ABSTRACT
The infectious form of Entamoeba histolytica is the mature, quadrinucleated cyst which, unlike trophozoites, remains viable for prolonged periods of time in a broad range of environmental conditions, even resisting the effect of gastric juice and digestive enzymes. Pathogenic strains seem to prevail, especially in communities with poor hygienic conditions, perhaps because they are more resistant to environmental conditions than their nonpathogenic counterparts. The basic mechanism of transmission of amebiasis is the ingestion of mature cysts of Entamoeba histolytica eliminated by carriers. The conditions frequently leading to this event are inadequate sewage disposal systems and faulty hygienic habits of both the reservoir and the recipient. Most individuals infected with Entamoeba histolytica fail to develop any form of amebic disease, i.e., the parasite dwells and reproduces freely in the intestine, without actually harming the tissues.
