Clinical Outcomes of Submicroscopic Infections and Correlates of Protection of VAR2CSA Antibodies in a Longitudinal Study of Pregnant Women in Colombia

Abstract

Malaria in pregnancy can cause serious adverse outcomes for the mother and the fetus. However, little is known about the effects of submicroscopic infections (SMIs) in pregnancy, particularly in areas where Plasmodium falciparum and Plasmodium vivax cocirculate. A cohort of 187 pregnant women living in Puerto Libertador in northwest Colombia was followed longitudinally from recruitment to delivery. Malaria was diagnosed by microscopy, reverse transcription-quantitative PCR (RT-qPCR), and placental histopathology. Gestational age, hemoglobin concentration, VAR2CSA-specific IgG levels, and adhesion-blocking antibodies were measured during pregnancy. Statistical analyses were performed to evaluate the impact of SMIs on birth weight and other delivery outcomes. Twenty-five percent of women (45/180) were positive for SMIs during pregnancy. Forty-seven percent of infections (21/45) were caused by P. falciparum, 33% were caused by P. vivax, and 20% were caused by mixed Plasmodium spp. Mixed infections of P. falciparum and P. vivax were associated with lower gestational age at delivery (P = 0.0033), while other outcomes were normal. Over 60% of women had antibodies to VAR2CSA, and there was no difference in antibody levels between those with and without SMIs. The anti-adhesion function of these antibodies was associated with protection from SMI-related anemia at delivery (P = 0.0086). SMIs occur frequently during pregnancy, and while mixed infections of both P. falciparum and P. vivax were not associated with a decrease in birth weight, they were associated with significant risk of preterm birth. We propose that the lack of adverse delivery outcomes is due to functional VAR2CSA antibodies that can protect pregnant women from SMI-related anemia.

Keywords: Colombia; Plasmodium falciparum; Plasmodium vivax; VAR2CSA; anemia; antibodies; malaria; pregnancy; submicroscopic.

FIG 1

Flow chart of pregnant women recruited into the study.

FIG 2

Submicroscopic malaria infections during pregnancy are not generally associated with changes in outcomes at delivery. Infant birth weight (A), gestational age at delivery (B), Z-scores of babies to determine small-for-gestational-age (SGA) (C), and maternal hemoglobin (Hb) levels at delivery (D) are shown. Solid horizontal lines indicate the means for each group, error bars indicate the standard deviations, and dotted horizontal lines represent the thresholds for low birth weight (2,500 g), preterm birth (37 weeks), SGA (10th percentile), and anemia (11 g/dl). *, P = 0.0033 (Mann-Whitney test).

FIG 3

Anti-VAR2CSA antibody levels are independent of parity. (A) Anti-VAR2CSA antibody levels were measured by ELISA at inclusion and at delivery in sera from Colombian primigravid (PG) and multigravid (MG) women, and levels were compared to those of a Colombian malaria-unexposed control group. (B) Matched antibody levels measured at enrollment and at delivery in individual subjects. Horizontal lines indicate the means for each group, error bars indicate SDs, and dotted horizontal lines mark the cutoff for seropositivity (AU, 19.7). ns, not significant.

FIG 4

CSA adhesion-blocking antibodies are observed in sera from Colombian pregnant women infected with submicroscopic malaria. (A) Binding inhibition profile for pregnant women infected by Plasmodium spp. (n = 45). The horizontal line indicates the means of three replicate measurements, error bars indicate SDs, and the horizontal dotted line represents the cutoff for inhibition (39.1%). (B) Inhibitory activity of antibodies from primigravid and multigravid women at enrollment. The horizontal dotted line represents the cutoff for inhibition (39.1%). *, P = 0.049 (Mann-Whitney test).

FIG 5

CSA adhesion-blocking antibodies correlate with hemoglobin levels at delivery but not with other delivery outcomes in women with a submicroscopic infection. Graphs represent linear regression analysis of the association of inhibitory antibodies and birth weight (A), gestational age at delivery (B), Z-scores of SGA (C), and maternal hemoglobin levels at delivery (D). Horizontal dotted lines indicate thresholds for low birth weight (2,500 g), preterm birth (37 weeks), SGA (10th percentile), and anemia (11 g/dl). The P value was determined by linear regression.