Evaluation under field conditions of the colourimetric DELI-microtest for the assessment of Plasmodium falciparum drug resistance

It has been frequently stressed that improved methods are needed to monitor the fast spread of drug-resistant Plasmodium falciparum parasites in endem ic areas. We recently developed a colourimetric microtest, double-site enzy me-linked lactate dehydrogenase enzyme immunodetection assay (DELI), to ass ess drug resistance in vitro. This method, which proved highly effective un der laboratory conditions, was evaluated under field conditions in 2 Africa n areas (in Senegal and Burkina Faso) in 1997 and 1998, respectively. The s ensitivities of isolates from symptomatic (n = 50) and asymptomatic individ uals (n = 26) infected with P. falciparum were assessed in parallel by the new DELI-microtest and the isotopic-microtest. IC50 values of the isolates determined for chloroquine, quinine, amodiaquine and mefloquine were well c orrelated (r = 0.79, P < 0.001). The proportions of sensitive and resistant isolates determined using the 2 methods were similar. The DELI-microtest p roved to be faster to implement than the isotopic-microtest, easier to perf orm, and did not require sophisticated equipment. Moreover, a larger number of isolates can be tested since parasitaemias as low as 0.005% could be re liably measured with the DELI-microtest. These initial field studies thus s upport the value of the DELI-microtest for large-scale drug-sensitivity mon itoring.