Cytofluorograf Detection of Plasmodium yoelii, Trypanosoma gambiense, and Trypanosoma equiperdum by Laser Excited Fluorescence of Stained Rodent Blood

Samples of rat blood infected with Plasmodium yoelii (3% parasitized erythrocytes), Trypanosoma gambiense, or Trypanosoma equiperdum (> 50 trypanosomes per microscope field at 400 x) were fixed with 0.5% glutaraldehyde in phosphate buffered saline, then stained with acridine orange (AO) at 10-4, 10-5, or 10-6 M for 0 to 15 min at 5 C or 25 C and/or ethidium bromide (EB) at 0.05 mg/ml for 20 min at 25 C. Stained cells were analyzed with a laser Cytofluorograf (Bio/Physics Systems, Inc.) to determine if parasites could be detected and differentiated from blood cells by their fluorescent characteristics. Samples of uninfected rat blood with and without leukocytes and P. yoelii-infected blood without leukocytes were treated similarly. In addition, suspensions of T. gambiense and T. equiperdum without all blood cells were stained with AO or EB and analyzed with the Cytofluorograf, as were mixed suspensions of both trypanosome species. EB- but not AO-stained P. yoelii-infected erythrocytes had fluorescent characteristics different from most blood cells. Neither AO- nor EB-stained T. gambiense or T. equiperdum could be differentiated from host blood cells or from each other. The results are discussed with respect to the use of laser flow systems in the detection and analysis of bloodstream dwelling protozoan parasites.