Skin test for amebiasis: an appraisal.

Abstract

Eighty-eight patients with amebic liver abscesses were skin-tested with an extract of Entamoeba histolytica trophozoites grown axenically in a defined medium (Diamond's TPS-1) in the presence of rabbit serum. Development of a wheal with a diameter at least double that of the initial antigen bleb at 15 to 20 minutes after intradermal inoculation of the antigen was regarded as positive. It was found that 92% (79/86) of the patients with amebic liver abscesses tested within a period of less than 4 years after the onset of clinical symptoms were positive, whereas only 4% (2/48) of patients with other diseases were positive. Two patients tested more than 4 years after the onset of symptoms of invasive amebiasis were negative. Ninety-four children in an orphanage were skin-tested, and it was found that 82% of the 57 cyst-passers and 30% of the 37 children not passing cysts were positive. Forty-eight healthy kindergarten children were also tested and all were found to be negative. Comparison between the results of the skin test and those of the immuno-electrophoresis test in 56 patients with amebic liver abscesses was made. Agreement was found in 48 patients (85.7%). Among the remaining 8 patients, 4, respectively were positive by each test. Skin reactivity takes longer to develop after the onset of clinical symptoms but once it has developed it is more persistent than the precipitins demonstrable by immuno-electrophoresis. The skin test for amebiasis should be valuable in epidemiological studies.