Combination of drug level measurement and parasite genotyping data for improved assessment of amodiaquine and sulfadoxine-pyrimethamine efficacies in treating Plasmodium falciparum malaria in Gabonese children

Slow clearance of histidine-rich protein-2 in Gabonese with uncomplicated malaria

Malaria rapid diagnostic tests (RDTs), which detect Plasmodium falciparum (Pf)-specific histidine-rich protein-2 (HRP2), have increasing importance for the diagnosis and control of malaria, especially also in regions where routine diagnosis by microscopy is not available. HRP2-based RDTs have a similar sensitivity to expert microscopy, but their reported low specificity can lead to high false positivity rates, particularly in high-endemic areas. Despite the widespread use of RDTs, models investigating the dynamics of HRP2 clearance following Pf treatment focus rather on short-term clearance of the protein. The goal of this observational cohort study was to determine the long-term kinetic of HRP2-levels in peripheral blood after treatment of uncomplicated malaria cases with Pf mono-infection using a 3-day course of artesunate/amodiaquine. HRP2 levels were quantified at enrollment and on days 1, 2, 3, 5, 7, 12, 17, 22, and 28 post-treatment initiation. The findings reveal an unexpectedly prolonged clearance of HRP2 after parasite clearance from capillary blood. Terminal HRP2 half-life was estimated to be 9 days after parasite clearance using a pharmacokinetic two-compartmental elimination model. These results provide evidence that HRP2 clearance has generally been underestimated, as the antigen remains detectable in capillary blood for up to 28 days following successful treatment, influencing RDT-based assessment following a malaria treatment for weeks. A better understanding of the HRP2 clearance dynamics is critical for guiding the diagnosis of malaria when relying on RDTs.

IMPORTANCE

Detecting Plasmodium falciparum, the parasite responsible for the severest form of malaria, typically involves microscopy, polymerase chain reaction (PCR), or rapid diagnostic tests (RDTs) targeting the histidine-rich protein 2 or 3 (HRP2/3). While microscopy and PCR quickly turn negative after the infection is cleared, HRP2 remains detectable for a prolonged period. The exact duration of HRP2 persistence had not been well defined. Our study in Gabon tracked HRP2 levels over 4 weeks, resulting in a new model for antigen clearance. We discovered that a two-compartment model accurately predicts HRP2 levels, revealing an initial rapid reduction followed by a much slower elimination phase that can take several weeks. These findings are crucial for interpreting RDT results, as lingering HRP2 can lead to false positives, impacting malaria diagnosis and treatment decisions.

Epidemiology of malaria in Gabon: A systematic review and meta-analysis from 1980 to 2023

The objective of this were conducted to elucidate spatiotemporal variations in malaria epidemiology in Gabon since 1980. For that, five databases, were used to collect and identify all studies published between 1980 and 2023 on malaria prevalence, antimalarial drug resistance, markers of antimalarial drug resistance and insecticide resistance marker. The findings suggest that Gabon continues to face malaria as an urgent public health problem, with persistently high prevalence rates. Markers of resistance to CQ persist despite its withdrawal, and markers of resistance to SP have emerged with a high frequency, reaching 100 %, while ACTs remain effective. Also, recent studies have identified markers of resistance to the insecticides Kdr-w and Kdr-e at frequencies ranging from 25 % to 100 %. Ace1R mutation was reported with a frequency of 0.4 %. In conclusion, the efficacy of ACTs remains above the threshold recommended by the WHO. Organo-phosphates and carbamates could provide an alternative for vector control.

High prevalence of genotypes associated with sulfadoxine/pyrimethamine resistance in the rural area of Fougamou, Gabon

OBJECTIVES

Pregnancy-associated malaria (PAM) is a complex form of malaria. To prevent PAM, several African countries have adopted intermittent preventive treatment with sulfadoxine/pyrimethamine (IPT-SP). However, resistance to SP has been reported, associated with mutations in the genes Plasmodium falciparum dihydropteroate synthase (Pfdhps) and P. falciparum dihydrofolate reductase (Pfdhfr). The aim of this study was to investigate the prevalence of mutations in Pfdhfr and Pfdhps in P. falciparum isolates from rural areas of Gabon.

METHODS

A cross-sectional survey of febrile patients (n = 202) who consulted Fougamou Health Center between February-May 2016 was performed. DNA was extracted from patient samples and the Pfdhfr and Pfdhps genes were genotyped using PCR-RFLP. Statistical analyses were performed.

RESULTS

The malaria prevalence in febrile patients included in the study was 60.4% (122/202). The main parasite species was P. falciparum (96.7%; 118/122), followed by Plasmodium malariae (3.3%; 4/122). Genotypes on codons 16, 51, 59 and 108 of Pfdhfr were highly mutated (>96%). In Pfdhps, codons 436, 437, 540 and 613 also expressed high mutation rates. The prevalence of triple mutations of Pfdhfr VIRNI and AIRNI was 12.1% and 84.5%, respectively. The prevalence of mutant haplotypes of Pfdhps SGEA, SGKA and AGEA was 37.9%, 25.9% and 12.1%, respectively. The prevalence of quadruple mutants IRN-A and IRN-G was 20.0% and 93.1%, respectively, whereas quintuple mutants were found at 57.8% (IRN-GE) and 5.0% (IRN-AE).

CONCLUSION

Our data show a high prevalence of genotypes associated with SP resistance. Clinical trials to investigate the efficacy of IPT-SP are much needed.

Malaria in urban, semi-urban and rural areas of southern of Gabon: comparison of the Pfmdr 1 and Pfcrt genotypes from symptomatic children

Background

Artesunate-amodiaquine (AS-AQ) and artemether-lumefantrine (AL) are first- and second-line treatments for uncomplicated Plasmodium falciparum malaria in Gabon. AL remains highly efficacious, but its widespread use has led to molecular selection of the NFD haplotype on Pfmdr1 and K76 in Pfcrt. In this study, plasmodial infection characteristics and the distribution of the Pfmdr1 and Pfcrt genotypes involved in reduced efficacy of artemisinin-based combination therapy (ACT) were investigated in four Gabonese localities.

Methods

A cross-sectional study was conducted in the paediatric units of rural (Lastourville and Fougamou), semi-urban (Koula-Moutou) and urban (Franceville) areas. Malaria was diagnosed with the rapid diagnostic test Optimal-IT^® and confirmed by blood smear. Pfmdr1 codons 86, 184 and 1246 and Pfcrt codon 76 were genotyped by PCR–RFLP and sequencing.

Results

Among 1129 included children, the prevalence of plasmodial infection was 79.5 % at Lastourville, 53.6 % at Fougamou, 36.1 % at Koula-Moutou, and 21.2 % at Franceville. The prevalence was significantly higher among children over 60 months of age in both semi-urban (p = 0.01) and urban (p = 0.004) areas. The prevalence of Pfmdr1 wild-type N86 differed significantly between Lastourville (57.8 %) and Koula-Moutou (45.4 %) (p = 0.039). No difference in 184F-carrying parasites was found between Lastourville (73.8 %), Fougamou (81.6 %), Koula-Moutou (83.2 %), and Franceville (80.6 %) (p = 0.240). The prevalence of wild-type D1246 was significantly different between Lastourville (94.1 %), Koula-Moutou (85.6 %) and Franceville (87.3 %) (p = 0.01). The frequency of wild-type K76 was not significantly different across the four sites: Lastourville (16.5 %), Fougamou (27.8 %), Koula-Moutou (17.4 %), and Franceville (29.4 %) (p = 0.09). The mixed genotypes were only found in Lastourville and Franceville. The NFD, YFD and NYD haplotypes were mainly Lastourville (46.6, 25.8, 14.0 %), Fougamou (45.5, 9.1, 42.4 %), Koula-Moutou (35, 6.7, 40.4 %), and Franceville (40.0, 16.0, 32.0 %).

Conclusion

This study shows an increase in the prevalence of childhood plasmodial infection in Gabon according to the low socio-economic level, and a high frequency of markers associated with AL treatment failure. Close monitoring of ACT use is needed.

Carriage of Mutant Dihydrofolate Reductase and Dihydropteroate Synthase Genes among Plasmodium falciparum Isolates Recovered from Pregnant Women with Asymptomatic Infection in Lagos, Nigeria

OBJECTIVE

To assess N51I, C59R and S108N polymorphisms of dihydrofolate reductase (dhfr) and A437G and K540E of dihydropteroate synthase (dhps) genes of P. falciparum isolates recovered from pregnant women with asymptomatic malaria in a coastal setting in Nigeria.

SUBJECTS AND METHODS

A total of 107 consenting and consecutively enrolled pregnant women (mean age ± standard deviation, 26.6 ± 4.5 years) attending antenatal care at the Iru/Victoria Island Primary Health Centre, Lagos, were screened for peripheral malaria by microscopy, by a histidine-rich protein-2-based rapid diagnostic test (RDT) and by polymerase chain reaction (PCR) using finger-pricked and dot blood samples. DNA was extracted from the blood and used for dhfr and dhps gene polymorphism analyses by PCR and restriction fragment length polymorphism. The sociodemographic and parasite data obtained were analysed.

RESULTS

Of the 107 patients, 34 (31.8%), 46 (43%) and 40 (37.4%) were found to be P. falciparum infected using microscopy, RDT and corrected RDT-PCR, respectively (p < 0.05). The prevalence of P. falciparum isolates with mutant and mixed genotypes of dhfr at codons 51, 59 and 108 was 70, 75 and 80%, respectively, and the triple mutation in the homozygous form was 35%. The prevalence of the homozygous quintuple dhfr plus dhps mutant was 5%, while that of the P. falciparum isolates with mutant or mixed genotypes of dhps at codons 437 and 540 was 37.5 and 22.5%, respectively.

CONCLUSION

This study revealed the emergence of the K540E mutation among the parasite population in Lagos. However, it supports the implementation of the intermittent preventive treatment of malaria during pregnancy with sulphadoxine-pyrimethamine with continuous effectiveness monitoring in the study area.

Pfcrt 76T and pfmdr1 86Y allele frequency in Plasmodium falciparum isolates and use of self-medication in a rural area of Gabon

BACKGROUND

Studies showed that chloroquine resistance may revert to sensitivity after its withdrawal mainly detected by a significant decrease of Plasmodium falciparum pfcrt 76T and pfmdr1 86Y alleles. Besides, self-medication is considered as a key factor of antimalarial drug resistance expansion. Thus, pfcrt 76T and pfmdr1 86Y allele frequency and its relationship with antimalarial drug self-medication was analyzed in P. falciparum isolates collected in Gabon.

METHODS

Samples were collected from febrile children screened for P. falciparum infection in 2005 and 2008 at the regional hospital of Oyem. Self-use of antimalarial drugs before the day of consultation was recorded. Polymorphic codons 76 and 86 of pfcrt and pfmdr1 genes were analyzed by PCR-RFLP.

RESULTS

The frequency of pfcrt 76T mutant allele was greater than 70.0% in 2005 and 2008. Wild type isolates were 1.7-fold more prevalent in 2008. The prevalence of pfmdr1 86Y mutant allele was comparable between 2005 and 2008 (p=0.1); the proportion of wild type allele reached 20.5% in 2008. The frequency of wild type allele pfcrt K76 or pfmdr1 N86 was higher among patients without anti-malarial drug self-medication compared to those who used it.

CONCLUSIONS

An increase of the frequency of P. falciparum wild type allele pfcrt 76K and pfmdr1 86N was observed within a short period after chloroquine withdrawal. The proportion of mutant genotypes is still high, mainly among patients using self-medication with antimalarial drugs.

A randomized trial of artesunate-amodiaquine versus artemether-lumefantrine in Ghanaian paediatric sickle cell and non-sickle cell disease patients with acute uncomplicated malaria

Background

Sickle cell disease (SCD) is a genetic disorder common in malaria endemic areas. In endemic areas, malaria is a major cause of morbidity and mortality among SCD patients. This suggests the need for prompt initiation of efficacious anti-malarial therapy in SCD patients with acute malaria. However, there is no information to date, on the efficacy or safety of artemisinin combination therapy when used for malaria treatment in SCD patients.

Methods

Children with SCD and acute uncomplicated malaria (n = 60) were randomized to treatment with artesunate-amodiaquine (AA), or artemether-lumefantrine (AL). A comparison group of non-SCD children (HbAA genotype; n = 59) with uncomplicated malaria were also randomized to treatment with AA or AL. Recruited children were followed up and selected investigations were done on days 1, 2, 3, 7, 14, 28, 35, and 42. Selected clinical and laboratory parameters of the SCD patients were also compared with a group of malaria-negative SCD children (n = 82) in steady state.

Results

The parasite densities on admission were significantly lower in the SCD group, compared with the non-SCD group (p = 0.0006). The parasite reduction ratio (PRR) was lower, clearance was slower (p < 0.0001), and time for initial parasitaemia to decline by 50 and 90% were longer for the SCD group. Adequate clinical and parasitological response (ACPR) on day 28 was 98.3% (58/59) in the SCD group and 100% (57/57) in the non-SCD group. Corresponding ACPR rates on day 42 were 96.5% (55/57) in the SCD group and 96.4% (53/55) in the non-SCD group. The fractional changes in haemoglobin, platelets and white blood cell counts between baseline (day 0) and endpoint (day 42) were 16.9, 40.6 and 92.3%, respectively, for the SCD group, and, 12.3, 48.8 and 7.5%, respectively, for the non-SCD group. There were no differences in these indices between AA- and AL-treated subjects.

Conclusions

The parasite clearance of SCD children with uncomplicated malaria was slower compared with non-SCD children. AA and AL showed similar clinical and parasitological effects in the SCD and non-SCD groups. The alterations in WBC and platelet counts may have implications for SCD severity.

Trial registration

Current controlled trials ISRCTN96891086.

A better resolution for integrating methods for monitoring Plasmodium falciparum resistance to antimalarial drugs

Effective chemotherapy is the mainstay of malaria control. However, resistance of falciparum malaria to antimalarial drugs compromised the efforts to eliminate the disease and led to the resurgence of malaria epidemics. Three main approaches are used to monitor antimalarial drug efficacy and drug resistance; namely, in vivo trials, in vitro/ex vivo assays and molecular markers of drug resistance. Each approach has its implications of use as well as its advantages and drawbacks. Therefore, there is a need to use an integrated approach that would give the utmost effect to detect resistance as early as its emergence and to track it once spread. Such integration becomes increasingly needed in the era of artemisinin-based combination therapy as a forward action to deter resistance. The existence of regional and global networks for the standardization of methodology, provision of high quality reagents for the assessment of antimalarial drug resistance and dissemination of open-access data would help in approaching an integrated resistance surveillance system on a global scale.

Low prevalence of the molecular markers of Plasmodium falciparum resistance to chloroquine and sulphadoxine/pyrimethamine in asymptomatic children in Northern Benin

Background

In Benin, very few studies have been done on the genetics of Plasmodium falciparum and the resistance markers of anti-malarial drugs, while malaria treatment policy changed in 2004. Chloroquine (CQ) and sulphadoxine pyrimethamine (SP) have been removed and replaced by artemisinin-combination therapy (ACT). The objective of this study was to determine the genetic diversity of P. falciparum and the prevalence of P. falciparum molecular markers that are associated with resistance to CQ and SP in northern Benin seven years after the new policy was instituted.

Methods

The study was conducted in northern Benin, a region characterized by a seasonal malaria transmission. Blood samples were collected in 2012 from children presenting with asymptomatic P. falciparum infections. Samples collected in filter paper were genotyped by primary and nested PCR in block 2 of msp-1 and block 3 of msp-2 to analyse the diversity of P. falciparum. The prevalence of critical point mutations in the genes of Pfcrt (codon 76), Pfmdr1 (codon 86), Pfdhfr (codons, 51, 59 and 108) and Pfdhps (codons 437, 540) was examined in parasite isolates by mutation-specific restriction enzyme digestion.

Results

Genotyping of 195 isolates from asymptomatic children showed 34 msp-1 and 38 msp-2 genotypes. The multiplicity of infection was 4.51 ± 0.35 for msp-1 and 4.84 ± 0.30 for msp-2. Only the codon 51 of Pfdhfr and codon 437 of Pfdhps showed a high mutation rate: I51: 64.4% (57.3; 71.2); G437: 47.4% (40.2; 54.7), respectively. The prevalence of Pfdhfr triple mutant IRN (I51, R59 and N108) was 1.5% (0.3; 3.9), and Pfdhfr/Pfdhps quadruple mutant IRNG (PfdhfrI51, R59, N108, and PfdhpsG437): 0. 5% (0; 2.5). No mutation was found with codon 540 of Pfdhps. Analysis of mutation according to age (younger or older than ten years) showed similar frequencies in each category without significant difference between the two groups.

Conclusions

This study showed a high diversity of P. falciparum in northern Benin with a very low prevalence of resistance markers to CQ and SP that dramatically contrasted with the pattern observed in southern Benin. No influence of age on genetic diversity of P. falciparum and on distribution of the mutations was observed.

Genetic polymorphism of merozoite surface protein-1 and merozoite surface protein-2 in Plasmodium falciparum isolates from children in South of Benin

The aim of this study was to determine the genetic diversity of Plasmodium falciparum by analyzing the polymorphism of the msp-1 and msp-2 genes and the multiplicity of infection in children with uncomplicated malaria in southern Benin. Blood samples of children with fever or history of fever with thick smear positive P. falciparum were collected on filter paper. After extraction of DNA by Chelex®, the samples underwent nested PCR. 93 isolates from children were genotyped. For the msp-1 gene, the K1 and R033 sequences were the most represented in the study population with 85.2% and 83% prevalence, respectively. Regarding the msp-2 gene, the FC27 family was more highly represented with 99% prevalence against 81.5% for 3D7. Mixed infections accounted for 80.4% of the samples. Twenty-five alleles were identified for msp-1 and 28 for msp-2. Fourteen and ten alleles belonged to the K1 (100-500 bp) and MAD20 (100-500 bp) families, respectively. The RO33 sequence did not show any polymorphism, with only one variant (160 bp) detected. The msp-2 gene was present as 16 FC27 family fragments (250-800 bp) and 12 of the 3D7 family (350-700 bp). The multiplicity of infection was estimated at 3.8 for msp-1 and 3.9 for msp-2 with 77 (87.5%) and 84 (91.3%) samples harboring more than one parasite genotype for msp-1 and msp-2, respectively. The multiplicity of infection (MOI) was influenced neither by age nor by parasite density. This study shows a significant diversity of P. falciparum in southern Benin with an MOI unaffected by age or by parasite density.

Methylerythritol phosphate pathway to isoprenoids: kinetic modeling and in silico enzyme inhibitions in Plasmodium falciparum

The methylerythritol phosphate (MEP) pathway of Plasmodium falciparum (P. falciparum) has become an attractive target for anti-malarial drug discovery. This study describes a kinetic model of this pathway, its use in validating 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) as drug target from the systemic perspective, and additional target identification, using metabolic control analysis and in silico inhibition studies. In addition to DXR, 1-deoxy-d-xylulose 5-phosphate synthase (DXS) can be targeted because it is the first enzyme of the pathway and has the highest flux control coefficient followed by that of DXR. In silico inhibition of both enzymes caused large decrement in the pathway flux. An added advantage of targeting DXS is its influence on vitamin B1 and B6 biosynthesis. Two more potential targets, 2-C-methyl-d-erythritol 2,4-cyclodiphosphate synthase and 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate synthase, were also identified. Their inhibition caused large accumulation of their substrates causing instability of the system. This study demonstrates that both types of enzyme targets, one acting via flux reduction and the other by metabolite accumulation, exist in P. falciparum MEP pathway. These groups of targets can be exploited for independent anti-malarial drugs.

Efficacy of chloroquine for the treatment of uncomplicated Plasmodium falciparum malaria in Honduras

Chloroquine (CQ) is officially used for the primary treatment of Plasmodium falciparum malaria in Honduras. In this study, the therapeutic efficacy of CQ for the treatment of uncomplicated P. falciparum malaria in the municipality of Puerto Lempira, Gracias a Dios, Honduras was evaluated using the Pan American Health Organization-World Health Organization protocol with a follow-up of 28 days. Sixty-eight patients from 6 months to 60 years of age microscopically diagnosed with uncomplicated P. falciparum malaria were included in the final analysis. All patients who were treated with CQ (25 mg/kg over 3 days) cleared parasitemia by day 3 and acquired no new P. falciparum infection within 28 days of follow-up. All the parasite samples sequenced for CQ resistance mutations (pfcrt) showed only the CQ-sensitive genotype (CVMNK). This finding shows that CQ remains highly efficacious for the treatment of uncomplicated P. falciparum malaria in Gracias a Dios, Honduras.

Sulfadoxine-pyrimethamine resistance in Plasmodium falciparum: a zoomed image at the molecular level within a geographic context

Antimalarial chemotherapy is one of the main pillars in the prevention and control of malaria. Following widespread resistance of Plasmodium falciparum to chloroquine, sulfadoxine-pyrimethamine came to the scene as an alternative to the cheap and well-tolerated chloroquine. However, widespread resistance to sulfadoxine-pyrimethamine has been documented. In vivo efficacy tests are the gold standard for assessing drug resistance and treatment failure. However, they have many disadvantages, such as influence of host immunity and drug pharmacokinetics. In vitro tests of antimalarial drug efficacy also have many technical difficulties. Molecular markers of resistance have emerged as epidemiologic tools to investigate antimalarial drug resistance even before becoming clinically evident. Mutations in P. falciparum dihydrofolate reductase and dihydrofolate synthase have been extensively studied as molecular markers for resistance to pyrimethamine and sulfadoxine, respectively. This review highlights the resistance of P. falciparum at the molecular level presenting both supporting and opposing studies on the utility of molecular markers.

Pharmacokinetic disposition of sulfadoxine in children with acute uncomplicated falciparum malaria treated with sulfadoxine-pyrimethamine in South West Nigeria

Sulfadoxine (SDX)-pyrimethamine is currently recommended as a partner drug with artesunate in the chemotherapy of malaria. However, information on pharmacokinetic disposition of SDX-pyrimethamine in children is limited. Efforts in this study were thus devoted to evaluation of pharmacokinetic disposition of SDX using high-pressure liquid chromatographic techniques and effects of pharmacokinetic variability on treatment outcome in Nigerian children with falciparum malaria. The blood concentration profile of SDX was similar in patients whose infection responded to treatment and those who failed treatment; mean SDX concentration values were similar for day 3 (179 vs 157 μg/mL, P = 0.734), day 7 (84 vs 51 μg/mL, P = 0.365), and day 14 (50 vs 14 μg/mL, P = 0.151). Extent of exposure (area under the curve) to SDX was also similar in the patients (1196 vs 1013 μg d/mL, P = 0.561). Pearson's correlation, showed significant correlation between area under the curve and D3 or D7 concentration of SDX (P = 0.001, r = 0.702 or P = 0.001, r = 0.835, respectively). Age-stratified analysis showed that SDX concentrations were significantly higher in older children (older than 5 years); the mean maximum concentration (125 vs 295 μg/mL, P = 0.001), extent of exposure (812 vs 1562 μg d/mL, P = 0.001), day 3 concentration (98 vs 250 μg/mL, P = 0.001), and day 7 concentration (54 vs 128 μg/mL, P = 0.007) were higher. The study revealed no differences in posttreatment blood SDX concentrations in patients who responded to treatment and those who failed to respond to treatment. Furthermore, there was an age-related pharmacokinetic variability of SDX in the group of children studied with potential impact on treatment outcome.

In vitro antimalarial susceptibility and molecular markers of drug resistance in Franceville, Gabon

Background

Malaria remains a major public health problem, due largely to emergence and widespread P. falciparum drug resistance. WHO recommends artemisinine combination based therapy (ACT) to overcome P. falciparum drug resistance, but reports of declining ACT efficacy have been published. A thorough understanding of the molecular bases of P. falciparum resistance to existing drugs is therefore needed. The aims of this study were to analyze the in vitro sensitivity of P. falciparum field isolates from Franceville, Gabon, to chloroquine (CQ), mefloquine (MF), dihydroartemisinine (DHA) and monodesethylamodiaquine (MDAQ), and to investigate polymorphisms associated with drug resistance.

Methods

We conducted a cross-sectional study of 53 field isolates. Field isolates sensitivity to CQ, MF, DHA and MDAQ was assessed using the colorimetric DELI test. The Pfmdr1 codons 86 and 1246, Pfcrt (haplotype codon 72 to 76) and the PfATPAse6 codons 110 and 2694 were analysed by PCR-RFLP. Associations between drug sensitivity and parasite gene polymorphisms were evaluated with the Chi square test, and routine hematological parameters were analyzed with Fisher’s exact test implemented with Epinfo software. In all statistical tests, significance was assumed at p<0.05.

Results

A total of 46 P. falciparum isolates were successfully cultured in vitro and their sensitivity was tested. The proportions of isolates resistant to CQ, MF and MDAQ were 43.5%, 23.4% and 56.5%, respectively. Some isolates (23.9%) had DHA IC₅₀ values higher than 10 nM. The median IC₅₀ values were 71.67 (interquartile range (IQR, 1–438.2), 6.59 (IQR, 0.08-96), 64.79 (IQR, 0.09-448) and 6.45 nM (IQR, 0.09-23) for CQ, MF, MDAQ and DHA, respectively. The strongest correlation between diminished DHA sensitivity and MF resistance was observed (r²=0.73), followed by correlation between diminished DHA sensitivity and CQ resistance. Cross-resistance between CQ and MF was also observed. The prevalence of the 86Y and 1246Y mutations in Pfmdr1, 76T in Pfcrt, and 110A and 2694T in PfATPase6 was respectively 42% and 17.1%, 97.8%, and 0% and 22.2%.

Conclusion

These high levels of antimalarial drug resistance in Franceville, Gabon, call for reinforced surveillance of drug efficacy.

Effects of amodiaquine and artesunate on sulphadoxine-pyrimethamine pharmacokinetic parameters in children under five in Mali

BACKGROUND

Sulphadoxine-pyrimethamine, in combination with artesunate or amodiaquine, is recommended for the treatment of uncomplicated malaria and is being evaluated for intermittent preventive treatment. Yet, limited data is available on pharmacokinetic interactions between these drugs.

METHODS

In a randomized controlled trial, children aged 6-59 months with uncomplicated falciparum malaria, received either one dose of sulphadoxine-pyrimethamine alone (SP), one dose of SP plus three daily doses of amodiaquine (SP+AQ) or one dose of SP plus 3 daily doses of artesunate (SP+AS). Exactly 100 μl of capillary blood was collected onto filter paper before drug administration at day 0 and at days 1, 3, 7, 14, 21 and 28 after drug administration for analysis of sulphadoxine and pyrimethamine pharmacokinetic parameters.

RESULTS

Fourty, 38 and 31 patients in the SP, SP+AQ and SP+AS arms, respectively were included in this study. The concentrations on day 7 (that are associated with therapeutic efficacy) were similar between the SP, SP+AQ and SP+AS treatment arms for sulphadoxine (median [IQR] 35.25 [27.38-41.70], 34.95 [28.60-40.85] and 33.40 [24.63-44.05] μg/mL) and for pyrimethamine (56.75 [46.40-92.95], 58.75 [43.60-98.60] and 59.60 [42.45-86.63] ng/mL). There were statistically significant differences between the pyrimethamine volumes of distribution (4.65 [3.93-6.40], 4.00 [3.03-5.43] and 5.60 [4.40-7.20] L/kg; p = 0.001) and thus elimination half-life (3.26 [2.74 -3.82], 2.78 [2.24-3.65] and 4.02 [3.05-4.85] days; p < 0.001). This study confirmed the lower SP concentrations previously reported for young children when compared with adult malaria patients.

CONCLUSION

Despite slight differences in pyrimethamine volumes of distribution and elimination half-life, these data show similar exposure to SP over the critical initial seven days of treatment and support the current use of SP in combination with either AQ or AS for uncomplicated falciparum malaria treatment in young Malian children.

Amodiaquine-associated adverse effects after inadvertent overdose and after a standard therapeutic dose

A case of an acute dystonic reaction in a child presumptively treated for malaria with amodiaquine, and a case of persistent asymptomatic bradycardia in another child with mild pulmonary stenosis treated with a standard dose of amodiaquine for parasitologically confirmed uncomplicated malaria, is reported. Both subjects were homozygous for the wild type allele of cytochrome P450 2C8, the main enzyme responsible for amodiaquine metabolism. In both subjects, plasma concentrations of N-desethylamodiaquine and N-bis-desethylamodiaquine, the main metabolites of amodiaquine, were normal. No other drugs were detectable in the plasma of these two subjects after further toxicological screening. These observations, which suggest altered metabolism in the subject with an acute dystonic reaction, support the assertion that amodiaquine-associated dystonia is an idiosyncratic reaction. However, the occurrence of bradycardia after a standard dose of amodiaquine, which coincided with the time of expected peak concentrations of the active metabolite of amodiaquine, suggests a direct drug effect. These less reported adverse effects are likely to increase in parallel with the increased use of amodiaquine as a partner drug for combination therapy of malaria in Ghana. Further studies aimed at elucidating the mechanisms underlying these effects are, therefore, required.

Efficacy of chloroquine plus primaquine treatment and pfcrt mutation in uncomplicated falciparum malaria patients in Rangamati, Bangladesh

A combination of chloroquine (CQ) and primaquine (PQ) had been used as the first-line treatment of uncomplicated Plasmodium falciparum malaria in Rangamati, Bangladesh until the end of 2004. Doctors or medical staffs had felt that CQ plus PQ had become less effective against uncomplicated falciparum malaria patients, but that it was more effective against the minority-indigenous patients than the Bengali patients. The efficacy of CQ plus PQ and the mutation status of the CQ resistance transporter (pfcrt) gene of infecting P. falciparum were, thus, investigated for 45 uncomplicated falciparum malaria patients in Rangamati in 2004. The total failure rate was 57.8%. One or two pfcrt sequences (CIETH and SMNTH at positions 72, 74-76, and 97, mutation underlined) with K76T mutation known to be related to CQ-resistant phenotype were detected in 38 patients' blood samples. Of the 38 patients, in total 15 patients (14/25 minority-indigenous and 1/13 Bengali patients) resulted in adequate clinical and parasitological response (ACPR). There was a statistically significant difference in ACPR rate between the minority-indigenous patients and the Bengali patients. P. falciparum with mutant or resistant pfcrt (pfcrt-resistant) was detected by PCR in blood samples on day 28 for 10 ACPR minority-indigenous patients but not for the only one Bengali ACPR patient, who all were infected with pfcrt-resistant P. falciparum on day 0. The minority-indigenous patients, but not Bengalis, are suggested to be often cured by CQ plus PQ, leaving a very few parasites detectable only by PCR, even when they are infected with pfcrt-resistant P. falciparum.

A molecular epidemiological study of var gene diversity to characterize the reservoir of Plasmodium falciparum in humans in Africa

BACKGROUND

The reservoir of Plasmodium infection in humans has traditionally been defined by blood slide positivity. This study was designed to characterize the local reservoir of infection in relation to the diverse var genes that encode the major surface antigen of Plasmodium falciparum blood stages and underlie the parasite's ability to establish chronic infection and transmit from human to mosquito.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated the molecular epidemiology of the var multigene family at local sites in Gabon, Senegal and Kenya which differ in parasite prevalence and transmission intensity. 1839 distinct var gene types were defined by sequencing DBLα domains in the three sites. Only 76 (4.1%) var types were found in more than one population indicating spatial heterogeneity in var types across the African continent. The majority of var types appeared only once in the population sample. Non-parametric statistical estimators predict in each population at minimum five to seven thousand distinct var types. Similar diversity of var types was seen in sites with different parasite prevalences.

CONCLUSIONS/SIGNIFICANCE

Var population genomics provides new insights into the epidemiology of P. falciparum in Africa where malaria has never been conquered. In particular, we have described the extensive reservoir of infection in local African sites and discovered a unique var population structure that can facilitate superinfection through minimal overlap in var repertoires among parasite genomes. Our findings show that var typing as a molecular surveillance system defines the extent of genetic complexity in the reservoir of infection to complement measures of malaria prevalence. The observed small scale spatial diversity of var genes suggests that var genetics could greatly inform current malaria mapping approaches and predict complex malaria population dynamics due to the import of var types to areas where no widespread pre-existing immunity in the population exists.

Increased prevalence of the Plasmodium falciparum Pfmdr1 86N genotype among field isolates from Franceville, Gabon after replacement of chloroquine by artemether-lumefantrine and artesunate-mefloquine

Despite global antimalarial measures, Plasmodium falciparum malaria remains a major public health problem. WHO has recommended the use of arteminisin-based combination therapy to limit the emergence of antimalarial drug resistance. However, ACT treatment failures have been linked to the selection of the wild types 86N genotype of P. falciparum multidrug resistance 1 (Pfmdr1) and the 76K genotype of P. falciparum chloroquine resistance (Pfcrt) genes. The aim of this study was to investigate the molecular impact of widespread implementation of artemether-lumefantrine and artesunate-mefloquine on local parasite population in Franceville, Gabon. We analyzed 230 pediatric field isolates (96 from 2004 and 134 from 2009). Routine hematological parameters were collected. Pfmdr1 codons 86 and 1246 and Pfcrt codon 76 were genotyped using PCR-RFLP and the prevalence of the genotypes was compared. The children's mean age did not differ between 2004 and 2009 (respectively 31.8 (6-84) months vs 38.6 (6-84) months, p=0.32), and neither did mean parasitemia [16,750 (1000-96,234) and 14,587 (1093-83,941) parasites/μL, respectively (p=0.21)]. The mean hemoglobin level was higher in 2009 than in 2004 (11.0 ± 2.4 vs 7.8 ± 2.0 g/dL, respectively; p=0.04). More interesting, the prevalence of Pfmdr1 wild type 86N increased from 15.6% (n=15/96) in 2004 to 31.3% (n=42/134) in 2009 (p=0.007). A significant increase combining pure and mixed genotypes (86N+86N/Y) was also found between 2004 and 2009 (p=0.02), while the prevalence of genotypes Pfmdr1 1246D, Pfcrt wild type 76T and all mixed genotypes (Pfmdr1 86N/Y and 1246D/Y, and 76K/T) remained stable. The complexity of isolates was high (around 2.9 and 2.4) and the FC27 allele of Pfmsp2 was more prevalent. These findings show a substantial benefice of artemether-lumefantrine and artesunate-mefloquine and of new control measures. The selection, in the general population, of wild type Pfmdr1 86N, which is associated with antiplasmodial resistance against some drugs, has been induced underlining the need for molecular surveillance of the impact of ACT on antimalarial resistance.

Population pharmacokinetics and pharmacodynamic considerations of amodiaquine and desethylamodiaquine in Kenyan adults with uncomplicated malaria receiving artesunate-amodiaquine combination therapy

Amodiaquine (AQ) is an antimalarial drug that was frequently combined with artesunate (AS) for the treatment of uncomplicated malaria due to Plasmodium falciparum and is now available as a fixed-dose combination. Despite its widespread use, the simultaneous pharmacokinetics in patients of AQ and its active metabolite, desethylamodiaquine (DAQ), were not characterized to date. The pharmacokinetics of AQ and DAQ in 54 adult patients receiving the AS/AQ combination were therefore investigated by the use of a population approach. AQ followed a 1-compartment model with first-order absorption and elimination, as well as a first-order and irreversible transformation into DAQ, which in turn followed a 2-compartment model with first-order elimination from its central compartment. The mean AQ apparent clearance and distribution volume were 3,410 liters/h and 39,200 liters, respectively. The mean terminal elimination half-life of DAQ was 211 h. Body weight was found to explain the interindividual variability of the apparent volume of distribution of AQ and the elimination rate constant of DAQ. A new dosage form consisting of a fixed-dose combination of AS and AQ was found to have no effect on the pharmacokinetic parameters of AQ and DAQ. All patients achieved parasite clearance within 4 days following the initiation of the treatment, which prevented investigation of the possible relationship between DAQ exposure and treatment outcome. This study provided the first simultaneous pharmacokinetic model for AQ and DAQ.

Pharmacokinetics of artemether-lumefantrine and artesunate-amodiaquine in children in Kampala, Uganda

The World Health Organization recommends the use of artemisinin-based combination therapies (ACTs) for the treatment of uncomplicated malaria. The two most widely adopted ACT regimens are artemether (AR)-lumefantrine (LR) (the combination is abbreviated AL) and amodiaquine (AQ)-artesunate (AS). Pharmacokinetic (PK) data informing the optimum dosing of these drug regimens is limited, especially in children. We evaluated PK parameters in Ugandan children aged 5 to 13 years with uncomplicated malaria treated with AL (n = 20) or AQ-AS (n = 21), with intensive venous sampling occurring at 0, 2, 4, 8, 24, and 120 h following administration of the last dose of 3-day regimens of AL (twice daily) or AQ-AS (once daily). AS achieved an estimated maximum concentration in plasma (C(max)) of 51 ng/ml and an area under the concentration-time curve from time zero to infinity (AUC(0-infinity)) of 113 ng.h/ml; and its active metabolite, dihydroartemisinin (DHA), achieved a geometric mean C(max) of 473 ng/ml and an AUC(0-infinity) of 1,404 ng.h/ml. AR-DHA exhibited a C(max) of 34/119 ng/ml and an AUC(0-infinity) of 168/382 ng.h/ml, respectively. For LR, C(max) and AUC(0-infinity) were 6,757 ng/ml and 210 microg.h/ml, respectively. For AQ and its active metabolite, desethylamodiaquine (DEAQ), the C(max)s were 5.2 ng/ml and 235 ng/ml, respectively, and the AUC(0-infinity)s were 39.3 ng.h/ml and 148 microg.h/ml, respectively. Comparison of the findings of the present study to previously published data for adults suggests that the level of exposure to LR is lower in children than in adults and that the level of AQ-DEAQ exposure is similar in children and adults. For the artemisinin derivatives, differences between children and adults were variable and drug specific. The PK results generated for children must be considered to optimize the dosing strategies for these widely utilized ACT regimens.

Pharmacokinetics of sulfadoxine and pyrimethamine in intermittent preventive treatment of malaria in pregnancy

Malaria during pregnancy is associated with maternal and fetal morbidity and mortality. In order to minimize the burden, sulfadoxine-pyrimethamine (SP) is widely used in Africa as an intermittent preventive treatment of malaria in pregnancy (IPTp). However, only limited data are available on the pharmacokinetics of sulfadoxine and pyrimethamine during pregnancy. We conducted a prospective, self-matched, multicenter study of 98 pregnant women in four African countries in order to determine the effects of pregnancy on SP pharmacokinetics. After adjusting for the effects of potential confounders, blood concentrations (associated with therapeutic efficacy) of pyrimethamine were higher (geometric mean ratio (GMR) 1.33; 95% confidence interval (CI) 1.18-1.51; P < 0.001) and those of sulfadoxine were lower (GMR 0.91; 95% CI 0.84-0.98; P = 0.013) on day 7 after SP administration during pregnancy than after the postpartum period. SP pharmacokinetic parameters differed significantly among the study sites. Given the inconsistency of changes in pharmacokinetic parameters between sulfadoxine and pyrimethamine as well as among the study sites, it is not possible to recommend any dose adjustment to prolong the therapeutic life span of the fixed dose combination of SP for IPTp on the basis of our study findings.

Plasmodium falciparum genotypes diversity in symptomatic malaria of children living in an urban and a rural setting in Burkina Faso

BACKGROUND

The clinical presentation of malaria, considered as the result of a complex interaction between parasite and human genetics, is described to be different between rural and urban areas. The analysis of the Plasmodium falciparum genetic diversity in children with uncomplicated malaria, living in these two different areas, may help to understand the effect of urbanization on the distribution of P. falciparum genotypes.

METHODS

Isolates collected from 75 and 89 children with uncomplicated malaria infection living in a rural and an urban area of Burkina Faso, respectively, were analysed by a nested PCR amplification of msp1 and msp2 genes to compare P. falciparum diversity.

RESULTS

The K1 allelic family was widespread in children living in the two sites, compared to other msp1 allelic families (frequency >90%). The MAD 20 allelic family of msp1 was more prevalent (p = 0.0001) in the urban (85.3%) than the rural area (63.2%). In the urban area, the 3D7 alleles of msp2 were more prevalent compared to FC27 alleles, with a high frequency for the 3D7 300bp allele (>30%). The multiplicity of infection was in the range of one to six in the urban area and of one to seven in the rural area. There was no difference in the frequency of multiple infections (p = 0.6): 96.0% (95% C.I: 91.6-100) in urban versus 93.1% (95%C.I: 87.6-98.6) in rural areas. The complexity of infection increased with age [p = 0.04 (rural area), p = 0.06 (urban area)].

CONCLUSION

Urban-rural area differences were observed in some allelic families (MAD20, FC27, 3D7), suggesting a probable impact of urbanization on genetic variability of P. falciparum. This should be taken into account in the implementation of malaria control measures.

Does the drug sensitivity of malaria parasites depend on their virulence?

Background

Chemotherapy can prompt the evolution of classical drug resistance, but selection can also favour other parasite traits that confer a survival advantage in the presence of drugs. The experiments reported here test the hypothesis that sub-optimal drug treatment of malaria parasites might generate survival and transmission advantages for virulent parasites.

Methods

Two Plasmodium chabaudi lines, one derived from the other by serial passage, were used to establish avirulent and virulent infections in mice. After five days, infections were treated with various doses of pyrimethamine administered over 1 or 4 days. Virulence measures (weight and anaemia), parasite and gametocyte dynamics were followed until day 21.

Results

All treatment regimes reduced parasite and gametocyte densities, but infections with the virulent line always produced more parasites and more gametocytes than infections with the avirulent line. Consistent with our hypothesis, drug treatment was disproportionately effective against the less virulent parasites. Treatment did not affect the relative transmission advantage of the virulent line. Neither of the lines contained known mutations conferring classical drug resistance.

Conclusion

Drug-sensitivity of malaria parasites can be virulence-dependent, with virulent parasites more likely to survive sub-optimal treatment. If this proves to be general for a variety of drugs and parasite species, selection imposed by sub-optimal drug treatment could result in the evolution of more aggressive malaria parasites.

Effect of concomitant artesunate administration and cytochrome P4502C8 polymorphisms on the pharmacokinetics of amodiaquine in Ghanaian children with uncomplicated malaria

Artesunate (AS) is used in combination with amodiaquine (AQ) as first-line treatment for uncomplicated malaria in many countries. We investigated the effect of concomitant AS administration on the pharmacokinetics of AQ and compared concentrations of desethylamodiaquine (DEAQ), the main metabolite of AQ, in plasma between patients with different variants of the cytochrome P4502C8 (CYP2C8) gene. A two-compartment model was fitted to 169 plasma DEAQ concentrations from 103 Ghanaian children aged 1 to 14 years with uncomplicated malaria treated either with AQ alone (n = 15) or with AS plus AQ (n = 88). The population clearance of DEAQ appeared to increase nonlinearly with body weight, and the central volume of distribution of DEAQ was higher (P < 0.001) in the AS-plus-AQ group than in the AQ-only group. The maximum plasma DEAQ concentration was higher (P < 0.001), and the population distribution half-life was shorter (P < 0.01), in the AQ-only group than in the AS-plus-AQ group. The total areas under the plasma DEAQ concentration-time curves (P = 0.68) and elimination half-lives (P = 0.39) were similar for the two groups. There was a high frequency (0.179) of the non-wild-type allele of CYP2C8, but no differences between CYP2C8 genotypes with regard to AQ efficacy or safety were evident. The sample size, however, was limited, so monitoring of AQ toxicity in the study area is still indicated. The nonlinear clearance of DEAQ and the wide variability in kinetic parameters have safety implications for weight-based dosing of higher-body-weight children with AQ. The pharmacokinetics of artemisinin combination therapies should be studied in malaria patients, because the rapid parasite clearance caused by the artemisinin may affect the kinetics of the partner drug and the combination.

Sulphadoxine/pyrimethamine versus amodiaquine for treating uncomplicated childhood malaria in Gabon: a randomized trial to guide national policy

BACKGROUND

In Gabon, following the adoption of amodiaquine/artesunate combination (AQ/AS) as first-line treatment of malaria and of sulphadoxine/pyrimethamine (SP) for preventive intermittent treatment of pregnant women, a clinical trial of SP versus AQ was conducted in a sub-urban area. This is the first study carried out in Gabon following the WHO guidelines.

METHODS

A random comparison of the efficacy of AQ (10 mg/kg/day x 3 d) and a single dose of SP (25 mg/kg of sulphadoxine/1.25 mg/kg of pyrimethamine) was performed in children under five years of age, with uncomplicated falciparum malaria, using the 28-day WHO therapeutic efficacy test. In addition, molecular genotyping was performed to distinguish recrudescence from reinfection and to determine the frequency of the dhps K540E mutation, as a molecular marker to predict SP-treatment failure.

RESULTS

The day-28 PCR-adjusted treatment failures for SP and AQ were 11.6% (8/69; 95% IC: 5.5-22.1) and 28.2% (20/71; 95% CI: 17.7-38.7), respectively This indicated that SP was significantly superior to AQ (P = 0.019) in the treatment of uncomplicated childhood malaria and for preventing recurrent infections. Both treatments were safe and well-tolerated, with no serious adverse reactions recorded. The dhps K540E mutation was not found among the 76 parasite isolates tested.

CONCLUSION

The level of AQ-resistance observed in the present study may compromise efficacy and duration of use of the AQ/AS combination, the new first-line malaria treatment. Gabonese policy-makers need to plan country-wide and close surveillance of AQ/AS efficacy to determine whether, and for how long, these new recommendations for the treatment of uncomplicated malaria remain valid.

Efficacy of sulfadoxine-pyrimethamine, amodiaquine, and sulfadoxine-pyrimethamine-amodiaquine combination for the treatment of uncomplicated falciparum malaria in the urban and suburban areas of Brazzaville (Congo)

Congo-Brazzaville has recently adopted artesunate-amodiaquine as the first-line antimalarial drug to replace chloroquine. Before the implementation of this new strategy, we conducted several clinical studies to assess the therapeutic efficacy of former, classical first-line antimalarial drugs in the city of Brazzaville, in which reside about 30% of the Congolese population. From 2003 to 2005, non-randomised trials were conducted to evaluate the efficacy of sulfadoxine-pyrimethamine (SP) (n=97 patients), amodiaquine (AQ) (n=62 patients), and the combination of sulfadoxine-pyrimethamine-amodiaquine (n=54 patients) in children aged between 6 months and 5 years with uncomplicated malaria using the 2003 WHO guidelines during the 28-day follow-up period. After excluding new infections by PCR, the proportion of treatment failure on day 28 was 30.2% (95% confidence interval, 19.2-43.0%) for sulfadoxine-pyrimethamine, 34.8% (95% confidence interval, 21.4-50.2%) for amodiaquine, and 14.2% (95% confidence interval, 5.9-27.2%) for sulfadoxine-pyrimethamine+amodiaquine combination. Treatment with sulfadoxine-pyrimethamine was associated with an increase of gametocyte charge. These results suggest that neither sulfadoxine-pyrimethamine nor amodiaquine is efficacious as monotherapy and that their combination may not remain effective in the coming years. Based on our results, the implementation of artemisinin-based combination therapy appears to be urgent in the country.

Population pharmacokinetics of amodiaquine and desethylamodiaquine in pediatric patients with uncomplicated falciparum malaria

The study aimed to characterize the population pharmacokinetics of amodiaquine (AQ) and its major metabolite N-desethylamodiaquine (N-DEAQ), and to assess the correlation between exposure to N-DEAQ and treatment outcome. Blood samples from children in two studies in Zanzibar and one in Papua New Guinea were included in the pharmacokinetic analysis (n = 86). The children had been treated with AQ in combination with artesunate or sulphadoxine-pyrimethamine. The population pharmacokinetics of AQ and N-DEAQ were modeled using the non-linear mixed effects approach as implemented in NONMEM. Bayesian post-hoc estimates of individual pharmacokinetic parameters were used to generate individual profiles of N-DEAQ exposure. The correlation between N-DEAQ exposure and effect was studied in 212 patients and modeled with logistic regression in NONMEM. The pharmacokinetics of AQ and N-DEAQ were best described by two parallel two-compartment models with a central and a peripheral compartment for each compound. The systemic exposure to AQ was low in comparison to N-DEAQ. The t(1/2 lambda) of N-DEAQ ranged from 3 days to 12 days. There was a statistically significant, yet weak, association between N-DEAQ concentration on day 7 and treatment outcome. The age-based dosing schedule currently recommended in Zanzibar appeared to result in inadequate exposure to N-DEAQ in many patients.

Assessment and continued validation of the malaria SYBR green I-based fluorescence assay for use in malaria drug screening

Several new fluorescence malaria in vitro drug susceptibility microtiter plate assays that detect the presence of malarial DNA in infected erythrocytes have recently been reported, in contrast to traditional isotopic screens that involve radioactive substrate incorporation to measure in vitro malaria growth inhibition. We have assessed and further characterized the malaria SYBR Green I-based fluorescence (MSF) assay for its ability to monitor drug resistance. In order to use the MSF assay as a drug screen, all assay conditions must be thoroughly examined. In this study we expanded upon the capabilities of this assay by including antibiotics and antifolates in the drug panel and testing folic acid-free growth conditions. To do this, we evaluated a more expansive panel of antimalarials in combination with various drug assay culture conditions commonly used in drug sensitivity screening for their activity against Plasmodium falciparum strains D6 and W2. The detection and quantitation limits of the MSF assay were 0.04 to 0.08% and approximately 0.5% parasitemia, respectively. The MSF assay quality was significantly robust, displaying a Z' range of 0.73 to 0.95. The 50% inhibitory concentrations for each drug and culture condition combination were determined by using the MSF assay. Compared to the standard [(3)H]hypoxanthine assay, the MSF assay displayed the expected parasite drug resistance patterns with a high degree of global and phenotypic correlation (r(2) >/= 0.9238), regardless of which culture condition combination was used. In conclusion, the MSF assay allows for reliable one-plate high-throughput, automated malaria in vitro susceptibility testing without the expense, time consumption, and hazard of other screening assays.

Short course of quinine plus a single dose of sulfadoxine/pyrimethamine for Plasmodium falciparum malaria

BACKGROUND

Quinine remains the treatment of choice in hospitalized malaria cases; however, adverse reactions and the long treatment duration of 7 days often hamper its adequate use. Shortening the treatment by adding sulfadoxine/pyrimethamine may enhance compliance and reduce side effects. We aimed to assess the efficacy of a 3-day course of quinine plus a single dose of sulfadoxine/pyrimethamine for the treatment of non-severe hospitalized malaria cases in Lambaréné, Gabon.

METHODS

Fifty children aged between 2 and 7 years received quinine dihydrochloride (12 mg/kg every 12 hours for 72 hours), and then a single dose of oral SP (500 mg/25 mg tablet) was given according to weight category. The children were hospitalized for the duration of the treatment and until two consecutive blood smears were negative for malaria parasites. The follow-up period lasted 28 days.

RESULTS

Parasites were cleared after 66 hours (SD: 15 hours) and the fever after 46 hours (SD: 24 hours). All patients evaluable by day 28 were negative for malaria parasites (100% efficacy rate, 95% CI: 0.92-1). Only two patients out of 49 had gametocytemia on days 7 and 14. There was no adverse event probably or possibly attributable to the study drugs.

CONCLUSIONS

A very high efficacy can be reached using a 3-day course of quinine plus a single dose of sulfadoxine/pyrimethamine for the treatment of non-severe hospitalized malaria cases in our study area.

Induction of cell cycle arrest and apoptosis in JAR trophoblast by antimalarial drugs

Chloroquine, quinine, artemisinin, and pyrimethamine are generally considered safe drugs for treatment of malaria during pregnancy; however, high doses of these drugs are detrimental with adverse outcome of pregnancy. Since antimalarial drugs interaction with placental cells has not been addressed, in this study, we employed a non-radioactive proliferation assay and lactate dehydrogenase (LDH) release assays to investigate the effect of these drugs on JAR trophoblastic cell survival. All drug treatment resulted in inhibition of cell proliferation in a dose-dependent fashion (p < 0.05) with IC50 at 6.96, 6.49, 6.69, and 6.89 microg/mL for chloroquine, quinine, artemisinin and pyrimethamine, respectively. In addition, the inhibition of cell proliferation was accompanied by increased cytotoxicity. Analysis of the progression of the cell cycle showed that these drugs triggered G0/G1 and S phase arrest. Furthermore, these antimalarial drugs induced apoptotic cell death as visualized by DNA fragmentation analysis techniques. Findings in this study revealed that cytotoxicity of these drugs on human placental trophoblast is mediated by both cell cycle arrest and induction of cell death and this could have important implications for the use of antimalarial drugs for treating malaria during pregnancy.

Epidemiology of drug-resistant malaria in Republic of Congo: using molecular evidence for monitoring antimalarial drug resistance combined with assessment of antimalarial drug use

In Congo, urgent efforts are needed to help with the revision of the national antimalarial drug policy. Despite its high resistance level, chloroquine (CQ) is still extensively used as the first-line treatment for uncomplicated Plasmodium falciparum malaria. The study was conducted in children under 5 years with uncomplicated malaria in Pointe-Noire and Brazzaville, the two largest cities that contain approximately 60% of the population of Congo. We investigated by polymerized chain reaction and sequencing methods the frequency distribution of molecular markers for antimalarial drug resistance, including mutations in P. falciparum chloroquine resistance transporter (pfcrt) gene associated with CQ resistance and mutations in dihydrofolate reductase (dhfr) and dihydropteroate synthetase (dhps) genes conferring resistance to sulphadoxine/pyrimethamine (SP) among pre-treatment P. falciparum isolates, as well as assessing antimalarial drug use in the community. pfcrt (K76T) mutation was present in most isolates (96.4%, n = 138) and high frequency (69.2%, n = 133) of triple-mutant dhfr-S108N, N51I, C59R was observed. The quintuple mutant (dhfr-S108N, N51I, C59R and dhps-A437G or S436A, K540E) considered as molecular marker for SP treatment failure was not found because dhps-K540E mutation was absent in isolates tested; this is a clear evidence for the excellent efficacy of SP that we previously described in the same population. The complete absence of the dhps-K540E mutation is a deterrent component for using this molecular marker as an early warning tool for SP resistance testing in that population. Poor compliance issues related to the antimalarial drug use including inappropriate manufacturing practices reported in this study require intensive attention and should be taken into account when implementing drug policy change. If Congo changes its treatment policy from CQ to SP monotherapy, this will not last long. The strategy of combining SP with other affordable and effective antimalarial drugs such as the artemisinin derivatives to improve efficacy and to delay the development of parasite resistance is essential.

The Methylerythritol Phosphate Pathway Is Functionally Active in All Intraerythrocytic Stages of Plasmodium falciparum

Two genes encoding the enzymes 1-deoxy-D-xylulose-5-phosphate synthase and 1-deoxy-D-xylulose-5-phosphate reductoisomerase have been recently identified, suggesting that isoprenoid biosynthesis in Plasmodium falciparum depends on the methylerythritol phosphate (MEP) pathway, and that fosmidomycin could inhibit the activity of 1-deoxy-D-xylulose-5-phosphate reductoisomerase. The metabolite 1-deoxy-D-xylulose-5-phosphate is not only an intermediate of the MEP pathway for the biosynthesis of isopentenyl diphosphate but is also involved in the biosynthesis of thiamin (vitamin B1) and pyridoxal (vitamin B6) in plants and many microorganisms. Herein we report the first isolation and characterization of most downstream intermediates of the MEP pathway in the three intraerythrocytic stages of P. falciparum. These include, 1-deoxy-D-xylulose-5-phosphate, 2-C-methyl-D-erythritol-4-phosphate, 4-(cytidine-5-diphospho)-2-C-methyl-D-erythritol, 4-(cytidine-5-diphospho)-2-C-methyl-D-erythritol-2-phosphate, and 2-C-methyl-D-erythritol-2,4-cyclodiphosphate. These intermediates were purified by HPLC and structurally characterized via biochemical and electrospray mass spectrometric analyses. We have also investigated the effect of fosmidomycin on the biosynthesis of each intermediate of this pathway and isoprenoid biosynthesis (dolichols and ubiquinones). For the first time, therefore, it is demonstrated that the MEP pathway is functionally active in all intraerythrocytic forms of P. falciparum, and de novo biosynthesis of pyridoxal in a protozoan is reported. Its absence in the human host makes both pathways very attractive as potential new targets for antimalarial drug development.

Polymorphism in two merozoite surface proteins of Plasmodium falciparum isolates from Gabon

BACKGROUND

Plasmodium falciparum antigenic diversity and polymorphism confuses the issue of antimalarial vaccine development. Merozoite surface protein (MSP)-1 and -2 are two highly polymorphic vaccine candidates. Characterisation of their precise polymorphism in endemic regions may facilitate the design of an effective vaccine.

METHODS

Isolates obtained in 52 Gabonese children presenting with uncomplicated malaria were genotyped by nested-PCR of msp-1 block 2, and msp-2 block 3, to analyze both parasite population polymorphism and clone fluctuations.

RESULTS

Twenty-five and 19 different alleles were respectively obtained for msp-1 and msp-2 loci, the RO33 family of msp-1 being poorly polymorphic. Four cases of non-random distribution of alleles were reported of the FC27, and/or 3D7 families of msp-2. All but two isolates were composed of more than one genotype, and the multiplicity of infection (MOI) was 4.0. Neither parasite density nor age was related to MOI. Clone fluctuations were studied for ten subjects who were sampled again at reappearance of parasites in blood. Disappearance and reappearance of alleles were observed following treatment, suggesting difficulties in assessing polymorphism and in distinguishing reinfection from recrudescence.

CONCLUSION

P. falciparum polymorphism is extensive in Southeast Gabon, and most of infections are composed of multiple clones. The fluctuation of clones contributes to parasite diversity.