Amebiasis is an infection of the large intestine produced by the protozoan Entamoeba kistolytica. The disease occurs worldwide but is most prevalent in South and West Africa, Southeast Asia, Mexico, and the western part of Latin America.' More than 10% of the world's population is estimated to be infected. E kistolytica is the third leading parasitic cause of death in developing nations, after malaria and schistosomiasis. In the United States, the prevalence has declined from 5% to 10% in 1960 to approximately 1% to 4% currently. However, amebiasis is one of the most important pathogens to which travelers to endemic countries are exposed.
Other groups also are at higher risk of acquiring E kistolytica infection. Sixteen percent to 32% of homosexual men have been found to have E kistolytica in stool specimens. E kistolytica also has been reported as an occupational disease in flight personnel working for commercial airlines.” Because humans are virtually the exclusive reservoir of E kistolytica, appropriate control measures could result in a substantial reduction in the incidence of the disease.
Entamoeba has seven species including Entamoeba hartmanni, Entamoeba coli, Entamoeba colecki, and Entamoeba gingivalis; only E kistolytica causes disease in humans. The morphologic classification of Entamoeba is based on the number of nuclei in the mature cyst.' E kistolytica is further characterized by its unique antigens, DNA characteristics, and isoenzyme analyses. In contrast to the free-living amoeba, E kistolytica requires the presence of either bacteria or tissue substrates to satisfy its nutritional needs. It can be cultivated on artificial media, but the diagnostic value of culture remains uncertain.