Application of a micro enzyme-linked immunosorbent assay (ELISA) to detection of anti-amebic antibody in various forms of amebic infection.

Techniques of a micro enzyme-linked immunosorbent assay (ELISA) used for the serodiagnosis of schistosomiasis were applied to amebic infection. Test sera were divided primary on the basis of serologic diagnosis and stool examination as follows; (I) gel diffusion precipitin test (GDP) positive and stool examination positive: 9 specimens, (II) GDP positive and stool examination negative: 29 specimens, (III) GDP negative and stool examination positive: 32 specimens. Virtually all of the individuals belonging to (III) were asymptomatic, while more than 75% of (I) and (II) were symptomatic. The upper limit of 99% critical range was calculated from the data of 70 serum specimens from healthy adult Japanese and was employed as the cut-off value. All of the specimens of (I) and (II) were judged positive by ELISA, generally with a much higher absorbance than the cut-off value; whereas, approximately 80% of (III) were judged positive. The average absorbance of (III) was lower than that of (I) and (II). These findings suggest that the ELISA is well in accord with GDP qualitatively as far as GDP-positive individuals are concerned, and that even asymptomatic cyst carriers with negative serology by GDP may often be producing anti-amebic antibodies, although the titers are low.