Immunodiagnosis of Strongyloides stercoralis infection: a method for increasing the specificity of the indirect ELISA

ABSTRACT

Indirect enzyme-linked immunosorbent (ELISA) allows sensitive detection of serum immunoglobulin (Ig) G against a soluble extract of Strongyloides stercoralis infective larvae. In this study, 40/40 (100 percent) human strongyloidiasis sera had high levels of anti-S. stercoralis IgG, but 30/40 (75 percent) filariasis sera, and 12/40 (30 percent) necartoriasis sera also had higher levels than control sera from UK residents. In attempts to increase the assay specificity by absorption of cross-reactive IgG, the effectiveness of pre-incubation of sera with extracts of different parasitic nematodes was investigated. One hour of incubation with 20 æ/ml aqueous extract of Onchocerca gutturosa absorbed cross-reactive IgG in most filariasis and necatoriasis sera, reducing the proportion with IgG levels above the positivity threshold by more one-half. Preliminary results suggest that absorption with extracts of other filarial nematodes is equally effective, and that some cross-reactive IgG is directed against phosphorylcholine. Cross-reactive IgG in most necatoriasis sera was effectively absorbed with an extract of Ascaris lumbricoides. Absorption of cross-reactive IgG is an effective means of increasing the specificity of the indirect ELISA, for use in the immunodiagnosis and immuno-epidemiology of S. stercoralis infection.