Light Photo Treatment at 405 nm Can Effectively Kill Leishmania Parasites

Cutaneous leishmaniasis is a protozoan disease which is responsible for significant morbidity in humans. Currently, there is no clinically approved vaccine to prevent infections, and, therefore, treatments to cure skin lesions are required. Ideally, a treatment that can be self-administered to affected areas is desirable. In this study, the effect of violet-blue light, of wavelength in the region of 405 nm, on the survival of Leishmania major and Leishmania mexicana was determined using in vitro and in vivo models. Light treatment caused significant killing of both promastigotes and intracellular amastigotes (p < 0.001) of both species in vitro, and L. mexicana intracellular amastigotes were more resistant to light treatment than L. major intracellular amastigotes. Treatment with violet-blue light at a dose of 45 J/cm² (0.15 W/cm² for 5 min) per day on days 3-7 post-infection in an in vivo footpad model caused a significant reduction in L. major parasite burdens on day 5 post-infection (p < 0.05) in one of two experiments, though by day 10 post-infection, parasite numbers had recovered to those of controls. The results of this study clearly demonstrate that violet-blue light can kill both L. major and L. mexicana parasites, but application to infected cutaneous tissues requires refinement.