header - publications

Community pyrimethamine-sulfadoxine use and prevalence of resistant Plasmodium falciparum genotypes in Mali: a model for deterring resistance

by Plowe CV, Djimde A, Wellems TE, Diop S, Kouriba B, Doumbo OK

Published in 1996

Pyrimethamine-sulfadoxine (PS, Fansidar; Hoffman-LaRoche, Basel, Switzerland) is now the first-line antimalarial therapy in parts of Africa with high rates of chloroquine-resistant Plasmodium falciparum. With PS resistance increasing and no suitably inexpensive and effective third antimalarial drug available, strategies for delaying the spread of PS resistance in Africa are needed. Community PS usage was measured in two Malian villages, one rural and one periurban, and prevalence of pyrimethamine-resistant P. falciparum genotypes was determined at these sites and two urban sites. The prevalence of resistant genotypes was 22.6% (n = 84) in the periurban village where PS was available from multiple sources and large stocks of PS were observed, and 13.5% (n = 89) and 23.4% (n = 77) in a large town and a city, respectively, where PS is widely available. No pyrimethamine-resistant genotypes (n = 58) were detected in Kolle, a rural village with a community-supported dispensary and clinic where PS is used sparingly and no PS was available in pharmacies or markets. The high rates of pyrimethamine resistant genotypes concurrent with higher PS usage argue for a policy of judicious PS use in Mali and in similar settings. A possible model for slowing the spread of drug-resistant malaria is illustrated by the example of the Kolle clinic.

Antifolate drug resistance and point mutations in Plasmodium falciparum in Kenya

by Khan B, Omar S, Kanyara JN, Warren-Perry M, Nyalwidhe J, Peterson DS, Wellems T, Kaniaru S, Gitonga J, Mulaa FJ, Koech DK

Published in 1997

Due to increased chloroquine resistance, the antifolate/sulpha drug combinations are becoming increasingly important in the chemotherapy of falciparum malaria. However, point mutations in the dihydrofolate reductase gene lead to resistance to the antifolate drugs. We therefore investigated the prevalence of the 6 reported point mutations in this gene among field isolates of Plasmodium falciparum from Kenya, to determine if the mutations correlated with resistance to pyrimethamine and the biguanides cycloguanil and chlorcycloguanil. We used a mutation-specific polymerase chain reaction technique to test for these reported mutations in 21 Kenyan isolates and 4 reference lines. We also amplified and directly sequenced the dihydrofolate reductase coding sequence from these parasites to confirm the results and test for other possible mutations. Of the reported mutations, we found S108N, which is the central mutation of pyrimethamine resistance, and mutations N51I and C59R, which modulate the levels of resistance and may confer decreases in response to cycloguanil that are folate and p-aminobenzoic acid dependent. No isolate possessed the paired point mutations S108T and A16V, or I164L and S108N, which have been associated with cycloguanil resistance in previous studies. These results provided supportive evidence for the combined use of a cycloguanil-class drug (e.g., chlorproguanil) and a sulpha drug (e.g., dapsone) against P.falciparum malaria in Kenya.

Mutations in Plasmodium falciparum dihydrofolate reductase and dihydropteroate synthase and epidemiologic patterns of pyrimethamine-sulfadoxine use and resistance

by Plowe CV, Cortese JF, Djimde A, Nwanyanwu OC, Watkins WM, Winstanley PA, Estrada-Franco JG, Mollinedo RE, Avila JC, Cespedes JL, Carter D, Doumbo OK

Published in 1997

To assess the relationship between mutations in Plasmodium falciparum dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) and clinical pyrimethamine-sulfadoxine resistance, polymerase chain reaction surveys and analyses for new mutations were conducted in four countries with increasing levels of pyrimethamine-sulfadoxine resistance: Mali, Kenya, Malawi, and Bolivia. Prevalence of mutations at DHFR codon 108 and a new mutation at DHPS 540 correlated with increased pyrimethamine-sulfadoxine resistance (P < .05). Mutations at DHFR 51, DHFR 59, and DHPS 437 correlated with resistance without achieving statistical significance. Mutations at DHFR 164 and DHPS 581 were common in Bolivia, where pyrimethamine-sulfadoxine resistance is widespread, but absent in African sites. Two new DHFR mutations, a point mutation at codon 50 and an insert at codon 30, were found only in Bolivia. DHFR and DHPS mutations occur in a progressive, stepwise fashion. Identification of specific sets of mutations causing in vivo drug failure may lead to the development of molecular surveillance methods for pyrimethamine-sulfadoxine resistance.

High prevalence of mutations in the dihydrofolate reductase gene of Plasmodium falciparum in isolates from Tanzania without evidence of an association to clinical sulfadoxine/pyrimethamine resistance

by Jelinek T, Ronn AM, Curtis J, Duraisingh MT, Lemnge M M, Mhina J, Bygbjerg IC, Warhurst DC

Published in 1997

Recently the efficacy of sulfadoxine/pyrimethamine (S/P) in treatment of uncomplicated falciparum malaria in Tanzania has been seriously compromised by the development of resistance. The occurrence of active site mutations in the Plasmodium falciparum gene sequence coding for dihydrofolate reductase (DHFR) is known to confer resistance to pyrimethamine. This study investigates the occurrence of these mutations in infected blood samples taken from Tanzanian children before treatment with S/P and their relationship to parasite breakthrough by day 7. The results confirm the occurrence of one or more DHFR mutations in all the samples, but no relationship was found with the presence of parasites in the blood at day 7. The results suggest that alterations in the coding region for dihydropteroate synthetase (DHPS), the enzyme target for sulfadoxine, should be studied in order to predict resistance to the S/P combination. It has been proposed earlier that sulfadoxine could itself act on DHFR, because of a false dihydrofolate produced by drug metabolism through DHPS and dihydrofolate synthase. The results of this treatment study suggest that such a possibility is unlikely.

Resistance to antifolates in Plasmodium falciparum monitored by sequence analysis of dihydropteroate synthetase and dihydrofolate reductase alleles in a large number of field samples of diverse origins

by Wang P, Lee CS, Bayoumi R, Djimde A, Doumbo O, Swedberg G, Dao LD, Mshinda H, Tanner M, Watkins WM, Sims P, Hyde JE

Published in 1997

Resistance of Plasmodium falciparum to antifolate chemotherapy is a significant problem where combinations such as Fansidar (pyrimethamine-sulfadoxine; PYR-SDX) are used in the treatment of chloroquine-resistant malaria. Antifolate resistance has been associated with variant sequences of dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS), the targets of PYR and SDX respectively. However, while the nature and distribution of mutations in the dhfr gene are well established, this is not yet the case for dhps. We have thus examined by DNA sequence analysis 141 field samples from several geographical regions with differing Fansidar usage (West and East Africa, the Middle East and Viet Nam) to establish a database of the frequency and repertoire of dhps mutations, which were found in 60% of the samples. We have also simultaneously determined from all samples their dhfr sequences, to better understand the relationship of both types of mutation to Fansidar resistance. Whilst the distribution of mutations was quite different across the regions surveyed, it broadly mirrored our understanding of relative Fansidar usage. In samples taken from individual patients before and after drug treatment, we found an association between the more highly mutated forms of dhps and/or dhfr and parasites that were not cleared by antifolate therapy. We also report a novel mutation in a Pakistani sample at position 16 of DHFR (A16S) that is combined with the familiar C59R mutation, but is wild-type at position 108. This is the first observation in a field sample of a mutant dhfr allele where the 108 codon is unchanged.

Molecular basis of in vivo resistance to sulfadoxine-pyrimethamine in African adult patients infected with Plasmodium falciparum malaria parasites

by Basco LK, Tahar R, Ringwald P

Published in 1998

In vitro sulfadoxine and pyrimethamine resistance has been associated with point mutations in the dihydropteroate synthase and dihydrofolate reductase domains, respectively, but the in vivo relevance of these point mutations has not been well established. To analyze the correlation between genotype and phenotype, 10 Cameroonian adult patients were treated with sulfadoxine-pyrimethamine and followed up for 28 days. After losses to follow-up (n = 1) or elimination of DNA samples due to mixed parasite populations with pyrimethamine-sensitive and pyrimethamine-resistant profiles (n = 3), parasite genomic DNA from day 0 blood samples of six patients were analyzed by DNA sequencing. Three patients who were cured had isolates characterized by a wild-type or mutant dihydrofolate reductase gene (with one or two mutations) and wild-type dihydropteroate synthase gene. Three other patients who failed to respond to sulfadoxine-pyrimethamine treatment carried isolates with triple dihydrofolate reductase gene mutations and either a wild-type or a mutant dihydropteroate synthase gene. Three dihydrofolate reductase gene codons (51, 59, and 108) may be reliable genetic markers that can accurately predict the clinical outcome of sulfadoxine-pyrimethamine treatment in Africa.

Kenyan Plasmodium falciparum field isolates: correlation between pyrimethamine and chlorcycloguanil activity in vitro and point mutations in the dihydrofolate reductase domain

by Nzila-Mounda A, Mberu EK, Sibley CH, Plowe CV, Winstanley P A, Watkins W M

Published in 1998

Sixty-nine Kenyan Plasmodium falciparum field isolates were tested in vitro against pyrimethamine (PM), chlorcycloguanil (CCG), sulfadoxine (SD), and dapsone (DDS), and their dihydrofolate reductase (DHFR) genotypes were determined. The in vitro data show that CCG is more potent than PM and that DDS is more potent than SD. DHFR genotype is correlated with PM and CCG drug response. Isolates can be classified into three distinct groups based on their 50% inhibitory concentrations (IC50s) for PM and CCG (P < 0.01) and their DHFR genotypes. The first group consists of wild-type isolates with mean PM and CCG IC50s of 3.71 +/- 6.94 and 0.24 +/- 0.21 nM, respectively. The second group includes parasites which all have mutations at codon 108 alone or also at codons 51 or 59 and represents one homogeneous group for which 25- and 6-fold increases in PM and CCG IC50s, respectively, are observed. Parasites with mutations at codons 108, 51, and 59 (triple mutants) form a third distinct group for which nine- and eightfold increases in IC50s, respectively, of PM and CCG compared to the second group are observed. Surprisingly, there is a significant decrease (P < 0.01) of SD and DDS susceptibility in these triple mutants. Our data show that more than 92% of Kenyan field isolates have undergone at least one point mutation associated with a decrease in PM activity. These findings are of great concern because they may indicate imminent PM-SD failure, and there is no affordable antimalarial drug to replace PM-SD (Fansidar).

Polymorphisms in the dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS) genes of Plasmodium falciparum and in vivo resistance to sulphadoxine/pyrimethamine in isolates from Tanzania

by Jelinek T, Ronn AM, Lemnge MM, Curtis J, Mhina J, Duraisingh MT, Bygbjerg IC, Warhurst DC

Published in 1998

The efficacy of sulphadoxine/pyrimethamine (S/P) in treatment of uncomplicated falciparum malaria in Africa is increasingly compromised by development of resistance. The occurrence of mutations associated with the active site sequence in the Plasmodium falciparum genes coding for dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS) is associated with in vitro resistance to pyrimethamine and sulphadoxine. This study investigates the occurrence of these mutations in infected blood samples taken from Tanzanian children before treatment with S/P and their relationship to parasite breakthrough by day 7. The results show that alleles of DHPS (436-alanine, 437-alanine and 540-lysine) were significantly reduced in prevalence on day 7 after S/P treatment. In this area, a DHPS with 436-serine, 437-glycine and 540-glutamate appears to play a major role in resistance to S/P in vivo. Evidence for the influence of mutations in the DHFR gene in this investigation is not clear, probably because of the high prevalence of 'resistance-related' mutations at day 0 in the local parasite population. For apparently the same reason, it was not possible to show a statistical association between S/P resistance and the presence of particular polymorphisms in the DHFR and DHPS genes before treatment.

In vivo selection for a specific genotype of dihydropteroate synthetase of Plasmodium falciparum by pyrimethamine-sulfadoxine but not chlorproguanil-dapsone treatment

by Curtis J, Duraisingh MT, Warhurst DC

Published in 1998

Plasmodium falciparum present in blood samples collected before and 3 weeks after treatment with either pyrimethamine-sulfadoxine or chlorproguanil-dapsone was analyzed for variants of the genes coding for the target enzymes of antifolate drugs, dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS). Fragments of the genes were amplified by polymerase chain reactions, and variants were identified by specific restriction endonuclease digestion. Treatment with either drug combination selected for the variants Ile51, Arg59, and Asn108 of DHFR, which have been associated with in vitro resistance to pyrimethamine and cycloguanil. The genotype Ser436, Gly437, and Glu540 of DHPS was selected by pyrimethamine-sulfadoxine but not chlorproguanil-dapsone treatment, showing that a combination of these three variants is important for in vivo resistance to sulfadoxine in the area studied.

Pyrimethamine-sulfadoxine efficacy and selection for mutations in Plasmodium falciparum dihydrofolate reductase and dihydropteroate synthase in Mali

by Diourte Y, Djimde A, Doumbo OK, Sagara I, Coulibaly Y, Dicko A, Diallo M, Diakite M, Cortese JF, Plowe CV

Published in 1999

To assess pyrimethamine-sulfadoxine (PS) efficacy in Mali, and the role of mutations in Plasmodium falciparum dihydrofolate reductase (DHFR) and dihydropteroate synthase (DHPS) in in vivo PS resistance, 190 patients with uncomplicated P. falciparum malaria were treated with PS and monitored for 56 days. Mutation-specific polymerase chain reactions and digestion with restriction endonucleases were used to detect DHFR and DHPS mutations on filter paper blood samples from pretreatment and post-treatment infections. Only one case each of RI and RII level resistance and no cases of RIII resistance or therapeutic failure were observed. Post-PS treatment infections had significantly higher rates of DHFR mutations at codons 108 and 59. No significant selection for DHPS mutations was seen. Pyrimethamine-sulfadoxine is highly efficacious in Mali, and while the low level of resistance precludes assessing the utility of molecular assays for in vivo PS resistance, rapid selection of DHFR mutations supports their role in PS failure.

Show next 10 »