Iodamoeba buetschlii

Cosmopolitan amoeba, parasite of pigs and some species of monkey. Iodamoeba buetschlii can colonize the human colon and caecum.  It is not pathogenic.


Size: 8 to 20 μm; usual range, 10-15 μm.

Motility: visible in fresh specimens only. The trophozoite rapidly extends a long pseudopod, and then withdraws it.  Subsequently, numerous small, round, hyaline pseudopods with a wide base appear but do not achieve any progressive movement (similar to the behavior of Entamoeba coli trophozoites).

A single specimen may contain vital, active trophozoites as well as trophozoites undergoing lysis or in a rounded form;  this latter appearance probably represents the phase before encystment.

Nucleus: rarely visible in the most active trophozoites, while in those undergoing lysis the nucleus appears as a large, refractile mass. Peripheral chromatin is absent.  With Lugol's iodine solution or, better, with permanent staining (trichrome, hematoxylin), it is possible to see a large karyosome centrally or eccentrically located (in this case, adjacent to the nuclear membrane). In the space between the karyosome and nuclear membrane, it is possible to observe achromatic granules (chromosomes) located either around the karyosome or distributed in a crescent pattern on one side. The presence of achromatic granules is an important element for the differential diagnosis with Endolimax nana.

Cytoplasm: contains numerous vacuoles and various kinds of inclusion bodies (bacteria, yeast, etc.).  Sphaerita may be present.


Size: 5 to 25 μm; usual range, 8-15 μm.

Shape: round or oval, very variable.

Nucleus:  the cyst has only one nucleus. Peripheral chromatin is absent.  The karyosome is large and centrally or eccentrically located. In fresh specimens, the nucleus displays a large round or oval refractile karyosome surrounded by a clear halo; the nuclear membrane is not visible.  This type of nucleus, which differs from the Entamoeba type (e.g. having a small karyosome with peripheral chromatin), is best seen on temporary wet mounts stained with Lugol's iodine solution, MIF or Bailenger's stain or on permanently stained smears. 

A useful diagnostic element is the constant presence in these cysts of one or occasionally two iodophilic glycogen masses of variable size. With transmission electron microscopy (TEM), these masses appear well defined and compact, free in the cytoplasm and not surrounded by any membrane: it is therefore incorrect to call them “glycogen vacuoles”. To identify such glycogen masses, it is recommended to use a Lugol's iodine solution that had been freshly made or, better, stabilized with PVP.

With permanent stains (e.g. trichrome, hematoxylin), the nucleus is clearly visible.  A thin nuclear membrane and a voluminous karyosome, often surrounded by achromatic granules, are visible.  Sometimes the granules are distributed in a half-moon pattern on one side of the karyosome.  With these stains, the glycogen mass is visible but remains colorless. Chromatoid bodies are absent.