Malaria in pregnancy: pathogenesis and immunity

Maternal natural killer cells at the intersection between reproduction and mucosal immunity

Many maternal immune cells populate the decidua, which is the mucosal lining of the uterus transformed during pregnancy. Here, abundant natural killer (NK) cells and macrophages help the uterine vasculature adapt to fetal demands for gas and nutrients, thereby supporting fetal growth. Fetal trophoblast cells budding off the forming placenta and invading deep into maternal tissues come into contact with these and other immune cells. Besides their homeostatic functions, decidual NK cells can respond to pathogens during infection, but in doing so, they may become conflicted between destroying the invader and sustaining fetoplacental growth. We review how maternal NK cells balance their double duty both in the local microenvironment of the uterus and systemically, during toxoplasmosis, influenza, cytomegalovirus, malaria and other infections that threat pregnancy. We also discuss recent developments in the understanding of NK-cell responses to SARS-Cov-2 infection and the possible dangers of COVID-19 during pregnancy.

Robust innate immune responses at the placenta during early gestation may limit in utero HIV transmission

In 2019, >90% of new HIV infections in infants globally occurred vertically. Studies suggest intrauterine transmission most often occurs in the third trimester; however, there are no mechanistic studies to support these observations. We therefore obtained early/mid-gestation and term placentae from 20 HIV/Hepatitis B/CMV negative women. Isolated primary placental macrophages (Hofbauer cells [HCs]) were exposed to HIV-1_BaL and/or interferon (IFN)-α, IFN-β, IFN-λ1, and RIG-I-like receptor (RLR) agonists. qRT-PCR, FACS, ELISA, Luminex, and Western blot analyses determined expression of activation markers, co-receptors, viral antigen, cytokines, antiviral genes, and host proteins. Early gestation HCs express higher levels of CCR5 and exhibit a more activated phenotype. Despite downregulation of CCR5, term HCs were more susceptible to HIV replication. Early gestation HCs displayed a more activated phenotype than term HCs and HIV exposure lead to the further up-regulation of T-cell co-stimulatory and MHC molecules. Limited HIV replication in early/mid gestation HCs was associated with increased secretion of anti-inflammatory cytokines, chemokines, and a more robust antiviral immune response. In contrast, term HCs were more susceptible to HIV replication, associated with dampening of IFN-induced STAT1 and STAT2 protein activation. Treatment of early/mid gestation and term HCs, with type I IFNs or RLR agonists reduced HIV replication, underscoring the importance of IFN and RLR signaling in inducing an antiviral state. Viral recognition and antiviral immunity in early gestation HCs may prevent in utero HIV infection, whereas diminished antiviral responses at term can facilitate transmission. Defining mechanisms and specific timing of vertical transmission are critical for the development of specific vaccines and antiviral therapeutics to prevent new HIV infections in children globally.

Mother-to-child transmission is the main source of HIV infection in children globally. Studies suggest vertical transmission most often occurs late in the third trimester; however, there are no studies to support these observations. Our study shows that gestational age plays a significant role in the ability of placental macrophages to generate robust antiviral responses, which are necessary to prevent or reduce viral burden. Specifically, we show that viral recognition by RIG-I-like receptors and robust antiviral immune responses in placental cells during early gestation may prevent in utero HIV infection. We also demonstrate that term placental macrophages are limited in their antiviral capacity due to restricted type I IFN signaling. Understanding the mechanisms and timing of vertical transmission are important to understand for the development of specific vaccines and antiviral therapeutics to prevent new HIV infections in children globally.

TLR4-Endothelin Axis Controls Syncytiotrophoblast Motility and Confers Fetal Protection in Placental Malaria

Pregnancy-associated malaria is often associated with adverse pregnancy outcomes. Placental circulatory impairments are an intriguing and unsolved component of malaria pathophysiology. Here, we uncovered a Toll-like receptor 4 (TLR4)-TRIF-endothelin axis that controls trophoblast motility and is linked to fetal protection during Plasmodium infection. In a cohort of 401 pregnancies from northern Brazil, we found that infection during pregnancy reduced expression of endothelin receptor B in syncytiotrophoblasts, while endothelin expression was only affected during acute infection. We further show that quantitative expression of placental endothelin and endothelin receptor B proteins are differentially controlled by maternal and fetal TLR4 alleles. Using murine malaria models, we identified placental autonomous responses to malaria infection mediated by fetally encoded TLR4 that not only controlled placental endothelin gene expression but also correlated with fetal viability protection. In vitro assays showed that control of endothelin expression in fetal syncytiotrophoblasts exposed to Plasmodium-infected erythrocytes was dependent on TLR4 via the TRIF pathway but not MyD88 signaling. Time-lapse microscopy in syncytiotrophoblast primary cultures and cell invasion assays demonstrated that ablation of TLR4 or endothelin receptor blockade abrogates trophoblast collective motility and cell migration responses to infected erythrocytes. These results cohesively substantiate the hypothesis that fetal innate immune sensing, namely, the TRL4-TRIF pathway, exerts a fetal protective role during malaria infection by mediating syncytiotrophoblast vasoregulatory responses that counteract placental insufficiency.

Developing a multivariate prediction model of antibody features associated with protection of malaria-infected pregnant women from placental malaria

Background

Plasmodium falciparum causes placental malaria, which results in adverse outcomes for mother and child. P. falciparum-infected erythrocytes that express the parasite protein VAR2CSA on their surface can bind to placental chondroitin sulfate A. It has been hypothesized that naturally acquired antibodies towards VAR2CSA protect against placental infection, but it has proven difficult to identify robust antibody correlates of protection from disease. The objective of this study was to develop a prediction model using antibody features that could identify women protected from placental malaria.

Methods

We used a systems serology approach with elastic net-regularized logistic regression, partial least squares discriminant analysis, and a case-control study design to identify naturally acquired antibody features mid-pregnancy that were associated with protection from placental malaria at delivery in a cohort of 77 pregnant women from Madang, Papua New Guinea.

Results

The machine learning techniques selected 6 out of 169 measured antibody features towards VAR2CSA that could predict (with 86% accuracy) whether a woman would subsequently have active placental malaria infection at delivery. Selected features included previously described associations with inhibition of placental binding and/or opsonic phagocytosis of infected erythrocytes, and network analysis indicated that there are not one but multiple pathways to protection from placental malaria.

Conclusions

We have identified candidate antibody features that could accurately identify malaria-infected women as protected from placental infection. It is likely that there are multiple pathways to protection against placental malaria.

Funding

This study was supported by the National Health and Medical Research Council (Nos. APP1143946, GNT1145303, APP1092789, APP1140509, and APP1104975).

Malaria in Pregnancy: Considerations for Health Care Providers in Nonendemic Countries

Malaria is a common infection world-wide, which carries significant risk of morbidity and mortality. Health care providers in the United States may lack experience in recognizing and treating this disease. The pathophysiology of malaria differs during pregnancy, resulting in increased risk for serious morbidity and mortality for the woman and her fetus. Screening for risk factors, especially immigration from and travel to endemic countries, is critical. Symptoms of malaria can mimic influenza-type illnesses, causing delay in diagnosis. Consultation with an infectious disease specialist and hospitalization may be required for appropriate testing and treatment. Chemoprophylaxis and counseling regarding methods to reduce risk are important components of prevention. The US Centers for Disease Control and Prevention and the World Health Organization have established protocols for treatment and are helpful resources for clinicians. A team approach to care based on the woman's stage of illness and recovery, can involve midwives, physicians, specialists and others.

Effect of Plasmodium berghei infection on fetuses in pregnant BALB/c mice at two periods of pregnancy

Malaria is a disease caused by a protozoan of the genus Plasmodium in humans and vertebrates. It has a high morbidity and mortality rate, especially in pregnant women living in countries with high transmission rates. Murine models have been an excellent tool to evaluate the effects of malarial infection in the mother-fetus relationship. For this reason, we evaluated the effect of malarial infection on fetal development at the beginning and middle of the gestational period in BALB/c mice infected with Plasmodium berghei ANKA. Our results show that malarial infection at the beginning of pregnancy markedly affects the development of the fetus in size, weight, and development of its limbs so that the control of the pregnant mother is relevant at the beginning of gestation

Plasmodium falciparum VAR2CSA-Specific IgG Subclass Responses Reflect Protection Against Low Birth Weight and Pregnancy-Associated Malaria

Sequestration of Plasmodium falciparum-infected erythrocytes expressing the VAR2CSA antigen in the placenta results in poor pregnancy outcomes, including low birth weight and maternal anemia. Antigen-specific antibody-mediated immunity is acquired during successive pregnancies. Thus, evaluating VAR2CSA-specific IgG profiles among pregnant women will increase knowledge on the immunological mechanisms associated with protection, and help in the development of VAR2CSA-based placental malaria vaccines. Using the PAMVAC candidate vaccine antigen, we assessed anti-VAR2CSA IgG subclass responses of a cohort of pregnant Beninese, and analyzed their relationships with pregnancy outcomes. Cytophilic IgG1 and IgG3 responses were the most frequent, with prevalences ranging from 28% (IgG3) up to 50% (IgG1). Elevated levels of VAR2CSA-specific total IgG and cytophilic IgG3 during pregnancy were consistently associated with higher birth weights, whilst high levels of IgG4 were associated with a reduced risk of placental infections. This suggests that protective anti-VAR2CSA IgG responses are coordinated between both cytophilic and non-cytophilic antibodies.

Acute Phase Responses Vary Between Children of HbAS and HbAA Genotypes During Plasmodium falciparum Infection

Purpose

Haemoglobin genotype S is known to offer protection against Plasmodium falciparum infections but the mechanism underlying this protection is not completely understood. Associated changes in acute phase proteins (APPs) during Plasmodium falciparum infections between Haemoglobin AA (HbAA) and Haemoglobin AS (HbAS) individuals also remain unclear. This study aimed to evaluate changes in three APPs and full blood count (FBC) indices of HbAA and HbAS children during Plasmodium falciparum infection.

Methods

Venous blood was collected from three hundred and twenty children (6 months to 15 years) in Begoro in Fanteakwa District of Ghana during a cross-sectional study. Full blood count (FBC) indices were measured and levels of previously investigated APPs in malaria patients; C-reactive protein (CRP), ferritin and transferrin measured using Enzyme-Linked Immunosorbent Assays.

Results

Among the HbAA and HbAS children, levels of CRP and ferritin were higher in malaria positive children as compared to those who did not have malaria. The mean CRP levels were significantly higher among HbAA children (p=0.2e-08) as compared to the HbAS children (p=0.43). Levels of transferrin reduced in both HbAA and HbAS children with malaria, but the difference was only significant among HbAA children (p=0.0038), as compared to the HbAS children. No significant differences were observed in ferritin levels between HbAA and HbAS children in both malaria negative (p=0.76) and positive (p=0.26) children. Of the full blood count indices measured, red blood cell count (p=0.044) and haemoglobin (Hb) levels (p=0.017) differed between HbAA and HbAS in those without malaria, with higher RBC counts and lower Hb levels found in HbAS children. In contrast, during malaria, lymphocyte and platelet counts were elevated, whilst granulocytes and Mean Cell Haematocrit counts were reduced among children of the HbAS genotypes.

Conclusion

Significant changes in APPs were found in HbAA children during malaria as compared to HbAS children, possibly due to differences in malaria-induced inflammation levels. This suggests that the HbAS genotype is associated with better control of P. falciparum infection-induced inflammatory response than HbAA genotype.

Relationships Between Measures of Malaria at Delivery and Adverse Birth Outcomes in a High-Transmission Area of Uganda

BACKGROUND

Clinical trials of interventions for preventing malaria in pregnancy often use measures of malaria at delivery as their primary outcome. Although the objective of these interventions is to improve birth outcomes, data on associations between different measures of malaria at delivery and adverse birth outcomes are limited.

METHODS

Data came from 637 Ugandan women enrolled in a randomized controlled trial of intermittent preventive treatment of malaria in pregnancy. Malaria at delivery was detected using peripheral and placental blood microscopy, placental blood loop-mediated isothermal amplification (LAMP), and placental histopathology. Multivariate analyses were used to estimate associations between measures of malaria at delivery and risks of low birth weight (LBW), small for gestational age (SGA), and preterm birth (PTB).

RESULTS

Detection of malaria parasites by microscopy or LAMP was not associated with adverse birth outcomes. Presence of malaria pigment detected by histopathology in ≥30% of high-powered fields was strongly associated with LBW (adjusted risk ratio [aRR] = 3.42, P = .02) and SGA (aRR = 4.24, P < .001) but not PTB (aRR = 0.88, P = .87).

CONCLUSIONS

A semiquantitative classification system based on histopathologically detected malaria pigment provided the best surrogate measure of adverse birth outcomes in a high-transmission setting and should be considered for use in malaria in pregnancy intervention studies.

The Development, Fine Specificity, and Importance of High-Avidity Antibodies to VAR2CSA in Pregnant Cameroonian Women Living in Yaoundé, an Urban City

Pregnant women infected with Plasmodium falciparum often produce antibodies (Abs) to VAR2CSA, a ligand that binds to placental chondroitin sulfate A causing placental malaria (PM). Antibodies to VAR2CSA are associated with improved pregnancy outcomes. Antibody avidity is a surrogate marker for the extent of maturation of the humoral immune response. Little is known about high avidity Abs to VAR2CSA for women living in urban African cities. Therefore, this study sought to determine: i) if high avidity Abs to full-length VAR2CSA (FV2) increase with gravidity in women in Yaoundé, Cameroon exposed to ~ 0.3-1.1 infectious mosquito bites per month, ii) if high avidity Abs to FV2 are directed against a specific region of VAR2CSA, and iii) if having high avidity Abs to FV2 improve pregnancy outcomes. Plasma samples collected at delivery from 695 women who had Abs to FV2 were evaluated. Ab levels and the Avidity Index (AI), defined as the percent Abs remaining bound to FV2 after incubation with 3M NH₄SCN, were determined. Similar Ab levels to FV2 were present in women of all gravidities (G1 through 6+; p=0.80), except significantly lower levels were detected in PM−negative (PM−) primigravidae (p <0.001). Median Ab avidities increased between gravidity 1 and 2 (p<0.001) and remained stable thereafter (G3-G6+: p=0.51). These results suggest that B cell clonal expansion began during the first pregnancy, with clonal selection primarily occurring during the second. However, the majority of women (84%) had AI <35, a level of high avidity Abs previously reported to be associated with improved pregnancy outcomes. When plasma from 107 Cameroonian women was tested against 8 different regions of FV2, high avidity Abs were predominately restricted to DBL5 with median AI of 50 compared to AI <25 for the other domains. The only significance influence of high avidity Abs on pregnancy outcome was that babies born to mothers with AI above the median were 104 g heavier than babies born to women with AI below the median (p=0.045). These results suggest that a vaccine that boosts maturation of the immune response to VAR2CSA may be beneficial for women residing in urban areas.

Activities of Andrographis paniculata (AS201-01) Tablet on Cox-2 and Prostaglandin Expression of Placental of Plasmodium berghei Infected Mice

Background:

Placental malaria has ability to upregulate prostaglandin synthesis by increasing cyclooxygenase-2 (Cox-2) enzyme activity. Cox-2 and prostaglandin have a role in causing uterine contraction and therefore can cause abortion or preterm labor. Tablet AS201-01 containing the ethyl acetate fraction of Andrographis paniculata was tested in vivo on pregnant mice infected with Plasmodium berghei. AS201-01 inhibited the growth of P. berghei, increased TGF-β expression, decreased TLR-4 expression and apoptosis index of placental tissue in P. berghei infected pregnant mice and thus prevented placental malaria complications. These effects were correlated with the decrease of Cox-2 and prostaglandin expression.

Methods:

Twenty-four pregnant mice (Balb/c) were divided into 4 groups (n=6). Mice were maintained at Animal Laboratory of Institute of Tropical Disease, Universitas Airlangga, Surabaya, Indonesia in 2016. G1 were uninfected pregnant mice, G2 untreated infected pregnant mice, G3 infected pregnant mice treated with AS201-01, and G4 infected pregnant mice treated with DHP tablet. All infection groups (G2-G4) were inoculated with 1x10⁶ of P. berghei parasite on day 9 of gestation and treated on day 11. All mice were terminated at day 15 of gestation, and placental tissue was collected. Cytokine expression of Cox-2 and prostaglandin were evaluated using immunohistochemistry.

Results:

G3 was found to have lower Cox-2 and prostaglandin expression compared to G4 and G2, but higher compared to G1. Cox-2 and prostaglandin expression was significantly different among groups (P<0.001).

Conclusion:

This study demonstrates the ability AS201-01 tablets have to decrease Cox-2 and prostaglandin expression on placental of P. berghei infected mice and therefore eliminates the adverse effects of placental malaria.

Antibody mediated activation of natural killer cells in malaria exposed pregnant women

Immune effector responses against Plasmodium falciparum include antibody-mediated activation of innate immune cells, which can induce Fc effector functions, including antibody-dependent cellular cytotoxicity, and the secretion of cytokines and chemokines. These effector functions are regulated by the composition of immunoglobulin G (IgG) Fc N-linked glycans. However, a role for antibody-mediated natural killer (NK) cells activation or Fc N-linked glycans in pregnant women with malaria has not yet been established. Herein, we studied the capacity of IgG antibodies from pregnant women, with placental malaria or non-placental malaria, to induce NK cell activation in response to placental malaria-associated antigens DBL2 and DBL3. Antibody-mediated NK cell activation was observed in pregnant women with malaria, but no differences were associated with susceptibility to placental malaria. Elevated anti-inflammatory glycosylation patterns of IgG antibodies were observed in pregnant women with or without malaria infection, which were not seen in healthy non-pregnant controls. This suggests that pregnancy-associated anti-inflammatory Fc N-linked glycans may dampen the antibody-mediated activation of NK cells in pregnant women with malaria infection. Overall, although anti-inflammatory glycans and antibody-dependent NK cell activation were detected in pregnant women with malaria, a definitive role for these antibody features in protecting against placental malaria remains to be proven.

High Prevalence of Molecular Markers of Plasmodium falciparum Resistance to Sulphadoxine-Pyrimethamine in Parts of Ghana: A Threat to ITPTp-SP?

Malaria in pregnancy is a huge public health problem as it is the cause of maternal anaemia, still birth, premature delivery, low birth weight among others. To tackle this problem, WHO recommended the administration, during pregnancy, of intermittent preventive treatment with sulphadoxine-pyrimethamine (IPTp-SP). The introduction of this policy is likely to create SP drug pressure which may lead to the emergence of parasite strains resistant to the drug. This study investigated the prevalence of the molecular markers of SP resistance as pointers to potential failure of IPTp-SP among pregnant women attending antenatal clinic, women at the point of baby delivery and out patients department (OPD) attendees. The study was conducted in health facilities located in parts of Ghana. Prevalence of mutations in dhfr and dhps genes of Plasmodium falciparum was determined using the method described by Duraisingh et al. The outcome of the study indicated the presence of high prevalence of strains of P.falciparum with the resistant alleles of the dhfr or dhps genes in the three categories of participants. There was a high prevalence of triple mutations (IRN) in the dhfr gene of P.falciparum isolates: 71.4% in peripheral blood of antenatal attendees; 74.1% in placenta cord blood of delivering mothers and 71.1% in OPD attendees. Quintuple mutations were only found in 2 (0.5%) isolates from OPD attendees. This observation might have occurred due to the increased use of SP for IPTp among others. There is the need for an interventional measure in order to protect pregnant women and their unborn children. Lay summaryWhen pregnant women get infected with the malaria parasites they are exposed to all manner of dangers including pre-term delivery, still birth, maternal anaemia and low birth weight. Taking sulphadoxine-pyrimethamine (SP) at predetermined periods during pregnancy, referred to as 'intermittent preventive treatment with SP' (IPTp-SP)' helps to curtail these problems. However, the frequent taking of these drugs is likely to create SP drug pressure which may lead to the emergence of parasite strains that are not readily killed by the drugs. In order to ascertain this phenomenon and advice stakeholders, this study determined the prevalence of certain 'materials' certified as markers of parasite resistance to SP. Alarmingly, more than 5% of all the category of women recruited to participate in this study were found to harbour the parasites that causes malaria. The outcome, also suggest the existence of high levels of strains of the malaria parasite, carrying the materials that make them to become resistant to SP. Policy makers must pay attention to these observations and institute measures to avoid escalation of the situation.

A longitudinal study of plasma BAFF levels in mothers and their infants in Uganda, and correlations with subsets of B cells

Malaria is a potentially life-threatening disease with approximately half of the world’s population at risk. Young children and pregnant women are hit hardest by the disease. B cells and antibodies are part of an adaptive immune response protecting individuals continuously exposed to the parasite. An infection with Plasmodium falciparum can cause dysregulation of B cell homeostasis, while antibodies are known to be key in controlling symptoms and parasitemia. BAFF is an instrumental cytokine for the development and maintenance of B cells. Pregnancy alters the immune status and renders previously clinically immune women at risk of severe malaria, potentially due to altered B cell responses associated with changes in BAFF levels. In this prospective study, we investigated the levels of BAFF in a malaria-endemic area in mothers and their infants from birth up to 9 months. We found that BAFF-levels are significantly higher in infants than in mothers. BAFF is highest in cord blood and then drops rapidly, but remains significantly higher in infants compared to mothers even at 9 months of age. We further correlated BAFF levels to P. falciparum-specific antibody levels and B cell frequencies and found a negative correlation between BAFF and both P. falciparum-specific and total proportions of IgG⁺ memory B cells, as well as CD27⁻ memory B cells, indicating that exposure to both malaria and other diseases affect the development of B-cell memory and that BAFF plays a part in this. In conclusion, we have provided new information on how natural immunity against malaria is formed.

Impact of placental malaria on maternal, placental and fetal cord responses and its role in pregnancy outcomes in women from Blue Nile State, Sudan

Background

The sequestration of Plasmodium falciparum infected cells in the placenta results in placental malaria (PM). It activates the mother's immune cells and induces secretion of inflammatory cytokines, which might influence pregnancy outcomes. This study aims to investigate the cytokines (levels IL-4, IL-6, IL-10, IL-17A, and INF γ) in maternal peripheral, placental, and umbilical cord blood in response to PM and the extent to which this may influence maternal haemoglobin levels and birth weight.

Methods

A total of 185 consenting Sudanese women from Blue Nile State were enrolled at delivery time in a cross-sectional study conducted between Jan 2012-Dec 2015. Malaria infection in the collected maternal peripheral, placental, umbilical cord samples was determined microscopically, and ELISA was used to measure the plasma levels IL-4, IL-6, IL-10, IL-17A, and INF γ in the collected positive and negative malaria samples.

Results

Elevated levels of IL-4 and IL-10 and reduced levels of IL-6 were detected in the malaria positive samples in comparison to the negative ones in the three types of the samples investigated. Maternal, IL-4 and IL-10 were significantly higher in the samples collected from the PM infected group compared to the non-infected control (P < 0.001). While the absence of PM was significantly associated with the IL-6 and maternal IFN-γ levels, maternal IL-17A, placental and umbilical cord IFN-γ levels showed no significant difference (P = 0.214, P = 0.065, P = 0.536, respectively) due to infection. Haemoglobin level and birth weight were increased in the group with high levels of IL-6 and IL-17A, but not in the group with IL-4 and IL-10 levels. While significantly negative correlation was found between IFN-γ levels and birth weight for all three types of samples, only maternal peripheral IFN-γ level was significantly positively correlated with maternal haemoglobin (r = 0.171, P = 0.020).

Conclusion

These results suggest that PM induces mother’s immune response and impairs her cytokine profile, which might alter maternal haemoglobin levels and the baby's birth weight.

The Role of Malaria Parasite Heat Shock Proteins in Protein Trafficking and Remodelling of Red Blood Cells

The genus Plasmodium comprises intracellular eukaryotic parasites that infect many vertebrate groups and cause deadly malaria disease in humans. The parasites employ a suite of heat shock proteins to help traffic other proteins to different compartments within their own cells and that of the host cells they parasitise. This review will cover the role of these chaperones in protein export and host cell modification in the asexual blood stage of the human parasite P. falciparum which is the most deadly and well-studied parasite species. We will examine the role chaperones play in the import of proteins into the secretory pathway from where they are escorted to the vacuole space surrounding the intraerythrocytic parasite. Here, other heat shock proteins unfold protein cargoes and extrude them into the red blood cell (RBC) cytosol from where additional chaperones of parasite and possibly host origin refold the cargo proteins and guide them to their final functional destinations within their RBC host cells. The secretory pathway also serves as a launch pad for proteins targeted to the non-photosynthetic apicoplast organelle of endosymbiotic origin, and the role of heat shock proteins in trafficking proteins here will be reviewed. Finally, the function of chaperones in protein trafficking into the mitochondrion, the remaining organelle of endosymbiotic origin, will be discussed.

Setting the stage: The initial immune response to blood-stage parasites

Individuals growing up in malaria endemic areas gradually develop protection against clinical malaria and passive transfer experiments in humans have demonstrated that this protection is mediated in part by protective antibodies. However, neither the target antigens, specific effector mechanisms, nor the role of continual parasite exposure have been elucidated, which complicates vaccine development. Progress has been made in defining the innate signaling pathways activated by parasite components, including DNA, RNA, hemozoin, and phospholipids, which initiate the immune response and will be the focus of this review. The challenge that remains within the field is to understand the role of these early responses in the development of protective adaptive responses that clear iRBC and block merozoite invasion so that optimal vaccines and therapeutics may be produced.

Cost-effectiveness of rapid diagnostic tests, compared to microscopic tests, for the diagnosis and treatment of gestational malaria in Colombia from an institutional perspective

BACKGROUND

Gestational malaria is associated with negative outcomes in maternal and gestational health; timely diagnosis is crucial to avoid complications. However, the limited infrastructure, equipment, test reagents, and trained staff make it difficult to use thick blood smear tests in rural areas, where rapid testing could be a viable alternative. The purpose of this study was to estimate the cost-effectiveness of rapid tests type III (Plasmodium falciparum/Plasmodium spp P.f/pan) versus microscopic tests for the diagnosis and treatment of gestational malaria in Colombia.

METHODS

Cost-effectiveness analyses of gestational malaria diagnosis from an institutional perspective using a decision tree. Standard costing was performed for the identification, measurement and assessment phases, with data from Colombian tariff manuals. The data was collected from Health Situation Analysis, SIVIGILA and meta-analysis. Average and incremental cost-effectiveness ratio were estimated. The uncertainty was assessed through probabilistic sensitivity analysis.

RESULTS

The cost of rapid diagnostic tests in 3,000 pregnant women with malaria was US$66,936 and 1,182 disability adjusted life years (DALYs) were estimated. The cost using thick blood smear tests was US$50,838 and 1,023 DALYs, for an incremental cost-effectiveness of US$ 101.2. The probabilistic sensitivity analysis of rapid diagnostic tests determined that they are highly cost-effective in 70% of the cases, even below the US$1,200 threshold; also, they showed an incremental net monetary benefit of $150,000 when payer's willingness is US$1,000.

CONCLUSION

The use of rapid diagnostic tests for timely diagnosis and treatment of gestational malaria is a highly cost-effective strategy in Colombia, with uncertainty analyses supporting the robustness of this conclusion and the increased net monetary benefit that the health system would obtain. This strategy may help in preventing the negative effects on maternal health and the neonate at a low cost.

Deleterious effects of malaria in pregnancy on the developing fetus: a review on prevention and treatment with antimalarial drugs

All malaria infections are harmful to both the pregnant mother and the developing fetus. One in ten maternal deaths in malaria endemic countries are estimated to result from Plasmodium falciparum infection. Malaria is associated with a 3-4 times increased risk of miscarriage and a substantially increased risk of stillbirth. Current treatment and prevention strategies reduce, but do not eliminate, malaria's damaging effects on pregnancy outcomes. Reviewing evidence generated from meta-analyses, systematic reviews, and observational data, the first paper in this Series aims to summarise the adverse effects of malaria in pregnancy on the fetus and how the current drug treatment and prevention strategies can alleviate these effects. Although evidence supports the safety and treatment efficacy of artemisinin-based combination therapies in the first trimester, these therapies have not been recommended by WHO for the treatment of malaria at this stage of pregnancy. Intermittent preventive treatment of malaria in pregnancy with sulfadoxine-pyrimethamine is contraindicated in the first trimester and provides imperfect chemoprevention because of inadequate dosing, poor (few and late) antenatal clinic attendance, increasing antimalarial drug resistance, and decreasing naturally acquired maternal immunity due to the decreased incidence of malaria. Alternative strategies to prevent malaria in pregnancy are needed. The prevention of all malaria infections by providing sustained exposure to effective concentrations of antimalarial drugs is key to reducing the adverse effects of malaria in pregnancy.

Generation of a malaria negative Ugandan birth weight standard for the diagnosis of small for gestational age

Objective

Placental malaria is a known risk factor for small for gestational age (SGA) neonates. However, currently utilized international and African birthweight standards have not controlled for placental malaria and/or lack obstetrical ultrasound dating. We developed a neonatal birthweight standard based on obstetrically dated pregnancies that excluded individuals with clinical malaria, asymptomatic parasitemia, and placental malaria infection. We hypothesized that current curves underestimate true ideal birthweight and the prevalence of SGA.

Study design

Participants were pooled from two double-blind randomized control trials of intermittent preventive therapy during pregnancy in Uganda. HIV-negative women without comorbidities were enrolled from 12–20 weeks gestation. Gestational age was confirmed by ultrasound dating. Women were followed through pregnancy and delivery for clinical malaria, asymptomatic parasitemia, and placental malaria. Women without malaria, asymptomatic parasitemia, or placental malaria formed the malaria negative cohort and generated the Ugandan birthweight standard. The Ugandan standard was then used to estimate the prevalence of SGA neonates in the malaria positive cohort. These findings were compared to international (Williams, World Health Organization (WHO), and INTERGROWTH-21st) and regional standards (Tanzanian and Malawi).

Results

926 women had complete delivery data; 393 (42.4%) met criteria for the malaria negative cohort and 533 (57.6%) were malaria positive. The Ugandan standard diagnosed SGA in 17.1% of malaria positive neonates; similar to the INTERGROWTH-21^st and Schmiegelow curves. The WHO curve diagnosed SGA in significantly more neonates (32.1%, p = <0.001), and the Malawi curve diagnosed SGA in significantly fewer neonates (8.3%, p <0.001).

Conclusion

Exclusion of women with subclinical placental malaria in malaria-endemic areas created birth weight norms at higher values and increased the detection of SGA. Birth weight standards that fail to account for endemic illness may underestimate the true growth potential of healthy neonates.

Placental Malaria

Purpose of Review

Placental malaria is the primary mechanism through which malaria in pregnancy causes adverse perinatal outcomes. This review summarizes recent work on the significance, pathogenesis, diagnosis, and prevention of placental malaria.

Recent Findings

Placental malaria, characterized by the accumulation of Plasmodium-infected red blood cells in the placental intervillous space, leads to adverse perinatal outcomes such as stillbirth, low birth weight, preterm birth, and small-for-gestational-age neonates. Placental inflammatory responses may be primary drivers of these complications. Associated factors contributing to adverse outcomes include maternal gravidity, timing of perinatal infection, and parasite burden.

Summary

Placental malaria is an important cause of adverse birth outcomes in endemic regions. The main strategy to combat this is intermittent preventative treatment in pregnancy; however, increasing drug resistance threatens the efficacy of this approach. There are studies dissecting the inflammatory response to placental malaria, alternative preventative treatments, and in developing a vaccine for placental malaria.

First-in-human, Randomized, Double-blind Clinical Trial of Differentially Adjuvanted PAMVAC, A Vaccine Candidate to Prevent Pregnancy-associated Malaria

BACKGROUND

Malaria in pregnancy has major impacts on mother and child health. To complement existing interventions, such as intermittent preventive treatment and use of impregnated bed nets, we developed a malaria vaccine candidate with the aim of reducing sequestration of asexual "blood-stage" parasites in the placenta, the major virulence mechanism.

METHODS

The vaccine candidate PAMVAC is based on a recombinant fragment of VAR2CSA, the Plasmodium falciparum protein responsible for binding to the placenta via chondroitin sulfate A (CSA). Healthy, adult malaria-naive volunteers were immunized with 3 intramuscular injections of 20 μg (n = 9) or 50 μg (n = 27) PAMVAC, adjuvanted with Alhydrogel or glucopyranosyl lipid adjuvant in stable emulsion (GLA-SE) or in a liposomal formulation with QS21 (GLA-LSQ). Allocation was random and double blind. The vaccine was given every 4 weeks. Volunteers were observed for 6 months following last immunization.

RESULTS

All PAMVAC formulations were safe and well tolerated. A total of 262 adverse events (AEs) occurred, 94 (10 grade 2 and 2 grade 3) at least possibly related to the vaccine. No serious AEs occurred. Distribution and severity of AEs were similar in all arms. PAMVAC was immunogenic in all participants. PAMVAC-specific antibody levels were highest with PAMVAC-GLA-SE. The antibodies inhibited binding of VAR2CSA expressing P. falciparum-infected erythrocytes to CSA in a standardized functional assay.

CONCLUSIONS

PAMVAC formulated with Alhydrogel or GLA-based adjuvants was safe, well tolerated, and induced functionally active antibodies. Next, PAMVAC will be assessed in women before first pregnancies in an endemic area.

CLINICAL TRIALS REGISTRATION

EudraCT 2015-001827-21; ClinicalTrials.gov NCT02647489.

Innate Immune Mechanisms to Protect Against Infection at the Human Decidual-Placental Interface

During pregnancy, the placenta forms the anatomical barrier between the mother and developing fetus. Infectious agents can potentially breach the placental barrier resulting in pathogenic transmission from mother to fetus. Innate immune responses, orchestrated by maternal and fetal cells at the decidual-placental interface, are the first line of defense to avoid vertical transmission. Here, we outline the anatomy of the human placenta and uterine lining, the decidua, and discuss the potential capacity of pathogen pattern recognition and other host defense strategies present in the innate immune cells at the placental-decidual interface. We consider major congenital infections that access the placenta from hematogenous or decidual route. Finally, we highlight the challenges in studying human placental responses to pathogens and vertical transmission using current experimental models and identify gaps in knowledge that need to be addressed. We further propose novel experimental strategies to address such limitations.

Malaria in pregnancy regulates P-glycoprotein (P-gp/Abcb1a) and ABCA1 efflux transporters in the Mouse Visceral Yolk Sac

Malaria in pregnancy (MiP) induces intrauterine growth restriction (IUGR) and preterm labour (PTL). However, its effects on yolk sac morphology and function are largely unexplored. We hypothesized that MiP modifies yolk sac morphology and efflux transport potential by modulating ABC efflux transporters. C57BL/6 mice injected with Plasmodium berghei ANKA (5 × 10⁵ infected erythrocytes) at gestational day (GD) 13.5 were subjected to yolk sac membrane harvesting at GD 18.5 for histology, qPCR and immunohistochemistry. MiP did not alter the volumetric proportion of the yolk sac's histological components. However, it increased levels of Abcb1a mRNA (encoding P‐glycoprotein) and macrophage migration inhibitory factor (Mif chemokine), while decreasing Abcg1 (P < 0.05); without altering Abca1, Abcb1b, Abcg2, Snat1, Snat2, interleukin (Il)‐1β and C‐C Motif chemokine ligand 2 (Ccl2). Transcripts of Il‐6, chemokine (C‐X‐C motif) ligand 1 (Cxcl1), Glut1 and Snat4 were not detectible. ABCA1, ABCG1, breast cancer resistance protein (BCRP) and P‐gp were primarily immunolocalized to the cell membranes and cytoplasm of endodermic epithelium but also in the mesothelium and in the endothelium of mesodermic blood vessels. Intensity of P‐gp labelling was stronger in both endodermic epithelium and mesothelium, whereas ABCA1 labelling increased in the endothelium of the mesodermic blood vessels. The presence of ABC transporters in the yolk sac wall suggests that this fetal membrane acts as an important protective gestational barrier. Changes in ABCA1 and P‐gp in MiP may alter the biodistribution of toxic substances, xenobiotics, nutrients and immunological factors within the fetal compartment and participate in the pathogenesis of malaria‐induced IUGR and PTL.

Lights and Shadows of TORCH Infection Proteomics

Congenital abnormalities cause serious fetal consequences. The term TORCH is used to designate the most common perinatal infections, where: (T) refers to toxoplasmosis, (O) means "others" and includes syphilis, varicella-zoster, parvovirus B19, zika virus (ZIKV), and malaria among others, (R) refers to rubella, (C) relates to cytomegalovirus infection, and (H) to herpes simplex virus infections. Among the main abnormalities identified in neonates exposed to congenital infections are central nervous system (CNS) damage, microcephaly, hearing loss, and ophthalmological impairment, all requiring regular follow-up to monitor its progression. Protein changes such as mutations, post-translational modifications, abundance, structure, and function may indicate a pathological condition before the onset of the first symptoms, allowing early diagnosis and understanding of a particular disease or infection. The term "proteomics" is defined as the science that studies the proteome, which consists of the total protein content of a cell, tissue or organism in a given space and time, including post-translational modifications (PTMs) and interactions between proteins. Currently, quantitative bottom-up proteomic strategies allow rapid and high throughput characterization of complex biological mixtures. Investigating proteome modulation during host-pathogen interaction helps in elucidating the mechanisms of infection and in predicting disease progression. This "molecular battle" between host and pathogen is a key to identify drug targets and diagnostic markers. Here, we conducted a survey on proteomic techniques applied to congenital diseases classified in the terminology "TORCH", including toxoplasmosis, ZIKV, malaria, syphilis, human immunodeficiency virus (HIV), herpes simplex virus (HSV) and human cytomegalovirus (HCVM). We have highlighted proteins and/or protein complexes actively involved in the infection. Most of the proteomic studies reported have been performed in cell line models, and the evaluation of tissues (brain, muscle, and placenta) and biofluids (plasma, serum and urine) in animal models is still underexplored. Moreover, there are a plethora of studies focusing on the pathogen or the host without considering the triad mother-fetus-pathogen as a dynamic and interconnected system.

Gravidity-dependent associations between interferon response and birth weight in placental malaria

BACKGROUND

Maternal malarial infection leads to poor perinatal outcomes, including low birth weight from preterm delivery and/or fetal growth restriction, particularly in primigravidas. In placental malaria, Plasmodium falciparum-infected red blood cells cause an inflammatory response that can interfere with maternal-fetal exchange, leading to poor growth. The type I interferon (IFN-I) pathway plays an immunomodulatory role in viral and bacterial infections, usually by suppressing inflammatory responses. However, its role in placental malaria is unknown. This study examines the cytokine responses in placental tissue from subsets of malaria-infected and uninfected women, and attempts to correlate them with particular birth outcomes.

METHODS

40 whole placental biopsy samples were obtained from pregnant women at least 16 years of age recruited to a larger prospective chemoprevention trial against malaria. These were patients at Tororo District Hospital in Uganda, an area of high malaria endemicity where approximately 40% of women have evidence of malaria infection at delivery. They were regularly followed at a local clinic and monitored for fever, with blood smears performed then and at time of delivery to diagnose malaria infection. Placenta biopsies were taken for histological diagnosis of placental malaria, as well as quantitative PCR analysis of genes in the IFN-I pathway (IFN-β, IL-10 and MX-1). Parameters such as infant birth weight and gestational age were also recorded.

RESULTS

Histological analysis revealed placental malaria in 18 samples, while 22 were found to be uninfected. RT-PCR analysis showed a four-fold increase in IFN-β and IL-10 expression in multigravidas with placental malaria when compared to gravidity-matched, uninfected controls. This effect was not observed in primigravidas. Interestingly, linear regression analysis showed a positive association between IFN-β levels and higher birth weights (β = 101.2 g per log2-fold increase in IFN-β expression, p = 0.042). This association was strongest in primigravidas with placental malaria (β = 339.0, p = 0.006).

CONCLUSIONS

These results demonstrate differential regulation of the IFN-I pathway in placental malaria according to gravidity, with the greatest anti-inflammatory response seen in multigravidas. The association between IFN-β levels and higher birth weight also suggests a protective role for IFN-I against fetal growth restriction in placental malaria.

Efficacy and tolerability of artemisinin-based and quinine-based treatments for uncomplicated falciparum malaria in pregnancy: a systematic review and individual patient data meta-analysis

BACKGROUND

Malaria in pregnancy affects both the mother and the fetus. However, evidence supporting treatment guidelines for uncomplicated (including asymptomatic) falciparum malaria in pregnant women is scarce and assessed in varied ways. We did a systematic literature review and individual patient data (IPD) meta-analysis to compare the efficacy and tolerability of different artemisinin-based or quinine-based treatments for malaria in pregnant women.

METHODS

We did a systematic review of interventional or observational cohort studies assessing the efficacy of artemisinin-based or quinine-based treatments in pregnancy. Seven databases (MEDLINE, Embase, Global Health, Cochrane Library, Scopus, Web of Science, and Literatura Latino Americana em Ciencias da Saude) and two clinical trial registries (International Clinical Trials Registry Platform and ClinicalTrials.gov) were searched. The final search was done on April 26, 2019. Studies that assessed PCR-corrected treatment efficacy in pregnancy with follow-up of 28 days or more were included. Investigators of identified studies were invited to share data from individual patients. The outcomes assessed included PCR-corrected efficacy, PCR-uncorrected efficacy, parasite clearance, fever clearance, gametocyte development, and acute adverse events. One-stage IPD meta-analysis using Cox and logistic regression with random-effects was done to estimate the risk factors associated with PCR-corrected treatment failure, using artemether-lumefantrine as the reference. This study is registered with PROSPERO, CRD42018104013.

FINDINGS

Of the 30 studies assessed, 19 were included, representing 92% of patients in the literature (4968 of 5360 episodes). Risk of PCR-corrected treatment failure was higher for the quinine monotherapy (n=244, adjusted hazard ratio [aHR] 6·11, 95% CI 2·57-14·54, p<0·0001) but lower for artesunate-amodiaquine (n=840, 0·27, 95% 0·14-0·52, p<0·0001), artesunate-mefloquine (n=1028, 0·56, 95% 0·34-0·94, p=0·03), and dihydroartemisinin-piperaquine (n=872, 0·35, 95% CI 0·18-0·68, p=0·002) than artemether-lumefantrine (n=1278) after adjustment for baseline asexual parasitaemia and parity. The risk of gametocyte carriage on day 7 was higher after quinine-based therapy than artemisinin-based treatment (adjusted odds ratio [OR] 7·38, 95% CI 2·29-23·82).

INTERPRETATION

Efficacy and tolerability of artemisinin-based combination therapies (ACTs) in pregnant women are better than quinine. The lower efficacy of artemether-lumefantrine compared with other ACTs might require dose optimisation.

FUNDING

The Bill & Melinda Gates Foundation, ExxonMobil Foundation, and the University of Oxford Clarendon Fund.

Safety of Artemisinin Derivatives in the First Trimester of Pregnancy: A Controversial Story

Artemisinin combination therapy (ACT) is recommended by the World Health Organization (WHO) as first line treatment for uncomplicated malaria both in adults and children. During pregnancy, ACT is considered safe only in the second and third trimester, since animal studies have demonstrated that artemisinin derivatives can cause foetal death and congenital malformation within a narrow time window in early embryogenesis. During this period, artemisinin derivatives induce defective embryonic erythropoiesis and vasculogenesis/angiogenesis in experimental models. However, clinical data on the safety profile of ACT in pregnant women have not shown an increased risk of miscarriage, stillbirth, or congenital malformation, nor low birth weight, associated with exposure to artemisinins in the first trimester. Although further studies are needed, the evidence collected up to now is prompting the WHO towards a change in the guidelines for the treatment of uncomplicated malaria, allowing the use of ACT also in the first trimester of pregnancy.

Systematic review of microeconomic analysis of pregnancy-associated malaria

Introduction

Pregnancy-associated malaria (PAM) is a health problem with serious clinical, epidemiological and economic effects.

Purpose

To analyze the microeconomic evaluations of PAM reported in the world scientific literature.

Methods

Systematic review with 15 different search strategies in PubMed, ScienceDirect, Scielo, Google Scholar and Malaria in Pregnancy (MiP) Library. A search, selection and extraction protocol was applied, which guaranteed completeness and reproducibility in accordance with preferred reporting items for systematic reviews and meta-analysis guidelines. The methodological quality was evaluated using the Consolidated Health Economic Evaluation Reporting Standards (CHEERS) guide. The analysis were based on frequencies, costs and average and incremental cost-effectiveness ratios in 2018 US dollars adjusted for purchasing power parity.

Results

Twenty-two evaluations published between 1990 and 2018 were analyzed, of which 82% addressed cost-effectiveness in Africa. Twelve interventions were studied; of these, intermittent preventive treatment in pregnant women with sulfadoxine-pyrimethamine (IPTp-SP) was the most frequent strategy. The main outcomes were low birth weight, anaemia and DALYs avoided. The best average cost-effectiveness ratio was reported in IPTp-SP with a cost of US$ 2 per DALY avoided, followed by the administration of IPTp-SP in pregnant women with HIV (US$ 14.2).

Conclusions

The studies focus on Africa with a high heterogeneity in the interventions, outcomes, resources and populations studied. All the interventions were highly cost-effective, which demonstrates the importance of including prevention, care and control resources for PAM as a priority in health sector budgets. This is especially true considering the importance of its intervention for social progress and overcoming poverty in endemic areas.

Impact of maternal death reviews at a rural hospital in Zambia: a mixed methods study

Background

Maternal mortality in sub-Saharan Africa remains high despite programmatic efforts to improve maternal health. In 2007, the Zambian Ministry of Health mandated facility-based maternal death review (MDR) programs in line with World Health Organization recommendations. We assessed the impact of an [MDR program] at a district-level hospital in rural Zambia.

Methods

We conducted a mixed methods convergent study using hospital data on maternal mortality and audit reports of 106 maternal deaths from 2007 to 2011. To evaluate the overall impact of MDR on maternal mortality, we compared baseline (2007) to late (2010–11) post-intervention inpatient maternal mortality indicators. MDR committee reports were coded and dominant themes were extracted in a qualitative analysis. We assessed potential risk factors for maternal mortality in a before-and-after design comparing the periods 2008–09 and 2010–11.

Results

In-hospital maternal mortality declined from 23 per thousand live births in 2007 to 8 per thousand in 2010–11 (P < 0.01). Maternal case fatality for puerperal sepsis and uterine rupture decreased significantly from 63 and 32% in 2007 to 10 and 9% in 2010–11 (P < 0.01). No significant reduction was seen in case fatality due to postpartum hemorrhage. Qualitative analysis of risk factors for maternal mortality revealed four core themes: standards of practice, health systems, accessibility, and patient factors. Specific risk factors included delayed referral, missed diagnoses, intra-hospital delays in care, low medication inventory, and medical error. We found no statistically significant differences in the prevalence of risk factors between the before-and-after periods.

Conclusions

Implementation of MDR was accompanied by a significant decrease in maternal mortality with reductions in maternal death from puerperal sepsis and uterine rupture, but not postpartum hemorrhage. Qualitative analysis of audit reports identified several modifiable risk factors within four core areas. Comparisons of potential explanatory factors did not show any differences over time. These results imply that MDR offers a means for hospitals to curtail maternal deaths, except deaths due to postpartum hemorrhage, suggesting additional interventions are needed. Documentation of MDR meetings provides an instrument to guide further quality improvements.

Systematic review of artemisinin embryotoxicity in animals: Implications for malaria control in human pregnancy

Pregnant women are one of the most susceptible and vulnerable groups to malaria, the most important parasitic disease worldwide. Artemisinin-based combination therapies (ACTs) are recommended for the treatment of uncomplicated malaria in all population groups including pregnant women. However, due to the embryotoxicity observed in animal studies, ACTs have long been contraindicated during the first trimester in pregnant women. Despite the safety concerns raised in pre-clinical studies, recent findings on ACTs's use in pregnant women appear to be reassuring regarding safety and have prompted a revision of malaria treatment guidelines for first trimester of pregnancy. To contribute to the risk-benefit assessment of ACTs, we conducted a systematic literature review of animal studies published between 2007 and 2019, which evaluated the embryotoxic effects of artemisinin and its derivatives among pregnant mammals. Eighteen experimental studies fitted the inclusion criteria. These studies confirmed and further characterized the severe embryolethal and embryotoxic dose-dependent effects of artemisinin and its derivatives when administered during the organogenesis period in rats, rabbits and monkeys. Timing of administration and dosage of the drug were found to be key factors in the appearance of embryo damage. Overall, the translation of the findings of artemisinin derivatives use in animal studies to pregnant women remains disturbing. Thus, a policy change in the use of ACTs during the first trimester in pregnant women for the treatment of uncomplicated malaria does not seem pertinent and if implemented, it should be accompanied by solid pharmacovigilance systems, which are challenging to establish in malaria endemic countries.

Associations of malaria, HIV, and coinfection, with anemia in pregnancy in sub-Saharan Africa: a population-based cross-sectional study

BACKGROUND

Malaria and HIV are common infections in Africa and cause substantial morbidity and mortality in pregnant women. We aimed to assess the association of malaria with anemia in pregnant women and to explore the joint effects of malaria and HIV infection on anemia in pregnant women.

METHODS

We used nationally representative, cross-sectional demographic and health surveys (DHS) that were conducted between 2012 and 2017 across 7 countries of sub-Saharan Africa (Burundi, the Democratic Republic of the Congo, Gambia, Ghana, Mali, Senegal and Togo). The outcome variables were anemia (defined as a hemoglobin concentration < 110 g/L), and hemoglobin concentration on a continuous scale, in pregnant women at the time of the interview. We used generalized linear mixed-effects models to account for the nested structure of the data. We adjusted models for individual covariates, with random effects of the primary sampling unit nested within a country.

RESULTS

A total of 947 pregnant women, ages, 15-49 y, were analyzed. Prevalence of malaria only, HIV only, and malaria- HIV coinfection in pregnant women was 31% (95% CI: 28.5 to 34.5%, n = 293), 1.3% (95% CI: 0.77 to 2.4%, n = 13) and 0.52% (95% CI: 0.02 to 1.3%, n = 5) respectively. Overall prevalence of anemia was 48.3% (95% CI: 45.1 to 51.5%). The anemia prevalence in pregnant women with malaria infection only was 56.0% (95% CI: 50.1 to 61.7%); HIV infection only, 62.5% (95% CI: 25.9 to 89.8%); malaria- HIV coinfection, 60.0 (95% CI: 17.0-92.7%) and without either infection, 44.6% (95% CI: 40.7 to 48.6%). In the fully adjusted models, malaria infection was associated with 27% higher prevalence of anemia (95% CI of prevalence ratio: 1.12 to 1.45; p = 0.004), and 3.4 g/L lower hemoglobin concentration (95% CI: - 5.01 to - 1.79; p = 0.03) compared to uninfected pregnant women. The prevalence of HIV infection and malaria-HIV coinfection was too low to allow meaningful analysis of their association with anemia or hemoglobin concentration.

CONCLUSION

Malaria was associated with an increased prevalence of anemia during pregnancy.

Overall, anti-malarial, and non-malarial effect of intermittent preventive treatment during pregnancy with sulfadoxine-pyrimethamine on birthweight: a mediation analysis

BACKGROUND

Trials of intermittent preventive treatment (IPTp) of malaria in pregnant women that compared dihydroartemisinin-piperaquine with the standard of care, sulfadoxine-pyrimethamine, showed dihydroartemisinin-piperaquine was superior at preventing malaria infection, but not at improving birthweight. We aimed to assess whether sulfadoxine-pyrimethamine shows greater non-malarial benefits for birth outcomes than does dihydroartemisinin-piperaquine, and whether dihydroartemisinin-piperaquine shows greater antimalarial benefits for birth outcomes than does sulfadoxine-pyrimethamine.

METHODS

We defined treatment as random assignment to sulfadoxine-pyrimethamine or dihydroartemisinin-piperaquine before pooling individual participant-level data from 1617 HIV-uninfected pregnant women in Kenya (one trial; n=806) and Uganda (two trials; n=811). We quantified the relative effect of treatment on birthweight (primary outcome) attributed to preventing placental malaria infection (mediator). We estimated antimalarial (indirect) and non-malarial (direct) effects of IPTp on birth outcomes using causal mediation analyses, accounting for confounders. We used two-stage individual participant data meta-analyses to calculate pooled-effect sizes.

FINDINGS

Overall, birthweight was higher among neonates of women randomly assigned to sulfadoxine-pyrimethamine compared with women assigned to dihydroartemisinin-piperaquine (mean difference 69 g, 95% CI 26 to 112), despite placental malaria infection being lower in the dihydroartemisinin-piperaquine group (relative risk [RR] 0·64, 95% CI 0·39 to 1·04). Mediation analyses showed sulfadoxine-pyrimethamine conferred a greater non-malarial effect than did dihydroartemisinin-piperaquine (mean difference 87 g, 95% CI 43 to 131), whereas dihydroartemisinin-piperaquine conferred a slightly larger antimalarial effect than did sulfadoxine-pyrimethamine (8 g, -9 to 26), although more frequent dosing increased the antimalarial effect (31 g, 3 to 60).

INTERPRETATION

IPTp with sulfadoxine-pyrimethamine appears to have potent non-malarial effects on birthweight. Further research is needed to evaluate monthly dihydroartemisinin-piperaquine with sulfadoxine-pyrimethamine (or another compound with non-malarial effects) to achieve greater protection against malarial and non-malarial causes of low birthweight.

FUNDING

Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bill & Melinda Gates Foundation, and Worldwide Antimalarial Resistance Network.

Pregnancy outcomes and risk of placental malaria after artemisinin-based and quinine-based treatment for uncomplicated falciparum malaria in pregnancy: a WorldWide Antimalarial Resistance Network systematic review and individual patient data meta-analysis

BACKGROUND

Malaria in pregnancy, including asymptomatic infection, has a detrimental impact on foetal development. Individual patient data (IPD) meta-analysis was conducted to compare the association between antimalarial treatments and adverse pregnancy outcomes, including placental malaria, accompanied with the gestational age at diagnosis of uncomplicated falciparum malaria infection.

METHODS

A systematic review and one-stage IPD meta-analysis of studies assessing the efficacy of artemisinin-based and quinine-based treatments for patent microscopic uncomplicated falciparum malaria infection (hereinafter uncomplicated falciparum malaria) in pregnancy was conducted. The risks of stillbirth (pregnancy loss at ≥ 28.0 weeks of gestation), moderate to late preterm birth (PTB, live birth between 32.0 and < 37.0 weeks), small for gestational age (SGA, birthweight of < 10th percentile), and placental malaria (defined as deposition of malaria pigment in the placenta with or without parasites) after different treatments of uncomplicated falciparum malaria were assessed by mixed-effects logistic regression, using artemether-lumefantrine, the most used antimalarial, as the reference standard. Registration PROSPERO: CRD42018104013.

RESULTS

Of the 22 eligible studies (n = 5015), IPD from16 studies were shared, representing 95.0% (n = 4765) of the women enrolled in literature. Malaria treatment in this pooled analysis mostly occurred in the second (68.4%, 3064/4501) or third trimester (31.6%, 1421/4501), with gestational age confirmed by ultrasound in 91.5% (4120/4503). Quinine (n = 184) and five commonly used artemisinin-based combination therapies (ACTs) were included: artemether-lumefantrine (n = 1087), artesunate-amodiaquine (n = 775), artesunate-mefloquine (n = 965), and dihydroartemisinin-piperaquine (n = 837). The overall pooled proportion of stillbirth was 1.1% (84/4361), PTB 10.0% (619/4131), SGA 32.3% (1007/3707), and placental malaria 80.1% (2543/3035), and there were no significant differences of considered outcomes by ACT. Higher parasitaemia before treatment was associated with a higher risk of SGA (adjusted odds ratio [aOR] 1.14 per 10-fold increase, 95% confidence interval [CI] 1.03 to 1.26, p = 0.009) and deposition of malaria pigment in the placenta (aOR 1.67 per 10-fold increase, 95% CI 1.42 to 1.96, p < 0.001).

CONCLUSIONS

The risks of stillbirth, PTB, SGA, and placental malaria were not different between the commonly used ACTs. The risk of SGA was high among pregnant women infected with falciparum malaria despite treatment with highly effective drugs. Reduction of malaria-associated adverse birth outcomes requires effective prevention in pregnant women.

Relationship Between Pregnancy-Associated Malaria and Adverse Pregnancy Outcomes: a Systematic Review and Meta-Analysis

BACKGROUND

Pregnancy-associated malaria (PAM) has been associated with adverse pregnancy outcomes like preterm birth (PTB) and low birthweight (LBW), which are among the leading causes of infant mortality globally. Rates of PTB and LBW are high in countries with a high burden of malaria. PAM may be a contributing factor to PTB and LBW, but is not well understood.

METHODS

We conducted a systematic review and meta-analysis of studies examining the relationship between PAM and PTB or LBW using PubMed. The title and abstract of all studies were screened by two reviewers, and the full text of selected studies was reviewed to ensure they met inclusion criteria. Information regarding study characteristics and of PTB and LBW births among women with and without PAM was abstracted for included studies.

RESULTS

Our search terms yielded 2237 articles, of which 18 met our final inclusion criteria. Eight studies examined associations between PAM and PTB, and 10 examined associations between PAM and LBW (population size ranging from 35 to 9956 women). The overall risk of LBW was 63% higher among women with PAM compared with women without PAM (95% CI = 1.48-1.80) and the risk of PTB was 23% higher among women with PAM compared with women without PAM (95% CI = 1.07-1.41).

CONCLUSIONS

These results indicate that infection with PAM is associated with PTB and LBW. Further understanding of the pathogenesis of disease and the immunologic changes that occur during pregnancy is essential for reducing the disproportional effects this disease has on this vulnerable population.

Malaria in Early Pregnancy and the Development of the Placental Vasculature

BACKGROUND

Pregnancy malaria has a negative impact on fetal outcome. It is uncertain whether infections in early pregnancy have a clinical impact by impeding the development of the placental vasculature.

METHODS

Tanzanian women (n = 138) were closely monitored during pregnancy. Placentas collected at birth were investigated using stereology to establish the characteristics of placental villi and vessels. Placental vasculature measures were compared between women infected with malaria and controls.

RESULTS

Compared with controls, placentas from women infected with malaria before a gestational age (GA) of 15 weeks had a decreased volume of transport villi (mean decrease [standard deviation], 12.45 [5.39] cm3; P = .02), an increased diffusion distance in diffusion vessels (mean increase, 3.33 [1.27] µm; P = .01), and a compensatory increase in diffusion vessel surface area (mean increase, 1.81 [0.74 m2]; P = .02). In women who had malaria before a GA of 15 weeks diffusion vessel surface area and transport vessel length distance were positive predictors for birth weight (multilinear regression: P = .007 and P = .055 for diffusion surface area and transport length, respectively) and GA at delivery (P = .005 and P = .04).

CONCLUSIONS

Malaria infection in early pregnancy impedes placental vascular development. The resulting phenotypic changes, which can be detected at delivery, are associated with birth weight and gestational length.

CLINICAL TRIALS REGISTRATION

NCT02191683.

Insight Into TLR4-Mediated Immunomodulation in Normal Pregnancy and Related Disorders

Unlike organ transplants where an immunosuppressive environment is required, a successful pregnancy involves an extremely robust, dynamic, and responsive maternal immune system to maintain the development of the fetus. A specific set of hormones and cytokines are associated with a particular stage of pregnancy. Any disturbance that alters this fine balance could compromise the development and function of the placenta. Although there are numerous underlying causes of pregnancy-related complications, untimely activation of Toll-like receptors (TLR), primarily TLR4, by intrauterine microbes poses the greatest risk. TLR4 is an important Pattern Recognition Receptor (PRR), which activates both innate and adaptive immune cells. TLR4 activation by LPS or DAMPs leads to the production of pro-inflammatory cytokines via the MyD88 dependent or independent pathway. Immune cells modulate the materno–fetal interface by TLR4-mediated cytokine production, which changes at different stages of pregnancy. In most pregnancy disorders, such as PTB, PE, or placental malaria, the TLR4 expression is upregulated in immune cells or in maternal derived cells, leading to the aberrant production of pro-inflammatory cytokines at the materno–fetal interface. Lack of functional TLR4 in mice has reduced the pro-inflammatory responses, leading to an improved pregnancy, which further strengthens the fact that abnormal TLR4 activation creates a hostile environment for the developing fetus. A recent study proposed that endothelial and perivascular stromal cells should interact with each other in order to maintain a homeostatic balance during TLR4-mediated inflammation. It has been reported that depleting immune cells or supplying anti-inflammatory cytokines can prevent PTB, PE, or fetal death. Blocking TLR4 signaling or its downstream molecule by inhibitors or antagonists has proven to improve pregnancy-related complications to some extent in clinical and animal models. To date, there has been a lack of knowledge regarding whether TLR4 accessories such as CD14 and MD-2 are important in pregnancy and whether these accessory molecules could be promising drug targets for combinatorial treatment of various pregnancy disorders. This review mainly focuses on the activation of TLR4 during pregnancy, its immunomodulatory functions, and the upcoming advancement in this field regarding the improvement of pregnancy-related issues by various therapeutic approaches.

Tissue tropism in parasitic diseases

Parasitic diseases, such as sleeping sickness, Chagas disease and malaria, remain a major cause of morbidity and mortality worldwide, but particularly in tropical, developing countries. Controlling these diseases requires a better understanding of host-parasite interactions, including a deep appreciation of parasite distribution in the host. The preferred accumulation of parasites in some tissues of the host has been known for many years, but recent technical advances have allowed a more systematic analysis and quantifications of such tissue tropisms. The functional consequences of tissue tropism remain poorly studied, although it has been associated with important aspects of disease, including transmission enhancement, treatment failure, relapse and clinical outcome. Here, we discuss current knowledge of tissue tropism in Trypanosoma infections in mammals, describe potential mechanisms of tissue entry, comparatively discuss relevant findings from other parasitology fields where tissue tropism has been extensively investigated, and reflect on new questions raised by recent discoveries and their potential impact on clinical treatment and disease control strategies.

mSphere of Influence: Going Native, or the Risk of Overreliance on Recombinant Antigens

Mary Lopez-Perez works on immunology and pathogenesis of malaria. In this mSphere of Influence article, she reflects on how the paper “Functional antibodies against VAR2CSA in nonpregnant populations from Colombia exposed to Plasmodium falciparum and Plasmodium vivax” by S. Gnidehou, J. Doritchamou, E. M. Arango, A. Cabrera, et al. (Infect Immun 82:2565−2573, 2014, https://doi.org/10.1128/IAI.01594-14) made her cautious of relying exclusively on recombinant proteins when evaluating antibody responses.

Mary Lopez-Perez works on immunology and pathogenesis of malaria. In this mSphere of Influence article, she reflects on how the paper “Functional antibodies against VAR2CSA in nonpregnant populations from Colombia exposed to Plasmodium falciparum and Plasmodium vivax” by S. Gnidehou, J. Doritchamou, E. M. Arango, A. Cabrera, et al. (Infect Immun 82:2565−2573, 2014, https://doi.org/10.1128/IAI.01594-14) made her cautious of relying exclusively on recombinant proteins when evaluating antibody responses.

Inflammasome activation and IL-1 signaling during placental malaria induce poor pregnancy outcomes

Placental malaria (PM) is associated with severe inflammation leading to abortion, preterm delivery, and intrauterine growth restriction. Innate immunity responses play critical roles, but the mechanisms underlying placental immunopathology are still unclear. Here, we investigated the role of inflammasome activation in PM by scrutinizing human placenta samples from an endemic area and ablating inflammasome components in a PM mouse model. The reduction in birth weight in babies from infected mothers is paralleled by increased placental expression of AIM2 and NLRP3 inflammasomes. Using genetic dissection, we reveal that inflammasome activation pathways are involved in the production and detrimental action of interleukin-1β (IL-1β) in the infected placenta. The IL-1R pharmacological antagonist Anakinra improved pregnancy outcomes by restoring fetal growth and reducing resorption in an experimental model. These findings unveil that IL-1β-mediated signaling is a determinant of PM pathogenesis, suggesting that IL-1R antagonists can improve clinical outcomes of malaria infection in pregnancy.

Pregnancy-specific malarial immunity and risk of malaria in pregnancy and adverse birth outcomes: a systematic review

BACKGROUND

In endemic areas, pregnant women are highly susceptible to Plasmodium falciparum malaria characterized by the accumulation of parasitized red blood cells (pRBC) in the placenta. In subsequent pregnancies, women develop protective immunity to pregnancy-associated malaria and this has been hypothesized to be due to the acquisition of antibodies to the parasite variant surface antigen VAR2CSA. In this systematic review we provide the first synthesis of the association between antibodies to pregnancy-specific P. falciparum antigens and pregnancy and birth outcomes.

METHODS

We conducted a systematic review and meta-analysis of population-based studies (published up to 07 June 2019) of pregnant women living in P. falciparum endemic areas that examined antibody responses to pregnancy-specific P. falciparum antigens and outcomes including placental malaria, low birthweight, preterm birth, peripheral parasitaemia, maternal anaemia, and severe malaria.

RESULTS

We searched 6 databases and identified 33 studies (30 from Africa) that met predetermined inclusion and quality criteria: 16 studies contributed estimates in a format enabling inclusion in meta-analysis and 17 were included in narrative form only. Estimates were mostly from cross-sectional data (10 studies) and were heterogeneous in terms of magnitude and direction of effect. Included studies varied in terms of antigens tested, methodology used to measure antibody responses, and epidemiological setting. Antibody responses to pregnancy-specific pRBC and VAR2CSA antigens, measured at delivery, were associated with placental malaria (9 studies) and may therefore represent markers of infection, rather than correlates of protection. Antibody responses to pregnancy-specific pRBC, but not recombinant VAR2CSA antigens, were associated with trends towards protection from low birthweight (5 studies).

CONCLUSIONS

Whilst antibody responses to several antigens were positively associated with the presence of placental and peripheral infections, this review did not identify evidence that any specific antibody response is associated with protection from pregnancy-associated malaria across multiple populations. Further prospective cohort studies using standardized laboratory methods to examine responses to a broad range of antigens in different epidemiological settings and throughout the gestational period, will be necessary to identify and prioritize pregnancy-specific P. falciparum antigens to advance the development of vaccines and serosurveillance tools targeting pregnant women.

Using two phases of the CD4 T cell response to blood-stage murine malaria to understand regulation of systemic immunity and placental pathology in Plasmodium falciparum infection

Plasmodium falciparum infection and malaria remain a risk for millions of children and pregnant women. Here, we seek to integrate knowledge of mouse and human T helper cell (Th) responses to blood-stage Plasmodium infection to understand their contribution to protection and pathology. Although there is no complete Th subset differentiation, the adaptive response occurs in two phases in non-lethal rodent Plasmodium infection, coordinated by Th cells. In short, cellular immune responses limit the peak of parasitemia during the first phase; in the second phase, humoral immunity from T cell-dependent germinal centers is critical for complete clearance of rapidly changing parasite. A strong IFN-γ response kills parasite, but an excess of TNF compared with regulatory cytokines (IL-10, TGF-β) can cause immunopathology. This common pathway for pathology is associated with anemia, cerebral malaria, and placental malaria. These two phases can be used to both understand how the host responds to rapidly growing parasite and how it attempts to control immunopathology and variation. This dual nature of T cell immunity to Plasmodium is discussed, with particular reference to the protective nature of the continuous generation of effector T cells, and the unique contribution of effector memory T cells.

Cerebral Plasmodium falciparum malaria: The role of PfEMP1 in its pathogenesis and immunity, and PfEMP1-based vaccines to prevent it

Malaria, a mosquito-borne infectious disease caused by parasites of the genus Plasmodium continues to be a major health problem worldwide. The unicellular Plasmodium-parasites have the unique capacity to infect and replicate within host erythrocytes. By expressing variant surface antigens Plasmodium falciparum has evolved to avoid protective immune responses; as a result in endemic areas anti-malaria immunity develops gradually over many years of multiple and repeated infections. We are studying the role of Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) expressed by asexual stages of P. falciparum responsible for the pathogenicity of severe malaria. The immunopathology of falciparum malaria has been linked to cyto-adhesion of infected erythrocytes to specific host receptors. A greater appreciation of the PfEMP1 molecules important for the development of protective immunity and immunopathology is a prerequisite for the rational discovery and development of a safe and protective anti-disease malaria vaccine. Here we review the role of ICAM-1 and EPCR receptor adhering falciparum-parasites in the development of severe malaria; we discuss our current research to understand the factors involved in the pathogenesis of cerebral malaria and the feasibility of developing a vaccine targeted specifically to prevent this disease.

Malaria-Associated Factors among Pregnant Women in Guinea

Introduction

Malaria is the leading cause of consultation in Guinea health facilities. During pregnancy, it remains a major health concern causing considerable risks for mother, fetus, and newborn. However, little is known about the epidemiology of malaria among pregnant women in Guinea. We aimed to provide information on malaria-associated factors in parturients.

Methods

It was a cross-sectional survey in two regional hospitals and two district hospitals. 1000 parturients and their newborns were surveyed. All patients were interviewed, and thick and thin blood smears were examined. To determine the predictive factors of malaria in parturients, the Classification and Regression Tree (CART) was first performed by using peripheral and placental malaria as dependent variables and sociodemographic and antenatal characteristics as independent variables; then, explanatory profile variables or clusters from these trees were included in the logistic regression models.

Results

We found 157 (15.8%) and 148 (14.8%) cases of peripheral and placental malaria, respectively. The regular use of long-lasting insecticide-treated nets (LLINs) before delivery was 53.8%, and only 35.5% used sulfadoxine-pyrimethamine doses ≥3. Factors significantly associated with malaria were as follows: women from Forécariah and Guéckédou who did not regularly use LLINs and accomplished less than four antenatal care visits (ANC <4) and primigravid and paucigravid women who did not regularly use LLINs. Similarly, the odds of having malaria infection were significantly higher among women who had not regularly used LLINs and among primigravid and paucigravid women who had regularly used LLINs compared to multigravida women who had regularly used LLINs.

Conclusion

This study showed that pregnant women remain particularly vulnerable to malaria; therefore, strengthening antenatal care visit strategies by emphasizing on promoting the use of LLINs and sulfadoxine-pyrimethamine, sexual education about early pregnancies, and family or community support during first pregnancies might be helpful.

In utero priming of highly functional effector T cell responses to human malaria

Malaria remains a significant cause of morbidity and mortality worldwide, particularly in infants and children. Some studies have reported that exposure to malaria antigens in utero results in the development of tolerance, which could contribute to poor immunity to malaria in early life. However, the effector T cell response to pathogen-derived antigens encountered in utero, including malaria, has not been well characterized. Here, we assessed the frequency, phenotype, and function of cord blood T cells from Ugandan infants born to mothers with and without placental malaria. We found that infants born to mothers with active placental malaria had elevated frequencies of proliferating effector memory fetal CD4⁺ T cells and higher frequencies of CD4⁺ and CD8⁺ T cells that produced inflammatory cytokines. Fetal CD4⁺ and CD8⁺ T cells from placental malaria-exposed infants exhibited greater in vitro proliferation to malaria antigens. Malaria-specific CD4⁺ T cell proliferation correlated with prospective protection from malaria during childhood. These data demonstrate that placental malaria is associated with the generation of proinflammatory malaria-responsive fetal T cells. These findings add to our current understanding of fetal immunity and indicate that a functional and protective pathogen-specific T cell response can be generated in utero.

Antibodies to Cryptic Epitopes in Distant Homologues Underpin a Mechanism of Heterologous Immunity between Plasmodium vivax PvDBP and Plasmodium falciparum VAR2CSA

In this work, we describe a molecular mechanism of heterologous immunity between two distant species of Plasmodium. Our results suggest a mechanism that subverts the classic parasite strategy of presenting highly polymorphic epitopes in surface antigens to evade immunity to that parasite. This alternative immune pathway can be exploited to protect pregnant women from falciparum placental malaria by designing vaccines to cryptic epitopes that elicit broadly inhibitory antibodies against variant parasite strains.

Many pathogens evolve extensive genetic variation in virulence proteins as a strategy to evade host immunity. This poses a significant challenge for the host to develop broadly neutralizing antibodies. In Plasmodium falciparum, we show that a mechanism to circumvent this challenge is to elicit antibodies to cryptic epitopes that are not under immune pressure. We previously discovered that antibodies to the Plasmodium vivax invasion protein, PvDBP, cross-react with P. falciparum VAR2CSA, a distantly related virulence factor that mediates placental malaria. Here, we describe the molecular mechanism underlying this cross-species immunity. We identified an epitope in subdomain 1 (SD1) within the Duffy binding-like (DBL) domain of PvDBP that gives rise to cross-reactive antibodies to VAR2CSA and show that human antibodies affinity purified against a synthetic SD1 peptide block parasite adhesion to chondroitin sulfate A (CSA) in vitro. The epitope in SD1 is subdominant and highly conserved in PvDBP, and in turn, SD1 antibodies target cryptic epitopes in P. falciparum VAR2CSA. The epitopes in VAR2CSA recognized by vivax-derived SD1 antibodies (of human and mouse origin) are distinct from those recognized by VAR2CSA immune serum. We mapped two peptides in the DBL5ε domain of VAR2CSA that are recognized by SD1 antibodies. Both peptides map to regions outside the immunodominant sites, and antibodies to these peptides are not elicited following immunization with VAR2CSA or natural infection with P. falciparum in pregnancy, consistent with the cryptic nature of these target epitopes.

The immune response to malaria in utero

Malaria causes tremendous early childhood morbidity and mortality, providing an urgent impetus for the development of a vaccine that is effective in neonates. However, the infant immune response to malaria may be influenced by events that occur well before birth. Placental malaria infection complicates one quarter of all pregnancies in Africa and frequently results in exposure of the fetus to malaria antigens in utero, while the immune system is still developing. Some data suggest that in utero exposure to malaria may induce immunologic tolerance that interferes with the development of protective immunity during childhood. More recently, however, a growing body of evidence suggests that fetal malaria exposure can prime highly functional malaria-specific T- and B-cells, which may contribute to postnatal protection from malaria. In utero exposure to malaria also impacts the activation and maturation of fetal antigen presenting cells and innate lymphocytes, which could have implications for global immunity in the infant. Here, we review recent advances in our understanding of how various components of the fetal immune system are altered by in utero exposure to malaria, discuss factors that may tilt the critical balance between tolerance and adaptive immunity, and consider the implications of these findings for malaria prevention strategies.