DIFFERENTIATION OF PATHOGENIC ENTAMOEBA-HISTOLYTICA INFECTIONS FROM NONPATHOGENIC INFECTIONS BY DETECTION OF GALACTOSE-INHIBITABLE ADHERENCE PROTEIN ANTIGEN IN SERA AND FECES

We determined whether epitope-specific monoclonal antibodies to the ga lactose-inhibitable adherence protein (GIAP) of Entamoeba histolytica could be used in an enzyme-linked immunosorbent assay (ELISA) to detec t antigen in serum and feces and differentiate between nonpathogenic z ymodemes and the potentially invasive pathogenic organisms that requir e treatment. Overall, 57% of subjects from Cairo, Egypt, with symptoma tic intestinal amebiasis and 42% with asymptomatic infection possessed GIAP antigen in their sera, whereas 4% of uninfected controls or subj ects with other parasitic infections possessed GIAP antigen in their s era (P < 0.001). In subjects from Durban, South Africa, only 6% of uni nfected controls or those with nonpathogenic E. histolytica infection were positive for GIAP in serum, whereas 3 of 4 with asymptomatic path ogenic intestinal infection and 75% with amebic liver abscess were pos itive for GIAP in serum. Fifteen stool samples from patients with inte stinal amebiasis were available for study; all had a positive ELISA re sult for fecal GIAP antigen. Epitope-specific monoclonal antibodies id entified 8 of 15 subjects with fecal antigen from pathogenic strains. Seven of those eight subjects had adherence protein antigen in their s era, whereas none of seven with apparent nonpathogenic E. histolytica infection had adherence protein antigen in their sera. In summary, we were able to detect E. histolytica adherence protein antigen directly in serum and fecal samples by ELISA. The presence of amebic antigen in serum demonstrated 94% specificity for pathogenic E. histolytica infe ction, and amebic antigen is present during asymptomatic intestinal in fection. In conjunction with antibody detection, this method should be very useful in the diagnosis and management of intestinal amebiasis.