Plasmodium knowlesi is the commonest cause of severe malaria at QEH, with parasitemia the major risk factor for severity. Early referral and treatment with artesunate was highly effective for severe malaria from all species and associated with zero mortality.

The widespread distribution and relapsing nature of Plasmodium vivax infection present major challenges for malaria elimination. To characterise the genetic diversity of this parasite within individual infections and across the population, we performed deep genome sequencing of >200 clinical samples collected across the Asia-Pacific region, and analysed data on >300,000 SNPs and 9 regions of the genome with large copy number variations. Individual infections showed complex patterns of genetic structure, with variation not only in the number of dominant clones but also in their level of relatedness and inbreeding. At the population level, we observed strong signals of recent evolutionary selection both in known drug resistance genes and at novel loci, and these varied markedly between geographical locations. These findings reveal a dynamic landscape of local evolutionary adaptation in P. vivax populations, and provide a foundation for genomic surveillance to guide effective strategies for control and elimination.

SummaryThere is an urgent need for new drugs to treat malaria, with broad therapeutic potential and novel modes of action, to widen the scope of treatment and to overcome emerging drug resistance. We describe the discovery of DDD107498, a compound with a potent and novel spectrum of antimalarial activity against multiple life-cycle stages of the parasite, with good pharmacokinetic properties, and an acceptable safety profile. DDD107498 demonstrates potential to address a variety of clinical needs, including single dose treatment, transmission blocking and chemoprotection. DDD107498 was developed from a screening programme against blood stage malaria parasites; its molecular target has been identified as translation elongation factor 2 (eEF2), which is responsible for the GTP-dependent translocation of the ribosome along mRNA, and is essential for protein synthesis. This discovery of eEF2 as a viable antimalarial drug target opens up new possibilities for drug discovery.

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.

We recently developed a new PCR-restriction fragment length polymorphism (RFLP)-based assay using the miniexon sequence from the genus Leishmania. Here we report the application of this new genotyping method to naturally infected clinical samples for the differentiation of New and Old World Leishmania species. Of the newly developed assay and four currently applied diagnostic tests (i.e., in vitro cultivation, serology, and two other molecular assays using either the small subunit-internal transcribed spacer sequence or a repetitive genomic sequence), the miniexon assay showed the highest sensitivity, 89.7%, compared to 70.6, 57.1, 51.7, and 79.3%, respectively. Species differentiation was robust and reliable compared with that by two other Leishmania genotyping techniques. The assay provides a valuable tool for the identification of Leishmania directly from clinical samples and enables determination of the infecting species by a facile technique with high discrimination power. Since Leishmania causes a broad spectrum of diseases distinguished by different parasite and host factors, detection and characterization of the infecting species is crucial for the confirmation of a diagnosis as well as the establishment of the clinical prognosis and the initiation of an adequate therapeutic approach. The miniexon PCR-RFLP assay will facilitate such determination and might improve diagnosis and treatment of leishmaniasis.

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.

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.