Differences in selective pressure on dhps and dhfr drug resistant mutations in western Kenya

Abstract

BackgroundUnderstanding the origin and spread of mutations associated with drug resistance, especially in the context of combination therapy, will help guide strategies to halt and prevent the emergence of resistance. Unfortunately, studies have assessed these complex processes when resistance is already highly prevalent. Even further, information on the evolutionary dynamics leading to multidrug-resistant parasites is scattered and limited to areas with low or seasonal malaria transmission. This study describes the dynamics of strong selection for mutations conferring resistance against sulphadoxine-pyrimethamine (SP), a combination therapy, in western Kenya between 1992 and 1999, just before SP became first-line therapy (1999). Importantly, the study is based on longitudinal data, which allows for a comprehensive analysis that contrasts with previous cross-sectional studies carried out in other endemic regions.MethodsThis study used 236 blood samples collected between 1992 and 1999 in the Asembo Bay area of Kenya. Pyrosequencing was used to determine the alleles of dihydrofolate reductase (dhfr) and dihydropterote synthase (dhps) genes. Microsatellite alleles spanning 138 kb around dhfr and dhps, as well as, neutral markers spanning approximately 100 kb on chromosomes 2 and 3 were characterized.ResultsBy 1992, the South-Asian dhfr triple mutant was already spreading, albeit in low frequency, in this holoendemic Kenyan population, prior to the use of SP as a first-line therapy. Additionally, dhfr triple mutant alleles that originated independently from the predominant Southeast Asian lineage were present in the sample set. Likewise, dhps double mutants were already present as early as 1992. There is evidence for soft selective sweeps of two dhfr mutant alleles and the possible emergence of a selective sweep of double mutant dhps alleles between 1992 and 1997. The longitudinal structure of the dataset allowed estimation of selection pressures on various dhfr and dhps mutants relative to each other based on a theoretical model tailored to P. falciparum. The data indicate that drug selection acted differently on the resistant alleles of dhfr and dhps, as evidenced by fitness differences. Thus a combination drug therapy such as SP, by itself, does not appear to select for "multidrug"-resistant parasites in areas with high recombination rate.ConclusionsThe complexity of these observations emphasizes the importance of population-based studies to evaluate the effects of strong drug selection on Plasmodium falciparum populations.

Characterizing the impact of sustained sulfadoxine/pyrimethamine use upon the Plasmodium falciparum population in Malawi

“…These frequencies are consistent with previous analyses highlighting the pan-African distribution of the dhfr triple mutant haplotypes in contrast to the East–West African differences in distribution of the A437G and K540E dhps variants [42, 43]. The SNP-based work is consistent with the results from microsatellite-based studies, considering the dynamics of strong selection for mutations conferring SP resistance, including support for the observation of the independent origin of sulfadoxine-resistant alleles across a number of regions [42, 44, 45]. Together, these observations reflect the early decline in chloroquine usage and early introduction and prolonged use of SP in Malawi when compared to other African populations.…”

Molecular Profile of Malaria Drug Resistance Markers of Plasmodium falciparum in Suriname

“…Seven neutral microsatellites (TA1, Poly␣, PfPK2, TA109, C2M34, C3M69, and 2490) located in chromosomes 2, 3, 4, 6, and 12 were PCR amplified using previously published methods for analyzing Plasmodium population structure (17,18). Fluorescently labeled PCR products were separated on an Applied Biosystems 3130 capillary sequencer and scored using Gene Marker v1.95 (SoftGenetics LLC).…”

Plasmodium falciparum Genetic Diversity in Continental Equatorial Guinea before and after Introduction of Artemisinin-Based Combination Therapy

“…Drug resistance is associated with genetic events that promote mechanisms to escape drug action, such as mutations or changes in the gene copy number that can be related to the drug target or can affect pumps regulating the withinparasite drug concentration (8). Studying the origin and spread of mutations associated with drug resistance may provide important insights into preventing the emergence of resistance, especially in the context of combination therapies (9).…”