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[Acanthamoeba spp.] [Balamuthia mandrillaris] [Naegleria fowleri] [Sappinia spp.]

There are two forms of trophozoites in Naegleria fowleri: ameboid and ameboflagellate, only the former of which is found in humans.  The ameboid trophozoites measure 10-35 µm but when rounded are usually 10-15 µm in diameter.  In culture, trophozoites may get over 40 µm.  The cytoplasm in granular and contains many vacuoles.  The single nucleus is large and has a large, dense karyosome and lacks peripheral chromatin.

A	B

A: Trophozoite of N. fowleri in CSF, stained with hematoxylin and eosin (H&E).
B: Trophozoite of N. fowleri in CSF, stained with trichrome.  Image courtesy of the Texas State Health Department.

C	D

C, D: Trophozoites of N. fowleri in brain tissue, stained with H&E.

E	F

E, F: Trophozoites of N. fowleri in brain tissue, stained with H&E.