Histoplasmosis, also known as Darling's disease, is a disease caused by the fungus Histoplasma capsulatum which was discovered in 1905. 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.
HistoryHistoplasma was discovered in 1905 by Darling, but was only discovered to be a widespread infection in the 1930s. Before then, many cases of histoplasmosis were mistakenly attributed to tuberculosis, and patients were mistakenly admitted to tuberculosis sanatoriums. Some patients contracted tuberculosis in these sanatoriums (reference: Mandell, Bennett and Dolin).
PathogenH. 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 bird or bat droppings (guano). 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. Histoplasmosis is not contagious, but is contracted by inhalation of the spores from disturbed soil or guano.
SymptomsIf 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. 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.
PreventionIt 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:
- Avoid areas that may harbor the fungus, e.g., accumulations of bird or bat droppings.
- Before starting a job or activity having a risk for exposure to H. capsulatum, consult the NIOSH/NCID Document Histoplasmosis: Protecting Workers at Risk. This document contains information on work practices and personal protective equipment that will reduce the risk of infection.
Histoplasmosis in Popular Culture
- Johnny Cash included a reference to the disease, even correctly noting its source in bird droppings, in the song "Beans for Breakfast".
- Bob Dylan was hospitalized due to histoplasmosis in 1997, causing the cancellation of concerts in the United Kingdom and Switzerland.
- In episode 21 of season 3 of the television show House, M.D. a patient was diagnosed with histoplasmosis.
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
- Histoplasmosis Resource Guide from the National Eye Institute (NEI).
- NIOSH - Histoplasmosis - Protecting Workers at Risk
- Fibrosing Mediastinitis
- Histoplasma information from doctorfungus.org
histoplasmosis in German: Histoplasmose
histoplasmosis in Spanish: Histoplasmosis
histoplasmosis in French: Histoplasmose
histoplasmosis in Italian: Istoplasmosi
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histoplasmosis in Polish: Histoplazmoza
histoplasmosis in Portuguese: Histoplasmose