Rapid diagnosis and prognosis of malaria infection using a microfluidic point-of-care immunoassay

Malaria is a major cause of illness and death worldwide. Rapid diagnostic tests are the most widely used tool for detecting malaria infection, however, they only provide binary results and lack the sensitivity needed to detect many asymptomatic infections. Molecular assays for quantifying malaria biomarkers offer higher detection sensitivity, however, they are time-consuming, and require expert training and expensive equipment, making them unsuitable for use in most of Africa. To address the need for simple, accurate and field-deployable malaria diagnostic tests, we have developed a microfluidic point-of-care (mPOC) immunoassay for rapid quantification of Plasmodium falciparum histidine-rich protein 2 (PfHRP2), a malaria parasite biomarker, in whole blood. This device features two diagnostic modes for detecting PfHRP2 at low (100's pg/mL) and high (1,000's ng/mL) concentrations, making it useful for multiple diagnostic applications, including the detection of asymptomatic infection, prediction of disease outcomes and diagnosis of cerebral malaria. Measurements of PfHRP2 in blood samples from malaria patients demonstrates that this platform offers similar accuracy as an ultra-sensitive PfHRP2 enzyme-linked immunosorbent assay (ELISA) test, while being 12× faster and simpler to use. This mPOC immunoassay can be deployed in rural health centers to assist clinicians in diagnosing and triaging malaria patients, ultimately improving patient outcomes.

SARS-CoV-2 Seroprevalence and Vaccine Uptake among Pregnant Women at First Antenatal Care Visits in Malawi

Many SARS-CoV-2 infections are asymptomatic, thus reported cases underestimate actual cases. To improve estimates, we conducted surveillance for SARS-CoV-2 seroprevalence among pregnant women attending their first antenatal care visit (ANC1) from June 2021 through May 2022. We administered a questionnaire to collect demographic, risk factors, and COVID-19 vaccine status information and tested dried blood spots for SARS-CoV-2 antibodies. Although <1% of ANC1 participants reported having had COVID-19, monthly SARS-CoV-2 seroprevalence increased from 15.4% (95% CI: 10.5-21.5) in June 2021 to 65.5% (95% CI: 55.5-73.7) in May 2022. Although COVID-19 vaccination was available in March 2021, uptake remained low, reaching a maximum of 9.5% (95% CI: 5.7-14.8) in May 2022. Results of ANC1 serosurveillance provided prevalence estimates helpful in understanding this population case burden that was available through self-report and national case reports. To improve vaccine uptake, efforts to address fears and misconceptions regarding COVID-19 vaccines are needed.

Cytolytic circumsporozoite-specific memory CD4+ T cell clones are expanded during Plasmodium falciparum infection

Clinical immunity against Plasmodium falciparum infection develops in residents of malaria endemic regions, manifesting in reduced clinical symptoms during infection and in protection against severe disease but the mechanisms are not fully understood. Here, we compare the cellular and humoral immune response of clinically immune (0-1 episode over 18 months) and susceptible (at least 3 episodes) during a mild episode of Pf malaria infection in a malaria endemic region of Malawi, by analysing peripheral blood samples using high dimensional mass cytometry (CyTOF), spectral flow cytometry and single-cell transcriptomic analyses. In the clinically immune, we find increased proportions of circulating follicular helper T cells and classical monocytes, while the humoral immune response shows characteristic age-related differences in the protected. Presence of memory CD4+ T cell clones with a strong cytolytic ZEB2+ T helper 1 effector signature, sharing identical T cell receptor clonotypes and recognizing the Pf-derived circumsporozoite protein (CSP) antigen are found in the blood of the Pf-infected participants gaining protection. Moreover, in clinically protected participants, ZEB2+ memory CD4+ T cells express lower level of inhibitory and chemotactic receptors. We thus propose that clonally expanded ZEB2+ CSP-specific cytolytic memory CD4+ Th1 cells may contribute to clinical immunity against the sporozoite and liver-stage Pf malaria.

Increased brain microvascular hemoglobin concentrations in children with cerebral malaria

Brain swelling is associated with death from cerebral malaria, but it is unclear whether brain swelling is caused by cerebral edema or vascular congestion-two pathological conditions with distinct effects on tissue hemoglobin concentrations. We used near-infrared spectroscopy (NIRS) to noninvasively study cerebral microvascular hemoglobin concentrations in 46 Malawian children with cerebral malaria. Cerebral malaria was defined by the presence of the malaria parasite Plasmodium falciparum on a blood smear, a Blantyre coma score of 2 or less, and retinopathy. Children with uncomplicated malaria (n = 33) and healthy children (n = 29) were enrolled as comparators. Cerebral microvascular hemoglobin concentrations were higher among children with cerebral malaria compared with those with uncomplicated malaria [median (25th, 75th): 145.2 (95.2, 190.0) μM versus 82.9 (65.7, 105.4) μM, P = 0.008]. Cerebral microvascular hemoglobin concentrations correlated with brain swelling score determined by MRI (r = 0.37, P = 0.03). Fluctuations in cerebral microvascular hemoglobin concentrations over a 30-min time period were characterized using detrended fluctuation analysis (DFA). DFA determined self-similarity of the cerebral microvascular hemoglobin concentration signal to be lower among children with cerebral malaria compared with those with uncomplicated malaria [0.63 (0.54, 0.70) versus 0.91 (0.82, 0.94), P < 0.0001]. The lower self-similarity of the hemoglobin concentration signal in children with cerebral malaria suggested impaired regulation of cerebral blood flow. The elevated cerebral tissue hemoglobin concentration and its correlation with brain swelling suggested that excess blood volume, potentially due to vascular congestion, may contribute to brain swelling in cerebral malaria.

Differential Effects of Antimalarial Drugs on Parasite Clearance Rates Are Reflected by Plasmodium falciparum Ring Ratio

Background

The location of Plasmodium falciparum within the body is determined by the life cycle of the parasite; young rings are in the peripheral blood, whereas mature parasites are sequestered in deep tissues. We can calculate a "ring ratio," the proportion of parasites in the periphery to the total number of parasites in the body. Artesunate acts on all parasite life stages, whereas quinine is effective only on sequestered parasites. Children with cerebral malaria (CM) treated with artesunate clear parasites faster than those treated with quinine. In this study, we established the relationship between ring ratio and parasite clearance rate and used the ring ratio to determine if the benefit derived from artesunate treatment could be attributed to its broader effect on life cycle stages.

Methods

Ring ratios were calculated for 400 hospitalized children with CM in Blantyre, Malawi between 2010 and 2019 (quinine: 2010-2013, artesunate: 2014-2019).

Results

In both treatment groups, parasite clearance rates were positively associated with the ring ratios, with a stronger association in the artesunate era than the quinine era. In the quinine era, an increase of 1-unit log₁₀ difference between parasitemia and plasma P falciparum histidine-rich protein 2 (a proxy for ring ratio) resulted in a 0.27-unit increase in the parasite clearance rate, whereas in the artesunate era an equal increase resulted in a 0.41-unit increase (P = .04 for the difference).

Conclusions

This analysis provides in vivo evidence supporting the hypothesis that more rapid parasite clearance rates in artesunate recipients are due to its superiority over quinine in killing ring-stage parasites.

Viral, Bacterial, Metabolic, and Autoimmune Causes of Severe Acute Encephalopathy in Sub-Saharan Africa: A Multicenter Cohort Study

OBJECTIVES

To assess whether viral, bacterial, metabolic, and autoimmune diseases are missed by conventional diagnostics among children with severe acute encephalopathy in sub-Saharan Africa.

STUDY DESIGN

One hundred thirty-four children (6 months to 18 years) presenting with nontraumatic coma or convulsive status epilepticus to 1 of 4 medical referral centers in Uganda, Malawi, and Rwanda were enrolled between 2015 and 2016. Locally available diagnostic tests could be supplemented in 117 patients by viral, bacterial, and 16s quantitative polymerase chain reaction testing, metagenomics, untargeted metabolomics, and autoimmune immunohistochemistry screening.

RESULTS

Fourteen (12%) cases of viral encephalopathies, 8 (7%) cases of bacterial central nervous system (CNS) infections, and 4 (4%) cases of inherited metabolic disorders (IMDs) were newly identified by additional diagnostic testing as the most likely cause of encephalopathy. No confirmed cases of autoimmune encephalitis were found. Patients for whom additional diagnostic testing aided causal evaluation (aOR 3.59, 90% CI 1.57-8.36), patients with a viral CNS infection (aOR 7.91, 90% CI 2.49-30.07), and patients with an IMD (aOR 9.10, 90% CI 1.37-110.45) were at increased risk for poor outcome of disease.

CONCLUSIONS

Viral and bacterial CNS infections and IMDs are prevalent causes of severe acute encephalopathy in children in Uganda, Malawi, and Rwanda that are missed by conventional diagnostics and are associated with poor outcome of disease. Improved diagnostic capacity may increase diagnostic yield and might improve outcome of disease.

Using Malarial Retinopathy to Improve the Diagnosis of Pediatric Cerebral Malaria

In malaria endemic areas, a high proportion of children have detectable parasitemia but show no clinical symptoms. When comatose from a cause other than malaria, this group confounds the cerebral malaria (CM) definition, making accurate diagnosis challenging. One important biomarker of CM is malarial retinopathy, a set of specific features visible in the ocular fundus. In this study, we quantified the contribution of malarial retinopathy in discriminating malaria-caused coma from non-malaria-caused coma. We estimated that 10% of our study cohort of N = 1,192 patients who met the WHO clinical definition of CM in Malawi had non-malarial coma based on a Gaussian mixture model using the parasite protein Plasmodium falciparum histidine-rich protein-2. A classification based on platelets, white blood cells, and retinopathy significantly improved the discriminative power of a previously established model including only platelets plus white blood cells (area under the receiver operating characteristic curve: 0.89 versus 0.75, P value < 0.001). We conclude that malarial retinopathy is highly predictive of malaria-caused versus non-malaria-caused coma and recommend that an ocular funduscopic examination to determine malarial retinopathy status be included in the assessment of parasitemic comatose African children.

Malawi ICEMR Malaria Research: Interactions and Results Influencing Health Policies and Practices

Malaria remains a threat to public health in Malawi. It is well acknowledged that malaria research and robust evidence can have an impact on malaria policy and practice, resulting in positive population health gains. We report policy-relevant research contributions that the Malawi International Center of Excellence for Malaria Research (ICEMR) in partnership with local and international collaborators has made. Findings from our ICEMR studies have shown that long-lasting insecticide-treated bed nets (LLINs) impregnated with piperonyl butoxide reduced mosquito blood feeding more compared with conventional LLINs. On the other hand, we showed that few LLINs are maintained up to the end of their 3-year life span, and that older nets are less effective. These results support the policy change decisions by the Malawi National Malaria Control Program to switch from conventional LLINs to piperonyl butoxide LLINs, and to conduct mass LLIN distribution campaigns every 2 years. Our studies on epidemiological patterns of malaria infection showed that school-age children have higher malaria infection rates and lower use of control measures compared with younger children and adults. These findings added to the evidence base that influenced the National Malaria Control Program to endorse school-based malaria interventions as part of its national policy. Research supported by the Malawi ICEMR is contributing to in-country policy decisions and to the implementation of evidence-based interventions. Through our long-term studies we intend to continue providing practical and policy-relevant evidence necessary, ultimately, to eliminate malaria infection in Malawi.

Multiple Organ Dysfunction Syndrome and Pediatric Logistic Organ Dysfunction-2 Score in Pediatric Cerebral Malaria

Malaria resulted in an estimated 627,000 deaths in 2020, the majority of which occurred in children under 5 years of age. Cerebral malaria (CM) is a severe manifestation of the disease with case fatality rates of up to 40%. Autopsies in children with CM have demonstrated sequestration of Plasmodium falciparum parasites in the brain as well as multiple other organs. Thus, multiple organ dysfunction syndrome (MODS) may be present in pediatric patients with CM, but its frequency and association with mortality have not been evaluated. This is a retrospective study of data collected prospectively from children with CM admitted in Blantyre, Malawi. Physical examination findings and laboratory values necessary to calculate a Pediatric Logistic Organ Dysfunction–2 (PELOD-2) score, a validated method that quantifies organ dysfunction in critically ill children, were abstracted. A total of 145 patients were included. Mortality was 15% (n = 22). Ten patients (7%) had single organ dysfunction, 36 (25%) had two organs involved, 68 (47%) had dysfunction of three organs, and 31 (21%) patients had four organs affected. Beyond neurologic dysfunction, other organ systems involved included hematologic (77%), renal (61%), cardiovascular (44%), and respiratory (1%). The median PELOD-2 score on admission was 4 (interquartile range [IQR] = 3–6) in survivors and 6.5 (IQR = 5–10) in the nonsurvivors (P < 0.0001). Admission PELOD-2 score predicted mortality with an area under the curve of 0.75. MODS is widespread in pediatric patients with CM. Objectively identifying children with MODS, and therefore at an increased risk of mortality, may allow for the allocation of limited resources.

Specific components associated with the endothelial glycocalyx are lost from brain capillaries in cerebral malaria

BACKGROUND

Cerebral malaria (CM) is a rare, but severe and frequently fatal outcome of infections with Plasmodium falciparum. Pathogenetic mechanisms include endothelial activation and sequestration of parasitized erythrocytes in the cerebral microvessels. Increased concentrations of glycosaminoglycans in urine and plasma of malaria patients have been described, suggesting involvement of endothelial glycocalyx.

METHODS

We used lectin histochemistry on postmortem samples to compare the distribution of multiple sugar epitopes on cerebral capillaries in children who died from CM and from non-malarial comas.

RESULTS

N-acetyl glucosamine residues detected by tomato lectin are generally reduced in children with CM compared to controls. We used the vascular expression of intercellular adhesion molecule-1 and mannose residues on brain capillaries of CM as evidence of local vascular inflammation, and both were expressed more highly in CM patients than controls. Sialic acid residues were found to be significantly reduced in patients with CM. By contrast, the levels of other sugar epitopes regularly detected on the cerebral vasculature were unchanged, and this suggests specific remodeling of cerebral microvessels in CM patients.

CONCLUSIONS

Our findings support and expand upon earlier reports of disruptions of the endothelial glycocalyx in children with severe malaria.

Delayed presentation to hospital care is associated with sequelae but not mortality in children with cerebral malaria in Malawi

Background

Cerebral malaria is still a major cause of death in children in sub-Saharan Africa. Among survivors, debilitating neurological sequelae can leave children with permanent cognitive impairments and societal stigma, resulting in taxing repercussions for their families. This study investigated the effect of delay in presentation to medical care on outcome in children with cerebral malaria in Malawi.

Methods

This retrospective study included participants enrolled in a longstanding study of cerebral malaria between 2001 and 2021 and considered coma duration prior to arrival at hospital (with or without anti-malarial treatment), HIV status, blood lactate levels at admission and age as factors that could affect clinical outcome. Outcomes were categorized as full recovery, sequelae at the time of discharge, or death. A multinomial regression was fit and run controlling for coma duration, HIV status, lactate levels and age, to determine the association between each explanatory variable and outcome.

Results

A total of 1663 children with cerebral malaria, aged 6 months to 14 years were included. Longer coma duration (in hours) was associated with greater odds of developing sequelae (OR = 1.023, 95% CI 1.007–1.039, p = 0.006) but not death (OR = 1.00, 95% CI 0.986–1.015, p = 0.961). Younger age (in months) was also correlated with higher rates of sequelae, (OR = 0.990, 95% CI 0.983–0.997, p = 0.004) but not with increased mortality (OR = 0.998, 95% CI 0.993–1.003, p = 0.335). Blood lactate levels on admission were correlated with mortality (OR = 1.125, 95% CI 1.090–1.161, p < 0.001) but not associated with increased rates of sequelae (OR = 1.016, 95% CI 0.973–1.060, p = 0.475). Positive HIV status and treatment with an anti-malarial (artemisinin or non-artemisinin-based) prior to arrival at the hospital were not significantly associated with either adverse outcome.

Conclusions

In Malawian children with cerebral malaria, higher rates of sequelae were significantly associated with extended coma duration prior to admission and younger age. Mortality rates were correlated with increased lactate levels on admission. The differential effects of variables on clinical outcomes suggest that there may be different pathogenic pathways leading to sequelae and death. Actions taken by parents and health care professionals are critical in defining when patients arrive at hospital and determining their ultimate outcome.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04080-2.

Pipecolic Acid, a Putative Mediator of the Encephalopathy of Cerebral Malaria and the Experimental Model of Cerebral Malaria

BACKGROUND

We explored a metabolic etiology of cerebral malaria (CM) coma.

METHODS

Plasma metabolites were compared between Malawian children with CM and mild Plasmodium falciparum malaria. A candidate molecule was further studied in animal models of malaria.

RESULTS

Clinically abnormal concentrations of pipecolic acid (PA) were present in CM plasma, and nearly normal in mild malaria samples. PA is renally cleared and the elevated PA blood levels were associated with renal insufficiency, which was present only in CM subjects. Prior studies demonstrate that PA has neuromodulatory effects and is generated by malaria parasites. PA brain levels in Plasmodium berghei ANKA-infected animals in the experimental cerebral malaria (ECM) model inversely correlated with normal behavior and correlated with blood-brain barrier (BBB) permeability. Mice infected with malaria species that do not induce neurological abnormalities or manifest BBB permeability had elevated plasma PA levels similar to ECM plasma at 7 days postinfection; however, they had low PA levels in the brain compared to ECM mice brains at 7 days postinfection.

CONCLUSIONS

Our model suggests that malaria-generated PA induces coma in CM and in ECM. The role of BBB permeability and the mechanisms of PA neuromodulation in CM will require additional investigation.

Plasmodium falciparum clearance time in Malawian children with cerebral malaria: a retrospective cohort study

BACKGROUND

Standard treatment for both uncomplicated and severe malaria is artemisinin derivatives. Delayed parasite clearance times preceded the appearance of artemisinin treatment failures in Southeast Asia. Most worldwide malaria cases are in sub-Saharan Africa (SSA), where clinically significant artemisinin resistance or treatment failure has not yet been detected. The recent emergence of a resistance-conferring genetic mutation in the Plasmodium falciparum parasite in Africa warrants continued monitoring throughout the continent.

METHODS

An analysis was performed on data from a retrospective cohort study of Malawian children with cerebral malaria admitted between 2010 and 2019 to a public referral hospital, ascertaining parasite clearance times across years. Data were collected from patients treated for severe malaria with quinine or artesunate, an artemisinin derivative. Parasite density was determined at admission and every subsequent 6 h until parasitaemia was below 1000 parasites/µl.The mean parasite clearance time in all children admitted in any one year was compared to the parasite clearance time in 2014, the first year of artesunate use in Malawi.

RESULTS

The median population parasite clearance time was slower from 2010 to 2013 (quinine-treated patients) compared to 2014, the first year of artesunate use in Malawi (30 h (95% CI: 30-30) vs 18 h (95% CI: 18-24)). After adjustment for admission parasite count, there was no statistically significant difference in the median population parasite clearance time when comparing 2014 with any subsequent year.

CONCLUSION

Malaria parasite clearance times in Malawian children with cerebral malaria remained constant between 2014 and 2019, arguing against evolving artemisinin resistance in parasites in this region.

Post-Malaria Anemia Is Rare in Malawian Children with Cerebral Malaria

Artesunate therapy for severe malaria syndromes has been associated with post-treatment hemolysis and anemia. We defined post-malaria anemia as any decrease in hematocrit between the index hospitalization for severe malaria and 1 month after. We determined the incidence and severity of post-malaria anemia in Malawian children surviving cerebral malaria (CM) by analyzing hospital and follow-up data from a long-standing study of CM pathogenesis. Children enrolled before 2014 and treated with quinine (N = 258) were compared with those admitted in 2014 and after, and treated with artesunate (N = 235). The last hematocrit value obtained during hospitalization was compared with the 1-month post-hospitalization hematocrit value. The overall rate of a post-hospitalization decrease in hematocrit in children surviving CM was 5.3% (11 of 235 or 4.7% for quinine, 15 of 258 or 5.8% for artesunate; odds ratio, 3.23 [0.88, 18.38]); no patients with a decrease in hematocrit were symptomatic, and none required transfusion after hospitalization. Of the 26 children who had a decrease in hematocrit 1 month after hospitalization, 23.1% had evidence of a new malaria infection. When children treated with quinine and artesunate were combined, a higher hematocrit level on admission, lower quantitative histidine-rich protein level, and splenomegaly were associated independently with post-malaria anemia. In African survivors of CM, post-malaria anemia is rare, mild, and unassociated with the anti-malarial treatment received.

Dimethyl fumarate reduces TNF and Plasmodium falciparum induced brain endothelium activation in vitro

Background

Cerebral malaria (CM) is associated with morbidity and mortality despite the use of potent anti-malarial agents. Brain endothelial cell activation and dysfunction from oxidative and inflammatory host responses and products released by Plasmodium falciparum-infected erythrocytes (IE), are likely the major contributors to the encephalopathy, seizures, and brain swelling that are associated with CM. The development of adjunctive therapy to reduce the pathological consequences of host response pathways could improve outcomes. A potentially protective role of the nuclear factor E2-related factor 2 (NRF2) pathway, which serves as a therapeutic target in brain microvascular diseases and central nervous system (CNS) inflammatory diseases such as multiple sclerosis was tested to protect endothelial cells in an in vitro culture system subjected to tumour necrosis factor (TNF) or infected red blood cell exposure. NRF2 is a transcription factor that mediates anti-oxidant and anti-inflammatory responses.

Methods

To accurately reflect clinically relevant parasite biology a unique panel of parasite isolates derived from patients with stringently defined CM was developed. The effect of TNF and these parasite lines on primary human brain microvascular endothelial cell (HBMVEC) activation in an in vitro co-culture model was tested. HBMVEC activation was measured by cellular release of IL6 and nuclear translocation of NFκB. The transcriptional and functional effects of dimethyl fumarate (DMF), an FDA approved drug which induces the NRF2 pathway, on host and parasite induced HBMVEC activation was characterized. In addition, the effect of DMF on parasite binding to TNF stimulated HBMVEC in a semi-static binding assay was examined.

Results

Transcriptional profiling demonstrates that DMF upregulates the NRF2-Mediated Oxidative Stress Response, ErbB4 Signaling Pathway, Peroxisome Proliferator-activated Receptor (PPAR) Signaling and downregulates iNOS Signaling and the Neuroinflammation Signaling Pathway on TNF activated HBMVEC. The parasite lines derived from eight paediatric CM patients demonstrated increased binding to TNF activated HBMVEC and varied in their binding and activation of HBMVEC. Overall DMF reduced both TNF and CM derived parasite activation of HBMVEC.

Conclusions

These findings provide evidence that targeting the NRF2 pathway in TNF and parasite activated HBMVEC mediates multiple protective pathways and may represent a novel adjunctive therapy to improve infection outcomes in CM.

Naturally acquired immunity against immature Plasmodium falciparum gametocytes

The recent decline in global malaria burden has stimulated efforts toward Plasmodium falciparum elimination. Understanding the biology of malaria transmission stages may provide opportunities to reduce or prevent onward transmission to mosquitoes. Immature P. falciparum transmission stages, termed stages I to IV gametocytes, sequester in human bone marrow before release into the circulation as mature stage V gametocytes. This process likely involves interactions between host receptors and potentially immunogenic adhesins on the infected red blood cell (iRBC) surface. Here, we developed a flow cytometry assay to examine immune recognition of live gametocytes of different developmental stages by naturally exposed Malawians. We identified strong antibody recognition of the earliest immature gametocyte-iRBCs (giRBCs) but not mature stage V giRBCs. Candidate surface antigens (n = 30), most of them shared between asexual- and gametocyte-iRBCs, were identified by mass spectrometry and mouse immunizations, as well as correlations between responses by protein microarray and flow cytometry. Naturally acquired responses to a subset of candidate antigens were associated with reduced asexual and gametocyte density, and plasma samples from malaria-infected individuals were able to induce immune clearance of giRBCs in vitro. Infected RBC surface expression of select candidate antigens was validated using specific antibodies, and genetic analysis revealed a subset with minimal variation across strains. Our data demonstrate that humoral immune responses to immature giRBCs and shared iRBC antigens are naturally acquired after malaria exposure. These humoral immune responses may have consequences for malaria transmission potential by clearing developing gametocytes, which could be leveraged for malaria intervention.

Clinical Implications of Asymptomatic Plasmodium falciparum Infections in Malawi

Background

Asymptomatic Plasmodium falciparum infections are common in Malawi; however, the implications of these infections for the burden of malaria illness are unknown. Whether asymptomatic infections eventually progress to malaria illness, persist without causing symptoms, or clear spontaneously remains undetermined. We identified asymptomatic infections and evaluated the associations between persistent asymptomatic infections and malaria illness.

Methods

Children and adults (N = 120) who presented at a health facility with uncomplicated malaria were followed monthly for 2 years. During follow-up visits, participants with malaria symptoms were tested and, if positive, treated. Samples from all visits were tested for parasites using both microscopy and polymerase chain reaction, and all malaria infections underwent genotyping. Cox frailty models were used to estimate the temporal association between asymptomatic infections and malaria illness episodes. Mixed models were used to estimate the odds of clinical symptoms associated with new versus persistent infections.

Results

Participants had a median follow-up time of 720 days. Asymptomatic infections were detected during 23% of visits. Persistent asymptomatic infections were associated with decreased risk of malaria illness in all ages (hazard ratio 0.50, P < .001). When asymptomatic infections preceded malaria illness, newly-acquired infections were detected at 92% of subsequent clinical episodes, independent of presence of persistent infections. Malaria illness among children was more likely due to newly-acquired infections (odds ratio, 1.4; 95% confidence interval, 1.3-1.5) than to persistent infections.

Conclusions

Asymptomatic P. falciparum infections are associated with decreased incidence of malaria illness, but do not protect against disease when new infection occurs.

Malawian children with uncomplicated and cerebral malaria have decreased activated Vγ9Vδ2 γδ T cells which increase in convalescence

Malaria is responsible for almost half a million deaths annually. The role of Vγ9Vδ2 γδ T cells in malaria is still unclear. Studies have reported an association between this cell subset and malaria symptoms and severity. Profiles of Vγ9Vδ2 γδ T cells in bigger cohorts with different levels of clinical severity have not been described. Proportion, numbers, and activation status of Vγ9Vδ2 γδ T cells were measured by flow cytometry in 59 healthy controls (HCs), 58 children with uncomplicated malaria (UM) and 67 with cerebral malaria (CM,) during acute malaria and in convalescence 28 days later. Vγ9Vδ2 γδ T cell were lower in children presenting with UM and CM than in HCs. Cell counts did not vary with malaria severity (CM median counts 40 x 10³ cells/μL, IQR [23–103]; UM median counts 30 x 10³ cells/μL [10–90], P = 0.224). Vγ9Vδ2 γδ T cell counts increased during convalescence for UM (70 [40–60] x 10³ cells/μL and CM (90 [60–140] x 10³ cells/μL), to levels similar to those in HCs (70 [50–140] x 10³ cells/μL), p = 0.70 and p = 0.40 respectively. Expression of the activation markers CD69 and HLA-DR on Vγ9Vδ2 γδ T cells was higher in malaria cases than in controls (HCs vs UM or CM, p < 0.0001) but was similar between UM and CM. HLA-DR expression remained elevated at 28 days, suggesting sustained activation of Vγ9Vδ2 γδ T cells during recovery. Vγ9Vδ2 γδ T cell proportions and cells counts were suppressed in acute disease and normalized in convalescence, a phenomenon previously hypothesized to be due to transient migration of the cells to secondary lymphoid tissue. The presence of highly activated Vγ9Vδ2 γδ T cells suggests that this T cell subset plays a specific role in response to malaria infection.

Comparison of msp genotyping and a 24 SNP molecular assay for differentiating Plasmodium falciparum recrudescence from reinfection

Background

Current World Health Organization guidelines for conducting anti-malarial drug efficacy clinical trials recommend genotyping Plasmodium falciparum genes msp1 and msp2 to distinguish recrudescence from reinfection. A more recently developed potential alternative to this method is a molecular genotyping assay based on a panel of 24 single nucleotide polymorphism (SNP) markers.

Methods

Performance parameters of these two genotyping methods were compared using data from two recently completed drug efficacy trials. Blood samples from two anti-malarial therapeutic trials were analysed by both msp genotyping and the 24 SNP assay. Additionally, to conserve time and resources, the statistical program R was used to select the most informative SNPs for a set of unrelated Malawian samples to develop a truncated SNP-based assay for the region surrounding Blantyre, Malawi. The ability of this truncated assay to distinguish reinfection from recrudescence when compared to the full 24 SNP assay was then analysed using data from the therapeutic trials.

Results

A total of 360 samples were analysed; 66 for concordance of msp and SNP barcoding methodologies, and 294 for assessing the most informative of the 24 SNP markers. SNP genotyping performed comparably to msp genotyping, with only one case of disagreement among the 50 interpretable results, where the SNP assay identified the sample as reinfection and the msp typing as recrudescence. Furthermore, SNP typing was more robust; only 6% of samples were uninterpretable by SNP typing, compared to 19.7% when msp genotyping was used. For discriminating reinfection from recrudescence, a truncated 6 SNP assay was found to perform at 95.1% the accuracy of the full 24 SNP bar code.

Conclusions

The use of SNP analysis has similar sensitivity to the standard msp genotyping in determining recrudescence from reinfection. Although more expensive, SNP typing is faster and less work intensive. Limiting the assay to those SNPs most informative in the geographical region of interest may further decrease the workload and the cost, making this technique a feasible and affordable alternative in drug efficacy trials.

Electronic supplementary material

The online version of this article (10.1186/s12936-019-2695-0) contains supplementary material, which is available to authorized users.

Association Between Age and Plasmodium falciparum Infection Dynamics

Few data exist on the incidence or duration of natural Plasmodium falciparum infections in high-transmission settings. School-aged children (SAC) carry a disproportionate burden of infections, suggesting either increased incidence or increased duration. We estimated the incidence and duration of unique infections according to age groups. The Mfera Cohort Study (2014-2017) in Malawi had 2 years of follow-up, with 120 participants tested monthly and during sick visits. Blood samples were collected to detect P. falciparum by microscopy and polymerase chain reaction. Positive samples underwent genotyping. Simulation was used to account for high rates of nondetection of infection among low-parasitemia infections, which increase in frequency with age. Adults had significantly fewer unique infections per person per year (median, 2.5) compared with SAC and children younger than 5 years of age (6.3 and 6.6, respectively). Over half of all genotypes were persistent. Infections lasted significantly longer in adults (median, 180 days) and SAC (median, 163 days) compared with children younger than 5 years of age (median, 97 days), after accounting for age-dependent nondetection of infection. SAC acquired new infections at the same rate as children younger than 5 years, but they maintained these infections for longer periods of time, similar to adults. This study provides new insights into P. falciparum infection dynamics that should be considered when designing malaria control strategies.

Brain swelling is independent of peripheral plasma cytokine levels in Malawian children with cerebral malaria

Background

Cerebral malaria (CM) is often fatal, and severe brain swelling is a predictor of CM-related mortality. CM is characterized by elevated circulating pro-inflammatory cytokines TNF and IFN-γ and anti-inflammatory cytokine IL-10, however whether cytokine levels correlate with brain swelling severity is unknown. This study therefore was conducted to investigate the relationship between cytokine levels and brain swelling severity in children presenting with CM.

Methods

A total of 195 Malawian children presenting with CM were recruited and had the concentrations of plasma cytokines determined and compared to brain swelling severity, determined by MRI examination, and graded as severe, moderate, mild or none.

Results

Levels of IL-1β, IL-6, IL-8 and IL-10 did not differ between CM patients with and without severe brain swelling. Compared to children without brain swelling, IL-12 levels were higher in children with severe swelling (p < 0.01, no swelling 1 pg/mL, IQR [1] vs. severe swelling 18.7 pg/mL, IQR [1–27]), whereas TNF concentrations were higher in children with moderate brain swelling compared to children with no swelling (p < 0.01, no swelling 3 pg/mL, IQR [1–20] vs. moderate swelling 24 pg/mL, IQR [8–58]. Multivariate analysis showed that no single cytokine independently predicted brain swelling.

Conclusion

Severe brain swelling in paediatric CM was independent of tested blood pro-inflammatory and anti-inflammatory cytokines which are markers of systemic inflammation.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2590-0) contains supplementary material, which is available to authorized users.

Type I Interferon Receptor Variants in Gene Regulatory Regions are Associated with Susceptibility to Cerebral Malaria in Malawi

Cerebral malaria (CM) remains an important cause of morbidity and mortality. Risk for developing CM partially depends on host genetic factors, including variants encoded in the type I interferon (IFN) receptor 1 (IFNAR1). Type I IFNs bind to IFNAR1 resulting in increased expression of IFN responsive genes, which modulate innate and adaptive immune responses. To comprehensively study IFNAR1 genetic variant associations in Malawians with CM or uncomplicated malaria, we used a tag single nucleotide polymorphism approach, based on the HapMap Yoruba in Ibadan, Nigeria, population database. We identified three novel (rs914142, rs12626750, and rs1041867) and one previously published (Chr21:34696785 [C > G]) IFNAR1 variants to be associated with CM. Some of these variants are in gene regulatory regions. Chr21:34696785 (C > G) is in a region encoding histone modifications and transcription factor-binding sites, which suggests gene regulatory activity. Rs12626750 is predicted to bind embryonic lethal abnormal vision system-like RNA-binding protein 1, a RNA-binding protein which can increase the type I IFN response. Furthermore, we examined these variants in an expression quantitative trait loci database and found that a protective variant, rs914142, is associated with lower expression of IFNAR1, whereas the CM-associated variant rs12626750 was associated with increased IFNAR1 expression, suggesting that activation of the type I IFN pathway may contribute to pathogenesis of CM. Future functional studies of IFNAR1 variants are now needed to clarify the role of this pathway in severe malarial diseases.

Using magnetic resonance imaging to elucidate the mechanism of experimental cerebral malaria rescue by 6-diazo-5-oxo-norleucine

We have previously demonstrated the efficacy of 6-diazo-5-oxo-L-norleucine (DON), a glutamine analog, as a possible adjunctive therapy to mitigate the clinical severity of human cerebral malaria (HCM) (Gordon et al. PNAS 2016). The pathology of HCM is heterogeneous, but generally includes the accumulation of infected red blood cells in the brain vascular endothelium, cerebral microhemorrhages, compromised blood-brain barrier and brain swelling. These changes manifest in severe neurologic symptoms including headache, fever, ataxia, seizures, retinopathy, and coma. The mouse model of CM, experimental cerebral malaria (ECM), approximates the main characteristics of HCM when susceptible C57BL/6 mice are infected with Plasmodium berghei ANKA (PbA) parasites. Studies in these mice found that treatment with DON, even in late stage ECM, rescued animals and increased survival while mitigating and reversing blood-brain barrier dysfunction and brain swelling. Recently, Seydel et al. (NEJM 2015) used magnetic resonance imaging (MRI) to characterize HCM pathology and correlate it to disease severity in children in Malawi. They observed increased brain volume in children that died from HCM that was uncommon in children that survived HCM. Herein, we perform MRI studies in the mouse model to determine if the disease course effectively recapitulates that of HCM, based on morphological changes in MRI. These studies may help elucidate the mechanisms underlying CM pathology, aiding the development of effective treatments. Furthermore, we utilize MRI to probe the mechanisms of action of recovery with DON treatment in order to evaluate the drug for possible clinical trials in HCM.

HIV coinfection influences the inflammatory response but not the outcome of cerebral malaria in Malawian children

Objectives

Study of the effect of HIV on disease progression in heterogeneous severe malaria syndromes with imprecise diagnostic criteria has led to varying results. Characteristic retinopathy refines cerebral malaria (CM) diagnosis, enabling more precise exploration of the hypothesis that HIV decreases the cytokine response in CM, leading to higher parasite density and a poor outcome.

Methods

We retrospectively reviewed data on clinical progression and laboratory parameters in 877 retinopathy-positive CM cases admitted 1996–2011 (14.4% HIV-infected) to a large hospital in Malawi. Admission plasma levels of TNF, interleukin-10, and soluble intercellular adhesion molecule (sICAM-1) were measured by ELISA in 135 retinopathy-positive CM cases.

Results

HIV-infected CM cases had lower median plasma levels of TNF (p = 0.008), interleukin-10 (p = 0.045) and sICAM-1 (p = 0.04) than HIV-uninfected cases. Although HIV-infected children were older and more likely to have co-morbidities, HIV-status did not significantly affect parasite density (p = 0.90) or outcome (24.8% infected, vs. 18.5% uninfected; p = 0.13).

Conclusion

In this well-characterised CM cohort, HIV-coinfection was associated with marked blunting of the inflammatory response but did not affect parasite density or outcome. These data highlight the complex influence of HIV on severe malaria and bring into question systemic inflammation as a primary driver of pathogenesis in human CM.

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Characteristic malaria retinopathy refined the diagnosis of cerebral malaria.

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HIV-infected cases had markedly lower TNF, IL10 and ICAM-1 than uninfected cases.

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HIV-infected children were older and more likely to have comorbidities.

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Peripheral parasite count, HRP2 and mortality were unaffected by HIV status.

Lipid metabolites of the phospholipase A2 pathway and inflammatory cytokines are associated with brain volume in paediatric cerebral malaria

Background

Cerebral malaria (CM) remains a significant cause of morbidity and mortality in children in sub-Saharan Africa. CM mortality has been associated with increased brain volume, seen on neuroimaging studies.

Methods

To examine the potential role of blood metabolites and inflammatory mediators in increased brain volume in Malawian children with CM, an association study was performed between plasma metabolites, cytokine levels and phospholipase A₂ (PLA₂) activity with brain volume.

Results

The metabolomics analysis demonstrated arachidonic acid and other lysophospholipids to be positively associated with brain swelling. These lipids are products of the PLA₂ enzyme and an association of plasma PLA₂ enzymatic activity with brain swelling was confirmed. TNFα, which can upregulate PLA₂ activity, was associated with brain volume. In addition, CCL2 and IL-8 were also associated with brain volume. Some of these cytokines can alter endothelial cell tight junction proteins and increase blood brain barrier permeability.

Conclusions

Taken together, paediatric CM brain volume was associated with products of the PLA₂ pathway and inflammatory cytokines. Their role in causality is unknown. These molecules will need to undergo testing in vitro and in animal models to understand their role in processes of increased brain volume. These observations provide novel data on host physiology associated with paediatric CM brain swelling, and may both inform pathogenesis models and suggest adjunct therapies that could improve the morbidity and mortality associated with paediatric CM.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-015-1036-1) contains supplementary material, which is available to authorized users.

Plasmodium falciparum gene expression measured directly from tissue during human infection

Background

During the latter half of the natural 48-h intraerythrocytic life cycle of human Plasmodium falciparum infection, parasites sequester deep in endothelium of tissues, away from the spleen and inaccessible to peripheral blood. These late-stage parasites may cause tissue damage and likely contribute to clinical disease, and a more complete understanding of their biology is needed. Because these life cycle stages are not easily sampled due to deep tissue sequestration, measuring in vivo gene expression of parasites in the trophozoite and schizont stages has been a challenge.

Methods

We developed a custom nCounter® gene expression platform and used this platform to measure malaria parasite gene expression profiles in vitro and in vivo. We also used imputation to generate global transcriptional profiles and assessed differential gene expression between parasites growing in vitro and those recovered from malaria-infected patient tissues collected at autopsy.

Results

We demonstrate, for the first time, global transcriptional expression profiles from in vivo malaria parasites sequestered in human tissues. We found that parasite physiology can be correlated with in vitro data from an existing life cycle data set, and that parasites in sequestered tissues show an expected schizont-like transcriptional profile, which is conserved across tissues from the same patient. Imputation based on 60 landmark genes generated global transcriptional profiles that were highly correlated with genome-wide expression patterns from the same samples measured by microarray. Finally, differential expression revealed a limited set of in vivo upregulated transcripts, which may indicate unique parasite genes involved in human clinical infections.

Conclusions

Our study highlights the utility of a custom nCounter® P. falciparum probe set, validation of imputation within Plasmodium species, and documentation of in vivo schizont-stage expression patterns from human tissues.

Electronic supplementary material

The online version of this article (doi:10.1186/s13073-014-0110-6) contains supplementary material, which is available to authorized users.

Inferring developmental stage composition from gene expression in human malaria

In the current era of malaria eradication, reducing transmission is critical. Assessment of transmissibility requires tools that can accurately identify the various developmental stages of the malaria parasite, particularly those required for transmission (sexual stages). Here, we present a method for estimating relative amounts of Plasmodium falciparum asexual and sexual stages from gene expression measurements. These are modeled using constrained linear regression to characterize stage-specific expression profiles within mixed-stage populations. The resulting profiles were analyzed functionally by gene set enrichment analysis (GSEA), confirming differentially active pathways such as increased mitochondrial activity and lipid metabolism during sexual development. We validated model predictions both from microarrays and from quantitative RT-PCR (qRT-PCR) measurements, based on the expression of a small set of key transcriptional markers. This sufficient marker set was identified by backward selection from the whole genome as available from expression arrays, targeting one sentinel marker per stage. The model as learned can be applied to any new microarray or qRT-PCR transcriptional measurement. We illustrate its use in vitro in inferring changes in stage distribution following stress and drug treatment and in vivo in identifying immature and mature sexual stage carriers within patient cohorts. We believe this approach will be a valuable resource for staging lab and field samples alike and will have wide applicability in epidemiological studies of malaria transmission.

Transcriptional profiling of Plasmodium falciparum parasites from patients with severe malaria identifies distinct low vs. high parasitemic clusters

Background

In the past decade, estimates of malaria infections have dropped from 500 million to 225 million per year; likewise, mortality rates have dropped from 3 million to 791,000 per year. However, approximately 90% of these deaths continue to occur in sub-Saharan Africa, and 85% involve children less than 5 years of age. Malaria mortality in children generally results from one or more of the following clinical syndromes: severe anemia, acidosis, and cerebral malaria. Although much is known about the clinical and pathological manifestations of CM, insights into the biology of the malaria parasite, specifically transcription during this manifestation of severe infection, are lacking.

Methods and Findings

We collected peripheral blood from children meeting the clinical case definition of cerebral malaria from a cohort in Malawi, examined the patients for the presence or absence of malaria retinopathy, and performed whole genome transcriptional profiling for Plasmodium falciparum using a custom designed Affymetrix array. We identified two distinct physiological states that showed highly significant association with the level of parasitemia. We compared both groups of Malawi expression profiles with our previously acquired ex vivo expression profiles of parasites derived from infected patients with mild disease; a large collection of in vitro Plasmodium falciparum life cycle gene expression profiles; and an extensively annotated compendium of expression data from Saccharomyces cerevisiae. The high parasitemia patient group demonstrated a unique biology with elevated expression of Hrd1, a member of endoplasmic reticulum-associated protein degradation system.

Conclusions

The presence of a unique high parasitemia state may be indicative of the parasite biology of the clinically recognized hyperparasitemic severe disease syndrome.

Genome-wide variation and identification of vaccine targets in the Plasmodium falciparum genome

One goal in sequencing the Plasmodium falciparum genome, the agent of the most lethal form of malaria, is to discover vaccine and drug targets. However, identifying those targets in a genome in which approximately 60% of genes have unknown functions is an enormous challenge. Because the majority of known malaria antigens and drug-resistant genes are highly polymorphic and under various selective pressures, genome-wide analysis for signatures of selection may lead to discovery of new vaccine and drug candidates. Here we surveyed 3,539 P. falciparum genes ( approximately 65% of the predicted genes) for polymorphisms and identified various highly polymorphic loci and genes, some of which encode new antigens that we confirmed using human immune sera. Our collections of genome-wide SNPs ( approximately 65% nonsynonymous) and polymorphic microsatellites and indels provide a high-resolution map (one marker per approximately 4 kb) for mapping parasite traits and studying parasite populations. In addition, we report new antigens, providing urgently needed vaccine candidates for disease control.

Ambulatory diagnoses-cluster statistics of patient visits at a clinic in the Amazon Region of Ecuador

INTRODUCTION

Mondana Clinic is a small rural clinic located in the Napo river region of the Amazon basin in Ecuador. Since its opening in 1997 the clinic has grown to be the primary health care facility for approximately 3000 individuals.

METHODS

A retrospective study was performed tabulating the ambulatory diagnosis, age, sex, and domicile of patients over a 9 month period in 1999.

RESULTS

During the study period there were 765 patient visits that resulted in at least one diagnosis. Of the patient visits, 175 (22.8%) resulted in multiple diagnoses. Women accounted for 58% of the patient visits, which is similar to the 60% of ambulatory patient visits made in the USA by women. The age distribution showed 66% of patients were under 25 years of age. When comparing diagnoses of males with females, several differences were noted. As expected, urinary tract infections were approximately four-fold more common in females than in males. Gastritis and headaches were also more common reasons for patient visits in the female population than in the male. Conversely, lacerations, abrasions, and contusions ranked higher in the male than in the female population for patient visits.

CONCLUSION

This study is the first to provide public health information for this region that will prove useful to the health professionals and funding agencies working in the region. Furthermore, it provides a baseline for comparison with other regions in Ecuador and South America in general, as well as comparisons with data-rich countries such as the USA.

Anti-CD8 abrogates effect of anti-CD4-mediated islet allograft survival in rat model

We studied the effects of anti-CD4 treatment of diabetic ACI rats on the induction of tolerance to allogeneic (Lewis) islet allografts. When given as a 4-day treatment regimen, OX38, a mouse anti-rat CD4 antibody, caused depletion of greater than 80% of CD4+ cells from the peripheral blood of treated rats. After induction of diabetes (a single high-dose bolus of streptozocin) and 3 days after the initiation of anti-CD4 immunotherapy, recipient ACI rats were transplanted with fully allogeneic (Lewis) islets of Langerhans via the portal circulation. These transplanted islets were capable of returning the anti-CD4-treated ACI recipients to normoglycemia, which was maintained indefinitely in the absence of further immunosuppression. In contrast, treatment of recipient rats with OX8, an anti-CD8 monoclonal antibody (MoAb), induced only a slight prolongation of graft survival (less than or equal to 30 days). Further characterization of the cellular requirements for the induction of long-term transplantation survival revealed that successful pretransplantation anti-CD4 therapy could be ablated by the coincident treatment of recipient rats with depleting levels of anti-CD8 MoAb. These data point to the necessity of a regulator CD8+ cell in the induction of anti-CD4-mediated transplantation survival in this rat model of islet transplantation.

Selective T-cell depletion with Ox-38 anti-CD4 monoclonal antibody prevents cardiac allograft rejection in rats

New monoclonal antibodies directed to membrane molecules unique to lymphocyte subsets have provided the means to alter the immune response to alloantigens in a more selective fashion. This investigation demonstrates that monoclonal antibody-induced depletion of CD4 helper/inducer T lymphocytes before transplantation of a fully mismatched heart allograft allows permanent engraftment in rats without further immunosuppression. Five adult male ACI (RT1a) rats received cell-depleting doses of the mouse anti-rat CD4 monoclonal antibody, MRC Ox-38, for 1 month before undergoing heterotopic abdominal heart transplantation. No other immunosuppression was administered, and immunotherapy was discontinued the day of transplantation. After all five Lewis rat (RT1(1)) hearts were maintained free of rejection for more than 3 months, a second heterotopic transplant was performed, this time to the femoral vessels, using either fresh Lewis heart allografts (n = 3) or third-party, Brown-Norway (RT1n) hearts (n = 2). Histologic evaluation was performed 3 weeks later and revealed severe rejection of the femoral Brown-Norway grafts with no evidence of rejection in any of the femoral or original abdominal Lewis grafts. These results suggested that limited, pretransplant anti-CD4 immunotherapy allowed permanent engraftment of fully mismatched cardiac allografts in rats and conferred donor-specific unresponsiveness.