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Free-living amebas and Prototheca

Carlos Seas, MD, FIDSA
Francisco Bravo, MD
Section Editors
Peter F Weller, MD, FACP
Carol A Kauffman, MD
Deputy Editor
Elinor L Baron, MD, DTMH


Free-living amebas are environmental protozoan parasites with worldwide distribution. They exist in nature without the need for a host; they are not well adapted to parasitism and do not require a vector for transmission to humans or animals [1].

Four genera of amebas cause disease in humans: Naegleria (only N. fowleri), Acanthamoeba (several species), Balamuthia (only B. mandrillaris), and Sappinia (only S. pedata) [2,3]. All of these species cause central nervous system (CNS) infections; several species of Acanthamoeba may cause localized extra-CNS infections in immunocompetent hosts or disseminated infections in immunocompromised hosts.

Members of the genus Prototheca are also environmental pathogens that are rare causes of human infection; Prototheca are classified as green algae, which are unicellular eukaryotes that do not have chlorophyll.

Issues related to infections caused by free-living amebas and members of the genus Prototheca will be reviewed here.


Two distinctive clinical syndromes associated with free-living amebas are well recognized: primary amebic meningoencephalitis (PAM) and granulomatous amebic encephalitis (GAE).


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