Leishmania inactivation in human pheresis platelets by a psoralen (amotosalen HCl) and long-wavelength ultraviolet irradiation

BACKGROUND: Leishmania spp. are protozoans that cause skin and visceral diseases. Leishmania are obligate intracellular parasites of mononuclear phagocytes and have been documented to be transmitted by blood transfusion. STUDY DESIGN AND METHODS: This study examines whether Leishmania can be inactivated in human platelet (PLT) concentrates by a photochemical treatment process that is applicable to blood bank use. Human PLT concentrates were contaminated with Leishmania mexicana metacyclic promastigotes or mouse-derived Leishmania major amastigotes and were exposed to long-wavelength ultraviolet (UV) A light (320-400 nm) plus the psoralen amotosalen HCl. RESULTS: Neither treatment with amotosalen nor UVA alone had an effect on Leishmania viability; however, treatment with 150 mu mol per L amotosalen plus 3 J per cm(2) UVA inactivated both metacyclic promastigotes and amastigotes to undetectable levels, more than a 10,000-fold reduction in viability. CONCLUSIONS: This study demonstrates the effectiveness of photochemical treatment to inactivate Leishmania in PLT concentrates intended for transfusion. Both metacylic promastigotes, which represent the infectious form from the sand fly vector, and amastigotes, which represent the form that grows in mononuclear phagocytes, were extremely susceptible to photochemical inactivation by this process. Thus, the photochemical treatment of PLT concentrates inactivates both forms of Leishmania that would be expected to circulate in blood products collected from infected donors.