Malaria antibody persistence correlates with duration of exposure.

ABSTRACT

BACKGROUND AND OBJECTIVES: In Australia, the risk of transfusion-transmitted malaria is managed through the identification of 'at-risk' donors, antibody screening enzyme-linked immunoassay (EIA) and, if reactive, exclusion from fresh blood component manufacture. Donor management depends on the duration of exposure in malarious regions (>6 months 'Resident', <6 months 'Visitor') or a history of malaria diagnosis. We analysed antibody testing and demographic data to investigate antibody persistence dynamics. To assess the yield from retesting 3 years after an initial EIA reactive result, we estimated the proportion of donors who would become non-reactive over this period. MATERIALS AND METHODS: Test results and demographic data from donors who were malaria EIA reactive were analysed. Time since possible exposure was estimated and antibody survival modelled. RESULTS: Among seroreverters, the time since last possible exposure was significantly shorter in 'Visitors' than in 'Residents'. The antibody survival modelling predicted 20% of previously EIA reactive 'Visitors', but only 2% of 'Residents' would become non-reactive within 3 years of their first reactive EIA. CONCLUSION: Antibody persistence in donors correlates with exposure category, with semi-immune 'Residents' maintaining detectable antibodies significantly longer than non-immune 'Visitors'.