[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

56
CHAPTER 3 The Amebas
Epidemiology
E. coli is found worldwide. In addition to warm
climates, E. coli also occurs in cold climates, such
as Alaska. Geographic areas that have poor
hygiene and sanitation practices are at the greatest
risk of becoming endemic with E. coli. As
with the other intestinal amebas, E. coli is transmitted
through the ingestion of the infected cyst
through contaminated food or drink.
Clinical Symptoms
Quick Quiz! 3-12
Which of the following is not true about E. coli?
(Objectives 3-2, 3-5, and 3-7C)
A. The parasite is found worldwide.
B. It is considered to be a pathogen.
C. The infection is transmitted through the ingestion
of the infected cyst through contaminated food
or drink.
D. The infection can be prevented by adequate disposal
of human feces and good personal hygiene
practices.
As with infections of E. hartmanni, infections
with E. coli are usually asymptomatic.
Treatment
E. coli is considered a nonpathogen. Treatment,
therefore, is usually not indicated.
Entamoeba polecki
(en’tuh-mee’buh/poh-lek’ee)
Common associated disease or condition names:
None (considered as a nonpathogen).
Prevention and Control
The adequate disposal of human feces, as well as
proper personal hygiene practices, is crucial for
preventing E. coli infections. Protection of food
and drink from flies and cockroaches is also necessary
to break the E. coli transmission cycle.
Notes of Interest and New Trends
The morphologic differentiation of E. coli from
E. histolytica, as well as the pathogenicity of
each of these parasites, was not established until
the early 1900s.
Morphology
Trophozoites. The average Entamoeba polecki
trophozoite measures 12 to 20 µm (Fig. 3-12;
Table 3-7). The trophozoites may vary in size,
however, ranging from 8 to 25 µm. Sluggish,
nonprogressive motility is observed in stools of
normal consistency containing E. polecki trophozoites.
In diarrheal stools, E. polecki trophozoites
exhibit progressive, unidirectional motility,
Central
karyosome
Cytoplasm
Quick Quiz! 3-11
The trophozoites of E. coli: (Objective 3-9A)
A. Have eight nuclei
B. Have a typical nucleus consists of a large, often
irregularly shaped karyosome that is eccentrically
located
C. Are characterized by a karyosome that is surrounded
by evenly distributed peripheral
chromatin
D. Contain red blood cell inclusions
Pseudopod
Even peripheral
chromatin
Ingested bacteria
Size range: 8-25 m
Average size: 12-20 m
FIGURE 3-12 Entamoeba polecki trophozoite.