Page 80 - parasitology for medical and clinical laboratoryprofessionals

60 CHAPTER 3

Life Cycle
Source: Centers for Disease Control and Prevention (CDC) gitudinal fission. Following excystation (when the cyst
The life cycle for E. hartmanni is the same as for other
intestinal amoebae, with reproduction by binary lon-

“hatches” and converts to a trophozoite), the phenom-
enon of binary fission occurs and trophozoites continue
to reproduce in the colon’s lumen (tubelike opening).

Disease Transmission
Amoebiasis by E. hartmanni as for most other enteric
parasites is transmitted by ingestion of food and water
FIGURE 3-16 Entamoeba hartmanni trophozoite
containing the cysts of the organism. Again, this organ-
ism is not considered a pathogen, even in great numbers.
of morphological characteristics except for the differ-
ences in their respective sizes (Figure 3-16). Trophozo- Laboratory Diagnosis
ites of E. hartmanni measure usually 8 to 10 μm (range
5 to 12 μm) and are smaller than those of E. histolytica Diagnosis of the presence of an E. hartmanni infection
(10 to 60 μm). The trophozoites of E. hartmanni have relies on a microscopic examination of a fresh fecal spec-
one nucleus (cysts have four nuclei) with fine periph- imen for ova and parasites. A permanent stained smear
eral chromatin and a small and centrally located karyo- would provide the best means for identifying this organ-
some (body included in the chromatin of nucleus that ism. Immature and mature cyst forms as well as tropho-
usually stains a darker color than the remainder of the zoites may be found in the fecal sample.
nucleus). The cytoplasm is finely granular. In summary,
the trophozoites of E. hartmanni strongly resemble the Treatment and Prevention
morphology of those of E. histolytica, with a small, often
centrally located karyosome, fine peripheral chromatin, The presence of nonpathogenic E. hartmanni does
and finely granular cytoplasm. But the main difference is not require any treatment. Ensuring cleanliness of food
in their small size: 5 to 12 μm compared to 10 to 60 μm and water that has been purified is necessary to prevent
for E. histolytica, but it should be noted that there may infection. Good personal sanitation practices as well as
be some overlap among the smaller size of E. histolytica. the availability of clean water and food will usually elimi-
Trophozoites of E. hartmanni also reveal ingestion nate infections by E. hartmanni.
of such materials as yeasts and other organic materi-
als including bacteria but with no RBC inclusions as a ENDOLIMAX NANA
diagnostic feature as is found in E. histolytica, and are
considered nonpathogenic. When red blood cells are Endolimax nana cysts are small, round or oval cysts
found in E. histolytica, this is called a pathognomic with two to four nuclei, encompassing a range in size
(indicative of a disease) condition (CDC). of 6 to 12 μm. The trophozoites of this organism are
slow-moving trophozoites (Limax is the genus for a slug-
Symptoms or snail-like creature). Endolimax is the genus of amoe-
boid organisms found in the intestines of various animals,
E. hartmanni is nonpathogenic and no symptoms are including the species E. nana found in humans. It causes
usually associated with the presence of the organisms, as no known disease and is most significant in medicine as
infections with the organism result in an asymptomatic it provides false positives when using other tests for iden-
condition. The organism is often found when examining tifying intestinal parasites. It is easy to confuse E. nana
microscopic slides of feces for other pathogenic enteric with the similar species Entamoeba histolytica, respon-
amoebae. sible for amoebic dysentery, and because its presence