Viability of Plasmodium falciparum parasites in human plasma under different storage conditions

Background and objectives: Malaria risk deferral policies are important for mitigating the risk of transfusion-transmitted malaria and apply to all transfusable components, including plasma. While donors of plasma components are deferred for malaria risk in the United States, the viability of intraerythrocytic Plasmodium falciparum parasites present in human plasma components stored under different temperatures and durations has not been previously reported.

Materials and methods: We spiked human plasma with a low level of ring-stage P. falciparum-infected red blood cells and then determined their viability in cultures after storage at room temperature (22°C), refrigeration (4°C) and frozen conditions at -20 and -80°C.

Results: P. falciparum parasites spiked in human plasma remained viable after storage at 22°C for a maximum of 7 days. When stored at 4°C, parasites were viable after 1 and 3 days of storage and only for 1 day after storage at -20°C. Storage at -80°C had a cryopreserving effect and parasites remained viable for up to 176 days, the longest period tested.

Conclusion: P. falciparum parasites can survive for short durations in human plasma when stored at room temperature, or in refrigerated or frozen conditions at -20°C. However, when stored at -80°C, viable parasites were detected for up to 176 days, the maximum duration for which viability was assessed. In summary, Plasmodium parasites can survive in human plasma under different storage conditions and pose a risk of transfusion-transmitted infection.