Influence of host factors and parasite biomass on the severity of imported Plasmodium falciparum malaria

Microfluidic device: A versatile biosensor platform to multiplex aptamer-based detection of malaria biomarkers

Plasmodium falciparum malaria remains a dominant infectious disease that affects Africa than the rest of the world, considering its associated cases and death rates. It's a febrile illness that produces several reliable biomarkers, for example, P. falciparum lactate dehydrogenase (PfLDH), P. falciparum Plasmodium glutamate dehydrogenase (PfGDH), and P. falciparum histidine-rich proteins (HRP-II) in blood circulatory system that can easily be employed as targets in rapid diagnostic tests (RDTs). In recent times, several DNA aptamers have been developed via SELEX technology to detect some specific malaria biomarkers (PfLDH, PvLDH, HRP-II, PfGDH) in a biosensor mode with good binding affinity properties to overcome the trend of cross-reactivity, limited sensitivity and stability problems that have been observed with immunodiagnostics. In this review, we summarized existing diagnostic methods and relevant biomarkers to suggest promising approaches to develop sensitive and species-specific multiplexed diagnostic devices enabling effective detection of malaria in complex biological matrices and surveillance in the endemic region.

OUP accepted manuscript

Cerebral malaria (CM) is the severest form of Plasmodium falciparum infection. Children under 5 years old are those most vulnerable to CM, and they consequently have the highest risk of malaria-related death. Parasite-associated factors leading to CM are not yet fully elucidated. We therefore sought to characterize the gene expression profile associated with CM, using RNA sequencing data from 15 CM and 15 uncomplicated malaria isolates from Benin. Cerebral malaria parasites displayed reduced circulation times, possibly related to higher cytoadherence capacity. Consistent with the latter, we detected increased var genes abundance in CM isolates. Differential expression analyses showed that distinct transcriptome profiles are signatures of malaria severity. Genes involved in adhesion, excluding variant surface antigens, were dysregulated, supporting the idea of increased cytoadhesion capacity of CM parasites. Finally, we found dysregulated expression of genes in the entry into host pathway that may reflect greater erythrocyte invasion capacity of CM parasites.

A comparative study of Plasmodium falciparum histidine-rich protein 2 (PfHRP2) blood levels and peripheral blood parasitemia as parameters of disease severity in individuals with imported falciparum malaria

BACKGROUND

In falciparum malaria the total parasite biomass can be estimated by blood levels of histidine-rich protein 2 (PfHRP2), a Plasmodium falciparum-specific protein, which has been widely studied in malaria-endemic regions. This study investigates the usefulness of PfHRP2 as marker for disease severity in imported falciparum malaria.

METHODS

A retrospective cohort analysis was done in 145 patients with imported falciparum malaria. Associations between PfHRP2, malaria disease severity and classic parameters of disease severity were examined by statistical analyses. Patients with different travel purposes were examined in two groups: visiting friends and relatives (VFRs) and other travel purposes (mainly tourists).

RESULTS

High PfHRP2 levels were clearly associated with disease severity. VFRs status showed to be an independent determinant protecting against severe malaria. At similar PfHRP2 levels VFRs patients had significantly lower levels of peripheral blood parasitemia compared to other patients.

CONCLUSION

Our study confirms the association between PfHRP2 and disease severity in patients with imported falciparum malaria, but for proper interpretation of PfHRP2 levels as disease severity marker in travellers, the possible presence of pre-existing acquired anti-malarial immunity should be taken into account as the correlation between PfHRP2 levels and disease severity differed significantly between VFRs patients and patients with other travel purposes.

Common virulence gene expression in adult first-time infected malaria patients and severe cases

Sequestration of Plasmodium falciparum(P. falciparum)-infected erythrocytes to host endothelium through the parasite-derived P. falciparum erythrocyte membrane protein 1 (PfEMP1) adhesion proteins is central to the development of malaria pathogenesis. PfEMP1 proteins have diversified and expanded to encompass many sequence variants, conferring each parasite a similar array of human endothelial receptor-binding phenotypes. Here, we analyzed RNA-seq profiles of parasites isolated from 32 P. falciparum-infected adult travellers returning to Germany. Patients were categorized into either malaria naive (n = 15) or pre-exposed (n = 17), and into severe (n = 8) or non-severe (n = 24) cases. For differential expression analysis, PfEMP1-encoding var gene transcripts were de novo assembled from RNA-seq data and, in parallel, var-expressed sequence tags were analyzed and used to predict the encoded domain composition of the transcripts. Both approaches showed in concordance that severe malaria was associated with PfEMP1 containing the endothelial protein C receptor (EPCR)-binding CIDRα1 domain, whereas CD36-binding PfEMP1 was linked to non-severe malaria outcomes. First-time infected adults were more likely to develop severe symptoms and tended to be infected for a longer period. Thus, parasites with more pathogenic PfEMP1 variants are more common in patients with a naive immune status, and/or adverse inflammatory host responses to first infections favor the growth of EPCR-binding parasites.

IL-4 Treatment Mitigates Experimental Cerebral Malaria by Reducing Parasitemia, Dampening Inflammation, and Lessening the Cytotoxicity of T Cells

Cytokine responses to malaria play important roles in both protective immunity development and pathogenesis. Although the roles of cytokines such as TNF-α, IL-12, IFN-γ, and IL-10 in immunity and pathogenesis to the blood stage malaria are largely known, the role of IL-4 remains less understood. IL-4 targets many cell types and induces multiple effects, including cell proliferation, gene expression, protection from apoptosis, and immune regulation. Accordingly, IL-4 has been exploited as a therapeutic for several inflammatory diseases. Malaria caused by Plasmodium falciparum manifests in many organ-specific fatal pathologies, including cerebral malaria (CM), driven by a high parasite load, leading to parasite sequestration in organs and consequent excessive inflammatory responses and endothelial damage. We investigated the therapeutic potential of IL-4 against fatal malaria in Plasmodium berghei ANKA-infected C57BL/6J mice, an experimental CM model. IL-4 treatment significantly reduced parasitemia, CM pathology, and mortality. The therapeutic effect of IL-4 is mediated through multiple mechanisms, including enhanced parasite clearance mediated by upregulation of phagocytic receptors and increased IgM production, and decreased brain inflammatory responses, including reduced chemokine (CXCL10) production, reduced chemokine receptor (CXCR3) and adhesion molecule (LFA-1) expression by T cells, and downregulation of cytotoxic T cell lytic potential. IL-4 treatment markedly reduced the infiltration of CD8⁺ T cells and brain pathology. STAT6, PI3K-Akt-NF-κB, and Src signaling mediated the cellular and molecular events that contributed to the IL-4-dependent decrease in parasitemia. Overall, our results provide mechanistic insights into how IL-4 treatment mitigates experimental CM and have implications in developing treatment strategies for organ-specific fatal malaria.

Plasma Plasmodium falciparum Histidine-Rich Protein-2 concentrations in children with malaria infections of differing severity in Kilifi, Kenya

Background

Most previous studies support a direct link between total parasite load and the clinical severity of Plasmodium falciparum malaria infections.

Methods

We estimated P. falciparum parasite loads in 3 groups of children with malaria infections of differing severity: (1) children with World Health Organization–defined severe malaria (n = 1544), (2) children admitted with malaria but without features of severity (n = 200), and (3) children in the community with asymptomatic parasitemia (n = 33).

Results

Peripheral parasitemias were highest in those with uncomplicated malaria (geometric mean [GM] parasite count, 111 064/μL; 95% confidence interval, CI, 86 798–141 819/μL), almost 3 times higher than in those with severe malaria (39 588/μL; 34 990–44 791/μL) and >100 times higher than in those with asymptomatic malaria (1092/μL; 523–2280/μL). However, the GM P. falciparum histidine-rich protein 2 (PfHRP2) values (95% CI) increased with severity, being 7 (4–12) ng/mL in asymptomatic malaria, 843 (655–1084) ng/mL in uncomplicated malaria, and 1369 (1244–1506) ng/mL in severe malaria. PfHRP2 concentrations were markedly lower in the subgroup of patients with severe malaria and concomitant invasive bacterial infections of blood or cerebrospinal fluid (GM concentration, 312 ng/mL; 95% CI, 175–557 ng/mL; P < .001) than in those without such infections (1439 ng/mL; 1307–1584; P < .001).

Conclusions

The clinical severity of malaria infections related strongly to the total burden of P. falciparum parasites. A quantitative test for plasma concentrations of PfHRP2 could be useful in identifying children at the greatest clinical risk and identifying critically ill children in whom malaria is not the primary cause.

Changes in the clinical presentation and outcomes of patients treated for severe malaria in a referral French university intensive care unit from 2004 to 2017

BACKGROUND

In France, the incidence of severe imported malaria cases increased since early 2000. Artesunate was available (temporarily use authorization) since mid-2011 in France and commonly used for severe malaria since early 2013. Thus, the study objectives were to describe the patients with severe imported malaria admitted in intensive care unit (ICU) and assess the changes in clinical presentation and outcomes before and after this date.

METHODS

Retrospective observational single-center study in the infectious diseases ICU of a referral university hospital, conducted on patients admitted for severe imported malaria from 2004 to 2017. Demographic variables, severity scores, WHO's severity criteria on admission, treatment, and ICU and hospital lengths of stay were collected. Patients' characteristics and outcomes were compared between both periods. A poor outcome was defined as the composite endpoint of death, or requirement for vasopressors, invasive mechanical ventilation and/or renal replacement therapy.

RESULTS

189 patients were included, 98 in 2004-2012 and 91 in 2013-2017, most often from West and Central African countries (96%). The number of WHO criteria for severe malaria was comparable in both groups, but SAPS II, SOFA and ICU length of stay were significantly higher in 2004-2012, while patients of African origin living in France were less frequent (p < 0.01). The outcome was poor for 41/98 cases in 2004-2012 and 12/91 cases in 2013-2017 (p < 0.01). The risk factors of poor outcome on the multivariate logistic regression were a neurological failure (adjusted odds ratio (adjOR = 3.23; 95% CI (1.03-10.08), p = 0.004), cardio-circulatory failure (adjOR = 9.92; 95% CI (2.34-42), p = <0.01) and creatinine blood levels > 265 µmol/L (adjOR = 10.76; 95% CI (3.17-36.53), p < 0.01). In the multivariate analysis, IV artesunate was not associated with a better outcome. Patients of African origin did not seem to have a better outcome than Caucasian patients or those from other origins (adjOR = 0.59; 95% CI (0.21-1.65), p = 0.31).

CONCLUSION

Patients with imported malaria admitted in ICU in 2013-2017 were less severely ill than those in 2004-2012. These trends could be partially explained by the increasing proportion of African patients visiting friends or relatives or living in endemic areas.

Evaluation of PCR To Monitor Plasmodium falciparum Treatment Efficacy in a Nonendemicity Setting

Adequate clinical and parasitological response (ACPR) after malaria treatment remains challenging to assess in settings of malaria nonendemicity. Biological evaluation of parasitological clearance relies on microscopic investigation of thick blood smears, which is a specific technique that not all diagnosis laboratories are able to perform. Rapid diagnosis tests (RDTs) and molecular biology techniques are proposed as alternatives to microscope conventional techniques; however, their performance for treatment efficacy evaluation is controversial. We present here a retrospective comparative study for RDT and PCR (nested and high-resolution-melting quantitative PCR [HRM-qPCR]) evaluation of ACPR in a nonendemicity context. Blood samples from 133 patients presenting a Plasmodium falciparum monoinfection were included. Samples obtained at the time of diagnosis and at 3, 7, and 28 days after diagnosis were investigated. Histidine-rich protein 2 (HRP-2)-based RDT results remained positive in 51% of cases 28 days after diagnosis and appropriate therapeutic management. Parasite DNA was detected by the two PCR techniques (nested PCR and HRM-qPCR) in 12% and 10% of samples 28 days after treatment initiation, respectively. No therapeutic failure was recorded in the studied patients. Persistence of positive signal might reflect the presence of circulating asexual parasites or persistence of HRP-2 and parasitic DNA in patient's peripheral blood after parasitic clearance.

[Malaria: immuno-permissive management in the prevention of transfusional malaria]

Malaria is a potentially life-threatening tropical infectious disease caused by a parasite that infects erythrocytes. Its transmission is vectorial, but the transfusion of infected red blood cells can cause a delicate diagnosis of transmitted malaria. Prevention is based on the selection of donors at risk by the search for antibodies reflecting past infection, in the absence of a sufficiently sensitive parasite detection technique to prevent all risks. Recent cases of transfusion malaria have reiterated that this preventive measure does not allow screening of all asymptomatic carriers.

Hyperparasitaemia during clinical malaria episodes in infants aged 0-24 months and its association with in utero exposure to Plasmodium falciparum

Objective

Existing information has shown that infants who are prenatally exposed to P. falciparum are susceptible to subsequent malaria infections. However, the effect of prenatal exposure to P. falciparum on parasite density during clinical malaria episodes has not been fully elucidated. This study is a component of a prospective cohort study for which initial results have been published. This component was designed to determine the effect of prenatal exposure to P. falciparum on parasite density during clinical malaria episodes in the first 24 months of life. A total of 215 infants were involved and monitored for clinical malaria episodes defined by fever (≥ 37 °C) and parasitaemia. The geometric mean parasite counts between exposed and unexposed infants were compared using independent samples t test. The effect of in utero exposure to P. falciparum on parasite density was assessed using binary logistic regression.

Results

The geometric mean parasite count per µl of blood during clinical malaria episodes in exposed infants was 24,889 (95% CI 18,286–31,490) while in unexposed infants it was 14,035 (95% CI 12,111–15,960), P < 0.05. Prenatal exposure to P. falciparum was associated with hyperparasitaemia during clinical malaria episodes (OR 7.04, 95% CI 2.31–21.74), while other factors were not significantly associated (P > 0.05).

Case Report: Delayed or Recurrent Plasmodium falciparum Malaria in Migrants: A Report of Three Cases with a Literature Review

Emerging evidence indicates that migrants from Plasmodium falciparum endemic regions are at risk of delayed presentation of P. falciparum malaria. We report three cases of P. falciparum malaria occurring years after arrival in Europe. All patients were originally from Sub-Saharan Africa. Two subjects had controlled human immunodeficiency virus infection and one was a pregnant woman. We performed a literature review of all published cases of delayed presentation of P. falciparum in migrants and identified 32 additional cases. All cases but one originate from sub-Saharan Africa. There was a median time of 36 months between the last visit to a malaria-endemic country and clinical malaria (range: 3 months to 10 years). Pregnancy was the most frequently reported risk factor (11/35 or 31.4%). Parasitemia was ≤ 0.1% in 38% of cases (11/29 reported), and no death was reported. The underlying possible mechanisms for this delayed presentation in migrants from an endemic area probably include the persistence of submicroscopic parasitemia combined with decaying P. falciparum-specific immunity. Suspicion of P. falciparum delayed malaria should remain high in migrants, mainly from sub-Saharan Africa, even without a recent travel history, especially in those presenting risk factors for impaired parasite clearance or distinct immune responses such as pregnancy and HIV infection. In these patients, new prevention and screening strategies should be studied and blood safety policies adapted.