Falciparum malaria persists in hard-to-reach areas or demographic groups that are missed by conventional healthcare systems but could be reached by trained community members in a malaria post (MP). ...The main focus of a MP is to provide uninterrupted and rapid access to rapid diagnostic tests (RDTs) and artemisinin-based combination therapy (ACT) too all inhabitants of a village. RDTs allow trained community members to perform malaria diagnosis accurately and prescribe appropriate treatment, reducing as much as possible any delay between the onset of fever and treatment. Early treatment with ACT and with a low-dose of primaquine prevents further transmission from human to mosquito. A functioning MP represents an essential component of any malaria elimination strategy. Implementing large-scale, high-coverage, community-based early diagnosis and treatment through MPs requires few technological innovations but relies on a very well structured organization able to train, supervise and supply MPs, to monitor activity and to perform strict malaria surveillance.
Single Encounter Radical Cure and Prophylaxis (SERCAP) describes an ideal anti-malarial drug that cures all malaria in a single dose. This target product profile has dominated anti-malarial drug ...discovery and development over the past decade. The operational advantage of a single encounter has to be balanced against the need for a high dose, reliable absorption, little variability in pharmacokinetic properties, slow elimination (to ensure curative drug exposures in all patients) and a very low rate of vomiting. The demanding aspirational target may have hindered anti-malarial drug development. Aiming for three-day regimens, as in current anti-malarial treatments, would be better.
KAE609 (cipargamin; formerly NITD609, Novartis Institute for Tropical Diseases) is a new synthetic antimalarial spiroindolone analogue with potent, dose-dependent antimalarial activity against ...asexual and sexual stages of Plasmodium falciparum.
We conducted a phase 2, open-label study at three centers in Thailand to assess the antimalarial efficacy, safety, and adverse-event profile of KAE609, at a dose of 30 mg per day for 3 days, in two sequential cohorts of adults with uncomplicated P. vivax malaria (10 patients) or P. falciparum malaria (11). The primary end point was the parasite clearance time.
The median parasite clearance time was 12 hours in each cohort (interquartile range, 8 to 16 hours in patients with P. vivax malaria and 10 to 16 hours in those with P. falciparum malaria). The median half-lives for parasite clearance were 0.95 hours (range, 0.68 to 2.01; interquartile range, 0.85 to 1.14) in the patients with P. vivax malaria and 0.90 hours (range, 0.68 to 1.64; interquartile range, 0.78 to 1.07) in those with P. falciparum malaria. By comparison, only 19 of 5076 patients with P. falciparum malaria (<1%) who were treated with oral artesunate in Southeast Asia had a parasite clearance half-life of less than 1 hour. Adverse events were reported in 14 patients (67%), with nausea being the most common. The adverse events were generally mild and did not lead to any discontinuations of the drug. The mean terminal half-life for the elimination of KAE609 was 20.8 hours (range, 11.3 to 37.6), supporting a once-daily oral dosing regimen.
KAE609, at dose of 30 mg daily for 3 days, cleared parasitemia rapidly in adults with uncomplicated P. vivax or P. falciparum malaria. (Funded by Novartis and others; ClinicalTrials.gov number, NCT01524341.).
sporozoites, the mosquito-transmitted forms of the malaria parasite, first infect the liver for an initial round of replication before the emergence of pathogenic blood stages. Sporozoites represent ...attractive targets for antimalarial preventive strategies, yet the mechanisms of parasite entry into hepatocytes remain poorly understood. Here we show that the two main species causing malaria in humans,
and
, rely on two distinct host cell surface proteins, CD81 and the Scavenger Receptor BI (SR-BI), respectively, to infect hepatocytes. By contrast, CD81 and SR-BI fulfil redundant functions during infection by the rodent parasite
. Genetic analysis of sporozoite factors reveals the 6-cysteine domain protein P36 as a major parasite determinant of host cell receptor usage. Our data provide molecular insights into the invasion pathways used by different malaria parasites to infect hepatocytes, and establish a functional link between a sporozoite putative ligand and host cell receptors.
Tafenoquine is an 8-aminoquinoline under investigation for the prevention of relapse in
malaria. This open-label, dose-escalation study assessed quantitatively the hemolytic risk with tafenoquine in ...female healthy volunteers heterozygous for the
glucose-6-phosphate dehydrogenase (G6PD)-deficient variant versus G6PD-normal females, and with reference to primaquine. Six G6PD-heterozygous subjects (G6PD enzyme activity 40-60% of normal) and six G6PD-normal subjects per treatment group received single-dose tafenoquine (100, 200, or 300 mg) or primaquine (15 mg × 14 days). All participants had pretreatment hemoglobin levels ≥ 12.0 g/dL. Tafenoquine dose escalation stopped when hemoglobin decreased by ≥ 2.5 g/dL (or hematocrit decline ≥ 7.5%) versus pretreatment values in ≥ 3/6 subjects. A dose-response was evident in G6PD-heterozygous subjects (
= 15) receiving tafenoquine for the maximum decrease in hemoglobin versus pretreatment values. Hemoglobin declines were similar for tafenoquine 300 mg (-2.65 to -2.95 g/dL
= 3) and primaquine (-1.25 to -3.0 g/dL
= 5). Two further cohorts of G6PD-heterozygous subjects with G6PD enzyme levels 61-80% (
= 2) and > 80% (
= 5) of the site median normal received tafenoquine 200 mg; hemolysis was less pronounced at higher G6PD enzyme activities. Tafenoquine hemolytic potential was dose dependent, and hemolysis was greater in G6PD-heterozygous females with lower G6PD enzyme activity levels. Single-dose tafenoquine 300 mg did not appear to increase the severity of hemolysis versus primaquine 15 mg × 14 days.
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.
Genetic crosses of phenotypically distinct strains of the human malaria parasite Plasmodium falciparum are a powerful tool for identifying genes controlling drug resistance and other key phenotypes. ...Previous studies relied on the isolation of recombinant parasites from splenectomized chimpanzees, a research avenue that is no longer available. Here we demonstrate that human-liver chimeric mice support recovery of recombinant progeny for the identification of genetic determinants of parasite traits and adaptations.
Artemisinin-based combination therapies are the first line of treatment for Plasmodium falciparum infections worldwide, but artemisinin resistance has risen rapidly in Southeast Asia over the past ...decade. Mutations in the kelch13 gene have been implicated in this resistance. We used longitudinal genomic surveillance to detect signals in kelch13 and other loci that contribute to artemisinin or partner drug resistance. We retrospectively sequenced the genomes of 194 P. falciparum isolates from five sites in Northwest Thailand, over the period of a rapid increase in the emergence of artemisinin resistance (2001-2014).
We evaluate statistical metrics for temporal change in the frequency of individual SNPs, assuming that SNPs associated with resistance increase in frequency over this period. After Kelch13-C580Y, the strongest temporal change is seen at a SNP in phosphatidylinositol 4-kinase, which is involved in a pathway recently implicated in artemisinin resistance. Furthermore, other loci exhibit strong temporal signatures which warrant further investigation for involvement in artemisinin resistance evolution. Through genome-wide association analysis we identify a variant in a kelch domain-containing gene on chromosome 10 that may epistatically modulate artemisinin resistance.
This analysis demonstrates the potential of a longitudinal genomic surveillance approach to detect resistance-associated gene loci to improve our mechanistic understanding of how resistance develops. Evidence for additional genomic regions outside of the kelch13 locus associated with artemisinin-resistant parasites may yield new molecular markers for resistance surveillance, which may be useful in efforts to reduce the emergence or spread of artemisinin resistance in African parasite populations.
Maternal mortality is high in developing countries, but there are few data in high-risk groups such as migrants and refugees in malaria-endemic areas. Trends in maternal mortality were followed over ...25 years in antenatal clinics prospectively established in an area with low seasonal transmission on the north-western border of Thailand.
All medical records from women who attended the Shoklo Malaria Research Unit antenatal clinics from 12(th) May 1986 to 31(st) December 2010 were reviewed, and maternal death records were analyzed for causality. There were 71 pregnancy-related deaths recorded amongst 50,981 women who attended antenatal care at least once. Three were suicide and excluded from the analysis as incidental deaths. The estimated maternal mortality ratio (MMR) overall was 184 (95%CI 150-230) per 100,000 live births. In camps for displaced persons there has been a six-fold decline in the MMR from 499 (95%CI 200-780) in 1986-90 to 79 (40-170) in 2006-10, p<0.05. In migrants from adjacent Myanmar the decline in MMR was less significant: 588 (100-3260) to 252 (150-430) from 1996-2000 to 2006-2010. Mortality from P. falciparum malaria in pregnancy dropped sharply with the introduction of systematic screening and treatment and continued to decline with the reduction in the incidence of malaria in the communities. P. vivax was not a cause of maternal death in this population. Infection (non-puerperal sepsis and P. falciparum malaria) accounted for 39.7 (27/68) % of all deaths.
Frequent antenatal clinic screening allows early detection and treatment of falciparum malaria and substantially reduces maternal mortality from P. falciparum malaria. No significant decline has been observed in deaths from sepsis or other causes in refugee and migrant women on the Thai-Myanmar border.
Plasmodium vivax merozoites only invade reticulocytes, a minor though heterogeneous population of red blood cell precursors that can be graded by levels of transferrin receptor (CD71) expression. The ...development of a protocol that allows sorting reticulocytes into defined developmental stages and a robust ex vivo P vivax invasion assay has made it possible for the first time to investigate the fine-scale invasion preference of P vivax merozoites. Surprisingly, it was the immature reticulocytes (CD71+) that are generally restricted to the bone marrow that were preferentially invaded, whereas older reticulocytes (CD71−), principally found in the peripheral blood, were rarely invaded. Invasion assays based on the CD71+ reticulocyte fraction revealed substantial postinvasion modification. Thus, 3 to 6 hours after invasion, the initially biomechanically rigid CD71+ reticulocytes convert into a highly deformable CD71− infected red blood cell devoid of host reticular matter, a process that normally spans 24 hours for uninfected reticulocytes. Concurrent with these changes, clathrin pits disappear by 3 hours postinvasion, replaced by distinctive caveolae nanostructures. These 2 hitherto unsuspected features of P vivax invasion, a narrow preference for immature reticulocytes and a rapid remodeling of the host cell, provide important insights pertinent to the pathobiology of the P vivax infection.
•Plasmodium vivax merozoites preferentially infect a subgroup of reticulocytes generally restricted to the bone marrow.•Accelerated “maturation” of infected reticulocytes.
PDF
