Plasmodium falciparum rosetting protects schizonts against artemisinin

Epidemiology, Detection and Treatment of Malaria

Malaria, one of the oldest infections to affect humans, incurs significant healthcare burdens across various parts of the world [...].

The artemisinin-induced dormant stages of Plasmodium falciparum exhibit hallmarks of cellular quiescence/senescence and drug resilience

Recrudescent infections with the human malaria parasite, Plasmodium falciparum, presented traditionally the major setback of artemisinin-based monotherapies. Although the introduction of artemisinin combination therapies (ACT) largely solved the problem, the ability of artemisinin to induce dormant parasites still poses an obstacle for current as well as future malaria chemotherapeutics. Here, we use a laboratory model for induction of dormant P. falciparum parasites and characterize their transcriptome, drug sensitivity profile, and cellular ultrastructure. We show that P. falciparum dormancy requires a ~ 5-day maturation process during which the genome-wide gene expression pattern gradually transitions from the ring-like state to a unique form. The transcriptome of the mature dormant stage carries hallmarks of both cellular quiescence and senescence, with downregulation of most cellular functions associated with growth and development and upregulation of selected metabolic functions and DNA repair. Moreover, the P. falciparum dormant stage is considerably more resistant to antimalaria drugs compared to the fast-growing asexual stages. Finally, the irregular cellular ultrastructure further suggests unique properties of this developmental stage of the P. falciparum life cycle that should be taken into consideration by malaria control strategies.

Pathogenicity and virulence of malaria: Sticky problems and tricky solutions

Infections with Plasmodium falciparum and Plasmodium vivax cause over 600,000 deaths each year, concentrated in Africa and in young children, but much of the world's population remain at risk of infection. In this article, we review the latest developments in the immunogenicity and pathogenesis of malaria, with a particular focus on P. falciparum, the leading malaria killer. Pathogenic factors include parasite-derived toxins and variant surface antigens on infected erythrocytes that mediate sequestration in the deep vasculature. Host response to parasite toxins and to variant antigens is an important determinant of disease severity. Understanding how parasites sequester, and how antibody to variant antigens could prevent sequestration, may lead to new approaches to treat and prevent disease. Difficulties in malaria diagnosis, drug resistance, and specific challenges of treating P. vivax pose challenges to malaria elimination, but vaccines and other preventive strategies may offer improved disease control.

Pathogenetic mechanisms and treatment targets in cerebral malaria

Malaria, the most prevalent mosquito-borne infectious disease worldwide, has accompanied humanity for millennia and remains an important public health issue despite advances in its prevention and treatment. Most infections are asymptomatic, but a small percentage of individuals with a heavy parasite burden develop severe malaria, a group of clinical syndromes attributable to organ dysfunction. Cerebral malaria is an infrequent but life-threatening complication of severe malaria that presents as an acute cerebrovascular encephalopathy characterized by unarousable coma. Despite effective antiparasite drug treatment, 20% of patients with cerebral malaria die from this disease, and many survivors of cerebral malaria have neurocognitive impairment. Thus, an important unmet clinical need is to rapidly identify people with malaria who are at risk of developing cerebral malaria and to develop preventive, adjunctive and neuroprotective treatments for cerebral malaria. This Review describes important advances in the understanding of cerebral malaria over the past two decades and discusses how these mechanistic insights could be translated into new therapies.

An artesunate pharmacometric model to explain therapeutic responses in falciparum malaria

BACKGROUND

The artemisinins are potent and widely used antimalarial drugs that are eliminated rapidly. A simple concentration-effect pharmacometric model does not explain why dosing more frequently than once daily fails to augment parasite clearance and improve therapeutic responses in vivo. Artemisinins can induce a temporary non-replicative or 'dormant' drug refractory state in Plasmodium falciparum malaria parasites which may explain recrudescences observed in clinical trials despite full drug susceptibility, but whether it explains the dosing-response relationship is uncertain.

OBJECTIVES

To propose a revised model of antimalarial pharmacodynamics that incorporates reversible asexual parasite injury and temporary drug refractoriness in order to explain the failure of frequent dosing to augment therapeutic efficacy in falciparum malaria.

METHODS

The model was fitted using a Bayesian Markov Chain Monte Carlo approach with the parasite clearance data from 39 patients with uncomplicated falciparum malaria treated with artesunate from western Cambodia and 40 patients from northwestern Thailand reported previously.

RESULTS

The revised model captured the dynamics of parasite clearance data. Its predictions are consistent with observed therapeutic responses.

CONCLUSIONS

A within-host pharmacometric model is proposed in which it is hypothesized that some malaria parasites enter a temporary drug refractory state after exposure to artemisinin antimalarials, which is followed by delayed parasite death or reactivation. The model fitted the observed sequential parasite density data from patients with acute P. falciparum malaria, and it supported reduced ring stage activity in artemisinin-resistant infections.

Molecular insights into artemisinin resistance in Plasmodium falciparum: An updated review

Malaria still poses a major burden on human health around the world, especially in endemic areas. Plasmodium resistance to several antimalarial drugs has been one of the major hindrances in control of malaria. Thus, the World Health Organization recommended artemisinin-based combination therapy (ACT) as a front-line treatment for malaria. The emergence of parasites resistant to artemisinin, along with resistant to ACT partner drugs, has led to ACT treatment failure. The artemisinin resistance is mostly related to the mutations in the propeller domain of the kelch13 (k13) gene that encodes protein Kelch13 (K13). The K13 protein has an important role in parasite reaction to oxidative stress. The most widely spread mutation in K13, with the highest degree of resistance, is a C580Y mutation. Other mutations, which are already identified as markers of artemisinin resistance, are R539T, I543T, and Y493H. The objective of this review is to provide current molecular insights into artemisinin resistance in Plasmodium falciparum. The trending use of artemisinin beyond its antimalarial effect is described. Immediate challenges and future research directions are discussed. Better understanding of the molecular mechanisms underlying artemisinin resistance will accelerate implementation of scientific findings to solve problems with malarial infection.

Perspectives of vector management in the control and elimination of vector-borne zoonoses

The complex transmission profiles of vector-borne zoonoses (VZB) and vector-borne infections with animal reservoirs (VBIAR) complicate efforts to break the transmission circuit of these infections. To control and eliminate VZB and VBIAR, insecticide application may not be conducted easily in all circumstances, particularly for infections with sylvatic transmission cycle. As a result, alternative approaches have been considered in the vector management against these infections. In this review, we highlighted differences among the environmental, chemical, and biological control approaches in vector management, from the perspectives of VZB and VBIAR. Concerns and knowledge gaps pertaining to the available control approaches were discussed to better understand the prospects of integrating these vector control approaches to synergistically break the transmission of VZB and VBIAR in humans, in line with the integrated vector management (IVM) developed by the World Health Organization (WHO) since 2004.

Rosette formation by Plasmodium vivax gametocytes favors the infection in Anopheles aquasalis

Plasmodium vivax is a public health problem and the most common type of malaria outside sub-Saharan Africa. The capacity of cytoadhesion, rosetting, and liver latent phase development could impact treatment and disease control. Although the ability to P. vivax gametocyte develop rosetting is known, it is not yet clear which role it plays during the infection and transmission process to the mosquito. Here, we used ex vivo approaches for evaluate the rosetting P. vivax gametocytes capacity and we have investigated the effect of this adhesive phenotype on the infection process in the vector Anopheles aquasalis mosquito. Rosette assays were performed in 107 isolates, and we have observed an elevated frequency of cytoadhesive phenomena (77,6%). The isolates with more than 10% of rosettes have presented a higher infection rate in Anopheles aquasalis (p=0.0252). Moreover, we found a positive correlation between the frequency of parasites in rosetting with the infection rate (p=0.0017) and intensity (p=0.0387) in the mosquito. The disruption of P. vivax rosette formation through mechanical rupture assay confirmed the previously findings, since the paired comparison showed that isolates with disrupted rosettes have a lower infection rate (p<0.0001) and intensity (p=0.0003) compared to the control group (no disruption). Herein we have demonstrated for the first time a potential effect of the rosette phenomenon on the infection process in the mosquito vector An. aquasalis, favoring its capacity and intensity of infection, thus allowing the perpetuation of the parasite cycle life.

Prevalence of malaria resistance-associated mutations in Plasmodium falciparum circulating in 2017–2018, Bo, Sierra Leone

Introduction

In spite of promising medical, sociological, and engineering strategies and interventions to reduce the burden of disease, malaria remains a source of significant morbidity and mortality, especially among children in sub-Saharan Africa. In particular, progress in the development and administration of chemotherapeutic agents is threatened by evolved resistance to most of the antimalarials currently in use, including artemisinins.

Methods

This study analyzed the prevalence of mutations associated with antimalarial resistance in Plasmodium falciparum from 95 clinical samples collected from individuals with clinically confirmed malaria at a hospital in Bo, Sierra Leone between May 2017 and December 2018. The combination of polymerase chain reaction amplification and subsequent high throughput DNA sequencing was used to determine the presence of resistance-associated mutations in five P. falciparum genes – pfcrt, pfmdr1, pfdhfr, pfdhps and pfkelch13. The geographic origin of parasites was assigned using mitochondrial sequences.

Results

Relevant mutations were detected in the pfcrt (22%), pfmdr1 (&gt;58%), pfdhfr (100%) and pfdhps (&gt;80%) genes while no resistance-associated mutations were found in the pfkelch13 gene. The mitochondrial barcodes were consistent with a West African parasite origin with one exception indicating an isolate imported from East Africa.

Discussion

Detection of the pfmdr1 NFSND haplotype in 50% of the samples indicated the increasing prevalence of strains with elevated tolerance to artemeter + lumefantrine (AL) threatening the combination currently used to treat uncomplicated malaria in Sierra Leone. The frequency of mutations linked to resistance to antifolates suggests widespread resistance to the drug combination used for intermittent preventive treatment during pregnancy.

Evolving perspectives on rosetting in malaria

The ability of the intraerythrocytic Plasmodium spp. to form spontaneous rosettes with uninfected red blood cells (URBCs) has been observed in the medically important malaria parasites. Since the discovery of rosettes in the late 1980s, different formation mechanisms and pathobiological roles have been postulated for rosetting; most of which have focused on Plasmodium falciparum. Recent breakthroughs, including new data from Plasmodium vivax, have highlighted the multifaceted roles of rosetting in the immunopathobiology and the development of drug resistance in human malaria. Here, we provide new perspectives on the formation and the role of rosetting in malaria rheopathobiology.

Rosetting Responses of Plasmodium-infected Erythrocytes to Antimalarials

In malaria, rosetting is a phenomenon involving the cytoadherence of uninfected erythrocytes to infected erythrocytes (IRBC) harboring the late erythrocytic stage of Plasmodium spp. Recently, artesunate-stimulated rosetting has been demonstrated to confer a survival advantage to P. falciparum late-stage IRBC. This study investigated the rosetting response of P. falciparum and P. vivax clinical isolates to ex vivo antimalarial treatments. Brief exposure of IRBC to chloroquine, mefloquine, amodiaquine, quinine, and lumefantrine increased the rosetting rates of P. falciparum and P. vivax. Furthermore, the ex vivo combination of artesunate with mefloquine and piperaquine also resulted in increased the rosetting rates. Drug-mediated rosette-stimulation has important implications for the therapeutic failure of rapidly cleared drugs such as artesunate. However, further work is needed to establish the ramifications of increased rosetting rates by drugs with longer half-lifves, such as chloroquine, mefloquine, and piperaquine.

Rosettes: a shield for Plasmodium falciparum against artemisinins?

Relative resistance of Plasmodium falciparum parasites to artesunate (AS) has been ascribed to mutations in the Kelch 13 gene. Lee et al. describe another potential contributor to resistance: the induction of increased rosetting by trophozoite-infected erythrocytes following short exposures to AS. Dissecting this phenomenon may lead to new insights into AS resistance.