Population genetic structure and adaptation of malaria parasites on the edge of endemic distribution.

To determine whether the major human malaria parasite Plasmodium falciparum exhibits fragmented population structure or local adaptation at the northern limit of its African distribution where the dry Sahel zone meets the Sahara, samples were collected from diverse locations within Mauritania over a range of ~1000 km. Microsatellite genotypes were obtained for 203 clinical infection samples from eight locations, and Illumina paired-end sequences were obtained to yield high coverage genomewide single nucleotide polymorphism (SNP) data for 65 clinical infection samples from four locations. Most infections contained single parasite genotypes, reflecting low rates of transmission and superinfection locally, in contrast to the situation seen in population samples from countries further south. A minority of infections shared related or identical genotypes locally, indicating some repeated transmission of parasite clones without recombination. This caused some multilocus linkage disequilibrium and local divergence, but aside from the effect of repeated genotypes there was minimal differentiation between locations. Several chromosomal regions had elevated integrated haplotype scores (|iHS|) indicating recent selection, including those containing drug resistance genes. A genomewide FST scan comparison with previous sequence data from an area in West Africa with higher infection endemicity indicates that regional gene flow prevents genetic isolation, but revealed allele frequency differentiation at three drug resistance loci and an erythrocyte invasion ligand gene. Contrast of extended haplotype signatures revealed none to be unique to Mauritania. Discrete foci of infection on the edge of the Sahara are genetically highly connected to the wider continental parasite population, and local elimination would be difficult to achieve without very substantial reduction in malaria throughout the region.

[Study of the incidence of malaria in febrile patients and among schoolchildren in the region of Trarza, Islamic Republic of Mauritania]. / Étude de la part du paludisme chez les consultants fébriles et des indices plasmodiques chez des écoliers dans la région du Trarza, République islamique de Mauritanie.

A study was performed to appreciate the importance of malaria in the low valley of the Senegal River North Bank in Mauritania. The malaria incidence was assessed among patients visiting the regional hospital of Rosso (Trarza region) for a "presumptive malaria", a diagnosis assigned by the clinicians based on fever and other suggestive symptoms of malaria. The malaria prevalence rate was also measured in schoolchildren. A total of 1431 febrile outpatients were sampled for thick and thin blood films, between December 2004 and March 2005, August and November 2005, and April and July 2006. The average malaria prevalence rate was 2.5% (36/1431). It varied from 0.7% (4/576) for the period from December 2004 to March 2005 to 3.8% (18/475) from August to November 2005 and 2.1% (8/380) from April to July 2006. Of the 1040 school children of 6 to 14 years of age, the average malaria parasite prevalence rate was 0.9% (9/1040). It was 0.4% (1/224), 1.7% (7/413) and 0.2% (1/402), Respectively, in February 2004 (cold and dry season), October 2005 (rainy season) and June 2006 (hot and dry season). These very low levels of malaria endemicity and incidence are comparable with those recorded in the same area on the (South) bank of the river in Senegal. In this context of unstable malaria, characterized by the absence or a low level of natural immunity of the population, an effective monitoring is essential for an early detection and a damming up of the malaria epidemic blazes that likely occur.