Inactivation of Leishmania donovani infantum and Trypanosoma cruzi in red cell suspensions with thiazole orange

BACKGROUND: Methods for pathogen inactivation are currently available in some European countries for treatment of plasma and platelet (PLT) components; no approved method for treatment of red cells (RBCs) or whole blood is ready for implementation. In a previous study, thiazole orange (TO), a dye commonly used to count reticulated RBCs and PLTs, exhibited potent photoactivity against human immunodeficiency virus-1 and several model viruses in RBC suspensions. The aim of this study is to further evaluate the ability of TO to inactivate pathogens by measuring its activity against the protozoa Leishmania donovani infantum and Trypanosoma cruzi. STUDY DESIGN AND METHODS: RBC suspensions were deliberately contaminated with L. donovani infantum promastigotes or T. cruzi trypomastigotes and either maintained as an untreated control, incubated with 80 μmol per L TO in the dark, or treated with TO and light. Control and treated samples were inoculated into medium and subsequently microscopically examined for growth. RESULTS: No growth was observed in samples treated with TO in the presence or absence of light, while matched control samples lacking TO and diluted up to 5 log consistently demonstrated Leishmania or T. cruzi growth (n = 3). CONCLUSION: TO inactivated Leishmania or T. cruzi to the limit of detection in RBC suspensions without intentional illumination.