Detection of parasites by flow cytometry analysis. Parasites were double stained with hydroethidine and thiazole orange as described previously . Fluorescence was expressed in Fluorescence Arbitrary Units (FAU) defined by the equipment. A: red blood cell profile. B: Untreated control culture. Red blood cells containing double stained (viable) parasites were visualized in R1. C: Parasites were cultivated without FQ pressure for 8 days. R1 represents the region where the parasite population is detected. Cells outside R1 (left) were unparasitized red blood cells. 38 parasites were counted in a total red blood cell population of 106. D: Parasites were cultivated without FQ pressure for 36 days. Only 2 parasitized RBC were counted in R1 out of 106 red blood cells.