The evolutionary dynamics of genetic determinants of plasmodium falciparum resistance to sulfadoxine/pyrimethamine (sp) in South Eastern Tanzania

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Sokoine University of Agriculture


This study reports a systematic follow up of genetic changes in the genes encoding the dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) enzymes of Plasmodium falciparum, in isolates from three rural districts of South-eastern Tanzania. The enzymes are the target of antimalarial drug, sulphadoxine- pyrimethamine (SP). The population-wide analysis of resistance mutations in the dhfr and dhps genes was applied to examine the influence of different drug use policies and their potential for the selection for SP resistance. A total of 47 244 bloodspot filter paper samples were collected from all individuals of all ages in randomly selected households in a series of annual surveys conducted between 2000 - 2006. Twenty percent (9 662) of all samples were found positive for P. falciparum infection on microscopy and hence were used for the genetic studies. DNA was extracted from P. falciparum-positxvz samples and dhfr and dhps genes were amplified by a nested polymerase chain reaction (PCR) and resistance conferring point mutations determined. Size polymorphisms at three sets of microsatellite loci linked to dhfr and three other sets of unlinked microsatellite loci were analysed by PCR amplification and electrophoresis on an automated sequencer. The influence of National treatment policy on the parasite reservoir was profound. The change of first line therapy from CQ to SP brought about highly significant increase of the frequencies of dhfr triple and dhps double mutants. Artemisinin-based combination therapy (ACT- SP+Artesunate) in Rufiji had a small and non-significant impact on the frequency of dhps double and dhfr triple mutant alleles, but significantly disrupted their association. Z)A/r-l inked microsatellites revealed high diversity around the dhfr sensitive alleles and significantly reduced diversity around mutant dhfr alleles. The majority of triple mutant alleles had one flanking microsatellite haplotype which has previously been shown to be derived from Southeast Asia, while the double mutant alleles had multiple haplotypes which were independently derived. Distribution of major lineages indicates that there is extensive genetic exchange among the geographic regions. Unlinked microsatellites confirmed the extent of allele sharing among the regions and revealed a major trend for reduced transmission intensity, which was apparently independent of the ACT intervention.




Evolutionary dynamics, Genetic determinants, Plasmodium falciparum resistance, Sulfadoxine - pyrimethamine (sp), South Eastern, Tanzania