A wide spectrum,
from asymptomatic infection ("luminal amebiasis"), to invasive intestinal
amebiasis (dysentery, colitis, appendicitis, toxic megacolon, amebomas),
to invasive extraintestinal amebiasis (liver abscess, peritonitis, pleuropulmonary
abscess, cutaneous and genital amebic lesions).
histolytica must be differentiated from other intestinal protozoa
including: E. coli, E. hartmanni,
E. gingivalis, Endolimax nana, and Iodamoeba buetschlii
(the nonpathogenic amebae);
Dientamoeba fragilis (which is a flagellate not an
the possibly pathogenic Entamoeba polecki. Differentiation is possible, but
not always easy, based on morphologic characteristics of the cysts and trophozoites.
The nonpathogenic Entamoeba dispar, however, is morphologically
identical to E. histolytica, and differentiation must be based on
isoenzymatic or immunologic analysis. Molecular methods are also
useful in distinguishing between E. histolytica and E. dispar
and can also be used to identify E. polecki.
Microscopic identification of cysts and trophozoites in the stool is the
common method for diagnosing E. histolytica. This can
be accomplished using:
- Fresh stool:
wet mounts and permanently stained preparations (e.g., trichrome).
from fresh stool: wet mounts, with or without iodine stain, and permanently
stained preparations (e.g., trichrome). Concentration procedures,
however, are not useful for demonstrating trophozoites.
In addition, E. histolytica
trophozoites can also be identified in aspirates or biopsy samples obtained during
colonoscopy or surgery.
For asymptomatic infections, iodoquinol, paromomycin,
or diloxanide furoate (not commercially available in the U.S.) are the
drugs of choice. For symptomatic intestinal disease,
or extraintestinal, infections (e.g., hepatic abscess), the drugs of choice
are metronidazole or tinidazole, immediately followed by treatment with iodoquinol, paromomycin,
or diloxanide furoate.