularly those of starlings). The fungus is thermally dimorphic. In the environment it grows as a brownish mycelium, whereas at body temperature (37°C in humans) it morphs into a yeast. The inoculum is represented principally by microconidia that once inhaled into the alveolar spaces germinate and then transform into budding yeast cells.
If symptoms of histoplasmosis infection occur, they will start within 3 to 17 days after exposure; the average is 12-14 days. Most affected individuals have clinically-silent manifestations and show no apparent ill effects.The acute phase of histoplasmosis is characterized by non-specific respiratory symptoms, often cough or flu-like. Chest X-ray findings are normal in 40-70% of cases. Chronic histoplasmosis cases can resemble tuberculosis; disseminated histoplasmosis affects multiple organ systems and is fatal unless treated.
While histoplasmosis is the most common cause of fibrosing mediastinitis, this remains a relatively rare disease. Severe infections can cause hepatosplenomegaly, lymphadenopathy, and adrenal enlargement. Lesions have a tendency to calcify as they heal.
Ocular histoplasmosis damages the retina of the eyes. Scar tissue is left on the retina which can experience leakage, resulting in a loss of vision not unlike macular degeneration.
Antifungal medications are used to treat severe cases of acute histoplasmosis and all cases of chronic and disseminated disease. Typical treatment of severe disease first involves treatment with amphotericin B, followed by oral itraconazole. In many milder cases, simply itraconazole is sufficient. Asymptomatic disease is typically not treated. Past infection results in partial protection against ill effects if reinfected.
It is not practical to test or decontaminate most sites that may be contaminated with H. capsulatum, but the following precautions can be taken to reduce a person's risk of exposure:
Histoplasmosis in Popular Culture
Note: The original version of this article is adapted from the U.S. CDC public domain document at http://www.cdc.gov/ncidod/dbmd/diseaseinfo/histoplasmosis_g.htm
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Histoplasmosis". A list of authors is available in Wikipedia.|