A colorimetric in vitro drug sensitivity assay for Plasmodium falciparum based on a highly sensitive double-site lactate dehydrogenase antigen-capture enzyme-linked immunosorbent assay

We report a double-site enzyme-linked lactate dehydrogenase immunodetection assay (DELI), a highly sensitive antigen-capture enzyme-linked immunosorbe nt assay, which proved to be more sensitive for the detection of Plasmodium falciparum than thick blood smears, as sensitive as the polymerase chain r eaction, and probably more reliable. This technique can help to detect infr a-microscopic parasitemias (one parasite in 10(6)-10(8) red blood cells) fr om biological samples, and being quantitative, provide a fast substitute to thick smears for epidemiologic purposes. The technique can also be used to measure the in vitro drug sensitivity of P. falciparum with greater ease, much greater speed, and simpler equipment than that required for the isotop ic microtest. Results obtained with four antimalarial drugs upon 16 strains closely paralleled those obtained by the isotopic assay (R = 0.95). In con trast with the latter, much lower parasite densities could be tested in the DELI assay (as low as 0.005%), thereby extending the number of isolates th at can be investigated. The ease of implementation and low cost of the DELI -microtest may contribute to a revived interest in using in vitro methods t o survey resistance to antimalarial drugs, so as to better predict future i n vivo drug failures and provide public health recommendations.