[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

CHAPTER 3 The Amebas
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Subphylum
Sarcodina
Class
Lobosea
Intestinal Species
Entamoeba histolytica
Entamoeba hartmanni
Entamoeba coli
Entamoeba polecki
Endolimax nana
Iodamoeba bütschlii
Extraintestinal Species
Entamoeba gingivalis
Naegleria fowleri
Acanthamoeba species
FIGURE 3-1 Parasite classification, the amebas.
countries that have poor sanitary conditions. In
the United States, amebiasis is often found
in immigrants from and people who have traveled
to underdeveloped countries. Furthermore,
amebas may be present and thus infect individuals
in areas and institutions in which crowded
conditions prevail.
It is important to note that only one of the
intestinal amebas, E. histolytica, may produce
characteristic symptoms, and is universally considered
to be a pathogen. Infections with each of
the extraintestinal amebas may cause symptoms
that are other than intestinal in nature, often
involving such areas as the mouth, eye, and
brain.
Quick Quiz! 3-3
Infections with intestinal amebas are prevalent in
which of the following? (Objective 3-2)
A. Underdeveloped countries with poor sanitary
conditions
B. Beef consumers in the United States
C. People traveling to Europe
D. Japan, because of seafood diet
CLASSIFICATION OF THE AMEBAS
The amebas, members of the subphylum Sarcodina
and class Lobosea, may be separated into
two categories, intestinal and extraintestinal
(meaning parasites that migrate and/or take up
residence outside the intestines). The species discussed
in this chapter are classified under these
categories and are listed in Figure 3-1.
Entamoeba histolytica
(en’tuh-mee’buh/his-toe-lit’i-kuh)
Common associated disease or condition names:
Intestinal amebiasis, amebic colitis, amebic dysentery,
extraintestinal amebiasis.
Morphology
Trophozoites. The trophozoites (trophs) of E.
histolytica range in size from 8 to 65 µm, with
an average size of 12 to 25 µm (Figs. 3-2 to 3-4;
Table 3-1). Note that parasite names are often
shortened to just the first letter of the genus followed
by the species name; E. histolytica is the
abbreviated version of Entamoeba histolytica.
Abbreviations will be used along with the entire
parasite names, as appropriate, throughout the
rest of this text.
The trophozoite exhibits rapid, unidirectional,
progressive movement, achieved with the help of
finger-like hyaline pseudopods. The single nucleus
typically contains a small central mass of chromatin
known as a karyosome (also referred to as
karyosomal chromatin). Variants of the karyosome
include eccentric or fragmented karyosomal
material. The karyosome of this amebic
parasite is surrounded by chromatin material, a