Ideally antimalarial drugs can be developed which target multiple life cycle stages, thus impacting prevention, treatment and transmission of disease. Here we introduce 4-(1H)-quinolone-3-diarylethers that are selectively potent inhibitors of the parasite’s mitochondrial cytochrome bc1 complex. These compounds are highly active against the primary human malarias (falciparum and vivax), targeting the parasite at both the liver and blood stages as well as the forms that are crucial to disease transmission: gametocytes ⇒ zygotes ⇒ ookinetes ⇒ oocysts. Chosen as the preclinical candidate, ELQ-300 has good oral bioavailability at efficacious dosages in mice, is metabolically stable, and is highly active in rodent malaria models. Given a low predicted dose in patients and a long predicted half-life, ELQ-300 offers the hope of a new molecule for the treatment, prevention and, ultimately, eradication of malaria.

The quest for new antimalarial drugs, especially those with novel modes of action, is essential in the face of emerging drug-resistant parasites. Here we describe a new chemical class of molecules, pyrazoleamides, with potent activity against human malaria parasites and showing remarkably rapid parasite clearance in an in vivo model. Investigations involving pyrazoleamide-resistant parasites, whole-genome sequencing and gene transfers reveal that mutations in two proteins, a calcium-dependent protein kinase (PfCDPK5) and a P-type cation-ATPase (PfATP4), are necessary to impart full resistance to these compounds. A pyrazoleamide compound causes a rapid disruption of Na+ regulation in blood-stage Plasmodium falciparum parasites. Similar effect on Na+ homeostasis was recently reported for spiroindolones, which are antimalarials of a chemical class quite distinct from pyrazoleamides. Our results reveal that disruption of Na+ homeostasis in malaria parasites is a promising mode of antimalarial action mediated by at least two distinct chemical classes.

Within the human host, the malaria parasite Plasmodium falciparum is exposed to multiple selection pressures. The host environment changes dramatically in severe malaria, but the extent to which the parasite responds to—or is selected by—this environment remains unclear. From previous studies, the parasites that cause severe malaria appear to increase expression of a restricted but poorly defined subset of the PfEMP1 variant, surface antigens. PfEMP1s are major targets of protective immunity. Here, we used RNA sequencing (RNAseq) to analyse gene expression in 44 parasite isolates that caused severe and uncomplicated malaria in Papuan patients. The transcriptomes of 19 parasite isolates associated with severe malaria indicated that these parasites had decreased glycolysis without activation of compensatory pathways; altered chromatin structure and probably transcriptional regulation through decreased histone methylation; reduced surface expression of PfEMP1; and down-regulated expression of multiple chaperone proteins. Our RNAseq also identified novel associations between disease severity and PfEMP1 transcripts, domains, and smaller sequence segments and also confirmed all previously reported associations between expressed PfEMP1 sequences and severe disease. These findings will inform efforts to identify vaccine targets for severe malaria and also indicate how parasites adapt to—or are selected by—the host environment in severe malaria.

Renewed global efforts toward malaria eradication have highlighted the need for novel antimalarial agents with activity against multiple stages of the parasite life cycle. We have previously reported the discovery of a novel class of antimalarial compounds in the imidazolopiperazine series that have activity in the prevention and treatment of blood stage infection in a mouse model of malaria. Consistent with the previously reported activity profile of this series, the clinical candidate KAF156 shows blood schizonticidal activity with 50% inhibitory concentrations of 6 to 17.4 nM against P. falciparum drug-sensitive and drug-resistant strains, as well as potent therapeutic activity in a mouse models of malaria with 50, 90, and 99% effective doses of 0.6, 0.9, and 1.4 mg/kg, respectively. When administered prophylactically in a sporozoite challenge mouse model, KAF156 is completely protective as a single oral dose of 10 mg/kg. Finally, KAF156 displays potent Plasmodium transmission blocking activities both in vitro and in vivo. Collectively, our data suggest that KAF156, currently under evaluation in clinical trials, has the potential to treat, prevent, and block the transmission of malaria.

Whole genome sequencing (WGS) of Plasmodium vivax is problematic due to the reliance on clinical isolates which are generally low in parasitaemia and sample volume. Furthermore, clinical isolates contain a significant contaminating background of host DNA which confounds efforts to map short read sequence of the target P. vivax DNA. Here, we discuss a methodology to significantly improve the success of P. vivax WGS on natural (non-adapted) patient isolates. Using 37 patient isolates from Indonesia, Thailand, and travellers, we assessed the application of CF11-based white blood cell filtration alone and in combination with short term ex vivo schizont maturation. Although CF11 filtration reduced human DNA contamination in 8 Indonesian isolates tested, additional short-term culture increased the P. vivax DNA yield from a median of 0.15 to 6.2 ng µl−1 packed red blood cells (pRBCs) (p = 0.001) and reduced the human DNA percentage from a median of 33.9% to 6.22% (p = 0.008). Furthermore, post-CF11 and culture samples from Thailand gave a median P. vivax DNA yield of 2.34 ng µl−1 pRBCs, and 2.65% human DNA. In 22 P. vivax patient isolates prepared with the 2-step method, we demonstrate high depth (median 654X coverage) and breadth (≥89%) of coverage on the Illumina GAII and HiSeq platforms. In contrast to the A+T-rich P. falciparum genome, negligible bias was observed in coverage depth between coding and non-coding regions of the P. vivax genome. This uniform coverage will greatly facilitate the detection of SNPs and copy number variants across the genome, enabling unbiased exploration of the natural diversity in P. vivax populations.

iThe declining efficacy of artemisinin derivatives against Plasmodium falciparum highlights the urgent need to identify alternative highly potent compounds for the treatment of malaria. In Papua Indonesia, where multidrug resistance has been documented against both P. falciparum and P. vivax malaria, comparative ex vivo antimalarial activity against Plasmodium isolates was assessed for the artemisinin derivatives artesunate (AS) and dihydroartemisinin (DHA), the synthetic peroxides OZ277 and OZ439, the semisynthetic 10-alkylaminoartemisinin derivatives artemisone and artemiside, and the conventional antimalarial drugs chloroquine (CQ), amodiaquine (AQ), and piperaquine (PIP). Ex vivo drug susceptibility was assessed in 46 field isolates (25 P. falciparum and 21 P. vivax). The novel endoperoxide compounds exhibited potent ex vivo activity against both species, but significant differences in intrinsic activity were observed. Compared to AS and its active metabolite DHA, all the novel compounds showed lower or equal 50% inhibitory concentrations (IC 50 s) in both species (median IC 50 s between 1.9 and 3.6 nM in P. falciparum and 0.7 and 4.6 nM in P. vivax). The antiplasmodial activity of novel endoperoxides showed different cross-susceptibility patterns in the two Plasmodium species: whereas their ex vivo activity correlated positively with CQ, PIP, AS, and DHA in P. falciparum, the same was not apparent in P. vivax. The current study demonstrates for the first time potent activity of novel endoperoxides against drug-resistant P. vivax. The high activity against drug-resistant strains of both Plasmodium species confirms these compounds to be promising candidates for future artemisinin-based combination therapy (ACT) regimens in regions of coendemicity.A pproximately 3.3 billion people (i.e., almost 50% of the world's population) are at risk of malaria with two Plasmodium species responsible for the majority of infections: P. falciparum and P. vivax (6,7,43). Traditionally, malaria control and research efforts have focused on P. falciparum, the dominant species in Africa. However, outside Africa, P. falciparum almost invariably coexists with P. vivax (7), with both species inflicting significant morbidity, particularly in infants and pregnant women (18,27).Chloroquine (CQ)-resistant P. falciparum is already well established, with emerging evidence that susceptibility to CQ in P. vivax is also declining across much of the world in which vivax is endemic. This combined threat is driving the investigation of alternative schizonticidal treatment regimens, such as artemisininbased combination therapy (ACT), for deployment against both P. falciparum and P. vivax (29). ACTs have become the mainstay of antimalarial chemotherapy, adopted in more than 100 countries worldwide (42). This huge demand for artemisinin and its derivatives relies on isolation from the plant source Artemisia annua and is vulnerable to harvest and production costs and intermittent supply (2, 11). Of particular concern are recent reports of prolonged ...

BackgroundThe World Health Organization recommends malaria be diagnosed by standard microscopy or rapid diagnostic test (RDT) before treatment. RDTs have been used with greater frequency in the absence of matching blood slide confirmation in the majority of RDT reported cases in Mimika Regency, Papua Province, Indonesia. Given the importance of RDT in current health system as point-of-care tool, careful validation of RDT product performance for providing accurate malaria diagnosis is critical.MethodsPlasmotec Malaria-3 (XW-P07) performance was evaluated by comparing it with paired blood film microscopy and quantitative real-time PCR (qPCR). Consecutive whole blood samples were derived from one clinic in Mimika as part of routine passive malaria case detection. RDT results were read by two trained technicians and interpreted by consensus. Expert microscopic examination of blood slides was cross-checked by observer-blinded second reader and a third examiner if discordant between examinations. qPCR was used as the ‘gold standard’, followed by microscopy for the outcome/disease variable. Comparison analysis included sensitivity (Sn), specificity (Sp), positive and negative predictive values (PPV & NPV), and other diagnostic screening performance measures for detecting Plasmodium falciparum and Plasmodium vivax infections.ResultsOverall malaria positive samples from qPCR was 42.2% (175/415 samples); and from matching blood slides 40.5% (168/415) of which those infections with relatively low parasite densities ≤100/μl blood was 5.7% of P. falciparum and 16.5% of P. vivax samples examined. Overall RDT performance when compared with microscopy for detecting P. falciparum was Sn:92%, Sp:96.6%, PPV:88%, NPV:97.8%, Kappa:0.87; and for P. vivax Sn:72.9%, Sp:99.1%, PPV:95.4%, NPV:93.4%, Kappa:0.79. Overall RDT performance when compared with qPCR for detecting P. falciparum was Sn:92%, Sp:96.6%, PPV:88%, NPV:97.8%, Kappa:0.87; and for P. vivax Sn:66%, Sp:99.1%, PPV:95.4%, NPV:90.9%, Kappa:0.73.ConclusionsPlasmotec Malaria-3 test showed good overall performance scores in precision for detecting P. falciparum, but lower values regarding sensitivity and negative likelihood ratio for detecting P. vivax, a finding partly associated with greater frequency of lower density P. vivax infections compared to P. falciparum in this study. In particular, the negative likelihood ratio (>0.1) for P. vivax detection indicates RDT lacked sufficient discriminating exclusion power falling below general acceptance criteria.

BackgroundPlasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) variants are encoded by var genes and mediate pathogenic cytoadhesion and antigenic variation in malaria. PfEMP1s can be broadly divided into three principal groups (A, B and C) and they contain conserved arrangements of functional domains called domain cassettes. Despite their tremendous diversity there is compelling evidence that a restricted subset of PfEMP1s is expressed in severe disease. In this study antibodies from patients with severe and uncomplicated malaria were compared for differences in reactivity with a range of PfEMP1s to determine whether antibodies to particular PfEMP1 domains were associated with severe or uncomplicated malaria.MethodsParts of expressed var genes in a severe malaria patient were identified by RNAseq and several of these partial PfEMP1 domains were expressed together with others from laboratory isolates. Antibodies from Papuan patients to these parts of multiple PfEMP1 proteins were measured.ResultsPatients with uncomplicated malaria were more likely to have antibodies that recognized PfEMP1 of Group C type and recognized a broader repertoire of group A and B PfEMP1s than patients with severe malaria.ConclusionThese data suggest that exposure to a broad range of group A and B PfEMP1s is associated with protection from severe disease in Papua, Indonesia.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1296-4) contains supplementary material, which is available to authorized users.