Infections by one of the three species of amebae— Naegleria fowleri, Acanthamoeba sp., and Entamoeba histolytica—are rare but detrimental. Immunocompromised individuals are at risk for the infection.

Naegleria fowleri is found in freshwater and soil. It infects the nasal cavity and reaches the brain along the olfactory nerves to produce a fulminant hemorrhagic meningoencephalitis with PNLs.

Acanthamoeba sp. are found in fresh- and seawater. They reach the brain via the bloodstream, producing a subacute or chronic multifocal necrotizing granuloma-tous encephalitis.

Infection by Entamoeba histolytica is acquired by fecal-oral contamination. The organisms spread hema-togenously from an intestinal infection or a liver abscess to the brain, producing single or multiple abscesses (Fig. 6.29).

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