RESUMEN
ABSTRACT: In humans, â¼0.1% to 0.3% of circulating red blood cells (RBCs) are present as platelet-RBC (P-RBC) complexes, and it is 1% to 2% in mice. Excessive P-RBC complexes are found in diseases that compromise RBC health (eg, sickle cell disease and malaria) and contribute to pathogenesis. However, the physiological role of P-RBC complexes in healthy blood is unknown. As a result of damage accumulated over their lifetime, RBCs nearing senescence exhibit physiological and molecular changes akin to those in platelet-binding RBCs in sickle cell disease and malaria. Therefore, we hypothesized that RBCs nearing senescence are targets for platelet binding and P-RBC formation. Confirming this hypothesis, pulse-chase labeling studies in mice revealed an approximately tenfold increase in P-RBC complexes in the most chronologically aged RBC population compared with younger cells. When reintroduced into mice, these complexes were selectively cleared from the bloodstream (in preference to platelet-free RBC) through the reticuloendothelial system and erythrophagocytes in the spleen. As a corollary, patients without a spleen had higher levels of complexes in their bloodstream. When the platelet supply was artificially reduced in mice, fewer RBC complexes were formed, fewer erythrophagocytes were generated, and more senescent RBCs remained in circulation. Similar imbalances in complex levels and senescent RBC burden were observed in humans with immune thrombocytopenia (ITP). These findings indicate that platelets are important for binding and clearing senescent RBCs, and disruptions in platelet count or complex formation and clearance may negatively affect RBC homeostasis and may contribute to the known risk of thrombosis in ITP and after splenectomy.
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Anemia de Células Falciformes , Malaria , Trombocitopenia , Humanos , Animales , Ratones , Anciano , Plaquetas/metabolismo , Eritrocitos/metabolismo , Trombocitopenia/metabolismo , Anemia de Células Falciformes/metabolismoRESUMEN
Malaria is resurging in many African and South American countries, exacerbated by COVID-19-related health service disruption. In 2021, there were an estimated 247 million malaria cases and 619 000 deaths in 84 endemic countries. Plasmodium falciparum strains partly resistant to artemisinins are entrenched in the Greater Mekong region and have emerged in Africa, while Anopheles mosquito vectors continue to evolve physiological and behavioural resistance to insecticides. Elimination of Plasmodium vivax malaria is hindered by impractical and potentially toxic antirelapse regimens. Parasitological diagnosis and treatment with oral or parenteral artemisinin-based therapy is the mainstay of patient management. Timely blood transfusion, renal replacement therapy, and restrictive fluid therapy can improve survival in severe malaria. Rigorous use of intermittent preventive treatment in pregnancy and infancy and seasonal chemoprevention, potentially combined with pre-erythrocytic vaccines endorsed by WHO in 2021 and 2023, can substantially reduce malaria morbidity. Improved surveillance, better access to effective treatment, more labour-efficient vector control, continued drug development, targeted mass drug administration, and sustained political commitment are required to achieve targets for malaria reduction by the end of this decade.
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Antimaláricos , Insecticidas , Malaria Falciparum , Malaria Vivax , Malaria , Embarazo , Femenino , Animales , Humanos , Antimaláricos/uso terapéutico , Malaria/tratamiento farmacológico , Malaria/epidemiología , Malaria/prevención & control , Malaria Vivax/tratamiento farmacológico , Plasmodium falciparum , Insecticidas/uso terapéutico , Malaria Falciparum/tratamiento farmacológico , Resistencia a MedicamentosRESUMEN
Splenomegaly frequently occurs in patients with Plasmodium falciparum (Pf) or P. vivax (Pv) malarial anemia, but mechanisms underlying this co-occurrence are unclear. In malaria-endemic Papua, Indonesia, we prospectively analyzed red blood cell (RBC) concentrations in the spleen and spleen-mimetic retention in 37 subjects splenectomized for trauma or hyperreactive splenomegaly, most of whom were infected with Plasmodium. Splenomegaly (median 357 g [range: 80-1918 g]) was correlated positively with the proportion of red-pulp on histological sections (median 88.1% [range: 74%-99.4%]; r = .59, p = .0003) and correlated negatively with the proportion of white-pulp (median 8.3% [range: 0.4%-22.9%]; r = -.50, p = .002). The number of RBC per microscopic field (>95% uninfected) was correlated positively with spleen weight in both Pf-infected (r = .73; p = .017) and Pv-infected spleens (r = .94; p = .006). The median estimated proportion of total-body RBCs retained in Pf-infected spleens was 8.2% (range: 1.0%-33.6%), significantly higher than in Pv-infected (2.6% [range: 0.6%-23.8%]; p = .015) and PCR-negative subjects (2.5% [range: 1.0%-3.3%]; p = .006). Retained RBCs accounted for over half of circulating RBC loss seen in Pf infections. The proportion of total-body RBC retained in Pf- and Pv-infected spleens correlated negatively with hemoglobin concentrations (r = -.56, p = .0003), hematocrit (r = -.58, p = .0002), and circulating RBC counts (r = -.56, p = .0003). Splenic CD71-positive reticulocyte concentrations correlated with spleen weight in Pf (r = 1.0; p = .003). Retention rates of peripheral and splenic RBCs were correlated negatively with circulating RBC counts (r = -.69, p = .07 and r = -.83, p = .008, respectively). In conclusion, retention of mostly uninfected RBC in the spleen, leading to marked congestion of the red-pulp, was associated with splenomegaly and is the major mechanism of anemia in subjects infected with Plasmodium, particularly Pf.
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Anemia , Malaria Falciparum , Malaria Vivax , Malaria , Humanos , Esplenomegalia/etiología , Eritrocitos , Anemia/complicaciones , Malaria/complicaciones , Malaria Falciparum/complicaciones , Plasmodium falciparum , Malaria Vivax/complicacionesRESUMEN
BACKGROUND AND OBJECTIVE: The importance of extracellular traps (ETs) in chronic respiratory conditions is increasingly recognized but their role in paediatric bronchiectasis is poorly understood. The specialized techniques currently required to study ETs preclude routine clinical use. A simple and cost-effective ETs detection method is needed to support diagnostic applications. We aimed to determine whether ETs could be detected using light microscopy-based assessment of Romanowsky-stained bronchoalveolar lavage (BAL) slides from children with bronchiectasis, and whether the ETs cellular origin could be determined. METHODS: Archived Romanowsky-stained BAL slides from a cross-sectional study of children with bronchiectasis were examined for ETs using light microscopy. The cellular origin of individual ETs was determined based on morphology and physical contact with surrounding cell(s). RESULTS: ETs were observed in 78.7% (70/89) of BAL slides with neutrophil (NETs), macrophage (METs), eosinophil (EETs) and lymphocyte (LETs) ETs observed in 32.6%, 51.7%, 4.5% and 9%, respectively. ETs of indeterminate cellular origin were present in 59.6% of slides. Identifiable and indeterminate ETs were co-detected in 43.8% of slides. CONCLUSION: BAL from children with bronchiectasis commonly contains multiple ET types that are detectable using Romanowsky-stained slides. While specialist techniques remain necessary to determining the cellular origin of all ETs, screening of Romanowsky-stained slides presents a cost-effective method that is well-suited to diagnostic settings. Our findings support further research to determine whether ETs can be used to define respiratory endotypes and to understand whether ETs-specific therapies may be required to resolve airway inflammation among children with bronchiectasis.
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Bronquiectasia , Trampas Extracelulares , Niño , Humanos , Líquido del Lavado Bronquioalveolar , Estudios Transversales , Lavado Broncoalveolar , Bronquiectasia/diagnóstico , FibrosisRESUMEN
BACKGROUND: Circulating myeloid-derived-suppressor-cells (MDSC) with immunosuppressive function are increased in human experimental Plasmodium falciparum infection, but have not been studied in clinical malaria. METHODS: Using flow-cytometry, circulating polymorphonuclear-MDSC were evaluated in cryopreserved samples from patients with uncomplicated Plasmodium vivax (n = 8) and uncomplicated (n = 4) and severe (n = 16) falciparum malaria from Papua, Indonesia. RESULTS: The absolute number of circulating polymorphonuclear-MDSC were significantly elevated in severe falciparum malaria patients compared to controls (n = 10). Polymorphonuclear-MDSC levels in uncomplicated vivax malaria were also elevated to levels comparable to that seen in severe falciparum malaria. CONCLUSION: Control of expansion of immunosuppressive MDSC may be important for development of effective immune responses in falciparum and vivax malaria.
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Malaria Falciparum , Malaria Vivax , Malaria , Células Supresoras de Origen Mieloide , Humanos , Indonesia , Malaria/complicaciones , Plasmodium falciparum , Plasmodium vivaxRESUMEN
BACKGROUND: A very large biomass of intact asexual-stage malaria parasites accumulates in the spleen of asymptomatic human individuals infected with Plasmodium vivax. The mechanisms underlying this intense tropism are not clear. We hypothesised that immature reticulocytes, in which P. vivax develops, may display high densities in the spleen, thereby providing a niche for parasite survival. METHODS AND FINDINGS: We examined spleen tissue in 22 mostly untreated individuals naturally exposed to P. vivax and Plasmodium falciparum undergoing splenectomy for any clinical indication in malaria-endemic Papua, Indonesia (2015 to 2017). Infection, parasite and immature reticulocyte density, and splenic distribution were analysed by optical microscopy, flow cytometry, and molecular assays. Nine non-endemic control spleens from individuals undergoing spleno-pancreatectomy in France (2017 to 2020) were also examined for reticulocyte densities. There were no exclusion criteria or sample size considerations in both patient cohorts for this demanding approach. In Indonesia, 95.5% (21/22) of splenectomy patients had asymptomatic splenic Plasmodium infection (7 P. vivax, 13 P. falciparum, and 1 mixed infection). Significant splenic accumulation of immature CD71 intermediate- and high-expressing reticulocytes was seen, with concentrations 11 times greater than in peripheral blood. Accordingly, in France, reticulocyte concentrations in the splenic effluent were higher than in peripheral blood. Greater rigidity of reticulocytes in splenic than in peripheral blood, and their higher densities in splenic cords both suggest a mechanical retention process. Asexual-stage P. vivax-infected erythrocytes of all developmental stages accumulated in the spleen, with non-phagocytosed parasite densities 3,590 times (IQR: 2,600 to 4,130) higher than in circulating blood, and median total splenic parasite loads 81 (IQR: 14 to 205) times greater, accounting for 98.7% (IQR: 95.1% to 98.9%) of the estimated total-body P. vivax biomass. More reticulocytes were in contact with sinus lumen endothelial cells in P. vivax- than in P. falciparum-infected spleens. Histological analyses revealed 96% of P. vivax rings/trophozoites and 46% of schizonts colocalised with 92% of immature reticulocytes in the cords and sinus lumens of the red pulp. Larger splenic cohort studies and similar investigations in untreated symptomatic malaria are warranted. CONCLUSIONS: Immature CD71+ reticulocytes and splenic P. vivax-infected erythrocytes of all asexual stages accumulate in the same splenic compartments, suggesting the existence of a cryptic endosplenic lifecycle in chronic P. vivax infection. Findings provide insight into P. vivax-specific adaptions that have evolved to maximise survival and replication in the spleen.
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Plasmodium vivax/fisiología , Reticulocitos/metabolismo , Bazo/metabolismo , Bazo/parasitología , Esplenectomía/estadística & datos numéricos , Adolescente , Adulto , Infecciones Asintomáticas , Femenino , Humanos , Indonesia , Malaria Vivax/parasitología , Malaria Vivax/fisiopatología , Masculino , Persona de Mediana Edad , Nueva Guinea , Estudios Prospectivos , Adulto JovenRESUMEN
Platelets are understood to assist host innate immune responses against infection, although direct evidence of this function in any human disease, including malaria, is unknown. Here we characterized platelet-erythrocyte interactions by microscopy and flow cytometry in patients with malaria naturally infected with Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, or Plasmodium knowlesi Blood samples from 376 participants were collected from malaria-endemic areas of Papua, Indonesia, and Sabah, Malaysia. Platelets were observed binding directly with and killing intraerythrocytic parasites of each of the Plasmodium species studied, particularly mature stages, and was greatest in P vivax patients. Platelets preferentially bound to the infected more than to the uninfected erythrocytes in the bloodstream. Analysis of intraerythrocytic parasites indicated the frequent occurrence of platelet-associated parasite killing, characterized by the intraerythrocytic accumulation of platelet factor-4 and terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling of parasite nuclei (PF4+TUNEL+ parasites). These PF4+TUNEL+ parasites were not associated with measures of systemic platelet activation. Importantly, patient platelet counts, infected erythrocyte-platelet complexes, and platelet-associated parasite killing correlated inversely with patient parasite loads. These relationships, taken together with the frequency of platelet-associated parasite killing observed among the different patients and Plasmodium species, suggest that platelets may control the growth of between 5% and 60% of circulating parasites. Platelet-erythrocyte complexes made up a major proportion of the total platelet pool in patients with malaria and may therefore contribute considerably to malarial thrombocytopenia. Parasite killing was demonstrated to be platelet factor-4-mediated in P knowlesi culture. Collectively, our results indicate that platelets directly contribute to innate control of Plasmodium infection in human malaria.
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Plaquetas/parasitología , Eritrocitos/parasitología , Interacciones Huésped-Parásitos , Malaria/sangre , Plasmodium/fisiología , Activación Plaquetaria , Adulto , Plaquetas/metabolismo , Plaquetas/patología , Eritrocitos/metabolismo , Eritrocitos/patología , Femenino , Humanos , Indonesia/epidemiología , Malaria/epidemiología , Malaria/parasitología , Malaria/patología , Malasia/epidemiología , Masculino , Factor Plaquetario 4/metabolismo , Adulto JovenRESUMEN
BACKGROUND: Neutrophil activation results in Plasmodium parasite killing in vitro, but neutrophil products including neutrophil extracellular traps (NETs) mediate host organ damage and may contribute to severe malaria. The role of NETs in the pathogenesis of severe malaria has not been examined. METHODS: In Papua, Indonesia, we enrolled adults with symptomatic Plasmodium falciparum (n = 47 uncomplicated, n = 8 severe), Plasmodium vivax (n = 37), or Plasmodium malariae (n = 14) malaria; asymptomatic P falciparum (n = 19) or P vivax (n = 21) parasitemia; and healthy adults (n = 23) without parasitemia. Neutrophil activation and NETs were quantified by immunoassays and microscopy and correlated with parasite biomass and disease severity. RESULTS: In patients with symptomatic malaria, neutrophil activation and NET counts were increased in all 3 Plasmodium species. In falciparum malaria, neutrophil activation and NET counts positively correlated with parasite biomass (Spearman rho = 0.41, P = .005 and r2 = 0.26, P = .002, respectively) and were significantly increased in severe disease. In contrast, NETs were inversely associated with parasitemia in adults with asymptomatic P falciparum infection (r2 = 0.24, P = .031) but not asymptomatic P vivax infection. CONCLUSIONS: Although NETs may inhibit parasite growth in asymptomatic P falciparum infection, neutrophil activation and NET release may contribute to pathogenesis in severe falciparum malaria. Agents with potential to attenuate these processes should be evaluated.
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Trampas Extracelulares/inmunología , Malaria/inmunología , Activación Neutrófila/inmunología , Neutrófilos/inmunología , Plasmodium/inmunología , Adulto , Estudios de Cohortes , Progresión de la Enfermedad , Femenino , Humanos , Indonesia , Masculino , Parasitemia/inmunologíaRESUMEN
Background: Splenectomy increases the risk of severe and fatal infections; however, the risk of Plasmodium vivax malaria is unknown. We quantified the Plasmodium species-specific risks of malaria and other outcomes following splenectomy in patients attending a hospital in Papua, Indonesia. Methods: Records of all patients attending Mitra-Masyarakat Hospital 2004-2013 were reviewed, identifying those who underwent splenectomy. Subsequent risks of specific clinical outcomes within 12 months for splenectomized patients were compared to nonsplenectomized patients from their first recorded hospital admission. In addition, patients splenectomized for trauma 2015-2016 were followed prospectively for 14 months. Results: Of the 10774 patients hospitalized during 2004-2013, 67 underwent splenectomy. Compared to nonsplenectomized inpatients, patients undergoing splenectomy had a 5-fold higher rate of malaria presentation within 12 months (adjusted hazard ratio [AHR] = 5.0 [95% confidence interval (CI): 3.4-7.3], P < .001). The AHR was 7.8 (95% CI: 5.0-12.3) for P. vivax and 3.0 (95% CI: 1.7-5.4) for P. falciparum (both P < .001). Splenectomized patients had greater risk of being hospitalized for any cause (AHR = 1.8 [95% CI: 1.0-3.0], P = .037) and diarrheal (AHR = 3.5 [95% CI: 1.3-9.6], P = .016). In the 14-month prospective cohort, 12 episodes of P. vivax and 6 episodes of P. falciparum were observed in 11 splenectomised patients. Conclusions: Splenectomy is associated with a high risk of malaria, greater for P. vivax than P. falciparum. Eradication of P. vivax hypnozoites using primaquine (radical cure) and subsequent malaria prophylaxis is warranted following splenectomy in malaria-endemic areas.
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Malaria Vivax/epidemiología , Esplenectomía/efectos adversos , Adolescente , Adulto , Animales , Niño , Femenino , Humanos , Indonesia/epidemiología , Masculino , Persona de Mediana Edad , Estudios Prospectivos , Medición de Riesgo , Adulto JovenAsunto(s)
Eritrocitos/parasitología , Plasmodium falciparum/aislamiento & purificación , Plasmodium vivax/aislamiento & purificación , Bazo/parasitología , Adolescente , Adulto , Animales , Infecciones Asintomáticas , Biomasa , Niño , Femenino , Humanos , Malaria Falciparum/parasitología , Malaria Vivax/parasitología , Masculino , Esplenectomía , Adulto JovenRESUMEN
BACKGROUND: Plasmodium falciparum and Plasmodium vivax infections compromise dendritic cell (DC) function and expand regulatory T (Treg) cells in both clinical disease (malaria) and experimental human sub-microscopic infection. Conversely, in asymptomatic microscopy-positive (patent) P. falciparum or P. vivax infection in endemic areas, blood DC increase or retain HLA-DR expression and Treg cells exhibit reduced activation, suggesting that DC and Treg cells contribute to the control of patent asymptomatic infection. The effect of sub-microscopic (sub-patent) asymptomatic Plasmodium infection on DC and Treg cells in malaria-endemic area residents remains unclear. METHODS: In a cross-sectional household survey conducted in Papua, Indonesia, 162 asymptomatic adults were prospectively evaluated for DC and Treg cells using field-based flow cytometry. Of these, 161 individuals (99 %) were assessed retrospectively by polymerase chain reaction (PCR), 19 of whom had sub-microscopic infection with P. falciparum and 15 with sub-microscopic P. vivax infection. Flow cytometric data were re-analysed after re-grouping asymptomatic individuals according to PCR results into negative controls, sub-microscopic and microscopic parasitaemia to examine DC and Treg cell phenotype in sub-microscopic infection. RESULTS: Asymptomatic adults with sub-microscopic P. falciparum or P. vivax infection had DC HLA-DR expression and Treg cell activation comparable to PCR-negative controls. Sub-microscopic P. falciparum infection was associated with lower peripheral CD4(+) T cells and lymphocytes, however sub-microscopic Plasmodium infection had no apparent effect on DC sub-set number or Treg cell frequency. CONCLUSIONS: In contrast to the impairment of DC maturation/function and the activation of Treg cells seen with sub-microscopic parasitaemia in primary experimental human Plasmodium infection, no phenotypic evidence of dysregulation of DC and Treg cells was observed in asymptomatic sub-microscopic Plasmodium infection in Indonesian adults. This is consistent with DC and Treg cells retaining their functional capacity in sub-microscopic asymptomatic infection with P. falciparum or P. vivax in malaria-endemic areas.
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Infecciones Asintomáticas , Células Dendríticas/inmunología , Malaria Falciparum/inmunología , Malaria Vivax/inmunología , Linfocitos T Reguladores/inmunología , Adulto , Estudios Transversales , Composición Familiar , Femenino , Citometría de Flujo , Humanos , Indonesia , Masculino , Reacción en Cadena de la Polimerasa , Estudios Prospectivos , Estudios Retrospectivos , Adulto JovenRESUMEN
Clinical illness with Plasmodium falciparum or Plasmodium vivax compromises the function of dendritic cells (DC) and expands regulatory T (Treg) cells. Individuals with asymptomatic parasitemia have clinical immunity, restricting parasite expansion and preventing clinical disease. The role of DC and Treg cells during asymptomatic Plasmodium infection is unclear. During a cross-sectional household survey in Papua, Indonesia, we examined the number and activation of blood plasmacytoid DC (pDC), CD141(+), and CD1c(+) myeloid DC (mDC) subsets and Treg cells using flow cytometry in 168 afebrile children (of whom 15 had P. falciparum and 36 had P. vivax infections) and 162 afebrile adults (of whom 20 had P. falciparum and 20 had P. vivax infections), alongside samples from 16 patients hospitalized with uncomplicated malaria. Unlike DC from malaria patients, DC from children and adults with asymptomatic, microscopy-positive P. vivax or P. falciparum infection increased or retained HLA-DR expression. Treg cells in asymptomatic adults and children exhibited reduced activation, suggesting increased immune responsiveness. The pDC and mDC subsets varied according to clinical immunity (asymptomatic or symptomatic Plasmodium infection) and, in asymptomatic infection, according to host age and parasite species. In conclusion, active control of asymptomatic infection was associated with and likely contingent upon functional DC and reduced Treg cell activation.
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Células Dendríticas/inmunología , Antígenos HLA-DR/genética , Malaria Falciparum/genética , Malaria Vivax/genética , Plasmodium falciparum/fisiología , Plasmodium vivax/fisiología , Linfocitos T Reguladores/inmunología , Adolescente , Adulto , Enfermedades Asintomáticas , Niño , Preescolar , Estudios Transversales , Regulación hacia Abajo , Femenino , Citometría de Flujo , Antígenos HLA-DR/inmunología , Humanos , Indonesia , Activación de Linfocitos , Malaria Falciparum/diagnóstico , Malaria Falciparum/inmunología , Malaria Falciparum/parasitología , Malaria Vivax/diagnóstico , Malaria Vivax/inmunología , Malaria Vivax/parasitología , Masculino , Plasmodium falciparum/inmunología , Plasmodium vivax/inmunología , Adulto JovenRESUMEN
BACKGROUND: The emergence and spread of multidrug-resistant Plasmodium falciparum and Plasmodium vivax highlights the need for objective measures of ex vivo drug susceptibility. Flow cytometry (FC) has potential to provide a robust and rapid quantification of ex vivo parasite growth. METHODS: Field isolates from Papua, Indonesia, underwent ex vivo drug susceptibility testing against chloroquine, amodiaquine, piperaquine, mefloquine, and artesunate. A single nucleic acid stain (i.e., hydroethidine (HE) for P. falciparum and SYBR Green I (SG) for P. vivax) was used to quantify infected red blood cells by FC-based signal detection. Data derived by FC were compared to standard quantification by light microscopy (LM). A subset of isolates was used to compare single and double staining techniques. RESULTS: In total, 57 P. falciparum and 23 P. vivax field isolates were collected for ex vivo drug susceptibility testing. Reliable paired data between LM and FC was obtained for 88 % (295/334) of these assays. The median difference of derived IC50 values varied from -5.4 to 6.1 nM, associated with 0.83-1.23 fold change in IC50 values between LM and FC. In 15 assays (5.1 %), the derived difference of IC50 estimates was beyond the 95 % limits of agreement; in eleven assays (3.7 %), this was attributable to low parasite growth (final schizont count < 40 %), and in four assays (1.4 %) due to low initial parasitaemia at the start of assay (<2000 µl(-1)). In a subset of seven samples, LM, single and double staining FC techniques generated similar IC50 values. CONCLUSIONS: A single staining FC-based assay using a portable cytometer provides a simple, fast and versatile platform for field surveillance of ex vivo drug susceptibility in clinical P. falciparum and P. vivax isolates.
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Antimaláricos/farmacología , Citometría de Flujo/métodos , Pruebas de Sensibilidad Parasitaria/métodos , Plasmodium falciparum/efectos de los fármacos , Plasmodium vivax/efectos de los fármacos , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Niño , Eritrocitos/parasitología , Femenino , Humanos , Indonesia , Masculino , Persona de Mediana Edad , Plasmodium falciparum/crecimiento & desarrollo , Plasmodium vivax/crecimiento & desarrollo , Coloración y Etiquetado/métodos , Adulto JovenRESUMEN
Plasmodium vivax contributes significantly to global malaria morbidity. Key advances include the discovery of pathways facilitating invasion by P. vivax merozoites of nascent reticulocytes, crucial for vaccine development. Humanized mouse models and hepatocyte culture systems have enhanced understanding of hypnozoite biology. The spleen has emerged as a major reservoir for asexual vivax parasites, replicating in an endosplenic life cycle, and contributing to recurrent and chronic infections, systemic inflammation, and anemia. Splenic accumulation of uninfected red cells is the predominant cause of anemia. Recurring and chronic infections cause progressive anemia, malnutrition, and death in young children in high-transmission regions. Endothelial activation likely contributes to vivax-associated organ dysfunction. The many recent advances in vivax pathobiology should help guide new approaches to prevention and management.
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Malaria Vivax , Plasmodium vivax , Humanos , Malaria Vivax/parasitología , Malaria Vivax/inmunología , Malaria Vivax/fisiopatología , Animales , Plasmodium vivax/fisiología , Plasmodium vivax/patogenicidad , Bazo/parasitología , Bazo/fisiopatología , Bazo/inmunologíaRESUMEN
The risk of severe malaria from the zoonotic parasite Plasmodium knowlesi approximates that from P. falciparum. In severe falciparum malaria, neutrophil activation contributes to inflammatory pathogenesis, including acute lung injury. The role of neutrophil activation in the pathogenesis of severe knowlesi malaria has not been examined. We evaluated 213 patients with P. knowlesi mono-infection (138 non-severe, 75 severe) and 49 Plasmodium-negative controls from Malaysia. Markers of neutrophil activation (soluble neutrophil elastase [NE], citrullinated histone [CitH3] and circulating neutrophil extracellular traps [NETs]) were quantified in peripheral blood by microscopy and immunoassays. Findings were correlated with malaria severity, ALI clinical criteria, biomarkers of parasite biomass, haemolysis, and endothelial activation. Neutrophil activation increased with disease severity, with median levels higher in severe than non-severe malaria and controls for NE (380[IQR:210-930]ng/mL, 236[139-448]ng/mL, 218[134-307]ng/mL, respectively) and CitH3 (8.72[IQR:3.0-23.1]ng/mL, 4.29[1.46-9.49]ng/mL, 1.53[0.6-2.59]ng/mL, respectively)[all p<0.01]. NETs were higher in severe malaria compared to controls (126/µL[IQR:49-323] vs 51[20-75]/µL, p<0.001). In non-severe malaria, neutrophil activation fell significantly upon discharge from hospital (p<0.03). In severe disease, NETs, NE, and CitH3 were correlated with parasitaemia, cell-free haemoglobin and angiopoietin-2 (all Pearson's r>0.24, p<0.05). Plasma NE and angiopoietin-2 were higher in knowlesi patients with ALI than those without (p<0.008); neutrophilia was associated with an increased risk of ALI (aOR 3.27, p<0.01). In conclusion, neutrophil activation is increased in ALI and in proportion to disease severity in knowlesi malaria, is associated with endothelial activation, and may contribute to disease pathogenesis. Trials of adjunctive therapies to regulate neutrophil activation are warranted in severe knowlesi malaria.
RESUMEN
Plasmodium vivax lactate dehydrogenase (PvLDH) is an essential enzyme in the glycolytic pathway of P. vivax. It is widely used as a diagnostic biomarker and a measure of total-body parasite biomass in vivax malaria. However, the dynamics of PvLDH remains poorly understood. Here, we developed mathematical models that capture parasite and matrix PvLDH dynamics in ex vivo culture and the human host. We estimated key biological parameters characterising in vivo PvLDH dynamics based on longitudinal data of parasitemia and PvLDH concentration collected from P. vivax-infected humans, with the estimates informed by the ex vivo data as prior knowledge in a Bayesian hierarchical framework. We found that the in vivo accumulation rate of intraerythrocytic PvLDH peaks at 10-20 h post-invasion (late ring stage) with a median estimate of intraerythrocytic PvLDH mass at the end of the life cycle to be 9.4 × 10-3ng. We also found that the median estimate of in vivo PvLDH half-life was approximately 21.9 h. Our findings provide a foundation with which to advance our quantitative understanding of P. vivax biology and will facilitate the improvement of PvLDH-based diagnostic tools.
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Malaria Vivax , Plasmodium vivax , Humanos , Malaria Vivax/diagnóstico , L-Lactato Deshidrogenasa , Teorema de BayesRESUMEN
Plasmodium knowlesi is the major cause of zoonotic malaria in Southeast Asia. Rapid and accurate diagnosis enables effective clinical management. A novel malaria diagnostic tool, Gazelle (Hemex Health, USA) detects haemozoin, a by-product of haem metabolism found in all Plasmodium infections. A pilot phase refined the Gazelle haemozoin identification algorithm, with the algorithm then tested against reference PCR in a larger cohort of patients with P. knowlesi mono-infections and febrile malaria-negative controls. Limit-of-detection analysis was conducted on a subset of P. knowlesi samples serially diluted with non-infected whole blood. The pilot phase of 40 P. knowlesi samples demonstrated 92.5% test sensitivity. P. knowlesi-infected patients (n = 203) and febrile controls (n = 44) were subsequently enrolled. Sensitivity and specificity of the Gazelle against reference PCR were 94.6% (95% CI 90.5-97.3%) and 100% (95% CI 92.0-100%) respectively. Positive and negative predictive values were 100% and 98.8%, respectively. In those tested before antimalarial treatment (n = 143), test sensitivity was 96.5% (95% CI 92.0-98.9%). Sensitivity for samples with ≤ 200 parasites/µL (n = 26) was 84.6% (95% CI 65.1-95.6%), with the lowest parasitaemia detected at 18/µL. Limit-of-detection (n = 20) was 33 parasites/µL (95% CI 16-65%). The Gazelle device has the potential for rapid, sensitive detection of P. knowlesi infections in endemic areas.
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Antílopes , Malaria , Parásitos , Plasmodium knowlesi , Animales , Humanos , Sistemas de Atención de Punto , Malaria/diagnósticoRESUMEN
Severe malaria after splenectomy has been reported with infections with Plasmodium falciparum, Plasmodium knowlesi, and Plasmodium malariae, but is less well-characterized with Plasmodium vivax. We describe a case of severe P. vivax malaria with hypotension, prostration, and acute kidney injury occurring 2 months after splenectomy in Papua, Indonesia. The patient was treated successfully with intravenous artesunate.
Asunto(s)
Malaria Vivax , Malaria , Humanos , Malaria Vivax/diagnóstico , Malaria Vivax/tratamiento farmacológico , Esplenectomía , Artesunato/uso terapéutico , Plasmodium vivax , Plasmodium falciparumRESUMEN
OBJECTIVE: Glucose-6-phosphate dehydrogenase (G6PD) deficiency offers some protection against malaria; however, the degree of protection is poorly described and likely to vary with G6PD genotype and Plasmodium species. We present a novel approach to quantify the differential invasion rates of P. falciparum between G6PD deficient and normal red blood cells (RBCs) in an ex vivo model. A flow-cytometry based assay was developed to distinguish G6PD deficient and normal, parasitized and non-parasitized RBCs within the same sample. Venous blood collected from a G6PD heterozygous female was infected and cultured ex vivo with a laboratory strain of P. falciparum (FC27). RESULTS: Aliquots of infected blood were assayed at schizont and subsequent synchronized ring stages. At schizont stage, 84.9% of RBCs were G6PD deficient of which 0.4% were parasitized compared to 2.0% of normal RBCs. In the subsequent ring stage, 90.4% of RBCs were deficient and 0.2% of deficient and 0.9% of normal cells respectively were parasitized. The pooled Odds Ratio for a deficient RBC to be parasitized was 0.2 (95% confidence interval: 0.18-0.22, p < 0.001) compared to a normal cell. Further studies are warranted to explore preferential parasitization with different G6PD variants and Plasmodium species.
Asunto(s)
Deficiencia de Glucosafosfato Deshidrogenasa , Glucosafosfato Deshidrogenasa , Malaria Falciparum , Femenino , Glucosafosfato Deshidrogenasa/genética , Deficiencia de Glucosafosfato Deshidrogenasa/genética , Humanos , Malaria Falciparum/genética , Plasmodium falciparumRESUMEN
Commercial point-of-care tests remain insufficient for accurately detecting and differentiating low-level malaria infections in regions co-endemic with multiple non-falciparum species, including zoonotic Plasmodium knowlesi (Pk). A 5-plex chemiluminescent assay simultaneously measures pan-Plasmodium lactate dehydrogenase (pLDH), P. falciparum (Pf)-LDH, P. vivax (Pv)-LDH, Pf-histidine-rich protein-2 (HRP2), and C-reactive protein. We assessed its diagnostic performance on whole blood (WB) samples from 102 healthy controls and 306 PCR-confirmed clinical cases of Pf, Pv, Pk, P. malariae (Pm) and P. ovale (Po) mono-infections from Southeast-Asia. We confirm its excellent HRP2-based detection of Pf. Cross-reactivity of Pf-LDH with all non-falciparum species tested was observed (specificity 57.3%). Pv-LDH performance was suboptimal for Pv (93.9% sensitivity and 73.9% specificity). Poor specificity was driven by strong Pk cross-reactivity, with Pv-LDH detecting 93.9% of Pk infections. The pan-LDH-to-Pf-LDH ratio was capable of discerning Pv from Pk, and robustly differentiated Pf from Pm or Po infection, useful in regions with hrp2/3 deletions. We tested the platform's performance in plasma for the first time, with WB outperforming plasma for all analytes except Pv-LDH for Pk. The platform is a promising tool for WB malaria diagnosis, although further development is warranted to improve its utility in regions co-endemic for multiple non-falciparum species.