Still around and still dangerous: Giardia lamblia and Entamoeba histolytica.

The discovery of new infectious agents often overshadows the continuing impact and importance of well-established organisms. In the case of diarrheal disease, Entamoeba histolytica and its complications remain a major cause of morbidity and mortality in developing countries. Although it is also present in developing countries, Giardia lamblia is a primary cause of waterborne outbreaks of diarrhea in developed countries. Persons at risk of developing giardiasis in these countries include backpackers and campers who drink untreated stream water or persons who drink improperly treated municipal water containing infective cysts. Investigators have recently identified the mechanisms used by these organisms to colonize the intestinal tract and to cause disease. New methods of identification using immunologic principles have been added to the traditional microscopic methods of identification.