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

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.

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.

Characterization of Plasmodium infections among inhabitants of rural areas in Gabon

Plasmodium infections in endemic areas are often asymptomatic, can be caused by different species and contribute significantly to transmission. We performed a cross-sectional study in February/March 2016 including 840 individuals ≥ 1 year living in rural Gabon (Ngounié and Moyen-Ogooué). Plasmodium parasitemia was measured by high-sensitive, real-time quantitative PCR. In a randomly chosen subset of P. falciparum infections, gametocyte carriage and prevalence of chloroquine-resistant genotypes were analysed. 618/834 (74%) individuals were positive for Plasmodium 18S-rRNA gene amplification, of these 553 (66.3%) carried P. falciparum, 193 (23%) P. malariae, 74 (8.9%) P. ovale curtisi and 38 (4.6%) P.ovale wallikeri. Non-falciparum infections mostly presented as mixed infections. P. malariae monoinfected individuals were significantly older (median age: 60 years) than coinfected (20 years) or P. falciparum monoinfected individuals (23 years). P. falciparum gametocyte carriage was confirmed in 109/223 (48.9%) individuals, prevalence of chloroquine-resistant genotypes was high (298/336, 89%), including four infections with a new SVMNK genotype. In rural Gabon, Plasmodium infections with all endemic species are frequent, emphasizing that malaria control efforts shall cover asymptomatic infections also including non-falciparum infections when aiming for eradication.

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.

Increased Prevalence of Mutant Allele Pfdhps 437G and Pfdhfr Triple Mutation in Plasmodium falciparum Isolates from a Rural Area of Gabon, Three Years after the Change of Malaria Treatment Policy

In Gabon, sulfadoxine-pyrimethamine (SP) is recommended for intermittent preventive treatment during pregnancy (IPTp-SP) and for uncomplicated malaria treatment through ACTs drug. P. falciparum strains resistant to SP are frequent in areas where this drug is highly used and is associated with the occurrence of mutations on Plasmodium falciparum dihydrofolate reductase (Pfdhfr) and dihydropteroate synthetase (Pfdhps) genes. The aim of the study was to compare the proportion of mutations on Pfdhfr and Pfdhps genes in isolates collected at Oyem in northern Gabon, in 2005 at the time of IPTp-SP introduction and three years later. Point mutations were analyzed by nested PCR-RFLP method. Among 91 isolates, more than 90% carried Pfdhfr 108N and Pfdhfr 59R alleles. Frequencies of Pfdhfr 51I (98%) and Pfdhps 437G (67.7%) mutant alleles were higher in 2008. Mutations at codons 164, 540, and 581 were not detected. The proportion of the triple Pfdhfr mutation and quadruple mutation including A437G was high: 91.9% in 2008 and 64.8% in 2008, respectively. The present study highlights an elevated frequency of Pfdhfr and Pfdhps mutant alleles, although quintuple mutations were not found in north Gabon. These data suggest the need of a continuous monitoring of SP resistance in Gabon.

Policy analysis for deciding on a malaria vaccine RTS,S in Tanzania

Background

Traditionally, it has taken decades to introduce new interventions in low-income countries. Several factors account for these delays, one of which is the absence of a framework to facilitate comprehensive understanding of policy process to inform policy makers and stimulate the decision-making process. In the case of the proposed introduction of malaria vaccines in Tanzania, a specific framework for decision-making will speed up the administrative process and shorten the time until the vaccine is made available to the target population.

Methods

Qualitative research was used as a basis for developing the Policy Framework. Interviews were conducted with government officials, bilateral and multilateral partners and other stakeholders in Tanzania to assess malaria treatment policy changes and to draw lessons for malaria vaccine adoption.

Results

The decision-making process for adopting malaria interventions and new vaccines in general takes years, involving several processes: meetings and presentations of scientific data from different studies with consistent results, packaging and disseminating evidence and getting approval for use by the Ministry of Health and Social Welfare (MOHSW). It is influenced by contextual factors; Promoting factors include; epidemiological and intervention characteristics, country experiences of malaria treatment policy change, presentation and dissemination of evidence, coordination and harmonization of the process, use of international scientific evidence. Barriers factors includes; financial sustainability, competing health and other priorities, political will and bureaucratic procedures, costs related to the adoption and implementations of interventions, supply and distribution and professional compliance with anti-malarial drugs.

Conclusion

The framework facilitates the synthesis of information in a coherent way, enabling a clearer understanding of the policy process, thereby speeding up the policy decision-making process and shortening the time for a malaria vaccine to become available.

No evidence of decline in malaria burden from 2006 to 2013 in a rural Province of Gabon: implications for public health policy

Background

The morbidity of malaria has steady declined in the urban regions of Gabon between 2000 and 2008, but caution should be exercised before generalizing this trend to the whole country because this finding has not been systematically confirmed in remote rural provinces.

Methods

We conducted a retrospective survey using data on malaria cases recorded in North Eastern Gabon between 2006 and 2013 at health facilities in Makokou. Malaria data were analyzed, and associations with annual variations and patient age were assessed.

Results

A global increase in clinical and confirmed malaria cases was observed over the study period. The rate of infection was significantly higher in children aged between 0 to 4 years than in children of 5 years and above, and in adults. Contrary to prior observations in urban and semi-urban areas of Gabon, malaria burden remained mostly unchanged or even increased in Makokou in the Ogooué-Ivindo province during these last 8 years.

Conclusions

The persistence of Plasmodium falciparum pockets of sustained malaria transmission in rural Gabon may be related to an inadequate coverage of key interventions, to poor treatment seeking behavior and/or to a decline efficacy of treatments. Our results highlight the need to better adapt malaria control strategies to local epidemiological contexts and to environmental constraints. Equitable delivery of health service to hard-to-reach populations constitutes a challenging issue for the health authorities of Gabon.

Electronic supplementary material

The online version of this article (doi:10.1186/s12889-015-1456-4) contains supplementary material, which is available to authorized users.

Effect of fluorescent dyes on in vitro-differentiated, late-stage Plasmodium falciparum gametocytes

Plasmodium falciparum gametocytes are not associated with clinical symptoms, but they are responsible for transmitting the pathogen to mosquitoes. Therefore, gametocytocidal interventions are important for malaria control and resistance containment. Currently available drugs and vaccines are not well suited for that purpose. Several dyes have potent antimicrobial activity, but their use against gametocytes has not been investigated systematically. The gametocytocidal activity of nine synthetic dyes and four control compounds was tested against stage V gametocytes of the laboratory strain 3D7 and three clinical isolates of P. falciparum with a bioluminescence assay. Five of the fluorescent dyes had submicromolar 50% inhibitory concentration (IC50) values against mature gametocytes. Three mitochondrial dyes, MitoRed, dihexyloxacarbocyanine iodide (DiOC6), and rhodamine B, were highly active (IC(50)s < 200 nM). MitoRed showed the highest activity against gametocytes, with IC(50)s of 70 nM against 3D7 and 120 to 210 nM against clinical isolates. All compounds were more active against the laboratory strain 3D7 than against clinical isolates. In particular, the endoperoxides artesunate and dihydroartemisinin showed a 10-fold higher activity against 3D7 than against clinical isolates. In contrast to all clinically used antimalarials, several fluorescent dyes had surprisingly high in vitro activity against late-stage gametocytes. Since they also act against asexual blood stages, they shall be considered starting points for the development of new antimalarial lead compounds.

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.

Submicroscopic infections among children with adequate clinical and parasitological response (ACPR)

The aim of the study was to re-assess the treatment outcomes of Gabonese children, treated with sulfadoxine-pyrimethamine (SP) and artesunate-mefloquine (AM) and categorized by microscopy as adequate clinical and parasitological response (ACPR), using polymerase chain reaction (PCR). Dried blood spots were collected at day 0 and day 28 and stevor gene amplification was performed to detect Plasmodium falciparum infections. Plasmodial DNA was found in 27.5% (n=19/69) of the isolates collected at day 28; this proportion was 34.3% (n=12/35) in the SP group and 20.6% (n=7/34) in the AM group. This study underlines the need of an accurate and more appropriate technique such as PCR to evaluate antimalarial drug efficacy during clinical trials.

A simple Chelex protocol for DNA extraction from Anopheles spp

Endemic countries are increasingly adopting molecular tools for efficient typing, identification and surveillance against malaria parasites and vector mosquitoes, as an integral part of their control programs^1,2,3,4,5. For sustainable establishment of these accurate approaches in operations research to strengthen malaria control and elimination efforts, simple and affordable methods, with parsimonious reagent and equipment requirements are essential^6,7,8. Here we present a simple Chelex-based technique for extracting malaria parasite and vector DNA from field collected mosquito specimens.

We morphologically identified 72 Anopheles gambiae sl. from 156 mosquitoes captured by pyrethrum spray catches in sleeping rooms of households within a 2,000 km² vicinity of the Malaria Institute at Macha. After dissection to separate the head and thorax from the abdomen for all 72 Anopheles gambiae sl. mosquitoes, the two sections were individually placed in 1.5 ml microcentrifuge tubes and submerged in 20 μl of deionized water. Using a sterile pipette tip, each mosquito section was separately homogenized to a uniform suspension in the deionized water. Of the ensuing homogenate from each mosquito section, 10 μl was retained while the other 10 μl was transferred to a separate autoclaved 1.5 ml tube. The separate aliquots were subjected to DNA extraction by either the simplified Chelex or the standard salting out extraction protocol^9,10. The salting out protocol is so-called and widely used because it employs high salt concentrations in lieu of hazardous organic solvents (such as phenol and chloroform) for the protein precipitation step during DNA extraction⁹.

Extracts were used as templates for PCR amplification using primers targeting arthropod mitochondrial nicotinamide adenine dinucleotide dehydrogenase (NADH) subunit 4 gene (ND4) to check DNA quality¹¹, a PCR for identification of Anopheles gambiae sibling species¹⁰ and a nested PCR for typing of Plasmodium falciparum infection¹². Comparison using DNA quality (ND4) PCR showed 93% sensitivity and 82% specificity for the Chelex approach relative to the established salting out protocol. Corresponding values of sensitivity and specificity were 100% and 78%, respectively, using sibling species identification PCR and 92% and 80%, respectively for P. falciparum detection PCR. There were no significant differences in proportion of samples giving amplicon signal with the Chelex or the regular salting out protocol across all three PCR applications. The Chelex approach required three simple reagents and 37 min to complete, while the salting out protocol entailed 10 different reagents and 2 hr and 47 min' processing time, including an overnight step. Our results show that the Chelex method is comparable to the existing salting out extraction and can be substituted as a simple and sustainable approach in resource-limited settings where a constant reagent supply chain is often difficult to maintain.

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.

Intermittent preventive treatment for malaria in children living in areas with seasonal transmission

BACKGROUND

In malaria endemic areas, pre-school children are at high risk of severe and repeated malaria illness. One possible public health strategy, known as Intermittent Preventive Treatment in children (IPTc), is to treat all children for malaria at regular intervals during the transmission season, regardless of whether they are infected or not.

OBJECTIVES

To evaluate the effects of IPTc to prevent malaria in preschool children living in endemic areas with seasonal malaria transmission.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group Specialized Register (July 2011), CENTRAL (The Cochrane Library 2011, Issue 6), MEDLINE (1966 to July 2011), EMBASE (1974 to July 2011), LILACS (1982 to July 2011), mRCT (July 2011), and reference lists of identified trials. We also contacted researchers working in the field for unpublished and ongoing trials.

SELECTION CRITERIA

Individually randomized and cluster-randomized controlled trials of full therapeutic dose of antimalarial or antimalarial drug combinations given at regular intervals compared with placebo or no preventive treatment in children aged six years or less living in an area with seasonal malaria transmission.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed eligibility, extracted data and assessed the risk of bias in the trials. Data were meta-analysed and measures of effects (ie rate ratio, risk ratio and mean difference) are presented with 95% confidence intervals (CIs). The quality of evidence was assessed using the GRADE methods.

MAIN RESULTS

Seven trials (12,589 participants), including one cluster-randomized trial, met the inclusion criteria. All were conducted in West Africa, and six of seven trials were restricted to children aged less than 5 years.IPTc prevents approximately three quarters of all clinical malaria episodes (rate ratio 0.26; 95% CI 0.17 to 0.38; 9321 participants, six trials, high quality evidence), and a similar proportion of severe malaria episodes (rate ratio 0.27, 95% CI 0.10 to 0.76; 5964 participants, two trials, high quality evidence). These effects remain present even where insecticide treated net (ITN) usage is high (two trials, 5964 participants, high quality evidence).IPTc probably produces a small reduction in all-cause mortality consistent with the effect on severe malaria, but the trials were underpowered to reach statistical significance (risk ratio 0.66, 95% CI 0.31 to 1.39, moderate quality evidence).The effect on anaemia varied between studies, but the risk of moderately severe anaemia is probably lower with IPTc (risk ratio 0.71, 95% CI 0.52 to 0.98; 8805 participants, five trials, moderate quality evidence).Serious drug-related adverse events, if they occur, are probably rare, with none reported in the six trials (9533 participants, six trials, moderate quality evidence). Amodiaquine plus sulphadoxine-pyrimethamine is the most studied drug combination for seasonal chemoprevention. Although effective, it causes increased vomiting in this age-group (risk ratio 2.78, 95% CI 2.31 to 3.35; two trials, 3544 participants, high quality evidence).When antimalarial IPTc was stopped, no rebound increase in malaria was observed in the three trials which continued follow-up for one season after IPTc.

AUTHORS' CONCLUSIONS

In areas with seasonal malaria transmission, giving antimalarial drugs to preschool children (age < 6 years) as IPTc during the malaria transmission season markedly reduces episodes of clinical malaria, including severe malaria. This benefit occurs even in areas where insecticide treated net usage is high.

High prevalence of dhfr triple mutant and correlation with high rates of sulphadoxine-pyrimethamine treatment failures in vivo in Gabonese children

Background

Drug resistance contributes to the global malaria burden. Plasmodium falciparum dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) polymorphisms confer resistance to sulphadoxine-pyrimethamine (SP).

Methods

The study assessed the frequency of SP resistance-conferring polymorphisms in Plasmodium falciparum-positive samples from two clinical studies in Lambaréné. Their role on treatment responses and transmission potential was studied in an efficacy open-label clinical trial with a 28-day follow-up in 29 children under five with uncomplicated malaria.

Results

SP was well tolerated by all subjects in vivo. Three subjects were excluded from per-protocol analysis. PCR-corrected, 12/26 (46%) achieved an adequate clinical and parasitological response, 13/26 (50%) were late parasitological failures, while 1/26 (4%) had an early treatment failure, resulting in early trial discontinuation. Of 106 isolates, 98 (92%) carried the triple mutant dhfr haplotype. Three point mutations were found in dhps in a variety of haplotypic configurations. The 437G + 540E double mutant allele was found for the first time in Gabon.

Conclusions

There is a high prevalence of dhfr triple mutant with some dhps point mutations in Gabon, in line with treatment failures observed, and molecular markers of SP resistance should be closely monitored.

Trial Registration

ClinicalTrials.gov: NCT00453856

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.

Burden of malaria during pregnancy at the time of IPTp/SP implementation in Gabon

The new recommendations to prevent malaria in pregnant women have recently been implemented in Gabon. There is little information on the pregnancy indicators that are useful for their evaluation. A cross-sectional study for the assessment of the prevalence of peripheral, placental, and cord malaria and anemia among delivering women was performed at the largest public hospital of Gabon. Malaria prevalence was 34.4%, 53.6%, and 18.2% for maternal peripheral, placental, and cord blood respectively, with no difference between primigravidae and multigravidae. Submicroscopic infections were frequent and concerned all the positive cord samples. Maternal peripheral, late placental, and cord infections were all associated with a reduced mean birth weight in primigravidae (P = 0.02). Anemia prevalence was 53%, low birth rate was 13%, and prematurity was 25%. The use of intermittent preventive treatment with sulfadoxine-pyrimethamine (greater than or equal to one dose) combined with bed net was associated with a reduction in infection only in multigravidae and with a reduced risk of maternal anemia.

High prevalence of sulfadoxine/pyrimethamine-resistant alleles of Plasmodium falciparum isolates in pregnant women at the time of introduction of intermittent preventive treatment with sulfadoxine/pyrimethamine in Gabon

OBJECTIVES

The frequency of dhfr and dhps point mutations was assessed in Plasmodium falciparum isolates from pregnant women in Libreville.

METHODS

PCR-restriction fragment length polymorphism of polymorphic codons of the dhfr gene (51, 59 and 108) and the dhps gene (436, 437 and 540) was performed in matched peripheral and placental blood samples.

RESULTS

The proportion of multiple mutations was high (98%), and was not different between women with and without a history of intermittent preventive treatment with sulfadoxine/pyrimethamine (IPTp/SP). The prevalence of triple dhfr mutation was 80%, and that of quadruple and quintuple mutations was 53% and 22%, respectively. The Glu540 mutation was present in two isolates. The concordance of resistant alleles in matched peripheral and placental isolates was >90% for both genes.

CONCLUSIONS

These findings underline the need for a regular assessment of the relationship between the presence of resistant isolates and in vitro/in vivo IPTp/SP efficacy, and evaluation of an alternative drug.

Selection of parasites with diminished drug susceptibility by amodiaquine-containing antimalarial regimens in Uganda

BACKGROUND

Amodiaquine (AQ) is paired with artesunate (AS) or sulfadoxine-pyrimethamine (SP) in recommended antimalarial regimens. It is unclear how readily AQ resistance will be selected with combination chemotherapy.

METHODS

We collected 61 Plasmodium falciparum samples from a cohort of Ugandan children randomized for treatment with AQ-SP, AS-AQ, or artemether-lumefantrine (AL) for uncomplicated malaria. In vitro susceptibility to monodesethylamodiaquine (MDAQ) was measured with a histidine-rich protein 2-based enzyme-linked immunosorbent assay, and potential resistance-mediating polymorphisms in pfmdr1 were evaluated.

RESULTS

Parasites collected from patients treated with AQ-SP or AS-AQ within the prior 12 weeks were less susceptible to MDAQ (n = 18; mean of the median inhibitory concentration [IC(50)], 62.9 nmol/L; range, 12.7-158.3 nmol/L) than were parasites from those not treated within 12 weeks (n = 43; mean IC(50), 37.5 nmol/L; range, 6.3-184.7 nmol/L; P=.009) or only from those patients in the treatment arm that did not receive AQ (n = 12; mean IC(50), 28.8 nmol/L; range, 6.3-121.8 nmol/L; P = .004). The proportion of strains with polymorphisms expected to mediate diminished response to AQ (pfmdr1 86Y and 1246Y) increased after AQ therapy, although differences were not statistically significant.

CONCLUSIONS

Prior therapy selected for diminished response to MDAQ, which suggests that AQ-containing regimens may rapidly lose efficacy in Africa. The mechanism of diminished MDAQ response is not fully explained by known mutations in pfmdr1.

Evaluation of rapid diagnostic tests for malaria case management in Gabon

A laboratory-confirmed diagnosis is the basis of malaria case management. Rapid diagnostic tests (RDTs) create new opportunities for improved care in endemic areas. Diagnostic performance of OptiMAL-IT and Acon was assessed in comparison with microscopy at 2 sites in Gabon. Between February 2008 and January 2009, 2125 febrile children under 11 years old were diagnosed using microscopy and RDTs. Plasmodial infection was detected more frequently using Acon (27%) and OptiMAL-IT (27%) compared to microscopy (20%) (P < 0.01). Among the samples diagnosed positive by OptiMAL-IT, 78% were infected by Plasmodium falciparum, whereas 99% of positive blood smears were P. falciparum infections, 0.5% Plasmodium malariae, and 0.5% Plasmodium ovale. Both RDTs had similar sensitivity (Se) (94.0%; 95% confidence interval [CI], 92-96), which varied depending on the site. When parasite density was >100 p/microL, the Se of the 2 tests was >98% (95% CI, 96-100). Likewise, the negative predictive values were high and comparable (>98%). Overtreatment with antimalarial drugs was 12%. These tests should be considered as a good alternative to microscopy, allowing not only an efficient and rapid diagnosis of malaria in primary health facilities but also to aid in promoting changes for antimalarial prescription behavior.