The application of photosensitisers to tropical pathogens in the blood supply

The onset of the HIV pandemic led both to significant alterations in blood collection and screening practice and to the development of more sophisticated methods of inactivation of infectious agents from the blood supply. Photodynamic (i.e. light activated) pathogen inactivation is one such method currently in limited use in various European states. The approach is based on the generation of a burst of reactive oxygen and nitrogen species, resulting in the activation of several cell death mechanisms. However, its application to tropical pathogens is perhaps less appreciated, despite the fact that the efficacies of photoantimicrobial agents such as methylene blue were originally reported following screening against organisms such as Trypanosoma cruzi and viruses such as those responsible for dengue and yellow fever. Since the objective of pathogen inactivation is to remove both established and emerging infective agents, it is necessary for photoantimicrobial agents to be broad-spectrum in activity. While this is demonstrable in plasma and platelet fractions, the application to red blood cells is currently under investigation.