BACKGROUND Recent gains in reducing the global burden of malaria are threatened by the emergence of Plasmodium falciparum resistance to artemisinins. The discovery that mutations in portions of a P. falciparum gene encoding kelch (K13)–propeller domains are the major determinant of resistance has provided opportunities for monitoring such resistance on a global scale. METHODS We analyzed the K13-propeller sequence polymorphism in 14,037 samples collected in 59 countries in which malaria is endemic. Most of the samples (84.5%) were obtained from patients who were treated at sentinel sites used for nationwide surveillance of antimalarial resistance. We evaluated the emergence and dissemination of mutations by haplotyping neighboring loci. RESULTS We identified 108 nonsynonymous K13 mutations, which showed marked geographic disparity in their frequency and distribution. In Asia, 36.5% of the K13 mutations were distributed within two areas — one in Cambodia, Vietnam, and Laos and the other in western Thailand, Myanmar, and China — with no overlap. In Africa, we observed a broad array of rare nonsynonymous mutations that were not associated with delayed parasite clearance. The gene-edited Dd2 transgenic line with the A578S mutation, which expresses the most frequently observed African allele, was found to be susceptible to artemisinin in vitro on a ring-stage survival assay. CONCLUSIONS No evidence of artemisinin resistance was found outside Southeast Asia and China, where resistance-associated K13 mutations were confined. The common African A578S allele was not associated with clinical or in vitro resistance to artemisinin, and many African mutations appear to be neutral.

We report a genome-wide association (GWA) study of severe malaria in The Gambia. The initial GWA scan included 2,500 children genotyped on the Affymetrix 500K GeneChip, and a replication study included 3,400 children. We used this to examine the performance of GWA methods in Africa. We found considerable population stratification, and also that signals of association at known malaria resistance loci were greatly attenuated owing to weak linkage disequilibrium (LD). To investigate possible solutions to the problem of low LD, we focused on the HbS locus, sequencing this region of the genome in 62 Gambian individuals and then using these data to conduct multipoint imputation in the GWA samples. This increased the signal of association, from P = 4 × 10 −7 to P = 4 × 10 −14 , with the peak of the signal located precisely at the HbS causal variant. Our findings provide proof of principle that fine-resolution multipoint imputation, based on population-specific sequencing data, can substantially boost authentic GWA signals and enable fine mapping of causal variants in African populations.The malaria parasite Plasmodium falciparum kills on the order of a million African children each year 1 , and this is a small fraction of the number of infected individuals in the population [1][2][3] . In communities where everyone is repeatedly infected with P. falciparum, host genetic factors account for ~25% of the risk of severe malaria, that is, life-threatening forms of the disease 3 . The strongest known determinant of risk, hemoglobin S (HbS), accounts for 2% of the total variation, implying that only a small fraction of genetic resistance factors have so far been discovered 3 . Identifying the genetic basis of protective immunity against severe malaria may provide important insights for vaccine development.Here we examine the possibility of approaching this problem by genome-wide association (GWA) analysis. There are many unsolved methodological questions about how to conduct an effective GWA study in Africa 4 . High levels of ethnic diversity may result in false-positive associations owing to population structure. Variations in haplotype structure between different ethnic groups may reduce power to detect GWA signals, particularly when data are amalgamated across multiple study sites. Low LD implies the need for denser genotyping arrays than are currently available: a crude estimate is that an African GWA study with 1.5 million SNPs would have approximately the same statistical power as a European study with Jallow et al.Page 2Nat Genet. Author manuscript; available in PMC 2010 September 21. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript 0.6 million SNPs5, but this is based on HapMap data from a single ethnic group and a larger number of SNPs may be needed to achieve adequate power across different ethnic groups.We carried out an initial GWA study in Gambian children that explores these methodological questions. Genotyping of ~500,000 SNPs was conducted on 1,060 cases of severe malaria and 1...

A detailed understanding of the human infectious reservoir is essential for improving malaria transmission-reducing interventions. Here we report a multi-regional assessment of population-wide malaria transmission potential based on 1209 mosquito feeding assays in endemic areas of Burkina Faso and Kenya. Across both sites, we identified 39 infectious individuals. In high endemicity settings, infectious individuals were identifiable by research-grade microscopy (92.6%; 25/27), whilst one of three infectious individuals in the lowest endemicity setting was detected by molecular techniques alone. The percentages of infected mosquitoes in the different surveys ranged from 0.05 (4/7716) to 1.6% (121/7749), and correlate positively with transmission intensity. We also estimated exposure to malaria vectors through genetic matching of blood from 1094 wild-caught bloodfed mosquitoes with that of humans resident in the same houses. Although adults transmitted fewer parasites to mosquitoes than children, they received more mosquito bites, thus balancing their contribution to the infectious reservoir.

The malaria parasite Plasmodium falciparum invades human red blood cells via interactions between host and parasite surface proteins. By analyzing genome sequence data from human populations, including 1269 individuals from sub-Saharan Africa, we identify a diverse array of large copy number variants affecting the host invasion receptor genes GYPA and GYPB. We find that a nearby association with severe malaria is explained by a complex structural rearrangement involving the loss of GYPB and gain of two GYPB-A hybrid genes, which encode a serologically distinct blood group antigen known as Dantu. This variant reduces the risk of severe malaria by 40% and has recently risen in frequency in parts of Kenya, yet it appears to be absent from west Africa. These findings link structural variation of red blood cell invasion receptors with natural resistance to severe malaria.

Many human genetic associations with resistance to malaria have been reported but few have been reliably replicated. We collected data on 11,890 cases of severe malaria due to Plasmodium falciparum and 17,441 controls from 12 locations in Africa, Asia and Oceania. There was strong evidence of association with the HBB, ABO, ATP2B4, G6PD and CD40LG loci but previously reported associations at 22 other loci did not replicate in the multi-centre analysis. The large sample size made it possible to identify authentic genetic effects that are heterogeneous across populations or phenotypes, a striking example being the main African form of G6PD deficiency, which reduced the risk of cerebral malaria but increased the risk of severe malarial anaemia. The finding that G6PD deficiency has opposing effects on different fatal complications of P. falciparum infection indicates that the evolutionary origins of this common human genetic disorder are more complex than previously supposed.