Amoebas are single-celled organisms. The so-called brain-eating amoeba is a species discovered in 1965 and formally named Naegleria fowleri. Although first identified in Australia, this amoeba is believed to have evolved in the United States. There are several species of naegleria, but only the N. fowleri species causes human disease. Like other amoebas, naegleria reproduce by cell division. When conditions are less than optimal, amoebas become inactive cysts. When conditions are favorable, the cysts turn into trophozoites -- their feeding form.