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Protozoal Microorganisms as Intestinal Parasites 63

E. histolytica and E. dispar before a course of treatment
or lack of treatment is established. Prevention includes
personal hygiene and avoidance of contaminated food
Source: Centers for Disease Control and Prevention (CDC) OTHER INTESTINAL AMOEBAE
and water.

In addition to the information contained in the Table 3-4,
just presented, there are several other non-pathogenic
amoebae that have morphology that may require compari-
son to distinguish them from E. histolytica. It should be
noted from earlier presentations that Dientamoeba fragilis,
although grouped with amoebae, is more morphologically
similar to flagellates such as Trichomonas spp. All three
FIGURE 3-18 Entamoeba dispar and E. histolytica
of the organisms presented in the next table have nuclei
appear the same but are not
without a large karyosome and do not possess chromatin.
Comparisons for differentiating nonpathogens and elimi-
nating them from consideration are presented in the table
specimens should be observed. Concentration techniques
(see Table 3-5).
enhance the recovery rate and the numbers of organ-
isms to be averaged for size, a method of differentiation
between E. dispar and E. histolytica, because there is an IDENTIFYING MISCELLANEOUS
overlap in the sizes of both trophozoites and cyst forms for AMOEBOID INFECTIONS
the two species. Serological procedures are available that
will definitively differentiate between the two species. A number of other organisms that may serve to confuse
the diagnosis of E. histolytica by providing false posi-
Treatment and Prevention tive identification are presented here. The basic micro-
scopic procedure using a stained specimen or wet prep
No treatment is indicated for infections with E. dispar is inexpensive and simple but it has several limitations.
but it is vital that a correct identification of the infectious The procedure does not easily allow for distinguishing
organism be accomplished for differentiation between between the cysts and trophozoites of the disease-causing

TABLE 3-5 Comparison of Several Common Nonpathogenic Amoebae

DIENTAMOEBA FRAGILIS ENDOLIMAX NANA IODOAMOEBA BUTSCHLII
Trophozoites Trophozoites Trophozoites

8–10 μm 8–10 μm 12–15 μm
May be binucleated
Broken (scattered) karyosome
Cysts Cysts Cysts
No cyst stage 6–8 μm 10–12 μm
4 nuclei 1 nucleus
Pronounced glycogen vacuole