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Chapter 1

Amebiasis

With KENJI KIMURA, MIGUEL STOOPEN, and ROGELIO MONCADA

Amebiasis is a widespread parasitic disease caused by the protozoan Entamoeba histolytica (E.h). This harmless appearing, fragile microorganism, measuring 10 to 40 µm has as its principal biological characteristic the ability to invade and destroy nearly every tissue of the human body. According to multiple reports, it is probably colonizing the large bowel in 10% to 20% of the world's population, with an average of 12% as reported by the World Health Organization (WHO). It is most common in the poor developing countries of the tropics where sanitation and a clean water supply are inadequate or nonexistent. Out of the total number of infected individuals, about 50 million become symptomatic annually as a result of invasive amebiasis and 40,000 to 100,000 deaths are reported per year. Amebiasis is the third leading cause of death from parasitic disease, surpassed only by malaria and schistosomiasis.

"Amebic dysentery" has for centuries conjured up a picture of steaming tropical jungles and sufferers dying with all the unpleasantness of an acute bowel infection. In fact, the disease is not confined only to the tropics but is worldwide in distribution and may affect not only the gut but the liver, chest, and other parts of the body. The illness may be so free from "dysentery" that it is often first recognized by the radiologist in patients who are suspected clinically of having colon cancer, cirrhosis, or an abscess of the liver or lung.

During the past 25 years, considerable progress has been achieved in the development of laboratory techniques to diagnose amebiasis, specifically using antibody titers for identification of the aggressive infectious stage of the parasite. Computerized tomography (CT) and ultrasonography have made major contributions to the diagnosis and management of amebic liver abscess. Currently, the ability to diagnose colitis, hepatic abscess, and other clinical manifestations of this parasitic disease has improved early decision making, enabling implementation of the most appropriate form of therapy. Drugs, such as Metronidazole, have had limited results in some segments of the population and, in some endemic areas, the morbidity and mortality have diminished. Even with these advances, however, the overall incidence of amebiasis in endemic areas is similar to 30 years ago. There are still many unanswered questions about amebiasis from the biological, epidemiological, and clinical standpoints, and much remains to be learned about this ubiquitous and often devastating disease.

Synonyms

Amebiasis. Amebic dysentery. Amebic enteritis. Amebic granulomatous colitis. Ricaldoni and Berta's amebic inflammatory disease. Sp: Amibiasis. Fr: Amibiase. Ger: Amöbenbefall, Amöbiasis.

The ameboma is referred to as "pseudotumor," pseudocancer, Kartuli's amebic tumor, typhlitic or nonspecific granulomatous tumor, ligneous tumor, pseudotuberculoma or neoplastiform amebiasis. Sp: Amiboma. Fr: Amibome. Ger: Amöbom.

Definition

Amebiasis is infection by the pathogenic protozoan, Entamoeba histolytica. Other strains and species of amebae infect man, but only rarely are these pathogenic. The clinical significance of the other strains would be negligible were it not for mistaken diagnoses: they resemble and are sometimes mistaken for Entamoeba histolytica.

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