The Elisa-U: An Enzyme-Linked Immunosorbent Assay using Urease as the Enzyme Marker for Rapid Detection of Plasmodium Falciparum Antibody in Human Serum

Melinda LeeMalaria Research Group, U.S. Army Medical Research Unit, Institute for Medical Research, 50588 Kuala Lumpur, Malaysia

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Chris LambrosMalaria Research Group, U.S. Army Medical Research Unit, Institute for Medical Research, 50588 Kuala Lumpur, Malaysia

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A visual, enzyme-linked immunosorbent assay using urease (ELISA-U) as the enzyme marker was adapted for rapid detection of antibody against Plasmodium falciparum. Flat-bottom, 96-well microtiter plates were coated with P. falciparum soluble antigen obtained by saponin and NP-40 treatment of parasite cultures. Antibody was detected by successive incubations with test sera, urease-conjugated rabbit-human antibody, and urease substrate. Reactive sera developed a definite and easily visualized purple color. Sera from patients with single infections of P. vivax or P. ovale were unreactive. No cross-reactivity was noted with sera from patients with rheumatoid arthritis, filariasis, amebiasis, schistosomiasis, dengue, scrub typhus, leptospirosis, or toxoplasmosis. The procedure can be performed at room temperature and completed within 1 hr. The sensitivity of the assay is comparable to that of the indirect fluorescent antibody test at all but the lowest dilutions tested.

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