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Molecular assays for monitoring sulfadoxine-pyrimethamine-resistant Plasmodium falciparum have not been implemented because of the genetic and statistical complexity of the parasite mutations that confer resistance and their relation to treatment outcomes. This study analyzed pretreatment dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) genotypes and treatment outcomes in a double-blind, placebo-controlled trial of sulfadoxine-pyrimethamine and chlorproguanil-dapsone treatment for uncomplicated P. falciparum malaria. Multiple logistic regression was used to identify mutations that were predictive of treatment failure and to identify interactions and confounding factors. Infections caused by parasites with 3 DHFR mutations and 2 DHPS mutations (the "quintuple mutant") were associated with sulfadoxine-pyrimethamine treatment failure but not with chlorproguanil-dapsone treatment failure. The presence of a single DHFR mutation (Arg-59) with a single DHPS mutation (Glu-540) accurately predicted the presence of the quintuple mutant. If this model is validated in other populations, it will finally be possible to use molecular markers for surveillance of antifolate-resistant P. falciparum malaria in Africa.

During the blood stages of malaria, several hundred parasite-encoded proteins are exported beyond the double-membrane barrier that separates the parasite from the host cell cytosol. These proteins have a variety of roles that are essential to virulence or parasite growth. There is keen interest in understanding how proteins are exported and whether common machineries are involved in trafficking the different classes of exported proteins. One potential trafficking machine is a protein complex known as the Plasmodium translocon of exported proteins (PTEX). Although PTEX has been linked to the export of one class of exported proteins, there has been no direct evidence for its role and scope in protein translocation. Here we show, through the generation of two parasite lines defective for essential PTEX components (HSP101 or PTEX150), and analysis of a line lacking the non-essential component TRX2 (ref. 12), greatly reduced trafficking of all classes of exported proteins beyond the double membrane barrier enveloping the parasite. This includes proteins containing the PEXEL motif (RxLxE/Q/D) and PEXEL-negative exported proteins (PNEPs). Moreover, the export of proteins destined for expression on the infected erythrocyte surface, including the major virulence factor PfEMP1 in Plasmodium falciparum, was significantly reduced in PTEX knockdown parasites. PTEX function was also essential for blood-stage growth, because even a modest knockdown of PTEX components had a strong effect on the parasite's capacity to complete the erythrocytic cycle both in vitro and in vivo. Hence, as the only known nexus for protein export in Plasmodium parasites, and an essential enzymic machine, PTEX is a prime drug target.