Introduction: Pregnant women are susceptible to malaria. The impact of malaria prevention tools, such as insecticide-treated nets (ITN) and intermittent preventive treatment during pregnancy (IPTp), on acquisition and maintenance of malarial antibody is not well understood.
Methods: 582 pregnant Papua New Guinean women were recruited at first antenatal visit (ANC) were randomised to receive one course of sulphadoxine-pyrimethamine (SP) with chloroquine (CQ) or three courses of SP with azithromycin (AZ) and followed to delivery. All women were given ITN. Matching plasma samples collected at ANC and delivery were tested for IgG levels to schizont extract and merozoite antigens (MSP2, MSP3, RH2A9) by ELISA. Opsonising IgG levels to non-pregnancy specific and pregnancy-specific infected erythrocytes (IEs) were measured by phagocytosis assay.
Results: At delivery, IgG levels measured by ELISA and levels of opsonising antibodies to IEs did not differ by treatment arm. In the SP and CQ arm, women with malaria infection had higher IgG levels to schizont extract p=0.0074 and merozoite antigens (all p<0.05), whereas levels of opsonising IgG to IEs did not vary with infection. In the SP and AZ arm, antibody responses did not vary with infection. Antibody levels measured by ELISA were higher in women receiving SP and CQ who had chronic or past placental infection, while women receiving SP and AZ who had past placental infection had higher antibody levels, all p<0.01.
Conclusion: The use of IPTp and ITN during pregnancy did not affect malarial antibody acquisition. An effect of infection on antibody levels was not observed in women receiving frequent IPTp due to a combination of lower infection prevalence and probable shorter infection duration. Opsonising IgG appears to be more stable during pregnancy. Effective prevention of malaria in the later part of pregnancy does not result in declining immunity, but effects on successive pregnancies remain unknown.