Dyes, flies, and sunny skies: photodynamic therapy and neglected tropical diseases

Photodynamic therapy, in its various applications, represents the focused combination of electromagnetic radiation, a chemical (usually a dye) capable of its absorption and conversion, and oxygen to provide cytotoxicity (cell killing). The effect has been known for over a century, and there is considerable clinical use in terms of its application to various cancers. However, the antimicrobial properties of the technology, which are considerable, have received only a lukewarm reception by healthcare providers, and the possibilities for tropical disease therapy are mainly unexplored. This is particularly vexatious given both the inexpensive nature of the photosensitisers and light sources available and the lack of conventional forward progress in widespread diseases such as leishmaniasis, trypanosomiasis, and tuberculosis in the Developing World. The following review therefore covers the use, or potential use, of the photodynamic approach in this area, mainly with reference to tropical diseases having current ‘neglected’ status according to the World Health Organisation.