IMMUNODIAGNOSIS OF STRONGYLOIDES-STERCORALIS INFECTION - A METHOD FORINCREASING THE SPECIFICITY OF THE INDIRECT ELISA

Indirect enzyme-linked immunosorbent assay (ELISA) allows sensitive de tection of serum immunoglobulin (Ig) G against a soluble extract of St rongyloides stercoralis infective larvae. In this study, 40/40 (100%) human strongyloidiasis sera had high levels of anti-S. stercoralis IgG , but 30/40 (75%) filariasis sera, and 12/40 (30%) necatoriasis sera a lso 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 differe nt parasitic nematodes was investigated. One hour of incubation with 2 0 mug/ml aqueous extract of Onchocerca gutturosa absorbed cross-reacti ve IgG in most filariasis and necatoriasis sera, reducing the proporti on with IgG levels above the positivity threshold by more than one-hal f. Preliminary results suggest that absorption with extracts of other filarial nematodes is equally effective, and that some of the cross-re active IgG is directed against phosphorylcholine. Cross-reactive IgG i n most necatoriasis sera was effectively absorbed with 20 mug/ml extra ct of Necator americanus. Cross-reactive IgG was not effectively absor bed with an extract of Ascaris lumbricoides. Absorption of cross-react ive IgG is an effective means of increasing the specificity of the ind irect ELISA, for use in the immunodiagnosis and immuno-epidemiology of S. stercoralis infection.