Ann M. Moormann

Malaria and Pregnancy: Placental Cytokine Expression and Its Relationship to Intrauterine Growth Retardation

Malaria infections during pregnancy can lead to the delivery of low-birth-weight infants. In this study, cytokine mRNA was measured in placentas from 23 malaria-infected and 21 uninfected primigravid women who had delivered in Mangochi, Malawi, a region with a high rate of transmission of falciparum malaria. Significantly increased expression of interleukin (IL)-1beta, IL-8, and tumor necrosis factor (TNF)-alpha and decreased expression of IL-6 and transforming growth factor-beta1 were found in malaria-infected compared with uninfected placentas. TNF-alpha and IL-8 were produced by maternally derived hemozoin-laden placental macrophages. Increased TNF-alpha expression was associated with increased placental hemozoin concentrations. Increased TNF-alpha or IL-8 expression in the placenta was associated with intrauterine growth retardation but not with preterm delivery. The results suggest that malaria infections induce a potentially harmful proinflammatory response in the placenta.

Evidence That Invasion-Inhibitory Antibodies Specific for the 19-kDa Fragment of Merozoite Surface Protein-1 (MSP-119) Can Play a Protective Role against Blood-Stage Plasmodium falciparum Infection in Individuals in a Malaria Endemic Area of Africa

The C-terminal 19-kDa fragment of Plasmodium falciparum merozoite surface protein-1 (MSP-119) is a target of protective Abs against blood-stage infection and a leading candidate for inclusion in a human malaria vaccine. However, the precise role, relative importance, and mechanism of action of Abs that target this protein remain unclear. To examine the potential protective role of Abs to MSP-119 in individuals naturally exposed to malaria, we conducted a treatment time to infection study over a 10-wk period in 76 residents of a highland area of western Kenya during a malaria epidemic. These semi-immune individuals were not all equally susceptible to reinfection with P. falciparum following drug cure. Using a new neutralization assay based on transgenic P. falciparum expressing the P. chabaudi MSP-119 orthologue, individuals with high-level MSP-119-specific invasion-inhibitory Abs (>75th percentile) had a 66% reduction in the risk of blood-stage infection relative to others in the population (95% confidence interval, 3–88%). In contrast, high levels of MSP-119 IgG or IgG subclass Abs measured by enzyme immunoassay with six different recombinant MSP-119 Ags did not correlate with protection from infection. IgG Abs measured by serology and functional invasion-inhibitory activity did not correlate with each other. These findings implicate an important protective role for MSP-119-specific invasion inhibitory Abs in immunity to blood-stage P. falciparum infection, and suggest that the measurement of MSP-119 specific inhibitory Abs may serve as an accurate correlate of protection in clinical trials of MSP-1-based vaccines.

Endemic Burkitt's lymphoma: a polymicrobial disease?

Endemic Burkitts lymphoma is the most common childhood cancer in equatorial Africa. Two ubiquitous human pathogens are thought to be responsible for the aetiology of this disease: Epstein–Barr virus and Plasmodium falciparum malaria. New data suggest how these two pathogens might interact to result in disease and provide insights into the emerging concepts of polymicrobial disease pathogenesis.

Exposure to holoendemic malaria results in elevated Epstein-Barr virus loads in children

Perennial and intense malaria transmission (holoendemic malaria) and Epstein-Barr virus (EBV) infection are 2 cofactors in the pathogenesis of endemic Burkitt lymphoma (eBL). In the present study, we compared EBV loads in children living in 2 regions of Kenya with differing malaria transmission intensities: Kisumu District, where malaria transmission is holoendemic, and Nandi District, where malaria transmission is sporadic. For comparison, blood samples were also obtained from US adults, Kenyan adults, and patients with eBL. Extraction of DNA from blood and quantification by polymerase chain reaction give an EBV load estimate that reflects the number of EBV-infected B cells. We observed a significant linear trend in mean EBV load, with the lowest EBV load detected in US adults and increasing EBV loads detected in Kenyan adults, Nandi children, Kisumu children, and patients with eBL, respectively. In addition, EBV loads were significantly higher in Kisumu children 1-4 years of age than in Nandi children of the same age. Our results support the hypothesis that repeated malaria infections in very young children modulate the persistence of EBV and increase the risk for the development of eBL.

Absence of Putative Artemisinin Resistance Mutations Among Plasmodium falciparum in Sub-Saharan Africa: A Molecular Epidemiologic Study

Plasmodium falciparum parasites that are resistant to artemisinins have been detected in Southeast Asia. Resistance is associated with several polymorphisms in the parasites K13-propeller gene. The molecular epidemiology of these artemisinin resistance genotypes in African parasite populations is unknown. We developed an assay to quantify rare polymorphisms in parasite populations that uses a pooled deep-sequencing approach to score allele frequencies, validated it by evaluating mixtures of laboratory parasite strains, and then used it to screen P. falciparum parasites from >1100 African infections collected since 2002 from 14 sites across sub-Saharan Africa. We found no mutations in African parasite populations that are associated with artemisinin resistance in Southeast Asian parasites. However, we observed 15 coding mutations, including 12 novel mutations, and limited allele sharing between parasite populations, consistent with a large reservoir of naturally occurring K13-propeller variation. Although polymorphisms associated with artemisinin resistance in P. falciparum in Southeast Asia are not prevalent in sub-Saharan Africa, numerous K13-propeller coding polymorphisms circulate in Africa. Although their distributions do not support a widespread selective sweep for an artemisinin-resistant phenotype, the impact of these mutations on artemisinin susceptibility is unknown and will require further characterization. Rapid, scalable molecular surveillance offers a useful adjunct in tracking and containing artemisinin resistance.

Malaria Enhances Expression of CC Chemokine Receptor 5 on Placental Macrophages

Malaria and human immunodeficiency virus (HIV) coinfections are common in pregnant women in sub-Saharan Africa. The current study shows that placentas of malaria-infected women contain 3 times as much CC chemokine receptor 5 (CCR5) RNA as placentas of women without malaria. By immunohistochemistry, CCR5(+) maternal macrophages were seen in placentas from malaria-infected women but not in placentas from malaria-uninfected women. In addition, CCR5 also was found on fetal Hofbauer cells in placentas from both groups. Thus, malaria infections increase the potential reservoir for HIV in the placenta by increasing the number of HIV target cells.

Exposure to Holoendemic Malaria Results in Suppression of Epstein-Barr Virus-Specific T Cell Immunosurveillance in Kenyan Children

BACKGROUND Malaria and Epstein-Barr virus (EBV) infection are cofactors in the pathogenesis of endemic Burkitt lymphoma (eBL). The mechanisms by which these pathogens predispose to eBL are not known. METHODS Healthy Kenyan children with divergent malaria exposure were measured for responses to EBV latent and lytic antigens by interferon (IFN)- gamma enzyme-linked immunospot (ELISPOT) assay and interleukin (IL)-10 ELISA. Phytohemagglutinin (PHA), purified protein derivative (PPD), and T cell epitope peptides derived from merozoite surface protein (MSP)-1, a malaria blood-stage antigen, were also evaluated. RESULTS Children 5-9 years old living in an area holoendemic for malaria had significantly fewer EBV-specific IFN- gamma responses than did children of the same age living in an area with unstable malaria transmission. This effect was not observed for children <5 years old or those >9 years old. In contrast, IFN- gamma responses to PHA, PPD, and Plasmodium falciparum MSP-1 peptides did not significantly differ by age. IL-10 responses to EBV lytic antigens, PPD, and PHA correlated inversely with malaria exposure regardless of age. CONCLUSIONS Children living in malaria-holoendemic areas have diminished EBV-specific T cell immunosurveillance between the ages of 5 and 9 years, which coincides with the peak age incidence of eBL.

Early Age at Time of Primary Epstein–Barr Virus Infection Results in Poorly Controlled Viral Infection in Infants From Western Kenya: Clues to the Etiology of Endemic Burkitt Lymphoma

BACKGROUND Infection with Epstein-Barr virus (EBV) early in life and repeated malaria exposure have been proposed as risk factors for endemic Burkitt lymphoma (eBL). METHODS Infants were enrolled from 2 rural sites in Kenya: the Kisumu District, where malaria transmission is holoendemic and risk for eBL is high, and the Nandi District, where malaria transmission is limited and the risk for eBL is low. Blood samples were taken from infants through 2 years of age to measure EBV viral load, EBV antibodies, and malaria parasitemia. RESULTS We observed a significantly younger age at time of primary EBV infection in children from Kisumu compared with children from Nandi (mean age, 7.28 months [±0.33 SEM] in Kisumu vs 8.39 months [±0.26 SEM] in Nandi), with 35.3% of children in Kisumu infected before 6 months of age. To analyze how different predictors affected EBV viral load over time, we performed multilevel mixed modeling. This modeling revealed that residence in Kisumu and younger age at first EBV infection were significant predictors for having a higher EBV viral load throughout the period of observation. CONCLUSIONS Children from a region at high risk for eBL were infected very early in life with EBV, resulting in higher viral loads throughout infancy.

Immune escape by Epstein-Barr virus associated malignancies

Persistent Epstein-Barr virus (EBV) infection remains asymptomatic in the majority of virus carriers, despite the potent growth transforming potential of this virus. The increased frequency of EBV associated B cell lymphomas in immune compromised individuals suggests that tumor-free chronic infection with this virus is in part due to immune control. Here we discuss the evidence that loss of selective components of EBV specific immunity might contribute to EBV associated malignancies, like nasopharyngeal carcinoma, Burkitts and Hodgkins lymphoma, in otherwise immune competent patients. Furthermore, we discuss how current vaccine approaches against EBV might be able to target these selective deficiencies.

Antibodies to Pre-erythrocytic Plasmodium falciparum Antigens and Risk of Clinical Malaria in Kenyan Children

BACKGROUND IgG antibodies to pre-erythrocytic antigens are involved in prevention of infection and disease in animal models of malaria but have not been associated with protection against disease in human malaria. METHODS Levels of IgG antibodies to circumsporozoite protein (CSP), liver-stage antigen type 1 (LSA-1), and thrombospondin-related adhesive protein (TRAP) were measured in 86 children in a malaria-holoendemic area of Kenya. The children were then monitored for episodes of clinical malaria for 52 weeks. RESULTS Children with high levels of IgG antibodies to CSP, LSA-1, and TRAP had a decreased risk of clinical malaria (adjusted hazard ratio, 0.29; 95% confidence interval 0.10-0.81; P = .02), a lower incidence of clinical malaria (P=.006), protection from clinical malaria with a parasite level of > or =4000 parasites/microL (P= .03), and a higher hemoglobin level at enrollment (P= .009), compared with children with lower antibody levels. Protection against malaria morbidity was associated primarily with antibodies to CSP and LSA-1. CONCLUSIONS Kenyan children with high levels of IgG antibodies to the pre-erythrocytic antigens CSP, LSA-1, and TRAP have a lower risk of developing clinical malaria than children without high levels of these antibodies. The decreased risk of clinical malaria may be mediated in part by prevention of high-density parasitemia.