Naegleria fowleri is a one-celled organism that the U.S. Centers for Disease Control explains is “often called the 'brain-eating ameba' because it can infect the brain and destroy brain tissue." This happens when water containing the amoeba goes up the nose to the brain, causing an infection called primary amebic meningoencephalitis (PAM).

Missouri health officials are investigating how the person was exposed, but they may have been in the water at Lake of the Ozarks before becoming ill.