Information about E. histolytica

Topics: Pages: 25 (6200 words) / Published: Oct 4th, 2013
Entamoeba histolytica

Entamoeba histolytica

I. Morphology

Among the Entamoeba family, E. histolytica is the most invasive. This eukaryotic organism has some atypical characteristics such as: lack of organelles, no endoplasmic reticulum and Golgi apparatus. The cyst is usually spherical with the size that ranges from 10-20μm. In a mature cyst there are four nucleuses while in an immature cyst there are 1-2 which are occasionally seen. Its karyosomal chromatin is small, discrete and usually central and the chromatoidal body is elongated with bluntly rounded ends. Its glycogen is usually diffuse; concentrated mass often present in young cysts; and stains reddish brown with iodine. The trophozoite is about 10-60 μm; possess a progressive motility with a single nucleus. Its karyosomal chromatin is small and usually central but often eccentric. It also has ingested red blood cells.

II. Life Cycle

The life cycle of all amebae is similar. The invasive stage, however, involving extra-intestinal infection, is seen only with E. histolytica. Following ingestion, the mature cyst passes through the stomach and into the small intestine. Excystation occurs in the lower ileum, when the cyst develops into the trophozoite form. Binary fission follows, and trophozoites continue to multiply in the lumen of the colon. Trophozoites often become encysted. These immature cysts are passed in the feces, or develop to maturity before being excreted. Both stages of cysts plus trophozoites may be found in the feces, although trophozoites are usually only found in liquid feces. Occasionally trophozoites invade the wall of the colon, multiply, and pass into the circulation.

III. Pathogenesis

E. histolytica has a wide geographic distribution and is considered one of the most important human protozoan parasites. Amebiasis is usually

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