Abstract
Postpartum women may have an altered susceptibility to Plasmodium falciparum and Plasmodium vivax. The relationship between naturally acquired malarial immunity and susceptibility to malaria postpartum is yet to be determined. IgG levels were measured against P. falciparum and P. vivax antigens from delivery in 201 postpartum and 201 nonpregnant controls over 12 weeks. Associations between time-varying antibody levels and time to first microscopically confirmed species-specific infection were determined by Cox regression. Associations between antibody levels and prospective risk of Plasmodium infection were similar in postpartum and control women. A 2-fold increase in P. falciparum antibody levels was associated with increased prospective risk of P. falciparum infection (hazard ratio [HR] range = 1.37–1.94). Antibody levels against most P. vivax antigens displayed no association with prospective risk of P. vivax infection (HR range = 1.02–1.05) with the exception of PvMSP119 antibodies that were weakly associated with prospective risk of P. vivax infection (HR = 1.14 (95% confidence interval = 1.02, 1.28) per 2-fold increase in levels). Associations between antibody levels and prospective risk of infection attenuated when adjusted for documented retrospective exposure. Serology may be a useful tool to predict and monitor women at increased risk of P. falciparum infection postpartum, particularly in the absence of a detailed history of retrospective infections.
Highlights
Pregnant women are at an increased risk of both Plasmodium falciparum and Plasmodium vivax infections compared with their nonpregnant counterparts.[1]
Studies undertaken in Senegal and Gabon reported that postpartum women were at an increased prospective risk of P. falciparum infection and clinical falciparum malaria relative to nonpregnant controls.[5,6]
In the first study investigating humoral immunity and prospective risk of P. falciparum and P. vivax infection postpartum, all P. falciparum antibodies investigated showed a positive association with prospective risk of P. falciparum infection, and there was no statistical evidence that this association differed for postpartum and control women
Summary
Pregnant women are at an increased risk of both Plasmodium falciparum and Plasmodium vivax infections compared with their nonpregnant counterparts.[1]. There is emerging evidence for an altered susceptibility to P. falciparum and P. vivax during the postpartum period.[8] Studies undertaken in Senegal and Gabon reported that postpartum women were at an increased prospective risk of P. falciparum infection (relative risk = 1.8 and 2.7, respectively) and clinical falciparum malaria (relative risk = 4.1 and 9.8, respectively) relative to nonpregnant controls.[5,6] Only one study, conducted on the Thailand– Myanmar border, has compared the prospective risk of both P. falciparum and P. vivax infection in postpartum and nonpregnant women and found that postpartum women experienced significantly less P. falciparum infections and significantly more P. vivax infections than nonpregnant controls (hazard ratio [HR] = 0.39, 95% confidence interval [CI] = 0.21, 0.72 and HR = 1.34, 95% CI: 1.05, 1.72, respectively).[7] Despite these epidemiological observations, there have been few immunological investigations on the association of acquired immune responses and risk of infection during the postpartum period.[1] We previously demonstrated. The present study sought to investigate the relationship between antibodies specific for P. falciparum and P. vivax antigens and prospective risk of microscopically confirmed species-specific infection in these postpartum and control (nonpregnant and nonpostpartum) women.[7]
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