Asymptomatic Malaria Infection Is Maintained by a Balanced Pro- and Anti-inflammatory Response

Subclinical Inflammation in Asymptomatic Schoolchildren With Plasmodium falciparum Parasitemia Correlates With Impaired Cognition

BACKGROUND

Subclinical inflammation and cognitive deficits have been separately associated with asymptomatic Plasmodium falciparum infections in schoolchildren. However, whether parasite-induced inflammation is associated with worse cognition has not been addressed. We conducted a cross-sectional pilot study to better assess the effect of asymptomatic P. falciparum parasitemia and inflammation on cognition in Kenyan schoolchildren.

METHODS

We enrolled 240 children aged 7-14 years residing in high malaria transmission in Western Kenya. Children performed five fluid cognition tests from a culturally adapted NIH toolbox and provided blood samples for blood smears and laboratory testing. Parasite densities and plasma concentrations of 14 cytokines were determined by quantitative PCR and multiplex immunoassay, respectively. Linear regression models were used to determine the effects of parasitemia and plasma cytokine concentrations on each of the cognitive scores as well as a composite cognitive score while controlling for age, gender, maternal education, and an interaction between age and P. falciparum infection status.

RESULTS

Plasma concentrations of TNF, IL-6, IL-8, and IL-10 negatively correlated with the composite score and at least one of the individual cognitive tests. Parasite density in parasitemic children negatively correlated with the composite score and measures of cognitive flexibility and attention. In the adjusted model, parasite density and TNF, but not P. falciparum infection status, independently predicted lower cognitive composite scores. By mediation analysis, TNF significantly mediated ~29% of the negative effect of parasitemia on cognition.

CONCLUSIONS

Among schoolchildren with PCR-confirmed asymptomatic P. falciparum infections, the negative effect of parasitemia on cognition could be mediated, in part, by subclinical inflammation. Additional studies are needed to validate our findings in settings of lower malaria transmission and address potential confounders that could affect both inflammation and cognitive performance.

Host-parasite interaction in severe and uncomplicated malaria infection in ghanaian children

PURPOSE

During malarial infection, both parasites and host red blood cells (RBCs) come under severe oxidative stress due to the production of free radicals. The host system responds in protecting the RBCs against the oxidative damage caused by these free radicals by producing antioxidants. In this study, we investigated the antioxidant enzyme; superoxide dismutase (SOD) activity and cytokine interactions with parasitaemia in Ghanaian children with severe and uncomplicated malaria.

METHODOLOGY

One hundred and fifty participants aged 0-12 years were administered with structured questionnaires. Active case finding approach was used in participating hospitals to identify and interview cases before treatment was applied. Blood samples were taken from each participant and used to quantify malaria parasitaemia, measure haematological parameters and SOD activity. Cytokine levels were measured by commercial ELISA kits. DNA comet assay was used to evaluate the extent of parasite DNA damage due to oxidative stress.

RESULTS

Seventy - Nine (79) and Twenty- Six (26) participants who were positive with malaria parasites were categorized as severe (56.75 × 103 ± 57.69 parasites/µl) and uncomplicated malaria (5.87 × 103 ± 2.87 parasites/µl) respectively, showing significant difference in parasitaemia (p < 0.0001). Significant negative correlation was found between parasitaemia and SOD activity levels among severe malaria study participants (p = 0.0428). Difference in cytokine levels (IL-10) amongst the control, uncomplicated and severe malaria groups was significant (p < 0.0001). The IFN-γ/IL-10 /TNF-α/IL-10 ratio differed significantly between the malaria infected and non- malaria infected study participants. DNA comet assay revealed damage to Plasmodium parasite DNA.

CONCLUSION

Critical roles played by SOD activity and cytokines as anti-parasitic defense during P. falciparum malaria infection in children were established.

Comparative analysis of peripheral whole blood transcriptome from asymptomatic carriers reveals upregulation of subsets of surface proteins implicated in Plasmodium falciparum phenotypic plasticity

The molecular mechanism underlying Plasmodium falciparum's persistence in the asymptomatic phase of infection remains largely unknown. However, large-scale shifts in the parasites' gene expression during asymptomatic infections may enhance phenotypic plasticity, maximizing their fitness and leading to the persistence of the asymptomatic infections. To uncover these mechanisms, we aimed to identify parasite genetic factors implicated in asymptomatic infections through whole transcriptome analysis. We analyzed publicly available transcriptome datasets containing asymptomatic malaria (ASM), uncomplicated malaria (SM), and malaria-naïve (NSM) samples from 35 subjects for differentially expressed genes (DEGs) and long noncoding RNAs. Our analysis identified 755 and 1773 DEGs in ASM vs SM and NSM, respectively. These DEGs revealed sets of genes coding for proteins of unknown functions (PUFs) upregulated in ASM vs SM and ASM, suggesting their role in underlying fundamental molecular mechanisms during asymptomatic infections. Upregulated genes in ASM vs SM revealed a subset of 24 clonal variant genes (CVGs) involved in host-parasite and symbiotic interactions and modulation of the symbiont of host erythrocyte aggregation pathways. Moreover, we identified 237 differentially expressed noncoding RNAs in ASM vs SM, of which 11 were found to interact with CVGs, suggesting their possible role in regulating the expression of CVGs. Our results suggest that P. falciparum utilizes phenotypic plasticity as an adaptive mechanism during asymptomatic infections by upregulating clonal variant genes, with long noncoding RNAs possibly playing a crucial role in their regulation. Thus, our study provides insights into the parasites' genetic factors that confer a fitness advantage during asymptomatic infections.

Cytokine gene polymorphisms implicated in the pathogenesis of Plasmodium falciparum infection outcome

Cytokines play a critical role in the immune mechanisms involved in fighting infections including malaria. Polymorphisms in cytokine genes may affect immune responses during an infection with Plasmodium parasites and immunization outcomes during routine administration of malaria vaccines. These polymorphisms can increase or reduce susceptibility to this deadly infection, and this may affect the physiologically needed balance between anti-inflammatory and pro-inflammatory cytokines. The purpose of this review is to present an overview of the effect of selected cytokine gene polymorphisms on immune responses against malaria.

N-(coumarin-3-yl)cinnamamide Promotes Immunomodulatory, Neuroprotective, and Lung Function-Preserving Effects during Severe Malaria

Plasmodium berghei ANKA (PbA) infection in mice resembles several aspects of severe malaria in humans, such as cerebral malaria and acute respiratory distress syndrome. Herein, the effects of N-(coumarin-3-yl)cinnamamide (M220) against severe experimental malaria have been investigated. Treatment with M220 proved to protect cognitive abilities and lung function in PbA-infected mice, observed by an object recognition test and spirometry, respectively. In addition, treated mice demonstrated decreased levels of brain and lung inflammation. The production and accumulation of microglia, and immune cells that produce the inflammatory cytokines TNF and IFN-γ, decreased, while the production of the anti-inflammatory cytokine IL-10 by innate and adaptive immune cells was enhanced. Treatment with M220 promotes immunomodulatory, neuroprotective, and lung function-preserving effects during experimental severe malaria. Therefore, it may be an interesting therapeutic candidate to treat severe malaria effects.

Vaccination with an in vitro culture attenuated Babesia bovis strain safely protects highly susceptible adult cattle against acute bovine babesiosis

Introduction

Live in vivo attenuated Babesia bovis vaccines produced by sequential passages in splenectomized calves have historically been used to control acute bovine babesiosis in endemic areas worldwide. However, several constraints prevent the widespread use of these vaccines, including the need for several splenectomized calves to produce vaccine batches, and potential inconsistent parasite attenuation, which contraindicates their use for highly Babesia-susceptible adult cattle. Thus, the use of vaccines based on well-defined in vitro culture attenuated B. bovis strains emerges as a more sustainable and efficient alternative. Previous work demonstrated that the culture attenuated strain Att-S74-T3Bo is non-tick transmissible and able to safely protect calves against needle challenge with a B. bovis virulent strain.

Methods and results

Herein we evaluated safety and efficacy of Att-S74-T3Bo in preventing acute babesiosis in adult (>1.5 year of age) cattle. Results demonstrated that Att-S74-T3Bo vaccination of adult animals (n=5) induced self-limiting signs of acute infection and protected the vaccinated animals against challenge with the homologous virulent B. bovis strain Vir-S74-T3Bo. Att-S74-T3Bo-vaccinated adult cattle developed significant (P<0.05) monocytosis, with concomitant neutropenia and CD4+ leukopenia, in peripheral blood early after vaccination. Also, vaccinated animals developed a specific signature of pro- and anti-inflammatory cytokine expression in peripheral blood and significant levels of IgM, total IgG, IgG1, and IgG2 against the B. bovis immunodominant antigen RAP-1 CT. Strikingly, none of the vaccinated animals showed any signs of acute babesiosis after challenge with Vir-S74-T3Bo. In contrast, control adult cattle (n=5) showed pathognomonic symptoms of acute babesiosis, and significant decrease (P<0.05) in lymphocytes, monocytes, and neutrophils, starting on day 7 post-challenge. All control animals developed severe acute disease and were euthanized on days 10 through 12 days post-challenge.

Discussion and conclusion

Evidence from this study indicates that Att-S74-T3Bo safely protects highly susceptible adult cattle against challenge with a homologous virulent strain of B. bovis. In conclusion, Att-S74-T3Bo may be considered as a potential efficient and sustainable attenuated candidate vaccine strain to control acute bovine babesiosis in highly susceptible adult cattle. Future studies should focus on increasing the number of animals vaccinated, duration of immunity, and efficacy of this attenuated strain against heterologous virulent parasite strains.

Inflammatory cytokines as potential biomarkers for early diagnosis of severe malaria in children in Ghana

BACKGROUND

Severe malaria (SM) is a fatal multi-system disease which accounted for an estimated 619,000 deaths in 2021. Less than 30% of children presenting with SM are diagnosed and treated promptly, resulting in increased mortality and neurologic impairments in survivors. Studies have identified cytokine profiles that differentiate the various clinical manifestations of malaria (severe and uncomplicated). However, the diagnostic capability of these cytokines in differentiating between the disease states in terms of cut-off values has not yet been determined.

METHODS

The plasma levels of 22 pro-inflammatory cytokines (Eotaxin/CCL 11, interferon-gamma (IFN-γ), interleukin (IL)- 2, IL-6, IL-1β, IL-12p40/p70, IL-17A, RANTES, MCP-1, IL-15, IL-5, IL-1RA, IL-2R, IFN-α, IP-10, TNF, MIG, MIP-1α, MIP-1β, IL-7, IL-8 and Granulocyte Macrophage-Colony Stimulating Factor (GM-CSF), and 3 anti-inflammatory cytokines-(IL-4, IL-13 and IL-10) in patients with SM, uncomplicated malaria (UM) and other febrile conditions, were measured and compared using the Human Cytokine Magnetic 25-Plex Panel. The receiver operating characteristic (ROC) curve analysis was used to determine the diagnostic value of these cytokines.

RESULTS

The level of the pro-inflammatory cytokine, IL-17A, was significantly higher in the SM group as compared to the UM group. Levels of the anti-inflammatory cytokines however did not differ significantly among the SM and UM groups. Only IL-1β and IL-17A showed good diagnostic potential after ROC curve analysis.

CONCLUSION

The data show that levels of pro-inflammatory cytokines correlate with malaria disease severity. IL-1β and IL-17A showed good diagnostic potentials and can be considered for use in clinical practice to target treatment.

Malaria prevalence in Commune 5 in Tumaco (Nariño, Colombia)

Background Urban malaria is a public health problem in Colombia and there is still lack of knowledge about its epidemiological characteristics, which are key to the implementation of control measures. The presence of urban malaria cases and disease diagnosis are some of the challenges faced by malaria elimination programs. The objective of this research was to estimate malaria prevalence, explore associated factors and detect pfhrp 2/3 genes, in the urban area of Tumaco between July and December 2019. Methods A prevalence study was conducted by using a stratified random probability sample. Structured surveys were administered and blood samples were taken and examined through optical microscopy, rapid diagnostic tests (RDT) and polymerase chain reaction (PCR). A logistic regression model was used to explore associated factors. Results 1,504 people living in 526 households were surveyed. The overall prevalence was 2.97% (95% CI: 2.1 - 4.3%). It was higher in males, in the 10-19 age group and in asymptomatic cases. The prevalence of pfhrp2 amplification was 2.16% (95% CI: 1.6 - 2.9%). Households with three or more people had a higher risk of malaria infection (adjusted odds ratio (ORa) 4.05; 95% confidence interval (CI) 1.57-10.43). All cases were due to P. falciparum. Conclusions The prevalence of urban malaria was low. Strategies to eliminate malaria in urban areas should be adjusted considering access to early diagnosis, asymptomatic infection, and the RDTs used to detect the presence of the pfhrp2 gene.

Immunogenomic profile at baseline predicts host susceptibility to clinical malaria

Introduction

Host gene and protein expression impact susceptibility to clinical malaria, but the balance of immune cell populations, cytokines and genes that contributes to protection, remains incompletely understood. Little is known about the determinants of host susceptibility to clinical malaria at a time when acquired immunity is developing.

Methods

We analyzed peripheral blood mononuclear cells (PBMCs) collected from children who differed in susceptibility to clinical malaria, all from a small town in Mali. PBMCs were collected from children aged 4-6 years at the start, peak and end of the malaria season. We characterized the immune cell composition and cytokine secretion for a subset of 20 children per timepoint (10 children with no symptomatic malaria age-matched to 10 children with >2 symptomatic malarial illnesses), and gene expression patterns for six children (three per cohort) per timepoint.

Results

We observed differences between the two groups of children in the expression of genes related to cell death and inflammation; in particular, inflammatory genes such as CXCL10 and STAT1 and apoptotic genes such as XAF1 were upregulated in susceptible children before the transmission season began. We also noted higher frequency of HLA-DR+ CD4 T cells in protected children during the peak of the malaria season and comparable levels cytokine secretion after stimulation with malaria schizonts across all three time points.

Conclusion

This study highlights the importance of baseline immune signatures in determining disease outcome. Our data suggests that differences in apoptotic and inflammatory gene expression patterns can serve as predictive markers of susceptibility to clinical malaria.

Plasmodium falciparum infection coinciding with the malaria vaccine candidate BK-SE36 administration interferes with the immune responses in Burkinabe children

Background

A vaccine targeting the erythrocyte stages of Plasmodium falciparum could play a role in preventing clinical disease. BK-SE36 is a promising malaria vaccine candidate that has shown a good safety profile and immunological responses during field evaluations. It was observed that repeated natural infections could result in immune tolerance against SE36 molecule.

Methods

The primary trial was conducted to assess the safety and immunogenicity of the BK-SE36 in two cohorts of children aged 25-60 months (Cohort 1) and 12-24 months (Cohort 2). Immunization was at full dose (1.0 mL) administered at 0, 1, and 6 months. Blood samples were collected before each vaccination for immunological assessments and detection of Plasmodium falciparum infection by microscopy. Blood samples were further collected one month post each vaccination to evaluate immunogenicity.

Results

Of seventy-two (72) subjects that have received BK-SE36 vaccination, 71 had available blood smears during vaccination days. One month post Dose 2, the geometric mean of SE36 antibodies was 263.2 (95% CI: 178.9-387.1) in uninfected individuals compared to 77.1 (95% CI: 47.3-125.7) in infected participants. The same trend was observed one-month post booster dose. Participants uninfected at the time of booster vaccination had significantly higher GMTs compared to those who were infected (424.1 (95% CI: 301.9-595.8) vs. 92.8 (95% CI: 34.9-246.6), p = 0.002. There was a 14.3 (95% CI: 9.7-21.1) and 2.4 (95% CI: 1.3-4.4) fold-change, respectively, in uninfected and infected participants between one-month post Dose 2 and booster. The difference was statistically significant (p &lt; 0.001).

Conclusion

Concomitant infection by P. falciparum during BK-SE36 vaccine candidate administration is associated with reduced humoral responses. However, it is to be noted that the BK-SE36 primary trial was not designed to investigate the influence of concomitant infection on vaccine-induced immune response and should be interpreted cautiously.

Trial registration

WHO ICTRP, PACTR201411000934120.

Impact of exposure to malaria and nutritional status on responses to the experimental malaria vaccine ChAd63 MVA ME-TRAP in 5-17 month-old children in Burkina Faso

The experimental malaria vaccine ChAd63 MVA ME-TRAP previously showed protective efficacy against Plasmodium falciparum infection in Phase IIa sporozoite challenge studies in adults in the United Kingdom and in a Phase IIb field efficacy trial in Kenyan adults. However, it failed to demonstrate efficacy in a phase IIb trial in 5-17 month-old children in an area of high malaria transmission in Burkina Faso. This secondary analysis investigated whether exposure to malaria or nutritional status might be associated with reduced responses to vaccination in this cohort. Parasite blood smears and anti-AMA-1 IgG titres were used to assess history of exposure to malaria and weight-for-length Z scores were calculated to assess nutritional status. Differences in vaccine-specific anti-TRAP IgG titre and ex vivo IFNγ ELISpot response were measured between groups. In total, n = 336 volunteers randomised to receive the experimental vaccine regimen were included in this analysis. A positive smear microscopy result was associated with reduced anti-TRAP IgG titre (geometric mean titre: 2775 (uninfected) vs 1968 (infected), p = 0.025), whilst anti-AMA-1 IgG titres were weakly negatively correlated with reduced ex vivo IFNγ ELISpot response (r = -0.18, p = 0.008). Nutritional status was not associated with either humoral or cellular immunogenicity. Vaccine efficacy was also measured separately for vaccinees with positive and negative blood smears. Although not significant in either group compared to controls, vaccine efficacy measured by Cox hazard ratio was higher in uninfected compared to infected individuals (19.8% [p = 0.50] vs 3.3% [p = 0.69]). Overall, this data suggests exposure to malaria may be associated with impaired vaccine immunogenicity. This may have consequences for the testing and eventual deployment of various vaccines, in areas with high endemicity for malaria.

Trial Registration

Pactr.org, identifier PACTR201208000404131; ClinicalTrials.gov, identifier NCT01635647.

Perturbations in the T cell receptor β repertoire during malaria infection in children: A preliminary study

The changes occurring in the T cell repertoire during clinical malaria infection in children remain unknown. In this study, we undertook the first detailed comparative study of the T cell repertoire in African children with and without clinical malaria to test the hypothesis that clonotypic expansions that occur during P. falciparum infection will contribute to the generation of a T cell repertoire that is unique to each disease state. We profiled the complementarity-determining region 3 (CDR3) of the TCRβ chain sequences from children with Plasmodium falciparum infections (asymptomatic, uncomplicated and severe malaria) and compared these with sequences from healthy children. Interestingly, we discovered that children with symptomatic malaria have a lower TCR diversity and frequency of shared (or “public”) TCR sequences compared to asymptomatic children. Also, TCR diversity was inversely associated with parasitemia. Furthermore, by clustering TCR sequences based on their predicted antigen specificities, we identified a specificity cluster, with a 4-mer amino acid motif, that is overrepresented in the asymptomatic group compared to the diseased groups. Further investigations into this finding may help in delineating important antigenic targets for vaccine and therapeutic development. The results show that the T cell repertoire in children is altered during malaria, suggesting that exposure to P. falciparum antigens disrupts the adaptive immune response, which is an underlying feature of the disease.

Effect of a single sub-dose of ketamine on postoperative fatigue syndrome in colorectal cancer patients undergoing radical laparoscopic surgery: A double-blind, pilot study

BACKGROUND

This study aimed at examining the effect of a single sub-anesthetic dose of ketamine on postoperative fatigue syndrome (POFS) in patients undergoing radical laparoscopic surgery for colorectal cancer (CRC).

METHODS

This prospective, double-blind, pilot study enrolled patients scheduled for radical laparoscopic surgery for CRC under general anesthesia. Eligible patients were randomized into the placebo and ketamine groups. The primary outcome was christensen score change at day 3. The secondary outcomes were the difference of Identity Consequence Fatigue Scale (ICFS) score between the placebo group and ketamine group at day 3 and level of serum tumor necrosis factor (TNF)-α, interleukin (IL)-6, S100β protein, and neuron-specific enolase (NSE).

RESULTS

32 participants were assigned to the ketamine group and 31 to the placebo group. Compared with placebo group, the Christensen score was lower in ketamine group at day 3 (absolute difference, -1.13; 95 % confidence interval [CI], -2.02 to -0.24; P = 0.012). Ketamine group was superior to the placebo group with regard to the ICFS scores at day 3 (absolute difference, -6.4; 95 % CI, -11.4 to -1.4; P = 0.013). The plasma TNF-α, IL-6, S100β, and NSE levels were increased after operation compared with baseline in both groups and were significantly higher in placebo group than in ketamine group within 24 h after surgery (all P < 0.05). There was no significant difference of each safety evaluation indicator between the two groups (all P > 0.05).

CONCLUSION

A single sub-anesthetic dose of ketamine may improve POFS in patients undergoing radical laparoscopic surgery for CRC, without postoperative adverse reactions.

Macrophage migration inhibitory factor contributes to immunopathogenesis during Plasmodium yoelii 17XL infection

Macrophage migration inhibitory factor (MIF) is a cytokine recognized regulator of the inflammatory immune response associated with several immune cells that produce inflammatory cytokines such as IL-1β, IL-6, IL-12, IL-18, and TNF-α. This study aimed to understand the effect of MIF on the immune response and pathogenesis during Plasmodium infection. Wild-type (Wt) and MIF knockout (Mif ^-/-) mice were intravenously infected with 1×10³ Plasmodium yoelii (Py) 17XL-parasitized red blood cells. Our data showed that Py17XL-infected Wt mice died 11 days postinfection, while Mif ^-/- mice showed reduced parasitemia and an increase in their survival at day 11 up to 58%, importantly they succumb up to day 21 postinfection. The increased survival rate in Mif ^-/- mice was associated with less severe cachexia and anemia as a result of a mixed Th1/Th2 cytokine profile, high levels of IL-12, IL-17/IL-4, and IL-10 in serum; and high levels of IL-4 and IL-10, and low levels of IFN-γ in spleen cells compared to Py17XL infected Wt mice. Moreover, macrophages (Mφs) from Mif ^-/- mice exhibited higher concentrations of IL-10 and IL-12 and reduced levels of TNF-α and nitric oxide (NO) compared to Py17XL-infected Wt mice. These results demonstrate that MIF has an important role in regulating the immune response associated with host pathogenesis and lethality, which is relevant to consider in preventing/reducing complications in Plasmodium infections.

Screening of imported malaria infection in asymptomatic migrants from Sub-Saharan Africa: A retrospective analysis of a 2010-2019 cohort

BACKGROUND

Up to 40% of cases of imported malaria in Europe are diagnosed in recently arrived migrants, who generally exhibit asymptomatic or mild symptoms and show low parasitaemia (submicroscopic). The study describes the prevalence of malaria infection among asymptomatic Sub-Saharan African migrants (ASSAM) and compares asymptomatic malaria-infected (AMI) vs non-malaria infected patients.

METHODS

An observational, comparative, retrospective study was carried out in ASSAM who underwent a medical examination, between 2010 and 2019 at the National Reference Unit for Tropical Diseases (NRU-Trop) in Madrid, Spain. Medical examination and systematic screening protocol for infectious diseases, including screening for malaria infection by Polymerase Chain Reaction (PCR) was performed.

RESULTS

During the study period, 632 out of 1061 ASSAM were screened for malaria, median age: 24 years (IQR:1-5); median time from arrival to diagnosis: 2 months (IQR:1-5). P. falciparum was the most frequent species: 61 patients (67.8%). Compared to non-malaria infected, AMI subjects had: higher rate of co-infection with S. stercoralis (41.1%VS 22.9%;p < 0.001) and filariae (8.9% VS 2.4%;p = 0.006), lower erythrocyte corpuscular volume (83.6 VS 84.4;p = 0.008) and lower levels of cholesterol (151.0 VS 167.3;p < 0.001).

CONCLUSIONS

We observed a high prevalence of AMI among ASSAM. This highlights the need to consider routing screening of migrants from endemic areas and to study if such screening could avoid the potential morbidities associated with chronic infection, reduce morbi-mortality of acute malaria and the risk of transmission in host communities.

Tumour necrosis factor-α as a prognostic biomarker of severe malaria: a systematic review and meta-analysis

BACKGROUND

Tumour necrosis factor-alpha (TNF-α) levels are reportedly altered during malaria. In this systematic review and meta-analysis, we aimed to collect and compare data on TNF-α levels between patients with malaria of varying severity and healthy asymptomatic positive controls.

METHODS

We searched PubMed, Scopus and Web of Science for studies that reported TNF-α levels in malaria cases of different severity and healthy asymptomatic positive controls using a combination of search terms. The quality of the included studies was assessed using the Strengthening the Reporting of Observational Studies in Epidemiology checklist. To compare the TNF-α levels among fatal cases, severe cases, uncomplicated cases and healthy asymptomatic positive controls, we applied the random-effects model that assumed the existence of variations between studies. The effect estimate was pooled mean difference (MD) with a 95% confidence interval (CI).

RESULTS

From 1694 studies, we included 31 studies that met our eligibility criteria for systematic review and meta-analysis. Patients with severe malaria showed higher mean TNF-α levels than those with uncomplicated malaria (P < 0.001, pooled MD = 79.02 pg/ml, 95% CI: 63.68-94.35 pg/ml, I2: 99.5%, n = 26 studies). Furthermore, fatal cases had no difference in the mean TNF-α levels in comparison with survived cases (P = 0.055, pooled MD = 82.38 pg/ml, 95% CI: -1.93 to 166.69 pg/ml, I2: 99.54%, n = 5 studies). Finally, patients with uncomplicated malaria showed higher mean TNF-α levels than those with asymptomatic malaria (P < 0.001, pooled MD = 45.10 pg/ml, 95% CI: 18.45-71.76 pg/ml, I2: 97.09%, n = 5 studies).

CONCLUSION

This systematic review and meta-analysis confirmed the increase of TNF-α levels in patients with severe malaria. Therefore, TNF-α may be alternatively used as a prognostic biomarker of severe malaria.

TRIAL REGISTRATION

Not applicable.

A systematic review and meta-analysis of blood interleukin-4 levels concerning malaria infection and severity

Background

Interleukin (IL)-4 had been linked to malaria severity, but the findings are controversial, and the evidence is inconsistent and imprecise. In the current investigation, data on IL-4 levels in patients with severe and uncomplicated malaria were compiled.

Methods

The systematic review was registered at PROSPERO (CRD42022323387). Searches for relevant articles on IL-4 levels in patients with severe malaria and studies that examined IL-4 levels in both uncomplicated malaria and healthy controls were performed in PubMed, Embase, and Scopus using the search strategy without limitation to publication years or language. The quality of all included studies was evaluated using The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement: standards for reporting observational studies. Qualitative and quantitative data syntheses were performed. The random-effects model, which weights each study according to its between- and within-study variance, was used to pool the mean difference (MD) of individual studies. The degree of heterogeneity was determined using Cochran's Q and I² statistics. Additionally, meta-regression and subgroup analyses were perfomed to investigate possible sources of heterogeneity. The outliers were identified using the leave-one-out method and assessed publication bias using funnel plots, Egger’s test, and a contour-enhanced funnel plot.

Results

A total of 2300 studies were identified through database searches, and 36 were included for analyses. The meta-analysis results showed lower mean IL-4 levels in severe malaria (434 cases) than in uncomplicated malaria (611 cases) (P = 0.01, pooled MD: −3.36 pg/mL, 95% confidence intervals CI −5.55 to −1.16 pg/mL, I²: 98.15%, 11 studies). The meta-analysis results showed no difference in mean IL-4 levels between cerebral malaria (96 cases) and noncerebral severe malaria (108 cases) (P = 0.71, pooled MD: 0.86 pg/mL, 95% CI −3.60 to 5.32 pg/mL, I² 92.13%, four studies). Finally, no difference was found in mean IL-4 levels between uncomplicated malaria (635 cases) and healthy controls (674 cases) (P = 0.57, pooled MD: 0.79 pg/mL, 95% CI −1.92 to 3.50 pg/mL, I²: 99.89%, 11 studies).

Conclusion

The meta-analysis revealed lower IL-4 levels in patients with severe malaria than in those with uncomplicated malaria, though a trend toward comparable IL-4 levels between both groups was more likely because several sources of heterogeneities were observed. Based on the limited number of studies included in the meta-analysis, until additional investigations have been conducted, IL-4 consideration as an alternative prognostic factor for malaria severity is not warranted.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04237-z.

Swertiamarin-mediated immune modulation/adaptation confers protection against Plasmodium berghei

Aims: Development of resistance by the malaria parasite, a systemic inflammatory and infectious pathogen, has raised the need for novel efficacious antimalarials. Plant-derived natural compounds are known to modulate the immune response and eradicate the infectious pathogens. Therefore we carried out experiments with swertiamarin to dissect its anti-inflammatory and immunomodulatory potential. Materials & methods: We carried out studies in Swiss albino mice that received infectious challenge with Plasmodium berghei and swertiamarin treatment in a prophylactic manner. Results & conclusion: Oral administration of swertiamarin prior to infectious challenge with P. berghei in experimental mice showed delayed parasite development as compared with untreated control. IFN-γ and IL-10 appeared to be adapted/modulated by regular swertiamarin treatment. Further, withdrawal of swertiamarin pressure did not affect parasite replication. However, the short half-life of swertiamarin limited its long-lasting therapeutic effect, requiring higher and frequent dosing schedules.

Dry season prevalence of Plasmodium falciparum in asymptomatic gambian children, with a comparative evaluation of diagnostic methods

BACKGROUND

Subclinical infection with Plasmodium falciparum remains highly prevalent, yet diagnosing these often low-density infections remains a challenge. Infections can be subpatent, falling below the limit of detection for conventional thick-film microscopy and rapid diagnostic testing (RDT). In this study, the prevalence of subclinical P. falciparum infections in school-aged children was characterised at the start of the dry season in the Upper River Region of The Gambia in 2017/2018, with a goal to also compare the utility of different diagnostic tools.

METHODS

In a cross-sectional survey of children living in 29 villages on the south bank of the Gambia river (median age of 10 years), matched microscopy, rapid diagnostic test (RDT, detecting histidine-rich protein 2) and polymerase chain reaction (PCR, targeting either 18S rRNA or var gene acidic terminal sequence) were used to determine the prevalence of patent and subpatent infections and to compare the performance of the different diagnostic methods.

RESULTS

The prevalence of var gene acidic terminal sequence (varATS) qPCR-detectable infections was 10.2% (141/1381) with a median density of 3.12 parasites/µL. Malaria prevalence was highly heterogeneous across the region, ranging from < 1% to ~ 40% prevalence in different village clusters. Compared to varATS, 18S rRNA PCR detected fewer low-density infections, with an assay sensitivity of 50% and specificity of 98.8%. Parasite prevalence in the cohort was 2.9% by microscopy and 1.5% by RDT. Compared to varATS qPCR, microscopy and RDT had sensitivities of 11.5% and 9.2%, respectively, although both methods were highly specific (> 98%). Samples that were positive by all three tests (varATS qPCR, RDT and microscopy) had significantly higher parasite densities (median = 1705 parasites/µL) than samples that were positive by varATS qPCR only (median = 2.4 parasites/µL).

CONCLUSIONS

The majority of subclinical malaria infections in school-aged children were of extremely low parasite density and detectable only by ultra-sensitive PCR analysis. Understanding the duration of these low density infections, their physiological impact and their contribution to sustained parasite transmission is necessary to inform malaria elimination strategies.

Increased interleukin-6 levels associated with malaria infection and disease severity: a systematic review and meta-analysis

Interleukin-6 (IL-6) is generated by immune cells during infection with malaria parasites and they are associated with the immunopathogenesis of malaria. The present systematic review and meta-analysis aimed to compare the differences in IL-6 levels between several groups of patients with malaria and healthy control groups. The systematic review was registered at PROSPERO with a registration number: CRD42021290753. Systematic literature searches were conducted in PubMed, Web of Science, and Scopus until November 7, 2021 to obtain studies that documented IL-6 levels in patients with malaria. The quality of the included studies was assessed using critical appraisal tools from the Joanna Briggs Institute. Differences in the mean IL-6 levels among patients with: (1) severe and non-severe malaria, (2) uncomplicated malaria and controls, (3) uncomplicated and asymptomatic malaria, (4) asymptomatic malaria and healthy controls, and (5) those that died or survived were estimated using a random-effects model. Forty-three of 1,969 studies were included in the systematic review. Results of the meta-analysis showed that patients with severe malaria had higher mean IL-6 levels than those with non-severe malaria [P = 0.04, weight mean difference (WMD) = 96.63 pg/mL, 95% confidence interval (CI) = 0.88 − 19.38 pg/mL, I² = 99.9%, 13 studies]. Patients with uncomplicated malaria had higher mean IL-6 levels than the controls (P < 0.001, WMD = 42.86 pg/mL, 95% CI = 30.17 − 55.56 pg/mL, I² = 100%, 17 studies). No differences in the mean levels of IL-6 were found between patients with uncomplicated malaria and those with asymptomatic malaria (P = 0.063, WMD = 42.07 pg/mL, 95% CI =  − 2.23 pg/mL to − 86.37 pg/mL, I² = 99.1%, 8 studies), or between patients with asymptomatic malaria and healthy controls (P = 0.45, WMD = 1.67 pg/mL, 95% CI =  − 2.73 pg/mL to − 6.07 pg/mL, I² = 98.1%, 2 studies). A higher mean level of IL-6 was observed in patients who died compared with the levels of those who survived (P = 0.007, WMD = 1,399.19 pg/mL, 95% CI = 384.16 − 2,414.2 pg/mL, I² = 93.1%, 4 studies). Our meta-analysis of the pooled evidence can be used to guide future studies in which IL-6 levels are measured during malaria outbreaks to monitor malaria severity. Heterogeneity of the effect estimate among the included studies was the main limitation of this analysis. In conclusion, significantly increased levels of IL-6 were observed in patients with severe malaria compared with those in patients with non-severe malaria, which indicates that IL-6 is a candidate marker for severe malaria. Future studies should investigate the sensitivity and specificity of increased IL-6 levels to determine the effectiveness of assessments of IL-6 levels monitoring of malaria infection and severity.

The Emerging Threat of Plasmodium knowlesi Malaria Infection: A Concept Paper on the Vulnerable Factors in Human

In South-East Asia (SEA), there has been an increase in the trend of detected and reported cases of Plasmodium knowlesi malaria in the last few decades. This higher transmission rate within SEA countries is attributed to the distribution of the Macaque, banded leaf monkeys, and Anopheles mosquito in this region. This study aims to propose a concept that highlights the integration of vulnerability factors to P. knowlesi malaria infection. The relevant literature on the vulnerability factors of P. knowlesi was reviewed. Any theories and models that could be integrated to support the factors were also explored throughout this study. Exposure to P. knowlesi malaria was found to be influenced by sociodemographic, socioeconomic, environmental, social context, belief, and human behaviour factors. However, these factors were commonly discussed separately in existing studies. For better disease prevention and control, all these factors should be explored collectively, to facilitate research aimed at generating a deeper understanding of the vulnerability factors to P. knowlesi malaria from various perspectives, including the genetic, sociodemographic, socioeconomic, environmental, sociocultural beliefs, and human behaviour of the population.

'Bouncing Back' From Subclinical Malaria: Inflammation and Erythrocytosis After Resolution of P. falciparum Infection in Gambian Children

Recent malaria is associated with an increased risk of systemic bacterial infection. The aetiology of this association is unclear but malaria-related haemolysis may be one contributory factor. To characterise the physiological consequences of persistent and recently resolved malaria infections and associated haemolysis, 1650 healthy Gambian children aged 8-15 years were screened for P. falciparum infection (by 18sRNA PCR) and/or anaemia (by haematocrit) at the end of the annual malaria transmission season (t₁). P. falciparum-infected children and children with moderate or severe anaemia (haemoglobin concentration < 11g/dl) were age matched to healthy, uninfected, non-anaemic controls and screened again 2 months later (t₂). Persistently infected children (PCR positive at t₁ and t₂) had stable parasite burdens and did not differ significantly haematologically or in terms of proinflammatory markers from healthy, uninfected children. However, among persistently infected children, IL-10 concentrations were positively correlated with parasite density suggesting a tolerogenic response to persistent infection. By contrast, children who naturally resolved their infections (positive at t₁ and negative at t₂) exhibited mild erythrocytosis and concentrations of pro-inflammatory markers were raised compared to other groups of children. These findings shed light on a 'resetting' and potential overshoot of the homeostatic haematological response following resolution of malaria infection. Interestingly, the majority of parameters tested were highly heterogeneous in uninfected children, suggesting that some may be harbouring cryptic malaria or other infections.

Inflammatory cytokine responses in children with asymptomatic malaria infection living in rural, semi-urban and urban areas in south-eastern Gabon

Cytokines are soluble mediators of the immune response, and their evolution influences the disease outcome. Gaining knowledge on cytokines has become important, as they can constitute biomarkers allowing the diagnosis of malaria and preventing severe forms of the disease. Here, we investigated 10 cytokines and their circulating levels in asymptomatic Gabonese children with Plasmodium falciparum infection living in urban, semi-urban and rural areas. Blood samples were collected from 273 schoolchildren (153 uninfected and 120 infected) aged 6 to 192 months. Hematological parameters were determined and P. falciparum diagnosis was performed using a rapid diagnosis test, microscopy and nested polymerase chain reaction (PCR). Plasma pro- [interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-12p70, IL-17A and IL-22] and anti-inflammatory [IL-10, IL-4, IL-13 and transforming growth factor (TGF)-β] cytokine levels were measured by enzyme-linked immunosorbent assay (ELISA) and compared between asymptomatic-infected and uninfected children. Results revealed that without distinction of area, IL-10 and IL-6 levels were higher in infected compared to uninfected children; however, the pro- and anti-inflammatory ratios (IL-6/IL-10 and TNF-α/IL-10) were similar. Furthermore, with area distinction significantly elevated levels of IL-10 in these asymptomatic children were always accompanied by either significantly low or high levels of a proinflammatory cytokine. Also, comparison between asymptomatic-infected children from the three areas showed significantly lower IL-17A, IL-22 and TGF-β levels in urban area compared to semi-urban and rural areas. These results suggest that asymptomatic malaria infections induce significantly high inflammatory cytokine levels without modifying the balanced between pro- and anti-inflammatory cytokines and underline the higher exposure to infections of children in rural areas.

High infectious disease burden as a basis for the observed high frequency of asymptomatic SARS-CoV-2 infections in sub-Saharan Africa

Following the coronavirus outbreaks described as severe acute respiratory syndrome (SARS) in 2003 and the Middle East respiratory syndrome (MERS) in 2012, the world has again been challenged by yet another corona virus, named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 infections were first detected in a Chinese Province in December 2019 and then declared a pandemic by the World Health Organization in March 2020. An infection caused by SARS-CoV-2 may result in asymptomatic, uncomplicated or fatal coronavirus disease 2019 (COVID-19). Fatal disease has been linked with the uncontrolled "cytokine storm" manifesting with complications mostly in people with underlying cardiovascular and pulmonary disease conditions. The severity of COVID-19 disease and the associated mortality has been disproportionately lower in terms of number of cases and deaths in Africa and also Asia in comparison to Europe and North America. Also, persons of colour residing in Europe and North America have been identified as a highly susceptible population due to a combination of several socioeconomic factors and poor access to quality healthcare. Interestingly, this has not been the case in sub-Saharan Africa where majority of the population are even more deprived of the aforementioned factors. On the contrary, sub-Saharan Africa has recorded the lowest levels of mortality and morbidity associated with the disease, and an overwhelming proportion of infections are asymptomatic. Whilst it can be argued that these lower number of cases in Africa may be due to challenges associated with the diagnosis of the disease such as lack of trained personnel and infrastructure, the number of persons who get infected and develop symptoms is proportionally lower than those who are asymptomatic, including asymptomatic cases that are never diagnosed. This review discusses the most probable reasons for the significantly fewer cases of severe COVID-19 disease and deaths in sub-Saharan Africa.

Elevated Levels of the Endothelial Molecules ICAM-1, VEGF-A, and VEGFR2 in Microscopic Asymptomatic Malaria

Background

In malaria, clinical disease has been associated with increased levels of endothelial activation due to the sequestration of infected erythrocytes. However, the levels and impact of endothelial activation and pro-angiogenic molecules such as vascular endothelial growth factor (VEGF)–A and its receptor vascular endothelial growth factor receptor 2 (VEGFR2) in asymptomatic malaria have not been well characterized.

Methods

Blood samples were obtained from community children for malaria diagnosis using microscopy and polymerase chain reaction. A multiplex immunoassay was used to determine the levels of intracellular adhesion molecule (ICAM)–1, vascular endothelial growth factor (VEGF)–A, and VEGFR2 in the plasma of children with microscopic or submicroscopic asymptomatic parasitemia and compared with levels in uninfected controls.

Results

Levels of ICAM-1, VEGF-A, and VEGFR2 were significantly increased in children with microscopic asymptomatic parasitemia compared with uninfected controls. Also, levels of VEGF-A were found to be inversely associated with age. Additionally, a receiver operating characteristic analysis revealed that plasma levels of ICAM-1 (area under the curve [AUC], 0.72) showed a moderate potential in discriminating between children with microscopic malaria from uninfected controls when compared with VEGF-A (AUC, 0.67) and VEGFR2 (AUC, 0.69).

Conclusions

These data imply that endothelial activation and pro-angiogenic growth factors could be one of the early host responders during microscopic asymptomatic malaria and may play a significant role in disease pathogenesis.