Bat Guano can carry the disease Histoplasmosis which is caused by a fungus in the Guano. Histoplasmosis affects the lungs and gives you mild influenza-type symptoms. However, in large quantities, you can develop high fever, blood abnormalities, pneumonia, and even death.
There are many hazards when extracting bat guano from the attic of a home, there is always the falling hazard, where some unqualified contractor falls through the ceiling of your home. This creates several problems. The first problem this creates is it breaks the Sheetrock on your ceiling; the ceiling is a very difficult place to repair damaged Sheetrock and often times a professional will have to be called in to make the area look correct again. The second and most important problem that this creates is it breaks the barrier that is shielding your home from the containment that is in your attic. When this happens, your entire home should be cleaned and disinfected. This is often very expensive and often done by a professional company that specializes in house remediation.