Improved antigens for IgG-ELISA diagnosis of strongyloidiasis.

Abstract

Two preparations of antigens for the diagnosis of strongyloidiasis were prepared from an extract of the infective larvae of Strongyloides stercoralis: a crude antigen (CA) and a molecular weight cut-off antigen (MWCOA). Both antigens were analysed by indirect ELISA against the sera of strongyloidiasis (26 cases), other helminthiases (167) and normal controls (30). The larvae were obtained from fecal culture by a modified polyethylene tube technique after screening tests by triple simple smears per case. The larvae were extracted with distilled water and further sonicated to obtain a supernatant, the CA. A part of the CA was separated for an antigen containing molecules of lower than 30 kDa by an ultrafree-MC centrifugal filter tube (PLTK): this was designed as the MWCOA. The CA gave 96.15% sensitivity and 40.12% (67/167) specificity at a cut-off value of 0.980 (5SD); false positives were produced by 19 of 20 different helminthiases. The MWCOA produced 96.15% sensitivity at cut-off value of 0.71 (4SD); the specificity of the test was 78.44% (131/167), higher than that of CA. False positives also appeared with 15 other helminthic infections. This study suggests that MWCOA is more specific than CA. A purified MWCOA will be necessary in order to reduce cross-reactivity and provide the suitable diagnosis of strongyloidiasis.