Michal Fried

Maternal antibodies block malaria.

Women are at increased risk from malaria during pregnancy, and, for unknown reasons, this risk is greatest during the first pregnancy. Plasmodium falciparum, the most virulent of the four malaria parasites of humans, adheres to a molecule called chondroitin sulphate A (CSA) on the surface of syncytiotrophoblasts (cells lining the intervillous space) and sequesters in the human placenta. Here we show that anti-adhesion antibodies, which limit the accumulation of parasites in the placenta, appear in pregnant women from Africa and Asia who have been pregnant on previous occasions (multigravidas), but not in those who are pregnant for the first time (primigravidas). Anti-adhesion antibodies against CSA-binding parasites are strain-independent and are associated with greatly reduced prevalence and density of infection. We conclude that malaria susceptibility in primigravidas is related to the lack of these anti-adhesion antibodies, and that an anti-adhesion vaccine for maternal malaria may be globally effective.

Antibodies That Inhibit Plasmodium falciparum Adhesion to Chondroitin Sulfate A Are Associated with Increased Birth Weight and the Gestational Age of Newborns

ABSTRACT Antibodies that inhibit Plasmodium falciparum adhesion to the placental receptor chondroitin sulfate A are associated with a reduced risk of placental malaria, but whether these antibodies lead to improved pregnancy outcomes is unknown. We measured antiadhesion antibody levels in parturient women in western Kenya, where malaria transmission is intense. Secundigravid women with antiadhesion activity in their plasma delivered babies that were on average 398 g heavier (P = 0.019) and 2 weeks more mature (P = 0.002) than babies delivered to secundigravidas without antiadhesion activity. Our findings support the development of antiadhesion vaccines to prevent poor fetal outcomes due to pregnancy malaria.

Maternal Malaria and Gravidity Interact to Modify Infant Susceptibility to Malaria

Background In endemic areas, placental malaria due to Plasmodium falciparum is most frequent and severe in first-time mothers, and increases the risk of infant mortality in their offspring. Placental malaria may increase the susceptibility of infants to malaria parasitemia, but evidence for this effect is inconclusive. Methods and Findings During 2002–2004, we monitored parasitemia in 453 infants, including 69 who were born to mothers with placental malaria, in a region of northeastern Tanzania where malaria transmission is intense. We used a Cox proportional hazards model to evaluate the time from birth to first parasitemia, and a generalized estimating equations logistic regression model to evaluate risk of any parasitemia throughout the first year of life. Compared with infants whose mothers did not have placental malaria at delivery (“PM-negative”), offspring of mothers with placental malaria at delivery (“PM-positive”) were 41% more likely to experience their first parasitemia at a younger age (adjusted hazard ratio [AHR] = 1.41, 95% confidence interval [CI] 1.01–1.99). The odds of parasitemia throughout infancy were strongly modified by the interaction between placental malaria and gravidity (p for interaction = 0.008, Type 3 likelihood ratio test). Offspring of PM-negative primigravidae had lower odds of parasitemia during infancy (adjusted odds ratio [AOR] = 0.67, 95% CI 0.50–0.91) than offspring of PM-negative multigravidae, and offspring of PM-positive primigravidae had the lowest odds (AOR = 0.21, 95% CI 0.09–0.47). In contrast, offspring of PM-positive multigravidae had significantly higher odds of parasitemia (AOR = 1.59, 95% CI 1.16–2.17). Conclusion Although parasitemia is more frequent in primigravid than multigravid women, the converse is true in their offspring, especially in offspring of PM-positive women. While placental malaria is known to increase mortality risk for first-born infants, it surprisingly reduced their risk of parasitemia in this study. Placental malaria of multigravidae, on the other hand, is a strong risk factor for parasitemia during infancy, and therefore preventive antimalarial chemotherapy administered to multigravid women close to term may reduce the frequency of parasitemia in their offspring.

Competitive facilitation of drug-resistant Plasmodium falciparum malaria parasites in pregnant women who receive preventive treatment.

Intermittent preventive treatment in pregnancy (IPTp) is used to prevent Plasmodium falciparum malaria. However, parasites resistant to the IPTp drug sulfadoxine-pyrimethamine (SP) have emerged worldwide, and infections with mixed resistant and susceptible parasites are exacerbated by pyrimethamine in mice. In a prospective delivery cohort in Muheza, Tanzania, we examined the effects of SP IPTp on parasite resistance alleles, parasite diversity, level of parasitemia, and inflammation in the placenta. IPTp use was associated with an increased fraction of parasites carrying the resistance allele at DHPS codon 581, an increase in the level of parasitemia, and more intense placental inflammation. The lowest mean level of parasite diversity and highest mean level of parasitemia occurred in women after recent IPTp use. These findings support a model of parasite release and facilitation, whereby the most highly resistant parasites out-compete less fit parasite populations and overgrow under drug pressure. Use of partially effective anti-malarial agents for IPTp may exacerbate malaria infections in the setting of widespread drug resistance.

Intermittent Treatment to Prevent Pregnancy Malaria Does Not Confer Benefit in an Area of Widespread Drug Resistance

BACKGROUND Millions of African women receive sulfadoxine-pyrimethamine (SP) as intermittent preventive treatment during pregnancy (IPTp) to avoid poor outcomes that result from malaria. However, parasites resistant to SP are widespread in parts of Africa, and IPTp may perversely exacerbate placental infections that contain SP-resistant parasites. METHODS The study used a cross-sectional design. We determined IPTp use in a delivery cohort of 880 pregnant women in Muheza, Tanzania, by report and by plasma sulfa measurements, and we examined its effects on maternal and fetal delivery outcomes. RESULTS In the overall cohort, IPTp was not associated with decreased odds of placental malaria or with increased mean maternal hemoglobin or mean birth weight. Unexpectedly, IPTp was associated with decreased cord hemoglobin level and increased risk of fetal anemia, which may be related to in utero SP exposure. CONCLUSIONS IPTp does not improve overall pregnancy outcomes in Muheza, Tanzania, where SP-resistant parasites predominate and may increase the odds of fetal anemia. As parasite resistance increases in a community, the overall effect of IPTp may transition from net benefit to neutral or net harm.

Iron Deficiency Protects Against Severe Plasmodium falciparum Malaria and Death in Young Children

BACKGROUND Iron supplementation may increase malaria morbidity and mortality, but the effect of naturally occurring variation in iron status on malaria risk is not well studied. METHODS A total of 785 Tanzanian children living in an area of intense malaria transmission were enrolled at birth, and intensively monitored for parasitemia and illness including malaria for up to 3 years, with an average of 47 blood smears. We assayed plasma samples collected at routine healthy-child visits, and evaluated the impact of iron deficiency (ID) on future malaria outcomes and mortality. RESULTS ID at routine, well-child visits significantly decreased the odds of subsequent parasitemia (23% decrease, P < .001) and subsequent severe malaria (38% decrease, P = .04). ID was also associated with 60% lower all-cause mortality (P = .04) and 66% lower malaria-associated mortality (P = .11). When sick visits as well as routine healthy-child visits are included in analyses (average of 3 iron status assays/child), ID reduced the prevalence of parasitemia (6.6-fold), hyperparasitemia (24.0-fold), and severe malaria (4.0-fold) at the time of sample collection (all P < .001). CONCLUSIONS Malaria risk is influenced by physiologic iron status, and therefore iron supplementation may have adverse effects even among children with ID. Future interventional studies should assess whether treatment for ID coupled with effective malaria control can mitigate the risks of iron supplementation for children in areas of malaria transmission.

Maternal malaria and parasite adhesion

Abstract Malaria during pregnancy continues to be a major health problem in endemic countries, with clinical consequences, including death, for both mother and child. Just as cerebral malaria results from parasite sequestration in the brain, maternal malaria results from parasite sequestration in the placenta, and a distinct subpopulation of parasites which bind chondroitin sulfate A but not CD36 causes the syndrome. Women have little or no immunological experience with this parasite prior to first pregnancy, making primigravid women particularly vulnerable to infection. Parasites adhere to the surface of trophoblastic villi, eliciting the accumulation of inflammatory leukocytes in the intervillous space, and the necrosis of adjacent placental tissue. Maternal malaria results in poor pregnancy outcomes, although the responsible mechanisms have not been defined. In holoendemic areas both placental infection and poor outcome decrease in frequency with successive pregnancies; protection may result from control of parasite adhesion, suggesting an attractive target for new therapies.

Hypertension and Maternal-Fetal Conflict during Placental Malaria

Background Malaria and hypertension are major causes of maternal mortality in tropical countries, especially during first pregnancies, but evidence for a relationship between these syndromes is contradictory. Methods and Findings In a cross-sectional survey of Tanzanian parturients, the rate of hypertension was similar in placental malaria (PM)-positive (11/85 = 13%) and PM-negative (73/602 = 12%) individuals. However, we found that PM was associated with hypertension in first-time mothers aged 18–20 y but not other mothers. Hypertension was also associated with histologic features of chronic malaria, which is common in first-time mothers. Levels of soluble vascular endothelial growth factor receptor 1 (sVEGFR1), a preeclampsia biomarker, were elevated in first-time mothers with either PM, hypertension, or both, but levels were not elevated in other mothers with these conditions. In first-time mothers with PM, the inflammatory mediator vascular endothelial growth factor (VEGF) was localized to maternal macrophages in the placenta, while sVEGFR1, its soluble inhibitor, was localized to the fetal trophoblast. Conclusions The data suggest that maternal–fetal conflict involving the VEGF pathway occurs during PM, and that sVEGFR1 may be involved in the relationship between chronic PM and hypertension in first-time mothers. Because placental inflammation causes poor fetal outcomes, we hypothesize that fetal mechanisms that promote sVEGFR1 expression may be under selective pressure during first pregnancies in malaria-endemic areas.

α-Tubulin II is a male-specific protein in Plasmodium falciparum

The tubulin gene family in Plasmodium falciparum consists of one beta-tubulin and two alpha-tubulin genes (alpha-tubulin I and II). We present here data indicating that alpha-tubulin II is expressed only in male sexual stage parasites. An IgM mAb, 5E7, specifically reacted with stage III (day 4-5) through mature (day 10-11) male gametocytes and with emerging, exflagellating, or freely moving male gametes. No reactivity was detected in female gametocytes, female gametes, sporozoites, or asexual parasites. mAb 5E7 also specifically recognized male gametes of the avian parasite, Plasmodium gallinaceum, and immunoblotted a 50 kDa protein in extracts of male gametes from both species. This 50 kDa antigen was localized by immunoelectron microscopy to axonemes of male gametes in a pattern similar to that obtained with anti-alpha- and anti-beta-tubulin antibodies. Furthermore, mAb 5E7 specifically reacted with recombinant alpha-tubulin II protein obtained using the PCR-amplified alpha-tubulin II gene from a gametocyte-specific cDNA library. The sex-specific expression of alpha-tubulin II and its localization to axoneme of the male parasite suggest a role for this molecule in the morphologic changes that occur during exflagellation and in the motility of the parasite. alpha-Tubulin II and mAb 5E7 may prove useful tools in studies of the biology of sexual stage differentiation and development in P. falciparum in addition to the general understanding of post-translational modifications of tubulin isoforms.

Decreased Susceptibility to Plasmodium falciparum Infection in Pregnant Women with Iron Deficiency

Iron plus folate supplementation increases mortality and morbidity among children in areas of malaria endemicity in Africa, but the effects of supplementation on pregnant women in malaria-endemic areas remain unclear. In northeastern Tanzania, where malaria and iron deficiency are common, we found that placental malaria was less prevalent (8.5% vs. 47.3% of women; P< .0001) and less severe (median parasite density, 4.2% vs. 6.3% of placental red blood cells; P< .04) among women with iron deficiency than among women with sufficient iron stores, especially during the first pregnancy. Multivariate analysis revealed that iron deficiency (P< .0001) and multigravidity (P< .002) significantly decreased the risk of placental malaria. Interventional trials of iron and folate supplementation during pregnancy in malaria-endemic regions in Africa are urgently needed to ascertain the benefits and risks of this intervention.