Cysts 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. 

Amebiasis is an infection of the large intestine produced by Entamoeba histolytica that causes symptoms that range from mild diarrhea to fulminant dysentery. Therapy includes treating the asymptomatic carrier of the cysts, as well as the acute amebic dysentery, and the amebic hepatitis and abscess in the symptomatic patient. 

Erdogrul, O. and ener, H. (2005) The contamination of various fruit and vegetables with Enterobius ver-micularis, Ascaris eggs, Entamoeba histolytica cysts and Giardia cysts. Food Control (5th International Meeting of the Noordwijk Food Safety and HACCP Forum) 16(6), 557-560. 

Amebiasis. The causative agent, Entamoeba histolytica, lives and multiplies in the colon (symptom diarrhea), its cyst form residing also in the liver among other sites. In tropical regions, up to half the population can be infested, transmission occurring by the fe-cal-oral route. The most effective treatment against both intestinal infestation and systemic disease is administration of metronidazole. If monotherapy fails, combination therapy with chloroquine, emetine or tetracyclines may be indicated. 

Amebiasis is diagnosed by finding the cysts of Entamoeba histolytica in a stool specimen examined under a microscope. Because the number of cysts in the stool can change from day to day, and cysts may not even be in every stool specimen, sometimes more than one stool specimen must be obtained for examination. A blood test is also available for detection of antibodies against the parasite. 

The antimicrobial properties of silver and its salts have been discussed in various books [14, 16-18] and particular reference must be made to Grier s review in 1983 [15]. Ag usually used in the form of silver nitrate, is bacteriostatic or bactericidal [19-29], antifungal [30-32], protozoicidal [33] and lethal to herpes simplex virus [34]. However, bacterial spores [19], cysts of Entamoeba histolytica [19] and mycobacteria [35] are not killed by Ag. Brown and Anderson [20] observed a non-linear order of death in Pseudomonas aeruginosa exposed to Ag, whereas Ricketts et al. [22] reported a rapid bactericidal action of Ag in water, but not in broth, at concentrations of silver nitrate of 0.5 and 1 pg/ml (2.9 x 10 and 5.8 x 10 M, respectively) with inactivation at concentrations above 1 p.g/ml being too fast for measurement. 

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... 

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. 

Protozoa may become another problem of water treatment. Usually, removal or inactivation of Entamoeba has been the central problem, but recent investigations also concerns Giardia [43]. Proper coagulation, flocculation, sedimentation, and filtration can remove up to 99% of protozoan cysts slow sand filtration can remove Giardia cysts [16]. Improper operation of treatment facilities can cause outbreaks of water-borne illnesses caused by protozoa [44]. Chlorination and disinfectants such as chloramines and ozone can further reduce levels of protozoa [45-47]. 

The biological filter reduces the level of Salmonella paratyphi B84 by 99%, Mycobacterium tuberculosis by 66%, total coliforms by 85 to 99%, enteric virus by 40 to 60% and cysts of Entamoeba histolytica by 88 to 99%. 

Hypochlorous acid, formed when chlorine dissolves in water, is antimicrobial. This is the basis for the use of chlorine and halazone in water purification. Organic matter binds chlorine, thus preventing antimicrobial actions. In a given water sample, this process is referred to as the chlorine demand, since the chlorine-binding capacity of the organic material must be exceeded before bacterial killing is accomplished. Many preparations of chlorine for water purification do not eradicate all bacteria or entamoeba cysts. 

This compound is used in tablet form to purify drinking water. If a large quantity of organic material is present, cysts of Entamoeba histolytica may not be eradicated. 

The addition of 4-8 mg of htilazone per liter will sterilize most water samples in about 30 minutes but will not kill cysts of Entamoeba histolytica. The answer is (D). 

Am(x. biu.sis is caused by infection with Entamoeba histolytica. Metronidazole (Chapter 37) is used in acute infections but in asymptomatic infections, where cysts arc present, diloxanide furoate is also necessary. 

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). 

Infestation with harmful amoebas, particularly Entamoeba histolytica. Cysts of the amoeba may be ingested in contaminated food or water. Also, flies, and infested animals may carry the organisms to foods. 

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