Summary Background Artemisinin-resistant falciparum malaria has arisen in western Cambodia. A concerted international effort is underway to contain artemisinin-resistant Plasmodium falciparum , but ...containment strategies are dependent on whether resistance has emerged elsewhere. We aimed to establish whether artemisinin resistance has spread or emerged on the Thailand–Myanmar (Burma) border. Methods In malaria clinics located along the northwestern border of Thailand, we measured six hourly parasite counts in patients with uncomplicated hyperparasitaemic falciparum malaria (≥4% infected red blood cells) who had been given various oral artesunate-containing regimens since 2001. Parasite clearance half-lives were estimated and parasites were genotyped for 93 single nucleotide polymorphisms. Findings 3202 patients were studied between 2001 and 2010. Parasite clearance half-lives lengthened from a geometric mean of 2·6 h (95% CI 2·5–2·7) in 2001, to 3·7 h (3·6–3·8) in 2010, compared with a mean of 5·5 h (5·2–5·9) in 119 patients in western Cambodia measured between 2007 and 2010. The proportion of slow-clearing infections (half-life ≥6·2 h) increased from 0·6% in 2001, to 20% in 2010, compared with 42% in western Cambodia between 2007 and 2010. Of 1583 infections genotyped, 148 multilocus parasite genotypes were identified, each of which infected between two and 13 patients. The proportion of variation in parasite clearance attributable to parasite genetics increased from 30% between 2001 and 2004, to 66% between 2007 and 2010. Interpretation Genetically determined artemisinin resistance in P falciparum emerged along the Thailand–Myanmar border at least 8 years ago and has since increased substantially. At this rate of increase, resistance will reach rates reported in western Cambodia in 2–6 years. Funding The Wellcome Trust and National Institutes of Health.
New antimalarial agents are needed, especially given the emergence of artemisinin resistance. In this study from Thailand, treatment with KAE609, the first in the new spiroindolone class, resulted in ...rapid parasite clearance in patients with
Plasmodium vivax
or
P. falciparum
malaria.
The treatment of
Plasmodium falciparum
malaria has changed considerably over the past decade, with a global change to the rapidly and reliably effective artemisinin-based combination therapies. The deployment of such therapies and insecticide-treated bed nets have been the two main contributors to the substantial recent declines in morbidity and mortality from malaria.
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Unfortunately, artemisinin resistance has emerged in Southeast Asia, threatening these gains
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–
5
and potentially derailing current control efforts. New medicines are needed,
6
but it has proved difficult to develop effective and safe antibacterial and antiparasitic drugs.
The new spiroindolone class of antimalarial agents was identified a few years . . .
Plasmodium vivax infects an estimated 7 million people every year. Previously, vivax malaria was perceived as a benign condition, particularly when compared to falciparum malaria. Reports of the ...severe clinical impacts of vivax malaria have been increasing over the last decade.
We describe the main clinical impacts of vivax malaria, incorporating a rapid systematic review of severe disease with meta-analysis of data from studies with clearly defined denominators, stratified by hospitalization status. Severe anemia is a serious consequence of relapsing infections in children in endemic areas, in whom vivax malaria causes increased morbidity and mortality and impaired school performance. P. vivax infection in pregnancy is associated with maternal anemia, prematurity, fetal loss, and low birth weight. More than 11,658 patients with severe vivax malaria have been reported since 1929, with 15,954 manifestations of severe malaria, of which only 7,157 (45%) conformed to the World Health Organization (WHO) diagnostic criteria. Out of 423 articles, 311 (74%) were published since 2010. In a random-effects meta-analysis of 85 studies, 68 of which were in hospitalized patients with vivax malaria, we estimated the proportion of patients with WHO-defined severe disease as 0.7% 95% confidence interval (CI) 0.19% to 2.57% in all patients with vivax malaria and 7.11% 95% CI 4.30% to 11.55% in hospitalized patients. We estimated the mortality from vivax malaria as 0.01% 95% CI 0.00% to 0.07% in all patients and 0.56% 95% CI 0.35% to 0.92% in hospital settings. WHO-defined cerebral, respiratory, and renal severe complications were generally estimated to occur in fewer than 0.5% patients in all included studies. Limitations of this review include the observational nature and small size of most of the studies of severe vivax malaria, high heterogeneity of included studies which were predominantly in hospitalized patients (who were therefore more likely to be severely unwell), and high risk of bias including small study effects.
Young children and pregnant women are particularly vulnerable to adverse clinical impacts of vivax malaria, and preventing infections and relapse in this groups is a priority. Substantial evidence of severe presentations of vivax malaria has accrued over the last 10 years, but reporting is inconsistent. There are major knowledge gaps, for example, limited understanding of the underlying pathophysiology and the reason for the heterogenous geographical distribution of reported complications. An adapted case definition of severe vivax malaria would facilitate surveillance and future research to better understand this condition.
Over the past 50 years, Plasmodium falciparum has developed resistance against all antimalarial drugs used against it: chloroquine, sulphadoxine–pyrimethamine, quinine, piperaquine and mefloquine. ...More recently, resistance to the artemisinin derivatives and the resulting failure of artemisinin‐based combination therapy (ACT) are threatening all major gains made in malaria control. Each time resistance has developed progressively, with delayed clearance of parasites first emerging only in a few regions, increasing in prevalence and geographic range, and then ultimately resulting in the complete failure of that antimalarial. Drawing from this repeated historical chain of events, this article presents context‐specific approaches for combating drug‐resistant P. falciparum malaria. The approaches begin with a context of drug‐sensitive parasites and focus on the prevention of the emergence of drug resistance. Next, the approaches address a scenario in which resistance has emerged and is increasing in prevalence and geographic extent, with interventions focused on disrupting transmission through vector control, early diagnosis and treatment, and the use of new combination therapies. Elimination is also presented as an approach for addressing the imminent failure of all available antimalarials. The final drug resistance context presented is one in which all available antimalarials have failed; leaving only personal protection and the use of new antimalarials (or new combinations of antimalarials) as a viable strategy for dealing with complete resistance. All effective strategies and contexts require a multipronged, holistic approach.
Combating the spread of drug‐resistant Plasmodium falciparum requires a comprehensive approach. Modern information technology provides the means to detect, enumerate, map and monitor cases of malaria resistance and the foci of transmission. Early detection and treatment of clinical cases, detection of submicroscopic reservoirs and adapted vector control are the three pillars of a successful elimination.
Evolving resistance to arte misi ni n-based compounds threatens to derail attempts to control malaria. Resistance has been confirmed in western Cambodia and has recently emerged in western Thailand, ...but is absent from neighboring Laos. Artemisinin resistance results in reduced parasite clearance rates (CRs) after treatment. We used a two-phase strategy to identify genome region(s) underlying this ongoing selective event. Geographical differentiation and haplotype structure at 6969 polymorphic single-nucleotide polymorphisms (SNPs) in 91 parasites from Cambodia, Thailand, and Laos identified 33 genome regions under strong selection. We screened SNPs and microsatellites within these regions in 715 parasites from Thailand, identifying a selective sweep on chromosome 13 that shows strong association (P = 10⁻⁶ to 10⁻¹²) with slow CRs, illustrating the efficacy of targeted association for identifying the genetic basis of adaptive traits.
With the rapidly increasing abundance and accessibility of genomic data, there is a growing interest in using population genetic approaches to characterize fine-scale dispersal of organisms, ...providing insight into biological processes across a broad range of fields including ecology, evolution and epidemiology. For sexually recombining haploid organisms such as the human malaria parasite P. falciparum, however, there have been no systematic assessments of the type of data and methods required to resolve fine scale connectivity. This analytical gap hinders the use of genomics for understanding local transmission patterns, a crucial goal for policy makers charged with eliminating this important human pathogen. Here we use data collected from four clinics with a catchment area spanning approximately 120 km of the Thai-Myanmar border to compare the ability of divergence (FST) and relatedness based on identity by descent (IBD) to resolve spatial connectivity between malaria parasites collected from proximal clinics. We found no relationship between inter-clinic distance and FST, likely due to sampling of highly related parasites within clinics, but a significant decline in IBD-based relatedness with increasing inter-clinic distance. This association was contingent upon the data set type and size. We estimated that approximately 147 single-infection whole genome sequenced parasite samples or 222 single-infection parasite samples genotyped at 93 single nucleotide polymorphisms (SNPs) were sufficient to recover a robust spatial trend estimate at this scale. In summary, surveillance efforts cannot rely on classical measures of genetic divergence to measure P. falciparum transmission on a local scale. Given adequate sampling, IBD-based relatedness provides a useful alternative, and robust trends can be obtained from parasite samples genotyped at approximately 100 SNPs.
Artemisinin and partner-drug resistance in Plasmodium falciparum are major threats to malaria control and elimination. Triple artemisinin-based combination therapies (TACTs), which combine existing ...co-formulated ACTs with a second partner drug that is slowly eliminated, might provide effective treatment and delay emergence of antimalarial drug resistance.
In this multicentre, open-label, randomised trial, we recruited patients with uncomplicated P falciparum malaria at 18 hospitals and health clinics in eight countries. Eligible patients were aged 2–65 years, with acute, uncomplicated P falciparum malaria alone or mixed with non-falciparum species, and a temperature of 37·5°C or higher, or a history of fever in the past 24 h. Patients were randomly assigned (1:1) to one of two treatments using block randomisation, depending on their location: in Thailand, Cambodia, Vietnam, and Myanmar patients were assigned to either dihydroartemisinin–piperaquine or dihydroartemisinin–piperaquine plus mefloquine; at three sites in Cambodia they were assigned to either artesunate–mefloquine or dihydroartemisinin–piperaquine plus mefloquine; and in Laos, Myanmar, Bangladesh, India, and the Democratic Republic of the Congo they were assigned to either artemether–lumefantrine or artemether–lumefantrine plus amodiaquine. All drugs were administered orally and doses varied by drug combination and site. Patients were followed-up weekly for 42 days. The primary endpoint was efficacy, defined by 42-day PCR-corrected adequate clinical and parasitological response. Primary analysis was by intention to treat. A detailed assessment of safety and tolerability of the study drugs was done in all patients randomly assigned to treatment. This study is registered at ClinicalTrials.gov, NCT02453308, and is complete.
Between Aug 7, 2015, and Feb 8, 2018, 1100 patients were given either dihydroartemisinin–piperaquine (183 17%), dihydroartemisinin–piperaquine plus mefloquine (269 24%), artesunate–mefloquine (73 7%), artemether–lumefantrine (289 26%), or artemether–lumefantrine plus amodiaquine (286 26%). The median age was 23 years (IQR 13 to 34) and 854 (78%) of 1100 patients were male. In Cambodia, Thailand, and Vietnam the 42-day PCR-corrected efficacy after dihydroartemisinin–piperaquine plus mefloquine was 98% (149 of 152; 95% CI 94 to 100) and after dihydroartemisinin–piperaquine was 48% (67 of 141; 95% CI 39 to 56; risk difference 51%, 95% CI 42 to 59; p<0·0001). Efficacy of dihydroartemisinin–piperaquine plus mefloquine in the three sites in Myanmar was 91% (42 of 46; 95% CI 79 to 98) versus 100% (42 of 42; 95% CI 92 to 100) after dihydroartemisinin–piperaquine (risk difference 9%, 95% CI 1 to 17; p=0·12). The 42-day PCR corrected efficacy of dihydroartemisinin–piperaquine plus mefloquine (96% 68 of 71; 95% CI 88 to 99) was non-inferior to that of artesunate–mefloquine (95% 69 of 73; 95% CI 87 to 99) in three sites in Cambodia (risk difference 1%; 95% CI −6 to 8; p=1·00). The overall 42-day PCR-corrected efficacy of artemether–lumefantrine plus amodiaquine (98% 281 of 286; 95% CI 97 to 99) was similar to that of artemether–lumefantrine (97% 279 of 289; 95% CI 94 to 98; risk difference 2%, 95% CI −1 to 4; p=0·30). Both TACTs were well tolerated, although early vomiting (within 1 h) was more frequent after dihydroartemisinin–piperaquine plus mefloquine (30 3·8% of 794) than after dihydroartemisinin–piperaquine (eight 1·5% of 543; p=0·012). Vomiting after artemether–lumefantrine plus amodiaquine (22 1·3% of 1703) and artemether–lumefantrine (11 0·6% of 1721) was infrequent. Adding amodiaquine to artemether–lumefantrine extended the electrocardiogram corrected QT interval (mean increase at 52 h compared with baseline of 8·8 ms SD 18·6 vs 0·9 ms 16·1; p<0·01) but adding mefloquine to dihydroartemisinin–piperaquine did not (mean increase of 22·1 ms SD 19·2 for dihydroartemisinin–piperaquine vs 20·8 ms SD 17·8 for dihydroartemisinin–piperaquine plus mefloquine; p=0·50).
Dihydroartemisinin–piperaquine plus mefloquine and artemether–lumefantrine plus amodiaquine TACTs are efficacious, well tolerated, and safe treatments of uncomplicated P falciparum malaria, including in areas with artemisinin and ACT partner-drug resistance.
UK Department for International Development, Wellcome Trust, Bill & Melinda Gates Foundation, UK Medical Research Council, and US National Institutes of Health.
New malaria maps Nosten, Francois H; Phyo, Aung Pyae
The Lancet,
07/2019, Letnik:
394, Številka:
10195
Journal Article
Recenzirano
Odprti dostop
...the data presented are the results of complex mathematical models and do not necessarily represent the actual truth on the ground. ...the user should pay attention to the statistical uncertainties ...around the estimates and carefully examine the corresponding uncertainty maps provided. ...one will need to digest the unusually large amount of information contained in the appendix, to fully comprehend the limitations of the information provided.
Multiple kelch13 alleles conferring artemisinin resistance (ART-R) are currently spreading through Southeast Asian malaria parasite populations, providing a unique opportunity to observe an ongoing ...soft selective sweep, investigate why resistance alleles have evolved multiple times and determine fundamental population genetic parameters for Plasmodium We sequenced kelch13 (n = 1,876), genotyped 75 flanking SNPs, and measured clearance rate (n = 3,552) in parasite infections from Western Thailand (2001-2014). We describe 32 independent coding mutations including common mutations outside the kelch13 propeller associated with significant reductions in clearance rate. Mutations were first observed in 2003 and rose to 90% by 2014, consistent with a selection coefficient of ∼0.079. ART-R allele diversity rose until 2012 and then dropped as one allele (C580Y) spread to high frequency. The frequency with which adaptive alleles arise is determined by the rate of mutation and the population size. Two factors drive this soft sweep: (1) multiple kelch13 amino-acid mutations confer resistance providing a large mutational target-we estimate the target is 87-163 bp. (2) The population mutation parameter (Θ = 2N
μ) can be estimated from the frequency distribution of ART-R alleles and is ∼5.69, suggesting that short term effective population size is 88 thousand to 1.2 million. This is 52-705 times greater than N
estimated from fluctuation in allele frequencies, suggesting that we have previously underestimated the capacity for adaptive evolution in Plasmodium Our central conclusions are that retrospective studies may underestimate the complexity of selective events and the N
relevant for adaptation for malaria is considerably higher than previously estimated.
We report a large multicenter genome-wide association study of Plasmodium falciparum resistance to artemisinin, the frontline antimalarial drug. Across 15 locations in Southeast Asia, we identified ...at least 20 mutations in kelch13 (PF3D7_1343700) affecting the encoded propeller and BTB/POZ domains, which were associated with a slow parasite clearance rate after treatment with artemisinin derivatives. Nonsynonymous polymorphisms in fd (ferredoxin), arps10 (apicoplast ribosomal protein S10), mdr2 (multidrug resistance protein 2) and crt (chloroquine resistance transporter) also showed strong associations with artemisinin resistance. Analysis of the fine structure of the parasite population showed that the fd, arps10, mdr2 and crt polymorphisms are markers of a genetic background on which kelch13 mutations are particularly likely to arise and that they correlate with the contemporary geographical boundaries and population frequencies of artemisinin resistance. These findings indicate that the risk of new resistance-causing mutations emerging is determined by specific predisposing genetic factors in the underlying parasite population.
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