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 Acanthamoeba, Balamuthia, Naegleria, and Sappinia.
Three major syndromes occur:
Acanthamoeba and Balamuthia can also cause skin lesions or disseminated disease in immunocompromised people.
Acanthamoeba amebic keratitis is limited to the eyes and treated topically. Granulomatous encephalitis and primary amebic meningoencephalitis are usually fatal, but some patients treated with miltefosine in combination with other drugs have survived.