Inactivation of Plasmodium falciparum by photodynamic excitation of heme-cycle intermediates derived from delta-aminolevulinic acid.

Transfusion-transmitted malaria (TTM), especially that caused by Plasmodium falciparum, is of great concern in malaria-endemic areas. As a result of increased international travel, migration, and the spread of drug-resistant parasites, TTM is also a growing problem in industrialized nations. An effective and inexpensive means of inactivating malaria parasites in blood products would represent an important advance. In this report, we demonstrate that photoactivation of plasmodial heme-cycle intermediates, derived from supplemental delta -aminolevulinic acid (ALA), by exposure to simple white light in the presence of ALA, reduces P. falciparum in culture to levels that are undetectable by light microscopy or lactate dehydrogenase assay. Photodynamic excitation of presumed heme-cycle intermediates, which was revealed by fluorescence microscopy, did not appear to adversely affect the viability of erythrocytes. These data suggest that this pathogen-inactivation strategy, which uses inexpensive reagents and white light, may represent an appropriate means of inactivating malaria parasites in blood products in resource-poor settings.