Stephen J. Rogerson

Malaria in pregnancy: pathogenesis and immunity

Understanding of the biological basis for susceptibility to malaria in pregnancy was recently advanced by the discovery that erythrocytes infected with Plasmodium falciparum accumulate in the placenta through adhesion to molecules such as chondroitin sulphate A. Antibody recognition of placental infected erythrocytes is dependent on sex and gravidity, and could protect from malaria complications. Moreover, a conserved parasite gene-var2csa-has been associated with placental malaria, suggesting that its product might be an appropriate vaccine candidate. By contrast, our understanding of placental immunopathology and how this contributes to anaemia and low birthweight remains restricted, although inflammatory cytokines produced by T cells, macrophages, and other cells are clearly important. Studies that unravel the role of host response to malaria in pathology and protection in the placenta, and that dissect the relation between timing of infection and outcome, could allow improved targeting of preventive treatments and development of a vaccine for use in pregnant women.

Adhesion of Plasmodium falciparum-infected erythrocytes to hyaluronic acid in placental malaria

Infection with Plasmodium falciparum during pregnancy leads to the accumulation of parasite-infected erythrocytes in the placenta, and is associated with excess perinatal mortality, premature delivery and intrauterine growth retardation in the infant, as well as increased maternal mortality and morbidity. P. falciparum can adhere to specific receptors on host cells, an important virulence factor enabling parasites to accumulate in various organs. We report here that most P. falciparum isolates from infected placentae can bind to hyaluronic acid, a newly discovered receptor for parasite adhesion that is present on the placental lining. In laboratory isolates selected for specific high-level adhesion, binding to hyaluronic acid could be inhibited by dodecamer or larger oligosaccharide fragments or polysaccharides, treatment of immobilized receptor with hyaluronidase, or treatment of infected erythrocytes with trypsin. In vitro flow-based assays demonstrated that high levels of adhesion occurred at low wall shear stress, conditions thought to prevail in the placenta. Our findings indicate that adhesion to hyaluronic acid is involved in mediating placental parasite accumulation, thus changing the present understanding of the mechanisms of placental infection, with implications for the development of therapeutic and preventative interventions.

Dexamethasone treatment in childhood bacterial meningitis in Malawi: a randomised controlled trial

BACKGROUND Steroids are used as adjuvant treatment in childhood pyogenic meningitis to attenuate host inflammatory responses to bacterial invasion. We aimed to assess the effectiveness of dexamethasone in management of acute bacterial meningitis in a developing country. METHODS In a double-blind, placebo controlled trial, we included 598 children with pyogenic meningitis who had been admitted to the childrens wards of the Queen Elizabeth Central Hospital, Blantyre, Malawi. We did physical, neurological, developmental, and hearing assessments at 1 and 6 months after discharge. The primary outcome was overall death. Secondary outcomes included sequelae, in-hospital deaths, and death after discharge. Analysis was done by intention to treat. FINDINGS Of the 598 included children, 307 (51%) were assigned to dexamethasone and 295 (49%) to placebo. 338 (40%) of 598 patients had Streptococcus pneumoniae, 170 (28%) Haemophilus influenzae type b, 66 (11%) Neisseria meningitidis, and 29 (5%) Salmonella spp. 78 (13%) patients had no growth on culture. The number of overall deaths was the same in the two treatment groups (relative risk 1.00 [95% CI 0.8-1.25], p=0.93). At final outcome, sequelae were identified in 84 (28%) of children on steroids and in 81 (28%) on placebo (relative risk 0.99 [95% CI 0.78-1.27], p=0.97). The number of children dying in hospital did not differ between groups. INTERPRETATION Steroids are not an effective adjuvant treatment in children with acute bacterial meningitis in developing countries.

Plasmodium falciparum isolates from infected pregnant women and children are associated with distinct adhesive and antigenic properties.

Plasmodium falciparum malaria during pregnancy is an important cause of maternal and infant morbidity and mortality. Accumulation of large numbers of P. falciparum-infected erythrocytes in the maternal blood spaces of the placenta may be mediated by adhesion of infected erythrocytes to molecules presented on the syncytiotrophoblast surface. In this study, isolates from placentas and peripheral blood of infected pregnant women and from children were tested for binding to purified receptors and for agglutination with adult sera. Results suggest that adhesion to chondroitin sulfate A may be involved in placental parasite sequestration in most cases, but other factors are also likely to be important. Agglutination assay results suggest that parasites infecting pregnant women are antigenically distinct from those common in childhood disease. The prevalence of agglutinating antibodies to pregnancy isolates was generally low, but it was highest in multigravidae who are likely to have had the greatest exposure.

The effect of Plasmodium falciparum malaria on HIV-1 RNA blood plasma concentration

OBJECTIVES This study was undertaken to determine the relative effect of malaria infection on HIV concentration in blood plasma, and prospectively to monitor viral concentrations after antimalarial therapy. DESIGN A prospective, double cohort study was designed to compare the blood HIV-1 RNA concentrations of HIV-positive individuals with and without acute malaria illness. Subjects were followed for 4 weeks after successful malaria therapy, or for 4 weeks from enrollment (controls). METHODS Malawian adults with symptomatic Plasmodium falciparum parasitemia (malaria group) and asymptomatic, aparasitemic blood donors (control group) were tested for HIV-1 antibodies to identify appropriate study groups. The malaria group received antimalarial chemotherapy only and were followed with sequential blood films. In both groups, blood plasma HIV-1 RNA viral concentrations were determined at enrollment and again at 1, 2 and 4 weeks. RESULTS Forty-seven malaria patients and 42 blood donors were enrolled. At enrollment blood plasma HIV-1 RNA concentrations were approximately sevenfold higher in patients with malaria than in blood donors (medians 15.1 x 10(4) and 2.24 x 10(4) copies/ml, respectively, P = 0.0001). No significant changes in median HIV-1 concentrations occurred in the 21 blood donors followed to week 4 (P = 0.68). In the 27 subjects successfully treated for malaria who were followed to week 4, a reduction in plasma HIV-1 RNA was observed from a median of 19.1 x 10(4) RNA copies/ml at enrollment, to 12.0 x 10(4) copies/ml at week 4, (P = 0.02). Plasma HIV-1 concentrations remained higher in malaria patients than controls (median 12.0 x 10(4) compared with 4.17 x 10(4) copies/ml, P = 0.086). CONCLUSIONS HIV-1 blood viral burden is higher in patients with P. falciparum malaria than in controls and this viral burden can, in some patients, be partly reduced with antimalarial therapy.

Cytokine Expression in the Brain in Human Cerebral Malaria

Evidence from clinical studies and murine models supports a role for cytokines in the pathogenesis of human cerebral malaria (CM). In this study, reverse transcriptase-polymerase chain reaction (RT-PCR) was used to investigate expression of mRNA for transforming growth factor (TGF)-beta, interleukin (IL)-1beta, and tumor necrosis factor (TNF)-alpha in human postmortem tissue. Immunohistochemistry was used to examine the distribution of cytokine protein. TGF-beta was expressed in normal brain, in CM, and in meningitis and encephalitis. IL-1beta was absent from normal brain but was detected in CM and other cerebral infections. TNF-alpha mRNA was expressed only in CM, although TNF-alpha protein was also seen in meningitis. Cytokine mRNA expression in the brain did not correlate with the density of parasitized erythrocytes detected using RT-PCR for major surface protein-2. This report of RT-PCR on postmortem human tissues infected with CM demonstrates induction of the proinflammatory cytokines TNF-alpha and IL-1beta in the brain.

Placental Tumor Necrosis Factor Alpha but Not Gamma Interferon Is Associated with Placental Malaria and Low Birth Weight in Malawian Women

ABSTRACT Malaria in pregnancy predisposes to maternal anemia and low birth weight (LBW). We examined the possible roles of the cytokines tumor necrosis factor alpha (TNF-α) and gamma interferon (IFN-γ) in these adverse outcomes. We measured cytokine concentrations in placental, peripheral, and cord blood plasma in relation to malaria parasitemia and placental monocyte accumulation in 276 Malawian women. Maternal hemoglobin concentration, human immunodeficiency virus status, and infant birth weight were determined. Concentrations of TNF-α in placental blood were correlated with densities of Plasmodium falciparum-infected erythrocytes (P < 0.0001) and of intervillous monocyte infiltrates (P < 0.0001) on placental histology. Peripheral blood TNF-α concentrations were relatively low and were weakly associated with malaria. TNF-α concentrations were higher in placental blood, where they were strongly associated with malaria. Placental plasma TNF-α levels were higher in women who had LBW babies (P = 0.0027), women with febrile symptoms (P < 0.0001), and teenage mothers (P = 0.04) than in other women. The presence of TNF-α in cord blood was not associated with malaria infection. IFN-γ levels were infrequently elevated, and elevated IFN-γ levels were not associated with poor pregnancy outcomes. Placental production of TNF-α, but not of IFN-γ, may be implicated in impaired fetal growth in Malawian women.

Intermittent sulfadoxine-pyrimethamine in pregnancy: effectiveness against malaria morbidity in Blantyre, Malawi, in 1997–1999

Plasmodium falciparum malaria in pregnancy predisposes to maternal and foetal morbidity. In 1993 Malawi adopted intermittent presumptive therapy with sulfadoxine-pyrimethamine (SP) as malaria prophylaxis for all pregnant women. To assess operational effectiveness of SP, we examined (in 1997-99) the relationship between number of doses of SP prescribed in antenatal clinic and indicators of malaria infection and morbidity at delivery, including peripheral and placental parasitaemia, maternal and neonatal anaemia, and birthweight. Among Malawian women delivering in a large urban hospital, SP prescription was associated with a decrease in placental malaria prevalence (from 31.9% with no SP prescription to 22.8% with > or = 2 doses SP) and density, decreased prevalence of low birthweight (from 23% in women not receiving SP to 10.3% in women given > or = 2 doses), and higher maternal haemoglobin concentrations. These effects were most marked in first and second pregnancies, in which malaria prevalence was highest. Maternal and cord blood malaria prevalence and mean cord blood haemoglobin concentrations did not differ with SP usage. Implementation of the SP administration policy was incomplete: 24% of women were not prescribed any SP, and only 30% were prescribed at least 2 doses as recommended. Intermittent presumptive treatment with SP is having a positive impact on some, but not all indicators of malaria infection and morbidity in Malawi. Improved implementation and continued surveillance are essential.

The effect of Plasmodium falciparum malaria on peripheral and placental HIV-1 RNA concentrations in pregnant Malawian women.

Objective: To investigate the effect of placental Plasmodium falciparum malaria infection on peripheral and/or placental HIV-1 viral load. Design: A cross-sectional study of HIV-infected pregnant women, with and without placental malaria, delivering at Queen Elizabeth Central Hospital in Malawi. Methods: Peripheral blood samples were collected from consenting women and tested for HIV. HIV-infected women received nevirapine at the onset of labor. At delivery, placental blood and tissue specimens were collected. HIV-1 RNA concentrations were measured in peripheral and placental plasma samples, and malaria infection was determined by placental histopathology. Results: Of the 480 HIV-infected women enrolled, 304 had placental histopathology performed, of whom 74 (24.3%) had placental malaria. Compared with women without placental malaria, those with placental malaria had a 2.5-fold higher geometric mean peripheral HIV-1 RNA concentration (62 359 versus 24 814 copies/ml; P = 0.0007) and a 2.4-fold higher geometric mean placental HIV-1 RNA concentration (11 733 versus 4919 copies/ml; P = 0.008). In multivariate analyses, after adjusting for CD4 cell count and other covariates, placental malaria was associated with a 1.7-fold increase in geometric mean peripheral HIV-1 RNA concentration (47 747 versus 27 317 copies/ml; P = 0.02) and a 2.0-fold increase in geometric mean placental HIV-1 RNA concentration (9670 versus 4874 copies/ml; P = 0.03). Conclusion: Placental malaria infection is associated with an increase in peripheral and placental HIV-1 viral load, which might increase the risk of mother-to-child transmission of HIV.

Impairment of humoral immunity to Plasmodium falciparum malaria in pregnancy by HIV infection

BACKGROUND HIV infection increases the risk of malaria infection in pregnant women. Antibodies to variant surface antigens (VSA) on infected erythrocytes might protect against malaria in pregnancy. We postulated that HIV-induced impairment of humoral immunity to VSA mediates the increased susceptibility to malaria. METHODS We compared serum concentrations of antibodies to VSA by flow cytometry or agglutination, and to merozoite proteins AMA-1 and MSP119 by ELISA, in 298 pregnant Malawian women, and related the findings to malaria and HIV infection, CD4-positive T-cell count, and HIV-1 viral load. FINDINGS Concentrations of IgG to placental type VSA were lower in HIV-infected women than in HIV-uninfected women (median 8 units [IQR 4-23] vs 20 [12-30]; p<0.0001), among women with malaria (p=0.009) and those without malaria (p=0.0062). The impairment was greatest in first pregnancy. Agglutinating antibodies to placental VSA were present in a lower proportion of HIV-infected than HIV-uninfected women (58 [35.1%] of 165 vs 50 [53.8%] of 93, p<0.001). The degree of antibody binding by flow cytometry was correlated with CD4-positive T-cell count (r=0.16, p=0.019) and inversely with HIV-1 viral load (r=-0.16, p=0.030). Concentrations of antibodies to AMA-1 were lower in HIV infection (p<0.0001) but were not correlated with CD4-positive T-cell count or viral load. Responses to MSP119 were little affected by HIV infection. In multivariate analyses, HIV was negatively associated with amount of antibody to both VSA and AMA-1 (p<0.001 for each) but not MSP119. INTERPRETATION HIV infection impairs antimalarial immunity, especially responses to placental type VSA. The impairment is greatest in the most immunosuppressed women and could explain the increased susceptibility to malaria seen in pregnant women with HIV infection.