Tracing the origins and signatures of selection of antifolate resistance in island populations of Plasmodium falciparum

• Published in: BMC infectious diseases Vol. 10; no. 1; p. 163
• Main Authors: Salgueiro, Patrícia, Vicente, José L, Ferreira, Conceição, Teófilo, Vânia, Galvão, André, do Rosário, Virgílio E, Cravo, Pedro, Pinto, João
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 09-06-2010; BioMed Central; BMC
• Subjects: Africa, Western; Antimalarials; Antiprotozoal Agents - pharmacology; Child; Child, Preschool; DNA, Protozoan - genetics; Drug Resistance; Drug resistance in microorganisms; Evolution, Molecular; Folic Acid Antagonists - pharmacology; Genes; Genetic aspects; Genotype; Health aspects; Humans; Infant; Infant, Newborn; Malaria, Falciparum - parasitology; Microsatellite Repeats; Peptide Synthases - genetics; Physiological aspects; Plasmodium falciparum; Plasmodium falciparum - classification; Plasmodium falciparum - drug effects; Plasmodium falciparum - genetics; Plasmodium falciparum - isolation & purification; Polymerase Chain Reaction; Protozoan Proteins - genetics; Tetrahydrofolate Dehydrogenase - genetics; Africa, Western; Portugal; ASE, Atlantic, Guinea Gulf, Sao Tome and Principe; ASE, Africa; ASE, Atlantic, Guinea Gulf, Sao Tome and Principe, Sao Tome
• ISSN: 1471-2334; 1471-2334
• DOI: 10.1186/1471-2334-10-163

Resistance of the malaria parasite Plasmodium falciparum to sulfadoxine-pyrimethamine (SP) has evolved worldwide. In the archipelago of São Tomé and Principe (STP), West Africa, although SP resistance is highly prevalent the drug is still in use in particular circumstances. To address the evolutionary origins of SP resistance in these islands, we genotyped point mutations at P. falciparum dhfr and dhps genes and analysed microsatellites flanking those genes.
Blood samples were collected in July and December 2004 in three localities of São Tomé Island and one in Principe Island. Species-specific nested-PCR was used to identify P. falciparum infected samples. Subsequently, SNPs at the dhfr and dhps genes were identified through PCR-RFLP. Isolates were also analysed for three microsatellite loci flanking the dhfr gene, three loci flanking dhps and four loci located at putative neutral genomic regions.
An increase of resistance-associated mutations at dhfr and dhps was observed, in particular for the dhfr/dhps quintuple mutant, associated with clinical SP failure. Analysis of flanking microsatellites suggests multiple independent introductions for dhfr and dhps mutant haplotypes, possibly from West Africa. A reduced genetic diversity and increased differentiation at flanking microsatellites when compared to neutral loci is consistent with a selective sweep for resistant alleles at both loci.
This study provides additional evidence for the crucial role of gene flow and drug selective pressures in the rapid spread of SP resistance in P. falciparum populations, from only a few mutation events giving rise to resistance-associated mutants. It also highlights the importance of human migration in the spread of drug resistant malaria parasites, as the distance between the islands and mainland is not consistent with mosquito-mediated parasite dispersal.