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Protozoal Microorganisms as Intestinal Parasites 41

Life Cycle
Source: Centers for Disease Control and Prevention (CDC) as does the trichomonad group, although it is theorized
The Dientamoeba fragilis life cycle is simple because it
is only characterized primarily by the trophozoite stage,

that there may be a cyst stage that is not readily visible but
that is implicated in fecal-oral transmission (Figure 3-4).
It is thought that Dientamoeba is transmitted along with
the eggs of other parasites such as intestinal worms, and
especially simultaneously with that of the pinworm,
Enterobius vermicularis. Because this organism does not
appear to have a cystic stage, the beginning medical sci-
entist upon seeing the non-motile forms with a circular
FIGURE 3-3 Trichrome stain of Dientamoeba outline, will often mistake them most commonly for the
fragilis, an amoebic parasite
cysts of E. histolytica.
Dientamoeba fragilis organisms reproduce by cel-
intense diarrhea accompanied with blood or mucus, lular division called binary fission (simple longitudinal
abdominal pain, and anal pruritis (a tingling itch or burn- division) and move by pseudopodia (false feet), a mode
ing sensation). of locomotion similar to many amoebae. Humans are

Source: Centers for Disease Control and Prevention (CDC)

FIGURE 3-4 Dientamoeba fragilis life cycle