Biomedical Engineering Reference
In-Depth Information
Genus Entamoeba contains the most commonly occurring pathogenic amoe-
bic species, Entamoeba histolytica [73]. Infection occurs through fecal
oral
transmission of the cyst form. It is estimated that about 50 million people are
infected by Entamoeba histolytica, with about 70 000 deaths per year, world-
wide. All of the other amoebozoan organisms discussed in this chapter, com-
bined, account for just a few dozen deaths. Most Entamoeba histolytica
infections do not result in clinical disease. The organism can live in the
intestine for years as a commensal. Unlike the pathogenic amoebas discussed
so far, Entamoeba histolytica is not found widely distributed in soil samples.
Entamoeba histolytica has adapted itself to life inside a narrow range of pre-
ferred hosts: primates. As such, its life is restricted to the GI tract of humans
and other primates, and to their feces. In the GI tract, the organism can be
found in its amoeboid feeding form (i.e. Trophozoite). In stools, the tropho-
zoites encyst; cysts can survive for months.
Entamoeba gingivalis is a species of Entamoeba that is routinely found in
a high percentage of specimens obtained from human saliva or from gingival
scrapings. Its pathogenicity in oral diseases is controversial. Surprisingly, a
recent case report has demonstrated Entamoeba gingivalis in a pulmonary
abscess [84].
Entamoeba comes with four taxonomic traps that have been used to mor-
tify generations of students.
1. First and foremost, do not confuse Entamoeba coli (abbreviation E. coli)
with Escherichia coli (likewise abbreviated as E. coli). Both live in the
colon, and both can be reported in stool specimens.
2. Of the Entamoeba genera that can be found on examination of human
stools, only one is frequently pathogenic, Entamoeba histolytica.
Entamoeba dispar, Entamoeba hartmanni, Entamoeba coli, Entamoeba
moshkovskii, Endolimax nana, and Iodamoeba butschlii, occasionally
found in stool specimens, are generally non-pathogenic.
3. Do not confuse Entamoeba (Class Amoebozoa, Chapter 22) with
Dientamoeba (Class Metamonada, Chapter 16).
4. Terminology for amoebic infections is somewhat confusing. It is com-
monly agreed that the term “amoebiasis,” with no qualifiers in the name,
refers exclusively to the intestinal infection by Entamoeba histolytica,
and is also known by the name “amoebic dysentery.” Encephalitides
caused by members of Class Amoebozoa (Acanthamoeba and
Balamuthia) are named granulomatous amoebic encephalitis. Encephalitis
caused by Naegleria fowleri (not an amoeba) is called primary amoebic
meningoencephalitis, an accepted misnomer. Naegleria is a member of
class Percolozoa (Chapter 18). A better name for the Naeglerian disease
would be primary percolozoan meningoencephalitis. Acanthamoeba
castellanii causes amoebic keratitis, and is an occasional cause of
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