Survival of Plasmodium falciparum in human blood during refrigeration

BACKGROUND: Transfusion-transmitted malaria remains a serious concern for blood safety. Viable Plasmodium parasites must be present in human blood to transmit malaria, but their survival in blood over time stored under refrigeration has never been carefully investigated. STUDY DESIGN AND METHODS: We spiked leukoreduced normal human blood with Plasmodium falciparum (3D7 strain) asexual ring-stage parasites and stored it at 4 degrees C for 28 days, taking samples at different days intervals. We evaluated the samples for parasitemia by blood film microscopy and by culturing red blood cells (RBCs) to allow further development of parasites. RESULTS: We observed a significant reduction in parasitemia (0.5% vs. 0.12%) after only 1 day in storage at 4 degrees C. Thereafter, reduction in parasitemia was relatively gradual. Microscopically detectable parasites were present even after 28 days of storage. However, after storing for more than 14 days at 4 degrees C, parasites no longer replicated when cultured in vitro. CONCLUSION: Although the storage of asexual blood-stage P. falciparum parasites at 4 degrees C is detrimental to their survival (a 7.1-fold reduction in parasitemia after 14 days in storage), parasites remained microscopically detectable for 28 days, the end time point of our study. Further in vitro and in vivo studies will be needed to confirm loss of viability of P. falciparum after 14 days in storage, but our initial efforts repeatedly failed to show maturation and development of the parasites in cultured RBCs after that time.