Psoralen photochemical inactivation of Orientia tsutsugamushi in platelet concentrates

BACKGROUND: The risk of transfusion transmission of disease has been reduce d by the combination of predonation questions and improved transfusion-tran smitted disease assays, but the risk is still present. This study was condu cted to determine if psoralen photochemistry could inactivate an obligate i ntracellular bacterium, with documented potential for transfusion, in PCs t o further improve safety. STUDY DESIGN AND METHODS: PCs were inoculated with MNCs infected with Orien tia tsutsugamushi. The concentrates were treated with amounts ranging from 0.86 to 138 mu mol per L of 4'-(aminomethyl)-4,5',8-trimethylpsoralen hydro chloride (AMT) combined with a constant long-wave UVA light (320-400 nm) ex posure of 5 J per cm(2). The effects of photochemical treatment were analyz ed by using a mouse infectivity assay along with in vitro testing by PCR, i ndirect fluorescence antibody, direct fluorescence antibody, and Giemsa sta ining. RESULTS: AMT, at 0.86 mu mol per L or more, combined with UVA light of 5 J per cm2, inactivated O. tsutsugamushi that contaminated PCs. The PCs that d id not receive the combined treatment caused infection. CONCLUSIONS: The psoralen AMT, in conjunction with UVA light exposure, effe ctively abolished the infectivity of PCs deliberately contaminated with the scrub typhus organism O. tsutsugamushi, as tested in a mouse infectivity a ssay.