Malarial Antibody Research Articles

Efficient transplacental transfer of SARS-CoV-2 antibodies between naturally exposed mothers and infants in Accra, Ghana

We aimed to determine SARS-CoV-2 antibody seropositivity among pregnant women and the transplacental transfer efficiency of SARS-CoV-2-specific antibodies relative to malaria antibodies among SARS-CoV-2 seropositive mother-cord pairs. This cross-sectional study was conducted in Accra, Ghana, from March to May 2022. Antigen- specific IgG antibodies against SARS-CoV-2 (nucleoprotein and spike-receptor binding domain) and malarial antigens (circumsporozoite protein and merozoite surface protein 3) in maternal and cord plasma were measured by ELISA. Plasma from both vaccinated and unvaccinated pregnant women were tested for neutralizing antibodies using commercial kit. Of the unvaccinated pregnant women tested, 58.12% at antenatal clinics and 55.56% at the delivery wards were seropositive for both SARS-CoV-2 nucleoprotein and RBD antibodies. Anti-SARS-CoV-2 antibodies in cord samples correlated with maternal antibody levels (N antigen rs = 0.7155, p < 0.001; RBD rs = 0.8693, p < 0.001). Transplacental transfer of SARS-CoV-2 nucleoprotein antibodies was comparable to circumsporozoite protein antibodies (p = 0.9999) but both were higher than transfer rates of merozoite surface protein 3 antibodies (p < 0.001). SARS-CoV-2 IgG seropositivity among pregnant women in Accra is high with a boost of SARS-CoV-2 RBD-specific IgG in vaccinated women. Transplacental transfer of anti-SARS-CoV-2 and malarial antibodies was efficient, supporting vaccination of mothers as a strategy to protect infants against SARS-CoV-2.

Malarial Antibodies and Endemicity: Does It Affect SARS-CoV-2 Severity and Outcomes?

Background India has a disproportionately lower rateof coronavirus disease 2019 (COVID-19) severe disease and lower death rates with respect to other parts of the world. It has been proposed that malaria-endemic countries such as India are relatively protected against severe COVID-19 disease and deaths. Methods This was a cross-sectional, analytical, observational study conducted from August 2020 to July 2021 at a tertiary care COVID-19-designated center in New Delhi, India. It aimed to study the association between antimalarial antibody levels and COVID-19 disease severity and outcomes. Results One hundred forty-six patients were included in the final analysis. The mean (standard deviation {SD}) age of the study population was 44.6 (17.2) years, and there were 85 (58.2%) males. Sixty-five patients had mild disease, 14 patients had moderatedisease, and 67 patients had severe disease at the time of enrolment in the study. Forty-six patients expired during the hospital stay. For the antimalarial antibody, there was a statistically significant difference between mild and moderate (p=0.018), mild and severe (p=0.016), and mild and combined moderate and severe diseases (p=0.013). However, there was no difference betweenthe patients who survived and those who did not. Conclusion Antimalarial antibody levels may not be associated with the outcomes of COVID-19 during hospital stay. However, this study has provided some insights into the relationship between the severity and outcomes of COVID-19 and the levels of antimalarial antibodies.

Malarial Antibody Detection with an Engineered Yeast Agglutination Assay.

Malaria, a disease caused by the Plasmodium parasite carried by Anopheles mosquitoes, is commonly diagnosed by microscopy of peripheral blood smears and with rapid diagnostic tests. Both methods show limited detection of low parasitemia that may maintain transmission and hinder malaria elimination. We have developed a novel agglutination assay in which modified Saccharomyces cerevisiae cells act as antigen-displaying bead-like particles to capture malaria antibodies. The Epidermal Growth Factor-1 like domain (EGF1) of the Plasmodium falciparum merozoite surface protein-1 (PfMSP-119) was displayed on the yeast surface and shown to be capable of binding antimalaria antibodies. Mixed with a second yeast strain displaying the Z domain of Protein A from Staphylococcus aureus and allowed to settle in a round-bottomed well, the yeast produce a visually distinctive agglutination test result: a tight "button" at a low level of malarial antibodies, and a diffuse "sheet" when higher antibody levels are present. Positive agglutination results were observed in malaria-positive human serum to a serum dilution of 1:100 to 1:125. Since the yeast cells are inexpensive to produce, the test may be amenable to local production in regions seeking malaria surveillance information to guide their elimination programs.

Optimization of the CIS43LS Malarial Monoclonal Antibody and Protection Against Malaria

Optimization of the CIS43LS Malarial Monoclonal Antibody and Protection Against Malaria

Adults with Plasmodium falciparum malaria have higher magnitude and quality of circulating T-follicular helper cells compared to children.

SummaryBackgroundProtective malarial antibodies are acquired more rapidly in adults than children, independently of cumulative exposure, however the cellular responses mediating these differences are unknown. CD4 T-follicular helper (Tfh) cells have key roles in inducing antibodies, with Th2-Tfh cell activation associated with antibody development in malaria. Whether Tfh cell activation in malaria is age dependent is unknown and no studies have compared Tfh cell activation in children and adults with malaria.MethodsWe undertook a comprehensive study of Tfh cells, along with B cells and antibody induction in children and adults with malaria. Activation and proliferation of circulating Tfh (cTfh) cell subsets was measured ex vivo and parasite-specific Tfh cell frequencies and functions studied with Activation Induced Marker (AIM) assays and intracellular cytokine staining.FindingsDuring acute malaria, the magnitude of cTfh cell activation was higher in adults than in children and occurred across all cTfh cell subsets in adults but was restricted only to the Th1-cTfh subset in children. Further, adults had higher levels of parasite-specific cTfh cells, and cTfh cells which produced more Th2-Tfh associated cytokine IL-4. Consistent with a role of higher Tfh cell activation in rapid immune development in adults, adults had higher activation of B cells during infection and higher induction of antibodies 7 and 28 days after malaria compared to children.InterpretationOur data provide evidence that age impacts Tfh cell activation during malaria, and that these differences may influence antibody induction after treatment. Findings have important implications for vaccine development in children.FundingThis word was supported by the National Health and Medical Research Council of Australia, Wellcome Trust, Charles Darwin University Menzies School of Health Research, Channel 7 Children's Research Foundation, and National Health Institute.

Performance evaluation of two SARS-CoV-2 IgG/IgM rapid tests (Covid-Presto and NG-Test) and one IgG automated immunoassay (Abbott).

The aim of this study was to assess the analytical performances, sensitivity and specificity, of two rapid tests (Covid- Presto® test rapid Covid-19 IgG/IgM and NG-Test® IgM-IgG COVID-19) and one automated immunoassay (Abbott SARS-CoV-2 IgG) for detecting anti- SARS-CoV-2 antibodies. This study was performed with: (i) a positive panel constituted of 88 SARS-CoV-2 specimens collected from patients with a positive SARS-CoV-2 RT-PCR, and (ii) a negative panel of 120 serum samples, all collected before November 2019, including 64 samples with a cross-reactivity panel. Sensitivity of Covid-Presto® test for IgM and IgG was 78.4% and 92.0%, respectively. Sensitivity of NG-Test® for IgM and IgG was 96.6% and 94.9%, respectively. Sensitivity of Abbott IgG assay was 96.5% showing an excellent agreement with the two rapid tests (κ = 0.947 and κ = 0.936 for NGTest ® and Covid-Presto® test, respectively). An excellent agreement was also observed between the two rapid tests (κ = 0.937). Specificity for IgM was 100% and 86.5% for Covid-Presto® test and NG-Test®, respectively. Specificity for IgG was 92.0%, 94.9% and 96.5% for Covid-Presto®, NGTest ®, and Abbott, respectively. Most of the false positive results observed with NG-Test® resulted from samples containing malarial antibodies. In conclusion, performances of these 2 rapid tests are very good and comparable to those obtained with automated immunoassay, except for IgM specificity with the NG-Test®. Thus, isolated IgM should be cautiously interpreted due to the possible false-positive reactions with this test. Finally, before their large use, the rapid tests must be reliably evaluated with adequate and large panel including early seroconversion and possible cross-reactive samples.

Differences in Anti Malarial Antibody Concentrations and Specificities between Male and Female Ugandan Children

Our current hypothesis is that there is differential antibody level and quality between the sexes. This is based on earlier work in schistosomiasis showing higher levels of antibodies in females. Females have also been shown to have lower malaria parasite density although the explanation for this was thought to be hormonal.

Changing plasma cytokine, chemokine and growth factor profiles upon differing malaria transmission intensities

BackgroundMalaria epidemiological and immunological data suggest that parasite tolerance wanes in the absence of continuous exposure to the parasite, potentially enhancing pathogenesis. The expansion of control interventions and elimination campaigns raises the necessity to better understand the host factors leading to susceptibility or tolerance that are affected by rapid changes in malaria transmission intensity (MTI). Mediators of cellular immune responses are responsible for the symptoms and pathological alterations during disease and are expected to change rapidly upon malaria exposure or cessation.MethodsThe plasma concentrations of 30 cytokine, chemokine and growth factors in individuals of all ages from a malaria endemic area of southern Mozambique were compared between 2 years of different MTI: 2010 (lower, n = 234) and 2013 (higher, n = 143). The effect of the year on the correlations between cytokines, chemokines and growth factors and IgGs to Plasmodium falciparum (markers of exposure) was explored. The effects of age, sex, neighbourhood and parasitaemia on analyte levels and their interactions with year were also assessed.ResultsAn inverse correlation of several cellular immune mediators with malarial antibodies in 2013, and a lack of correlation or even a positive correlation in 2010 were observed. Most cytokines, chemokines and growth factors, regardless of their immune function, had higher concentrations in 2010 compared with 2013 in P. falciparum-infected and uninfected subjects. Age and neighbourhood showed an effect on analyte concentrations.ConclusionsThe results show a different regulation of the cellular immune response in 2010 vs 2013 which could be related to a loss of immune-tolerance after a decline in MTI in 2010 and previous years, and a rapid re-establishment of tolerance as a consequence of more continuous exposure as MTI began increasing in 2012. Cellular immune mediators warrant further investigation as possible surrogates of MTI-associated host susceptibility or tolerance.

Comparison of non-magnetic and magnetic beads multiplex assay for assessment of Plasmodium falciparum antibodies.

BackgroundNew reagents have emerged allowing researchers to assess a growing number of vaccine-associated immune parameters. Multiplex immunoassay(s) are emerging as efficient high-throughput assays in malaria serology. Currently, commercial vendors market several bead reagents for cytometric bead assays (CBA) but relative performances are not well published. We have compared two types of bead-based multiplex assays to measure relative antibody levels to malarial antigens.MethodsAssays for the measurement of antibodies to five Plasmodium falciparum vaccine candidates using non-magnetic and magnetic fluorescent microspheres were compared for their performances with a Bio-Plex200 instrument. Mean fluorescence intensity (MFI) was determined from individuals from western Kenya and compared to known positive and negative control plasma samples.ResultsP. falciparum recombinant antigens were successfully coupled to both non-magnetic and magnetic beads in multiplex assays. MFIs between the two bead types were comparable for all antigens tested. Bead recovery was superior with magnetic beads for all antigens. MFI values of stored non-magnetic coupled beads did not differ from freshly coupled beads, though they showed higher levels of bead aggregation.DiscussionMagnetic and non-magnetic beads performed similarly in P. falciparum antibody assays. Magnetic beads were more expensive, but had higher bead recovery, were more convenient to use, and provided rapid and easy protocol manipulation. Magnetic beads are a suitable alternative to non-magnetic beads in malarial antibody serology.

Effect of nutrient supplementation on the acquisition of humoral immunity to Plasmodium falciparum in young Malawian children

BackgroundThere is evidence that suggests that undernutrition has a detrimental effect on malarial immunity in children. The aim of the study was to discover whether nutrient supplementation improved development of malarial antibody immunity in children up to 18 months of age.MethodsThe study was conducted with a subset of 432 Malawian children from a randomized controlled trial of nutritional supplements. The arms included pre- and postnatal small-quantity lipid-based nutrient supplements for both mother and child; prenatal supplementation with iron and folic acid; and pre- and postnatal supplementation with multiple micronutrients. Paired plasma samples were collected at 6 and 18 months of age. The levels of antibodies against merozoite surface protein 1 (MSP1 19kD) and MSP2, erythrocyte binding antigen 175 (EBA175), reticulocyte binding protein homologue 2A (Rh2A9), schizont extract and variant antigens expressed on the surface of infected erythrocytes were measured.ResultsAt 18 months of age, 5.4% of children were parasitaemic by microscopy and 49.1% were anaemic. Antibodies to the tested merozoite antigens and schizont extract increased between 6 and 18 months and this increase was statistically significant for MSP1, MSP2 and EBA175 (p < 0.0001) whereas IgG to variant surface antigens decreased with increasing age (p < 0.0001). However, the supplementation type did not have any impact on the prevalence or levels of antibodies at either 6 or 18 months of age to any of the tested malaria antigens in either univariate analysis or multivariate analysis after adjusting for covariates.ConclusionsPre- and postnatal lipid-based nutrient supplementation did not alter malaria antibody acquisition during infancy, compared to prenatal supplementation with iron and folic acid or pre- and postnatal supplementation with multiple micronutrients.Trail registeration Clinicaltrials.gov registration number NCT01239693

Asymptomatic infections in blood donors harbouring Plasmodium: an invisible risk detected by molecular and serological tools.

Transfusion-transmitted malaria due to asymptomatic Plasmodium infections is a challenge for blood banks. There is a lack of data on the prevalence of asymptomatic infected blood donors and the incidence of transfusion-transmitted malaria in low endemicity areas worldwide. We estimated the frequency of blood donors harbouring Plasmodium in an area in which asymptomatic infections have been reported. To estimate the frequency of blood donors harbouring Plasmodium we used microscopy and molecular tools. Serological tests were applied to measure the exposure of candidates to Plasmodium antigens. Venous blood was collected from 91 candidates attending the "Pró-Sangue" Blood Centre Foundation in São Paulo, who lived in the municipality of Juquitiba, São Paulo, Brazil, where sporadic autochthonous cases of malaria have been described. Blood samples were used for parasitological, molecular and serological studies. Among the 91 samples examined, rare Plasmodium forms were observed in two donors. Genus real-time polymerase chain reaction analysis demonstrated Plasmodium amplification in three candidates and species-specific nested polymerase chain reaction identified P. malariae in two. ELISA-IgG was reactive in 42.9% of samples for P. vivax (Pv-MSP119) and in 6.6% for P. falciparum (Pf-Zw). ELISA-IgM was reactive in 2.2% of samples for P. vivax and in 4.4% for P. falciparum. An indirect immunofluorescence assay was reactive for P. malariae in 15.4% of cases. Reservoirs of Plasmodium represent a challenge for blood banks, since studies have shown that high levels of submicroscopic infections can occur in low transmission areas. The risk of transfusion-transmitted malaria presented here points to the need to conduct molecular investigations of candidate donors with any positive malarial antibody test.

Immunity as a predictor of anti-malarial treatment failure: a systematic review

BackgroundNaturally acquired immunity can reduce parasitaemia and potentially influence anti-malarial treatment outcomes; however, evidence for this in the current literature provides conflicted results. The available evidence was synthesized to determine and quantify the association between host immunity and anti-malarial treatment failure.MethodsFour databases were searched to identify studies investigating malaria antibody levels in patients receiving anti-malarial treatment for symptomatic malaria with treatment failure recorded according to the World Health Organization classification. Odds ratios or hazard ratios were extracted or calculated to quantify the association between malarial antibody levels and treatment failure, and findings from different studies were visualized using forest plots.ResultsEight studies, including patients with falciparum malaria treated with mono- and combination therapy of artemisinin derivatives, sulfadoxine, pyrimethamine and chloroquine, were identified. Reported and calculated effect estimates varied greatly between studies, even those assessing the same antigens and treatments. An association between blood-stage IgG responses and treatment efficacy was observed. The greatest magnitudes of effect were observed for artemisinin [OR/HR (95% CI) range 0.02 (0.00, 0.45)–1.08 (0.57, 2.06)] and chloroquine [0.24 (0.04, 1.37)–0.32 (0.05, 1.96)] treatments, and larger magnitudes of effect were observed for variant surface antigen responses [0.02 (0.00, 0.45)–1.92 (0.94, 3.91)] when compared with merozoite specific responses [0.24 (0.04, 1.37)–2.83 (1.13, 7.09)].ConclusionsNaturally acquired malarial immunity is associated with reduced anti-malarial treatment failure in malaria endemic populations. Anti-malarial IgG effects treatment outcome differently for different anti-malarial drugs and antigen targets, and had the greatest impact during treatment with the current first-line treatments, the artemisinins. This has implications for the assessment of the therapeutic efficacy of anti-malarials, particularly in the context of emerging artemisinin resistance.

Association between malaria immunity and pregnancy outcomes among Malawian pregnant women receiving nutrient supplementation.

BackgroundMalaria antibody responses measured at delivery have been associated with protection from maternal anaemia and low birth weight deliveries. Whether malarial antibodies present in the first half of pregnancy may protect from these or other poor birth outcomes is unclear. To determine whether malaria antibodies in the first half of pregnancy predict pregnancy outcomes, antibodies were measured to a range of merozoite antigens and to antigens expressed on the surface of parasitized red blood cells (pRBCs) in plasma samples collected at 14–20 weeks of gestation from Malawian women. The latter antibodies were measured as total IgG to pRBCs, and antibodies promoting opsonic phagocytosis of pRBCs. Associations between antibodies and maternal haemoglobin in late pregnancy or newborn size were investigated, after adjusting for potential covariates.ResultsAntibodies to pRBC surface antigens were associated with higher haemoglobin concentration at 36 weeks. Total IgG to pRBCs was associated with 0.4 g/l [(95% confidence interval (0.04, 0.8)] increase in haemoglobin, and opsonizing antibody with 0.5 (0.05, 0.9) increase in haemoglobin for each 10% increase in antibody. These antibodies were not associated with birthweight, placental malaria, or newborn anthropometrics. Antibodies to merozoite antigens and non-placental-binding IEs were not associated with decreased risk of any of these outcomes. In some instances, they were negatively associated with outcomes of interest.ConclusionAntibodies to placental-binding infected erythrocytes may be associated with higher haemoglobin levels in pregnancy, whereas antibodies to other malaria antigens may instead be markers of malaria exposure. Trial registration clinicaltrials.gov NCT01239693. Registered Nov 10, 2010.

Evaluating IgG Antibody to Variant Surface Antigens Expressed on Plasmodium falciparum Infected Erythrocytes Using Flow Cytometry.

Constant exposure to Plasmodium falciparum leads to acquisition of malarial antibodies that can protect against the clinical consequences of infection. One important target of such antibodies is against the parasite-infected erythrocyte (IEs). Current established assays to test the efficacy of antibodies in preventing parasite growth include direct parasite growth inhibition, the agglutination of IEs, and the inhibition of adhesion of IEs (to quantify antibody that inhibits adhesion to purified receptors or cells).However, many of these assays are labor-intensive and low-output which limits study sizes to small cohorts. Here we present an alternative assay that measures the levels of protective antibodies to variant surface antigens (VSA) of IEs. This assay can be performed using a microtitre plate and requires only a small volume of test serum sample. Serum samples are incubated with IEs and are then analyzed using a semi-automated autosampler attached to a flow cytometer. The assay is accurate, quick, and reproducible. Ultimately this assay could be used on large population-based studies, which could increase the statistical power of clinical studies.

Plasmodium vivax infection: atypical memory B cells are expanded and associated with the persistence of Duffy binding protein II (DBPII) antibody response

Antibody responses generated during malaria infection represent an important component of acquired clinical immunity. Despite that, B cell subpopulations induced by the Plasmodium vivax (Pv) infection remains largely unknown. Here, we demonstrated that activated as well as “atypical” memory B cells (MBCs) are expanded in peripheral blood of Pv-exposed individuals, but their frequencies were not associated with acute infection. Aiming to investigate the association between peripheral B cells subsets and Pv-specific antibodies, we further followed-up 34 individuals exposed to P. vivax in the Brazilian Amazon area, an area of markedly unstable malaria transmission; after three cross-sectional survey (at 6-months intervals), ELISA-detected specific IgG (AMA-1, MSP1-19, DBPII) allowed the classification of those individuals as non-responder (NR), temporary (TR) or persistent responder (PR). For AMA-1 and MSP1-19 serological groups, the frequencies of MBCs (classical and atypical) and plasma cells (PCs) were similar among the groups. For DBPII group, we found a trend toward decreases classical MBCs according to the antibody response (NR>TR>PR). On the other hand, the frequencies of atypical MBCs increased according to the presence and persistence of DBPII antibody response (PR>TR>NR). Altogether, these results showed that atypical MBCs are expanded in Pv-exposed individuals (infected and non-infected), and it seems to be associated with the persistence of DBPII antibody response. Although preliminary, these results suggest that atypical MBCs contribute in generation of malarial antibody responses and provide insight into the role of atypical MBCs in P. vivax malaria immunity.

Plasmodium genome in blood donors at risk for malaria after several years of residence in Italy

At present, the main risk of transfusion-transmitted malaria (TTM) in nonendemic countries is chronic, asymptomatic immigrants from malaria-endemic areas. Semi-immune donors may carry undetected parasitemia. This study examines Plasmodium infection in at-risk blood donors in Northern Italy. Plasma samples from 97 candidate donors and 80 controls were tested for malarial antibodies using a commercial enzyme immunoassay. The conserved 18S rRNA and the mitochondrial genes of Plasmodium were amplified to detect and quantify parasite genomes (copies/mL). Plasmodium species were identified with a species-specific nested polymerase chain reaction. Parasitemic samples were further tested by amplification of polymorphic repetitive regions in MSP-1 Block 2, MSP-2 Block 3, and glutamate-rich protein (GLURP) confirmed by sequencing. Three of 83 seropositive (3.6%) and one of 14 seronegative at-risk candidate donors carried Plasmodium genome (4 × 10(3) -8.5 × 10(4) copies/mL): two P. falciparum, one P. malariae (seronegative sample), and one coinfection with P. malariae and P. ovale. Alleles of MSP-1 (MAD20 and K1), MSP-2 (3D7 and FC27), and GLURP were amplified from Sample 261. In Sample 282 only one allele in MSP-2 (FC27) and GLURP was amplified. No alleles were detected in Samples 283 and 331. Immigrants from endemic countries might carry infectious Plasmodium after 2 to 5 years of continuous residence in Italy. Serologic screening may miss donors carrying P. malariae. Permanent exclusion or screening for both antibodies and genome are needed to prevent TTM.

Surface plasmon resonance characterization of monoclonal and polyclonal antibodies of malaria for biosensor applications

Surface plasmon resonance (SPR) screening of monoclonal and polyclonal antibodies of Plasmodium falciparum (MoabPf and PoabPf) for recombinant Histidine rich protein-II antigen (Ag) of Pf (rHRP-II Ag) was conducted in a real-time and label-free manner to select an appropriate antibody (Ab) for biosensor applications. In this study 4-mercaptobenzoic acid (4-MBA) modified gold SPR chip was used for immobilizing the Ag and then Ab was interacted. SEM image showed modification of SPR chip with 4-MBA and EDAX confirmed the presence of 4-MBA on the SPR chip. Equilibrium constant (KD) and maximum binding capacity of analyte (Bmax) values for the interaction of MoabPf or PoabPf with the immobilized rHRP-II Ag were calculated and found to be 0.517nM and 48.61m° for MoabPf and 2.288nM and 46.80m° for PoabPf, respectively. In addition, thermodynamic parameters such as ΔG, ΔH and ΔS were determined for the interaction between rHRP-II Ag and MoabPf or PoabPf and the values revealed that the interaction is spontaneous, exothermic and driven by entropy. The kinetics and thermodymanic results of this study revealed that the interaction between MoabPf and rHRP-II Ag is more effective than that of PoabPf due to the fact that MoabPf was derived from a single epitope (single clone) whereas the PoabPf was from the mixture of a number of epitopes (polyclones). Finally, SPR methodology was developed for the sensing of malarial antibodies. The limit of detection was found to be 5.6pg with MoabPf which was found to be the best in our study.

Serological Measures of Malaria Transmission in Haiti: Comparison of Longitudinal and Cross-Sectional Methods

BackgroundEfforts to monitor malaria transmission increasingly use cross-sectional surveys to estimate transmission intensity from seroprevalence data using malarial antibodies. To date, seroconversion rates estimated from cross-sectional surveys have not been compared to rates estimated in prospective cohorts. Our objective was to compare seroconversion rates estimated in a prospective cohort with those from a cross-sectional survey in a low-transmission population.Methods and FindingsThe analysis included two studies from Haiti: a prospective cohort of 142 children ages ≤11 years followed for up to 9 years, and a concurrent cross-sectional survey of 383 individuals ages 0–90 years old. From all individuals, we analyzed 1,154 blood spot specimens for the malaria antibody MSP-119 using a multiplex bead antigen assay. We classified individuals as positive for malaria using a cutoff derived from the mean plus 3 standard deviations in antibody responses from a negative control set of unexposed individuals. We estimated prospective seroconversion rates from the longitudinal cohort based on 13 incident seroconversions among 646 person-years at risk. We also estimated seroconversion rates from the cross-sectional survey using a reversible catalytic model fit with maximum likelihood. We found the two approaches provided consistent results: the seroconversion rate for ages ≤11 years was 0.020 (0.010, 0.032) estimated prospectively versus 0.023 (0.001, 0.052) in the cross-sectional survey.ConclusionsThe estimation of seroconversion rates using cross-sectional data is a widespread and generalizable problem for many infectious diseases that can be measured using antibody titers. The consistency between these two estimates lends credibility to model-based estimates of malaria seroconversion rates using cross-sectional surveys. This study also demonstrates the utility of including malaria antibody measures in multiplex assays alongside targets for vaccine coverage and other neglected tropical diseases, which together could comprise an integrated, large-scale serological surveillance platform.

Detection of malarial DNA in blood donors – evidence of persistent infection

The English transfusion service has screened donations from malaria-risk donors for malarial antibodies for over 10years. The donor population includes migrants from many malaria-endemic countries and, from our experiences with post-transfusion malaria, some of these may remain parasitaemic and need clinical review. Malarial antibody screen-reactive donations with serological evidence of malaria identified by the reference laboratory were further investigated for the presence of malarial DNA. Malarial DNA was found in 14 of 1955 samples investigated; three P.falciparum, five P.vivax, three P.ovale, two P.malariae and one dual parasitaemia P.falciparum/P.malariae. All of these were donors whose malaria risk was residency rather than travel. Malarial parasitaemia in healthy donors occurs, and donor malaria-risk strategies must take into account the possibility of such donors presenting. Countries not utilizing malarial antibody screening should consider carefully the collection of donations from donors previously resident in endemic countries; temporary deferral is insufficient.

Low Antibody Levels to Pregnancy-specific Malaria Antigens and Heightened Cytokine Responses Associated With Severe Malaria in Pregnancy

Pregnant women living in unstable malaria transmission settings may develop severe malaria (SM). The pathogenesis of SM in pregnancy is poorly understood. To determine whether SM in pregnancy is associated with lower malarial antibody responses and higher cytokine responses, plasma samples were collected from 121 Sudanese pregnant women of whom 39 were diagnosed with SM. Antibodies to pregnancy-specific and non-pregnancy-specific Plasmodium falciparum variant surface antigens (VSA) and concentrations of cytokines TNF, IFNγ, IL-1β, IL-6, IL-8 and IL-10 were measured. Pregnant women with SM demonstrated significantly lower antibody levels to pregnancy-specific VSA (P = .020) and higher plasma IFNγ (P = .020), IL-10 (P = .0002) and IL-6 levels (P < .0001) than uninfected pregnant women. Concentrations of inflammatory cytokines IL-1β (P = .001), IL-6 (P = .004) and IL-8 (P = .020) were inversely correlated with antibodies to VAR2CSA-DBL5 in pregnant women with SM. Lower haemoglobin levels and higher parasite densities were associated with lack of pregnancy-specific antibodies (P = .028) and higher levels of inflammatory cytokines, in particular IL-6 and IL-8. Pregnant women with SM lack pregnancy-specific malaria immunity, and this correlates with heightened inflammatory cytokine concentrations, low haemoglobin levels and high parasite density, suggesting that failure of antibody to control parasitaemia may contribute to SM pathogenesis.