[Utility and limitations of laboratory diagnosis of amebiasis]

Abstract

Entamoeba histolytica is an invasive and pathogenic protozoan parasite that causes amebiasis. It must be distinguished from Entamoeba dispar, a nonpathogenic commensal parasite of the human gut lumen that is morphologically identical to Entamoeba histolytica. Diagnosis of amoebic colitis currently requires combination of microscopic examination of stool specimens with another technique allowing positive identification of the two species. Stool culture followed by zymodem analysis is considered as gold standard but is not applicable in routine practice. Detection of specific Entamoeba histolytica antigens in stools is a fast, sensitive technique that should be considered as the method of choice. Stool PCR is a highly sensitive and specific technique but high cost make it unsuitable for use in endemic areas where economic conditions are difficult. The utility of serologic tests in distinguishing Entamoeba dispar from Entamoeba histolytica is controversial. However serology is still considered as the method of choice for diagnosis of extraintestinal amebiasis. Circulating Gal/GalNac lectin antigens can be detected in the serum of 96% of patients with untreated amoebic liver abscess. In the future this method should allow early diagnosis and treatment of extraintestinal amoebiasis in patients who have not yet developed detectable serum antibodies.