Histoplasmosis is an infection caused by the spores of a fungi (Histoplasma Capsulatum). This fungi is endemic to the Ohio and Mississippi River valley. People become infected by inhaling the spores from multiple sources: bird or bat droppings, plowing or tilling fields, or construction projects. People working in construction, landscaping, and farming may be at higher risk of exposure.
The spores initially enter the lungs and in the majority of people do not cause any symptoms. Most individuals never know they were exposed or infected. Some individuals develop symptoms a few weeks after exposure, including fever, chills, cough, body aches or pains. The fungus can travel through the blood stream and infect the eye. This is called “presumed ocular histoplasmosis.” Most people are unaware that histoplasma has spread to their eyes, and only on routine dilated eye exams can eye care professionals see evidence of retinal scars or “histo spots” on the retina.
It’s estimated that up to 60% of people living in endemic areas test positive for exposure to this fungus, but only about 1.5% show retinal lesions. And among those who show evidence of spread to the eye, under 4% develop bleeding under their retina leading to vision changes or loss.