title: Malaria antibody persistence correlates with duration of exposure.
abstract: OBJECTIVE
  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.
  
  
  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.
  
  
  CONCLUSIONS
  Antibody persistence in donors correlates with exposure category, with semi-immune 'Residents' maintaining detectable antibodies significantly longer than non-immune 'Visitors'.
authors.affiliation: Research and Development, Australian Red Cross Blood Service, Brisbane, Qld, Australia. hfaddy@redcrossblood.org.au
authors.forename: H M
authors.initials: HM
authors.lastname: Faddy
authors.forename: C R
authors.initials: CR
authors.lastname: Seed
authors.forename: M J
authors.initials: MJ
authors.lastname: Faddy
authors.forename: R L
authors.initials: RL
authors.lastname: Flower
authors.forename: R J
authors.initials: RJ
authors.lastname: Harley
mesh_terms: D000913:Antibodies, Protozoan / Q000097:blood*; D000918:Antibody Specificity; D001782:Blood Donors; D001803:Blood Transfusion / Q000379:methods*; D046148:Donor Selection / Q000379:methods*; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D008288:Malaria / Q000097:blood* / Q000175:diagnosis / Q000276:immunology*; D008297:Male; D010961:Plasmodium / Q000276:immunology; D013997:Time Factors
chemical_list: D000913:Antibodies, Protozoan