Parasite Sequestration Research Articles

A systems serology approach to identifying key antibody correlates of protection from cerebral malaria in Malawian children

BackgroundPlasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) proteins are expressed on the surface of infected erythrocytes, mediating parasite sequestration in the vasculature. PfEMP1 is a major target of protective antibodies, but the features of the antibody response are poorly defined.MethodsIn Malawian children with cerebral or uncomplicated malaria, we characterized the antibody response to 39 recombinant PfEMP1 Duffy binding like (DBL) domains or cysteine-rich interdomain regions (CIDRs) in detail, including measures of antibody classes, subclasses, and engagement with Fcγ receptors and complement. Using elastic net regularized logistic regression, we identified a combination of seven antibody targets and Fc features that best distinguished between children with cerebral and uncomplicated malaria. To confirm the role of the selected targets and Fc features, we measured antibody-dependent neutrophil and THP-1 cell phagocytosis of intercellular adhesion molecule-1 (ICAM-1) and endothelial protein C (EPCR) co-binding infected erythrocytes.ResultsThe selected features distinguished between children with cerebral and uncomplicated malaria with 87% accuracy (median, 80–96% interquartile range) and included antibody to well-characterized DBLβ3 domains and a less well-characterized CIDRγ12 domain. The abilities of antibodies to engage C1q and FcγRIIIb, rather than levels of IgG, correlated with protection. In line with a role of FcγRIIIb binding antibodies to DBLβ3 domains, antibody-dependent neutrophil phagocytosis of ICAM-1 and EPCR co-binding IE was higher in uncomplicated malaria (15% median, 8–38% interquartile range) compared to cerebral malaria (7%, 30–15%, p < 0.001).ConclusionsAntibodies associated with protection from cerebral malaria target a subset of PfEMP1 domains. The Fc features of protective antibody response include engagement of FcγRIIIb and C1q, and ability to induce antibody-dependent neutrophil phagocytosis of infected erythrocytes. Identifying the targets and Fc features of protective immunity could facilitate the development of PfEMP1-based therapeutics for cerebral malaria.

Overview of Malaria in Pregnancy: Challenges and Strategies for Effective Prevention

Malaria in pregnancy is a significant public health issue in sub-Saharan Africa, with 30 million pregnancies at risk each year. Pregnant women are particularly vulnerable due to immunological changes and the placental environment that facilitates parasite sequestration. The predominant malaria parasite, Plasmodium falciparum, is associated with significant maternal and fetal complications. Effective malaria prevention strategies include insecticide-treated nets (ITNs) and intermittent preventive treatment (IPTp) with Sulfadoxine-pyrimethamine. However, adherence to preventive chemotherapy is challenging due to side effects and socioeconomic barriers. Health education programs are crucial for increasing awareness and promoting preventive behaviors. Early diagnosis and prompt treatment are critical for managing severe malaria cases. Environmental and vector control measures, such as indoor residual spraying and larval source management, are vital for reducing mosquito populations and transmission. Nutritional interventions support immune function and overall health. Access to healthcare services, innovative technologies, and cultural and socioeconomic factors are essential for overcoming barriers to malaria prevention and treatment. Continuous monitoring and evaluation are crucial for refining interventions and improving health outcomes. Keywords: Malaria, Pregnancy, Challenges, Strategies, Effective Prevention

SEVUparin as a potential Adjunctive Treatment in children with severe malaria: A phase I trial safety and dose finding trial (SEVUSMAART).

Even on the best antimalarial treatments (injectable artesunate) African children with severe malaria have poor outcomes with most deaths occurring early in the course of hospital admission (<24hours). Lactic acidosis, largely due to impairment of the microcirculatory flow due to parasite sequestration, is a main risk factor for poor outcome. There are no adjuvant treatments for severe malaria that target this complication. Sevuparin, a heparin-like drug, binds to Plasmodium falciparum erythrocyte membrane protein blocking merozoite invasion, preventing cytoadherence and transiently de-sequestering infected erythrocytes. Leading to improved microcirculatory flow by reversing/preventing parasite sequestration. If given early during admission this could result in improvements in outcomes. Sevuparin has been shown to be safe and well tolerated in adults with only some mild transient effects on activated partial thromboplastin time (APTT) were reported, without clinical consequences. A Phase I trial designed to provide data on safety, dosing, feasibility of sevuparin as an adjuvant therapy in Kenya and Zambian children with severe malaria complicated by lactic acidosis (> 2mmol/l). Three intravenous doses will be given at admission (0 hours), 8 and 16 hours. APPT will be measured 1 hour after each dose (to assess maximum toxicity). Studying 20 children will allow sufficient data on safety to be generated across a range of doses to identify the maximum tolerated dose (MTD) using the Continual Reassessment Method, which adapts or informs subsequent doses for each child based on the data from previously enrolled children. The MTD will be identified based on the dose-toxicity model updated by each previous patient's APTT results using standard methods. The results of the Phase I trial will identify the final dose to be tested in a Phase II trial in terms of both efficacy and safety outcomes. PACTR number: 202007890194806 (date 20/07/2020) ISRCTN32271864 (date 28/07/2021).

RNAscope in situ hybridization reveals microvascular sequestration of Plasmodium relictum pSGS1 blood stages but absence of exo-erythrocytic dormant stages during latent infection of Serinus canaria

BackgroundBirds chronically infected with avian malaria parasites often show relapses of parasitaemia after latent stages marked by absence of parasites in the peripheral circulation. These relapses are assumed to result from the activation of dormant exo-erythrocytic stages produced during secondary (post-erythrocytic) merogony of avian Plasmodium spp. Yet, there is no morphological proof of persistent or dormant tissue stages in the avian host during latent infections. This study investigated persistence of Plasmodium relictum pSGS1 in birds with latent infections during winter, with the goal to detect presumed persisting tissue stages using a highly sensitive RNAscope® in situ hybridization technology.MethodsFourteen domestic canaries were infected with P. relictum pSGS1 by blood-inoculation in spring, and blood films examined during the first 4 months post infection, and during winter and spring of the following year. After parasitaemia was no longer detectable, half of the birds were dissected, and tissue samples investigated for persisting tissue stages using RNAscope ISH and histology. The remaining birds were blood-checked and dissected after re-appearance of parasitaemia, and their tissues equally examined.ResultsSystematic examination of tissues showed no exo-erythrocytic stages in birds exhibiting latent infections by blood-film microscopy, indicating absence of dormant tissue stages in P. relictum pSGS1-infected canaries. Instead, RNAscope ISH revealed rare P. relictum blood stages in capillaries of various tissues and organs, demonstrating persistence of the parasites in the microvasculature. Birds examined after re-appearance of parasitemia showed higher numbers of P. relictum blood stages in both capillaries and larger blood vessels, indicating replication during early spring and re-appearance in the peripheral circulation.ConclusionsThe findings suggest that persistence of P. relictum pSGS1 during latent infection is mediated by continuous low-level erythrocytic merogony and possibly tissue sequestration of infected blood cells. Re-appearance of parasitaemia in spring seems to result from increased erythrocytic merogony, therefore representing recrudescence and not relapse in blood-inoculated canaries. Further, the study highlights strengths and limitations of the RNAscope ISH technology for the detection of rare parasite stages in tissues, providing directions for future research on persistence and tissue sequestration of avian malaria and related haemosporidian parasites.

Infected erythrocytes and plasma proteomics reveal a specific protein signature of severe malaria

Cerebral malaria (CM), the most lethal complication of Plasmodium falciparum severe malaria (SM), remains fatal for 15–25% of affected children despite the availability of treatment. P. falciparum infects and multiplies in erythrocytes, contributing to anemia, parasite sequestration, and inflammation. An unbiased proteomic assessment of infected erythrocytes and plasma samples from 24 Beninese children was performed to study the complex mechanisms underlying CM. A significant down-regulation of proteins from the ubiquitin–proteasome pathway and an up-regulation of the erythroid precursor marker transferrin receptor protein 1 (TFRC) were associated with infected erythrocytes from CM patients. At the plasma level, the samples clustered according to clinical presentation. Significantly, increased levels of the 20S proteasome components were associated with SM. Targeted quantification assays confirmed these findings on a larger cohort (n = 340). These findings suggest that parasites causing CM preferentially infect reticulocytes or erythroblasts and alter their maturation. Importantly, the host plasma proteome serves as a specific signature of SM and presents a remarkable opportunity for developing innovative diagnostic and prognostic biomarkers.

Neuropilin-1 identifies a subset of highly activated CD8+ T cells during parasitic and viral infections.

Neuropilin-1 (Nrp-1) expression on CD8+ T cells has been identified in tumor-infiltrating lymphocytes and in persistent murine gamma-herpes virus infections, where it interferes with the development of long-lived memory T cell responses. In parasitic and acute viral infections, the role of Nrp-1 expression on CD8+ T cells remains unclear. Here, we demonstrate a strong induction of Nrp-1 expression on CD8+ T cells in Plasmodium berghei ANKA (PbA)-infected mice that correlated with neurological deficits of experimental cerebral malaria (ECM). Likewise, the frequency of Nrp-1+CD8+ T cells was significantly elevated and correlated with liver damage in the acute phase of lymphocytic choriomeningitis virus (LCMV) infection. Transcriptomic and flow cytometric analyses revealed a highly activated phenotype of Nrp-1+CD8+ T cells from infected mice. Correspondingly, in vitro experiments showed rapid induction of Nrp-1 expression on CD8+ T cells after stimulation in conjunction with increased expression of activation-associated molecules. Strikingly, T cell-specific Nrp-1 ablation resulted in reduced numbers of activated T cells in the brain of PbA-infected mice as well as in spleen and liver of LCMV-infected mice and alleviated the severity of ECM and LCMV-induced liver pathology. Mechanistically, we identified reduced blood-brain barrier leakage associated with reduced parasite sequestration in the brain of PbA-infected mice with T cell-specific Nrp-1 deficiency. In conclusion, Nrp-1 expression on CD8+ T cells represents a very early activation marker that exacerbates deleterious CD8+ T cell responses during both, parasitic PbA and acute LCMV infections.

SEVUparin as a potential Adjunctive Treatment in children with severe malaria: A phase I trial safety and dose finding trial (SEVUSMAART)

Background Even on the best antimalarial treatments (injectable artesunate) African children with severe malaria have poor outcomes with most deaths occurring early in the course of hospital admission (&lt;24hours). Lactic acidosis, largely due to impairment of the microcirculatory flow due to parasite sequestration, is a main risk factor for poor outcome. There are no adjuvant treatments for severe malaria that target this complication. Sevuparin, a heparin-like drug, binds to Plasmodium falciparum erythrocyte membrane protein blocking merozoite invasion, preventing cytoadherence and transiently de-sequestering infected erythrocytes. Leading to improved microcirculatory flow by reversing/preventing parasite sequestration. If given early during admission this could result in improvements in outcomes . Sevuparin has been shown to be safe and well tolerated in adults with only some mild transient effects on activated partial thromboplastin time (APTT) were reported, without clinical consequences. Methods A Phase I trial designed to provide data on safety, dosing, feasibility of sevuparin as an adjuvant therapy in Kenya and Zambian children with severe malaria complicated by lactic acidosis (&gt; 2mmol/l). Three intravenous doses will be given at admission (0 hours), 8 and 16 hours. APPT will be measured 1 hour after each dose (to assess maximum toxicity). Studying 20 children will allow sufficient data on safety to be generated across a range of doses to identify the maximum tolerated dose (MTD) using the Continual Reassessment Method, which adapts or informs subsequent doses for each child based on the data from previously enrolled children. The MTD will be identified based on the dose-toxicity model updated by each previous patient’s APTT results using standard methods. Conclusions The results of the Phase I trial will identify the final dose to be tested in a Phase II trial in terms of both efficacy and safety outcomes. Registration PACTR number: 202007890194806 (date 20/07/2020) ISRCTN32271864 (date 28/07/2021)

Cellular iron governs the host response to malaria.

Malaria and iron deficiency are major global health problems with extensive epidemiological overlap. Iron deficiency-induced anaemia can protect the host from malaria by limiting parasite growth. On the other hand, iron deficiency can significantly disrupt immune cell function. However, the impact of host cell iron scarcity beyond anaemia remains elusive in malaria. To address this, we employed a transgenic mouse model carrying a mutation in the transferrin receptor (TfrcY20H/Y20H), which limits the ability of cells to internalise iron from plasma. At homeostasis TfrcY20H/Y20H mice appear healthy and are not anaemic. However, TfrcY20H/Y20H mice infected with Plasmodium chabaudi chabaudi AS showed significantly higher peak parasitaemia and body weight loss. We found that TfrcY20H/Y20H mice displayed a similar trajectory of malaria-induced anaemia as wild-type mice, and elevated circulating iron did not increase peak parasitaemia. Instead, P. chabaudi infected TfrcY20H/Y20H mice had an impaired innate and adaptive immune response, marked by decreased cell proliferation and cytokine production. Moreover, we demonstrated that these immune cell impairments were cell-intrinsic, as ex vivo iron supplementation fully recovered CD4+ T cell and B cell function. Despite the inhibited immune response and increased parasitaemia, TfrcY20H/Y20H mice displayed mitigated liver damage, characterised by decreased parasite sequestration in the liver and an attenuated hepatic immune response. Together, these results show that host cell iron scarcity inhibits the immune response but prevents excessive hepatic tissue damage during malaria infection. These divergent effects shed light on the role of iron in the complex balance between protection and pathology in malaria.

Endothelial protein C receptor binding induces conformational changes to severe malaria-associated group A PfEMP1

Severe Plasmodium falciparum malaria infections are caused by microvascular sequestration of parasites binding to the human endothelial protein C receptor (EPCR) via the multi-domain P. falciparum erythrocyte membrane protein 1 (PfEMP1) adhesion ligands. Using cryogenic electron microscopy (Cryo-EM) and PfEMP1 sequence diversity analysis, we found that group A PfEMP1 CIDRα1 domains interact with the adjacent DBLα1 domain through central, conserved residues of the EPCR-binding site to adopt a compact conformation. Upon EPCR binding, the DBLα1 domain is displaced, and the EPCR-binding helix of CIDRα1 is turned, kinked, and twisted to reach a rearranged, stable EPCR-bound conformation. The unbound conformation and the required transition to the EPCR-bound conformation may represent a conformational masking mechanism of immune evasion for the PfEMP1 family.

Babesia microti alleviates disease manifestations caused by Plasmodium berghei ANKA in murine co-infection model of complicated malaria.

Malaria remains one of the most significant health issues worldwide, accounting for 2.6% of the total global disease burden, and efforts to eliminate this threat continue. The key focus is to develop an efficient and long-term immunity to this disease via vaccination or therapeutic approach, and innovative strategies would enable us to achieve this target. Previously, using a mouse co-infection disease model, cross-protection was illustrated between Babesia microti and Plasmodium chabaudi. Hence, this study was planned to elucidate the impact of acute B. microti Peabody mjr and Plasmodium berghei ANKA co-infection on the consequence of complicated malaria in the C57BL/6J mouse model of malaria. Furthermore, immune response and pathological features were analyzed, and the course of the disease was compared among experimental groups. Our study established that acute B. microti infection activated immunity which was otherwise suppressed by P. berghei. The immunosuppressive tissue microenvironment was counteracted as evidenced by the enhanced immune cell population in co-infected mice, in contrast to P. berghei-infected control mice. Parasite sequestration in the brain, liver, lung, and spleen of co-infected mice was significantly decreased and tissue injury was ameliorated. Meanwhile, the serum levels of IFN-γ, TNF-α, and IL-12p70 were reduced while the secretion of IL-10 was promoted in co-infected mice. Eventually, co-infected mice showed an extended rate of survival. Hereby, the principal cytokines associated with the severity of malaria by P. berghei infection were TNF-α, IFN-γ, and IL-12p70. Moreover, it was evident from our flow cytometry results that innate immunity is crucial and macrophages are at the frontline of immunity against P. berghei infection. Our study recommended further investigations to shed light on the effects of babesiosis in suppressing malaria with the goal of developing Babesia-based therapy against malaria.

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

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

The Impact of Sequestration on Artemisinin-Induced Parasite Clearance in Plasmodium falciparum Malaria in Africa.

Artemisinin-resistant Plasmodium falciparum is spreading in Southeast Asia and Africa. In vivo susceptibility to artemisinin is studied by looking at the rate of decline of peripheral parasitemia (parasite clearance half-life). However, parasites that are adhered/sequestered to the endothelium and undetectable in the peripheral blood are not considered in the estimation of parasite clearance. Here, we evaluated the influence of sequestration on in vivo artemisinin efficacy in Uganda, where artemisinin resistance is spreading. We analyzed 133 patients with P. falciparum malaria included in an in vivo study on artemisinin efficacy in northern Uganda in 2018 and 2019. The parasite clearance half-life was estimated from peripheral parasitemia after artemisinin monotherapy. P. falciparum histidine-rich protein 2 (PfHRP2) was measured in pretreatment plasma. The number of sequestered parasites was estimated from PfHRP2 concentration and peripheral parasitemia. The estimated number of sequestered parasites per plasma volume ranged from 0 to 2 564 000/μL. Inflammation, thrombocytopenia, and dyslipidemia were significantly associated with sequestration independent of peripheral parasitemia. The median parasite clearance half-lives were 1.65 hours in patients infected with Pfkelch13 wild-type parasites (n = 104) and 3.95 hours in those with A675V artemisinin-resistant mutant (n = 18). In the multivariable model for the wild-type population, 1 000 000/μL of sequestered parasites were estimated to delay parasite clearance by 16.8% (95% confidence interval, 5.1%-28.5%), although it was not clear in the A675V population. In patients with P. falciparum malaria without artemisinin-resistant mutations, intensive sequestration delays parasite clearance after treatment, which may contribute to reduced artemisinin efficacy.

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.

Phase 3 Evaluation of an Innovative Simple Molecular Test for the Diagnosis of Malaria and Follow-Up of Treatment Efficacy in Pregnant Women in Sub-Saharan Africa (Preg-Diagmal).

The malaria parasite Plasmodium falciparum (Pf) can sequester in the placenta resulting in low density of peripheral parasitemia and consequently in false negative malaria diagnosis (by microscopy) in pregnant women. Moreover, the use of rapid diagnostic tests (RDTs) in diagnostic strategies, including those for the detection of a malaria infection during pregnancy, is constrained by either persistent malaria antigen (histidine-rich protein 2; HRP2) after successful treatment, leading to false positive test results, or by false negative results as previously mentioned due to parasite sequestration (which is further exacerbated due to the low limited of detection [LoD] of conventional RDTs) or to HRP2 deletion. Recently, a direct blood polymerase chain reaction combined with a nucleic acid lateral flow immunoassay (dbPCR-NALFIA) has been developed, which circumvents these challenges and has demonstrated its diagnostic potential in phase 1 and 2 studies. The PREG-DIAGMAL trial presented in this manuscript will assess the diagnostic performance of dbPCR-NALFIA for the diagnostic of malaria in pregnant women and its potential to monitor treatment efficacy in these subjects. The work is ancillary embedded in an ongoing EDCTP funded trial, the PyraPreg project (PACTR202011812241529) in which the safety and efficacy of a newly registered Artemisinin-Based Combination (Pyronaridine-Artesunate) is being evaluated in pregnant women. This is a Phase 3 diagnostic evaluation conducted in 2 African countries: Democratic Republic of the Congo (DRC) and Burkina Faso. Pregnant women fulfilling the inclusion criteria of the PyraPreg study will be also invited to participate in the PREG-DIAGMAL study. Diagnostic accuracy will be assessed following the WHO/TDR guidelines for the evaluation of diagnostics and reported according to STARD principles. Due to the lack of a 100% specific and sensitive standard diagnostic test for malaria, the sensitivity and specificity of the new test will be compared to the available diagnostic practice in place at the selected settings (microscopy and/or RDT) and to quantitative PCR as the reference test. This phase 3 diagnostic study is designed towards the evaluation of the performance of a new diagnostic tool for the screening of malaria and the monitoring of treatment in pregnant women under real conditions life. If successful, the dbPCR-NALFIA could be a valuable tool to add to the diagnostic arsenal for malaria, in particular during pregnancy. Trial registration: Pan African Clinical Trial Registry database (PACTR202203780981413). Registered on 17 March 2022.

Experimental malaria-associated acute kidney injury is independent of parasite sequestration and resolves upon antimalarial treatment.

Malaria remains a important global disease with more than 200 million cases and 600 000 deaths each year. Malaria-associated acute kidney injury (MAKI) may occur in up to 40% of patients with severe malaria and is associated with increased mortality. Histopathological characteristics of AKI in malaria are acute tubular injury, interstitial nephritis, focal segmental glomerulosclerosis, collapsing glomerulopathy and glomerulonephritis. We observed that C57BL/6 mice infected with Plasmodium berghei NK65 (PbNK65) develop MAKI in parallel with malaria-associated acute respiratory distress syndrome (MA-ARDS). MAKI pathology was associated with proteinuria, acute tubular injury and collapse of glomerular capillary tufts, which resolved rapidly after treatment with antimalarial drugs. Importantly, parasite sequestration was not detected in the kidneys in this model. Furthermore, with the use of skeleton binding protein-1 (SBP-1) KO PbNK65 parasites, we found that parasite sequestration in other organs and its subsequent high parasite load are not required for the development of experimental MAKI. Similar proteinuria, histopathological features, and increases in kidney expression of interferon-γ, TNF-α, kidney injury molecule-1 (KIM-1) and heme oxygenase-1 (HO-1) was observed in both infected groups despite a significant difference in parasite load. Taken together, we introduce a model of experimental AKI in malaria with important similarities to AKI in malaria patients. Therefore, this mouse model might be important to further study the pathogenesis of AKI in malaria.

Immunopathology and Trypanosoma congolense parasite sequestration cause acute cerebral trypanosomiasis.

Trypanosoma congolense causes a syndrome of variable severity in animals in Africa. Cerebral trypanosomiasis is a severe form, but the mechanism underlying this severity remains unknown. We developed a mouse model of acute cerebral trypanosomiasis and characterized the cellular, behavioral, and physiological consequences of this infection. We show large parasite sequestration in the brain vasculature for long periods of time (up to 8 hr) and extensive neuropathology that associate with ICAM1-mediated recruitment and accumulation of T cells in the brain parenchyma. Antibody-mediated ICAM1 blocking and lymphocyte absence reduce parasite sequestration in the brain and prevent the onset of cerebral trypanosomiasis. Here, we establish a mouse model of acute cerebral trypanosomiasis and we propose a mechanism whereby parasite sequestration, host ICAM1, and CD4+ T cells play a pivotal role.

Host lung microbiota promotes malaria-associated acute respiratory distress syndrome

Severe malaria can manifest itself with a variety of well-recognized clinical phenotypes that are highly predictive of death – severe anaemia, coma (cerebral malaria), multiple organ failure, and respiratory distress. The reasons why an infected individual develops one pathology rather than another remain poorly understood. Here we use distinct rodent models of infection to show that the host microbiota is a contributing factor for the development of respiratory distress syndrome and host mortality in the context of malaria infections (malaria-associated acute respiratory distress syndrome, MA-ARDS). We show that parasite sequestration in the lung results in sustained immune activation. Subsequent production of the anti-inflammatory cytokine IL-10 by T cells compromises microbial control, leading to severe lung disease. Notably, bacterial clearance with linezolid, an antibiotic commonly used in the clinical setting to control lung-associated bacterial infections, prevents MA-ARDS-associated lethality. Thus, we propose that the host’s anti-inflammatory response to limit tissue damage can result in loss of microbial control, which promotes MA-ARDS. This must be considered when intervening against life-threatening respiratory complications.

Listeria monocytogenes Inoculation Impedes the Development of Brain Pathology in Experimental Cerebral Malaria by Inhibition of Parasitemia.

Cerebral malaria (CM) is a serious central nervous system dysfunction caused by Plasmodium falciparum infection. In this study, we investigated the effect of Listeria monocytogenes (Lm) inoculation on experimental cerebral malaria (ECM) using Plasmodium berghei ANKA (PbA)-infected C57BL/6 mice. Live Lm inoculation inhibited the parasitemia and alleviated ECM symptoms. The protective effect against ECM symptoms was connected with improved brain pathology manifested as a less-damaged blood-brain barrier, decreased parasite sequestration, and milder local inflammation. Meanwhile, Lm inoculation decreased expression of cell adhesion molecules (ICAM-1 and VCAM-1) and accumulation of pathogenic CD8+ T cells in the brain. In keeping with the suppression of parasitemia, there was an upregulation of IFN-γ, IL-12, MCP-1, and NO expression in the spleen by Lm inoculation upon PbA infection. Early treatment with exogenous IFN-γ exhibited a similar effect to Lm inoculation on PbA infection. Taken together, Lm inoculation impedes the development of brain pathology in ECM, and early systemic IFN-γ production may play a critical role in these protective effects.

Plasmodium falciparum in Aotus nancymaae: A New Model for Placental Malaria

Plasmodium falciparum (Pf)-infected erythrocytes that display the variant surface antigen VAR2CSA bind chondroitin sulfate A (CSA) to sequester in placental intervillous spaces, causing severe sequelae for mother and offspring. Here, we establish a placental malaria (PM) monkey model. Pregnant Aotus infected with CSA-binding Pf-CS2 parasites during 3rd trimester developed pronounced sequestration of late-stage parasites in placental intervillous spaces that express VAR2CSA and bind specifically to CSA. Similar to immune multigravid women, a monkey infected with Pf-CS2 parasites over successive pregnancies acquired antibodies against VAR2CSA, with potent functional activity that was boosted upon subsequent pregnancy infections. Aotus also developed functional antibodies after multiple acute PM episodes and subsequent VAR2CSA immunization. In summary, Pf infections in pregnant Aotus monkeys recapitulate all the prominent features of human PM infection and immunity, and this model can be useful for basic mechanistic studies and preclinical studies to qualify candidate PM vaccines.

Diagnosis of malaria in pregnancy: accuracy of CareStart\u2122 malaria Pf/PAN against light microscopy among symptomatic pregnant women at the Central Hospital in Yaound\xe9, Cameroon

BackgroundThe need to start treatment early for pregnant women who present with clinical features of malaria usually conflicts with the need to confirm diagnosis by microscopy (MP) before treatment, due to delays in obtaining results. Parasite sequestration in the placenta is also a problem. Rapid diagnostic tests (RDT), which detect soluble antigens, are a valuable alternative. The objective of this study was to evaluate pretreatment parasite prevalence by microscopy and by RDT and to assess the accuracy of RDT with MP as reference.MethodsA prospective cross-sectional study was carried out at the obstetrical unit of the Central Hospital in Yaoundé, during the period January-August 2015. Consenting patients with symptoms of suspected malaria in pregnancy were recruited and a blood sample taken for MP and RDT before treatment was started. The estimates of diagnostic performance (with 95% confidence interval) were calculated in OpenEpi online software using the Wilson’s score. The agreement, as reflected by the Cohen’s kappa, was calculated and interpreted using known intervals.ResultsThe results showed that, out of the 104 patients recruited, 69.2% (95%CI: 59.1–77.5) were MP positive while 77.94% (95%CI: 63.1–80.9) were RDT positive. The sensitivity of the malaria RDT was 91.67% (95%CI: 83.69–96.77) while the specificity was 53.13% (95%CI: 31.39–65.57). The diagnostic accuracy of the RDT with MP as reference was 79.81% (95%CI: 70.0–86.1). All cases were due to Plasmodium falciparum. A Cohen’s kappa of 0.45 (95%CI: 0.26–0.64) was obtained, consistent with a moderate agreement between the tests.ConclusionsThe diagnostic accuracy of the CareStart™ malaria Pf/PAN compared to microscopy was high, but not as desirable, with a false negative RDT at very high parasitaemia. In tertiary facilities, RDTs appear to provide a better diagnostic solution compared to microscopy. However, future studies with larger sample sizes should make this observation more generalizable; as missing a case could have serious consequences on pregnancy outcome.