Free-living amebas are protozoa that live independently in soil or water and do not require a human or animal host. They rarely cause disease, in contrast to the parasitic ameba Entamoeba histolytica, which is a common cause of intestinal infection (amebiasis). Pathogenic free-living amebas are of the genera Naegleria, Acanthamoeba, Balamuthia, and Sappinia.
Three major syndromes occur:
Acanthamoeba and Balamuthia can also cause skin lesions or disseminated disease in immunocompromised people; Acanthamoeba can also cause infection of the sinuses or lungs.