I wanted to do my blog on histoplasmosis this week because I have a good friend whose mother lost her eyesight due to the disease. Some of you may know that Indianapolis had a large histoplasmosis outbreak in 1978. Many epidemiologists in the city believed it was related to the old Riverside Amusement Park being demolished. The amusement park was vacant for 8 years prior to demolition and was a popular bird roost. My friend’s parents lived near the amusement park during the demolition and her mother contracted a severe case of histoplasmosis during the city outbreak. Blood cultures taken from high school students in 1978 showed the highest concentration of infections in the census tract directly adjacent to the amusement park (Wheat, 1992).
Histoplasmosis is an infection caused by the soil fungus Histplasma capsulatum. The fungus is widespread in the Midwestern U.S. and is most common in areas that have three to five years of accumulated bird and/or bat droppings. Once those droppings are disturbed in any way they literally release billions of spores into the air, ready to be inhaled into the lungs – the primary infection site. This puts construction and demolition workers at particularly high risk, especially if they work in old buildings which may have bird or bat roost areas.
The disease usually results in mild respiratory illness similar to the common cold, but it can be more severe depending on the immune status of the patient and the dose of inhaled spores. Signs of more severe histoplasmosis infection can include chronic cough, chest pain, hemoptysis and fever. The disease is diagnosed by looking in sputum, lung tissue and CSF for signs of the fungus. Chest x-ray and/or chest CT is usually performed. Treatment is with antifungal medications to control lung infection but lung scarring (granulomas) often occur. This CT image shows granulomas from histoplasmosis. Severe illness can lead to permanent lung damage and blindness.
Most people who live in Indiana will have been infected by the spores by the time they reach adulthood and usually the body’s immune system will overcome the infection without any kind of treatment. However, anyone who has had a severe case of histoplasmosis with lung involvement should be regularly monitored for Ocular Histoplasmosis Syndrome (OHS), which is a leading cause of vision loss in Americans between the ages of 20 and 40. This is what happened to my friend’s mom. OHS occurs when the histoplasmosis spores spread from the lungs to the choroid layer of the eye. The spores cause scar tissue to form which then damages the retina resulting in vision loss. These scars are called “histo spots” and can be seen in an eye examination. Those spots along with retinal swelling indicate the OHS disease in the eye. Laser treatment can sometimes slow the progression of the disease.
References:
Histoplasmosis. Accessed January 12, 2010 at http://www.nlm.nih.gov/medlineplus/ency/article/001082.htm
IN.gov. Histoplasmosis: A Hoosier Concern. Accessed January 12, 2010 at http://www.in.gov/isdh/23254.htm
Medic8.com. Ocular Histoplasmosis Syndrome (OHS). Accessed January 12, 2010 at http://www.medic8.com/eye-disorders/histoplasmosis.htm
Wheat, L. (1992). Histoplasmosis in Indianapolis. Clinical Infectious Diseases, March 1992. Vol. 14, S1. The University of Chicago Press. Accessed January 12, 2010 at http://www.jstor.org/pss/4456398
Image:
http://www.medscape.com/content/2003/00/46/10/461046/art-ar461046.fig5.jpg
