Trophozoites Entamoeba

Entamoeba histolytica is an anaerobic rhizopod that occurs in tropical and subtropical areas. It can cause intestinal and extraintestinal manifestations. It is transmitted orally by ingestion of cysts that develop into trophozoites in the large intestine. Amebic trophozoites release several cytolytic factors, e.g. amoe-bapore, which enable the parasite to invade tissue. In intestinal amoebiasis, E. histolyticatrophozoites invade the intestinal mucosa, causing a form of ulcerative colitis with bloody and mucous diarrhoea. Extraintestinal manifestation of amebiasis results in abscess formation, usually in the liver but sometimes in the brain. 

In an ideal stain, the cytoplasm of cysts and trophozoites is blue-green tinged with purple. Entamoeba coli cyst cytoplasm is often more purple than that of other species. Nuclear chromatin, chromatoid bodies, erythrocytes, and bacteria stain red or purplish red. Other ingested particles such as yeasts often stain green. Parasite eggs and larvae usually stain red. Inflammatory cells and tissue cells stain in a fashion similar to that of protozoa. Color reactions may vary from the above. 

The protozoan Entamoeba histolytica causes amebiasis, an infection that is endemic in parts of the United States. The parasite can be present in the host as either an encysted or a trophozoite form. Initial ingestion of the cyst may result either in no symptoms or in severe amebic dysentery characterized by the frequent passage of bloodstained stools. The latter symptom occurs after invasion of the intestinal mucosa by the actively motile and phagocytic trophozoite form of the protozoan. 

A model for unscheduled DNA replication in Entamoeba histolytica trophozoites. Arch Med Res 28 24-26... 

R. Lopez-Revilla and R. Gomez-Dominiguez (1985). Incorporation and toxicity of 32P orthophosphate and occurrence of polyphosphate in Entamoeba trophozoites. J. Protozool., 32, 353-355. 

FIGURE 2.14 Phase contrast photomicrograph of cultured Entamoeba histolytica trophozoites. 

FIGURE 2.15 Entamoeba histolytica trophozoites in section of intestine. 

Quinfamide acts on the trophozoites of Entamoeba histolytica, making the trophozoite incapable of propagation. It is not active against amebic cysts. In doses of 100-1200 mg adverse effects have been frequent but... 

Intestinal amebiasis is diagnosed by demonstrating Entamoeba histolytica cysts or trophozoites (may contain ingested erythrocytes) in fresh stool or from a specimen obtained by sigmoidoscopy. Three stool samples obtained 24 hours apart will produce a 60% to 90% yield for E. histolytica. 

Amebiasis is primarily an intestinal disease caused by Entamoeba histolytica, which is a cosmopolitan organism usually transmitted by ingestion of materials contaminated by cysts that descend the GI tract. Trophozoites develop and remain in the colon, caecum, and sigmoidal area. Ulceration of the intestinal wall results, causing symptoms of dysentery. Metastatic lesions sometimes develop in other organs such as the liver (hepatic amebiasis). This is more difficult to treat. Amebicides in use today have all been developed empirically. The nitroimidazoles metronidazole, tinidazole, and the toxic nitro heterocycle niri-dazole (Fig. 7-4) are effective at all sites. 

This review has so far concentrated on the multiplicative, feeding stages (trophozoites) of the three main groups of parasites, the stages that are parasitic and responsible for the diseases. Transmission of both Giardia and Entamoeba, however, involves a cyst stage. Cysts are resistant, non-feeding forms able to survive an... 

Keene, W. E., Hidalgo, M. E., Orozco, E. and McKerrow, J. H. (1990) Entamoeba histolytica correlation of the cytopathic effect of virulent trophozoites with secretion of a cysteine proteinase. Exp. Parasitol. 71 199-206. 

Amebiasis ajfects 10% of the world s population. In the U.S., amebiasis is usually seen in those living in crowded, unsanitary conditions. Entamoeba dispar accounts for 90% of human infections and E. histolytica/or only 10%, but only E. histolytica causes human disease. Humans are the only known hosts for these protozoa, which are transmitted almost exclusively by the fecal-oral route. E. histolytica cysts ingested from contaminated food or water transform into trophozoites that reside in the large intestine. Many individuals infected with E. histolytica are asymptomatic but excrete infectious cysts, making them a source for further infections. In others, E. histolytica trophozoites invade the colonic mucosa with resulting colitis and bloody diarrhea (amebic dysentery). Rarely, E. histolytica trophozoites invade through the colonic mucosa and reach the liver via the portal circulation, where they establish an amebic liver abscess. 

Allicin not only shows antibacterial activity, but also antifungal [63], antiprotozoal [87], anti-parasitic [88] and antiviral activities [89]. It has recently been shown to inhibit the ability of Entamoeba histolytica trophozoites to destroy monolayers of baby hamster kidney cells [90]. Cysteine proteinases, an imporatant contributor to amebic virulence, as well as alcohol dehydrogenase, are strongly inhibited by allicin [90]. 

Amoebiasis, due to infection with Entamoeba histolytica, is conveyed between humans by its cysts which are 10 microns in diameter. They survive well outside the body and are ingested in water and uncooked food. In the colon, the larger vegetative forms (trophozoites) emerge and cause chronic diarrhoea and, often, ulceration of the bowel wall. Unlike bacterial dysentery, this disease is seldom self-limiting without proper medication. Abscesses in the liver form a common complication. A ready cure can be effected with metronidazole (Section 6.3.3). 

MacFarlane RC, Shah PH, Singh U. Transcriptional profiling of Entamoeba histolytica trophozoites. Int J Parasitol. 2005 35 533- 2. 

Entamoeba histolytica trophozoite Gal/GalNAc lectin Gal/GalNAc... 

Kobiler D and Mirelman D (1980) A lectin activity in Entamoeba histolytica trophozoites. Arch Invest Med (Mex) 11(1 Suppl) 101-8. 

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