In-vitro susceptibility of Plasmodium falciparum to monodesethylamodiaquine, dihydroartemisinin and quinine in an area of high chloroquine resistance in Rwanda

Dynamic changes in genetic diversity, drug resistance mutations, and treatment outcomes of falciparum malaria from the low-transmission to the pre-elimination phase on the islands of São Tomé and Príncipe

Background

With effective vector control and case management, substantial progress has been made towards eliminating malaria on the islands of São Tomé and Príncipe (STP). This study assessed the dynamic changes in the genetic diversity of Plasmodium falciparum, the anti-malarial drug resistance mutations, and malaria treatment outcomes between 2010 and 2016 to provide insights for the prevention of malaria rebounding.

Methods

Polymorphic regions of merozoite surface proteins 1 and 2 (msp1 and msp2) were sequenced in 118 dried blood spots (DBSs) collected from malaria patients who had visited the Central Hospital in 2010–2016. Mutations in the multi-drug resistance I (pfmdr1), chloroquine resistance transporter (pfcrt), and kelch 13 (pfk13) genes were analysed by polymerase chain reaction-restriction fragment length polymorphism (PCR–RFLP) and sequencing in 111 DBSs. A total of 7482 cases that completed a 28-day follow-up were evaluated for treatment outcomes based on the microscopic results. Regression models were used to characterize factors associated with levels of parasite density and treatment failures.

Results

Parasite strains in STP showed significant changes during and after the peak incidence in 2012. The prevalent allelic type in msp1 changed from K1 to MAD20, and that in msp2 changed from 3D7/IC to FC27. The dominant alleles of drug-resistance markers were pfmdr1 86Y, 184F, D1246, and pfcrt 76 T (Y-F-D-T, 51.4%). The average parasite density in malaria cases declined threefold from low-transmission (2010–2013) to pre-elimination period (2014–2016). Logistic regression models showed that patients with younger age (OR for age = 0.97–0.98, p < 0.001), higher initial parasite density (log₁₀-transformed, OR = 1.44, p < 0.001), and receiving quinine treatment (compared to artemisinin-based combination therapy, OR = 1.91–1.96, p < 0.001) were more likely to experience treatment failures during follow-up.

Conclusions

Plasmodium falciparum in STP had experienced changes in prevalent strains, and increased mutation frequencies in drug-resistance genes from the low-transmission to the pre-elimination settings. Notably, patients with younger age and receiving quinine treatment were more likely to show parasitological treatment failure during follow-up. Therapeutic efficacy should be carefully monitored to inform future treatment policy in STP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-04007-3.

Pharmacotherapy for artemisinin-resistant malaria

INTRODUCTION

Malaria, the most devastating parasitic disease, is currently treated with artemisinin-based combination therapies (ACTs). Unfortunately, some ACTs are unable to rapidly clear Plasmodium falciparum parasites from the blood stream and are failing to cure malaria patients; a problem, so far, largely confined to Southeast Asia. There is a fear of resistant Plasmodium falciparum emerging in other parts of the world including Sub-Saharan Africa. Strategies for alternative treatments, ideally non-artemisinin based, are needed.

AREAS COVERED

This narrative review gives an overview of approved antimalarials and of some compounds in advanced drug development that could be used when an ACT is failing. The selection was based on a literature search in PubMed and WHO notes for malaria treatment.

EXPERT OPINION

The ACT drug class can still cure malaria in malaria endemic regions. However, the appropriate ACT drug should be chosen considering the background resistance of the partner drug of the local parasite population. Artesunate-pyronaridine, the 'newest' recommended ACT, and atovaquone-proguanil are, so far, effective, and safe treatments for uncomplicated falciparum malaria. Therefore, all available ACTs should be safeguarded from parasite resistance and the development of new antimalarial drug classes needs to be accelerated.

In vivo/ex vivo efficacy of artemether-lumefantrine and artesunate-amodiaquine as first-line treatment for uncomplicated falciparum malaria in children: an open label randomized controlled trial in Burkina Faso

BACKGROUND

Artemisinin-based combination therapy (ACT) is recommended to improve malaria treatment efficacy and limit drug-resistant parasites selection in malaria endemic areas. 5 years after they were adopted, the efficacy and safety of artemether-lumefantrine (AL) and artesunate-amodiaquine (ASAQ), the first-line treatments for uncomplicated malaria were assessed in Burkina Faso.

METHODS

In total, 440 children with uncomplicated Plasmodium falciparum malaria were randomized to receive either AL or ASAQ for 3 days and were followed up weekly for 42 days. Blood samples were collected to investigate the ex vivo susceptibility of P. falciparum isolates to lumefantrine, dihydroartemisinin (the active metabolite of artemisinin derivatives) and monodesethylamodiaquine (the active metabolite of amodiaquine). The modified isotopic micro test technique was used to determine the 50% inhibitory concentration (IC50) values. Primary endpoints were the risks of treatment failure at days 42.

RESULTS

Out of the 440 patients enrolled, 420 (95.5%) completed the 42 days follow up. The results showed a significantly higher PCR unadjusted cure rate in ASAQ arm (71.0%) than that in the AL arm (49.8%) on day 42, and this trend was similar after correction by PCR, with ASAQ performing better (98.1%) than AL (91.1%). Overall adverse events incidence was low and not significantly different between the two treatment arms. Ex vivo results showed that 6.4% P. falciparum isolates were resistant to monodesthylamodiaquine. The coupled in vivo/ex vivo analysis showed increased IC50 values for lumefantrine and monodesethylamodiaquine at day of recurrent parasitaemia compared to baseline values while for artesunate, IC50 values remained stable at baseline and after treatment failure (p > 0.05).

CONCLUSION

These findings provide substantial evidence that AL and ASAQ are highly efficacious for the treatment of uncomplicated malaria in children in Burkina Faso. However, the result of P. falciparum susceptibility to the partner drugs advocates the need to regularly replicate such surveillance studies. This would be particularly indicated when amodiaquine is associated in seasonal malaria chemoprophylaxis (SMC) mass drug administration in children under 5 years in Burkina Faso. Trial registration clinicaltrials, NCT00808951. Registered 05 December 2008,https://clinicaltrials.gov/ct2/show/NCT00808951?cond=NCT00808951&rank=1.

Malaria

Malaria is a significant cause of morbidity and mortality throughout the world, and environmental changes are likely to increase its importance in the coming years. Diagnosing this disease is difficult and requires a high index of suspicion, especially in non-endemic countries. Critical care providers play a major role in treating severe malaria and its complications, which has management particularities that might not be readily apparent. Fluid resuscitation should be carefully tailored to avoid complications, and dysperfusion seems more related to degree of parasitemia than hypovolemia. Antimalarial agents are effective, but resistance is growing. Complications can be found in nearly every organ, including cerebral malaria, acute respiratory distress syndrome, and acute kidney injury. As such, a critical care unit is frequently required for organ support when they appear. Superimposed infections are not infrequent. Despite all of this, mortality is encouragingly low with a timely diagnosis and access to appropriate treatment.

Recurrence of Plasmodium falciparum after treatment with quinine and doxycycline in the Amazon basin

OBJECTIVE

To investigate whether the recurrence of infection by Plasmodium falciparum in patients from the Brazilian Amazon was caused by an inadequate exposure to quinine.

METHODS

A retrospective study was carried out using blood samples from patients with slide-confirmed infection by P. falciparum, classified according to the parasitological response after 28 days of follow-up. Quinine and doxycycline were measured in plasma samples by high-performance liquid chromatography. A statistical model was used to estimate parasite clearance rates.

RESULTS

Six of 40 patients who met the criteria for inclusion in the study showed recurrence of parasitaemia within 28 days after the commencement of treatment. A group of six patients with adequate parasitological response was formed to avoid bias when the variables were compared. Parasitaemia at admission was similar in both groups. Plasma quinine concentrations were similar in both groups on days 1, 2 and 3 and ranged from 1.07 to 4.35 μg/ml in cured patients and from 1.1 to 3.2 μg/ml in patients with parasite recurrence. Concentrations of doxycycline were similar in both groups on day 3. The parasite clearance rate constant was 0.131 ± 0.16 h in the cured patients and 0.117 ± 0.02 h in those showing recurrence. The slope half-life in the cured patients was 4.8 h and 5.4 h in recurrence cases. The hillslope of the cured group (14.24) increased sharply compared to the recurrence group (4.13).

CONCLUSION

There is evidence of a decreased in vivo sensitivity to quinine of P. falciparum strains in the Brazilian Amazon basin.

Assessment of anti-plasmodial activity of non-hemolytic, non-immunogenic, non-toxic antimicrobial peptides (AMPs LR14) produced by Lactobacillus plantarum LR/14

BACKGROUND AND OBJECTIVES

Lactobacillus plantarum strains are known to exhibit an antimicrobial property against bacteria and fungi. In the present investigation, AMPs LR14, antimicrobial peptides produced by L. plantarum strain LR/14, were tested against a protozoan system, Plasmodium falciparum and its non-toxic nature was envisaged on a mammalian system.

METHODS

Human erythrocytes infected with chloroquine-sensitive and -resistant strains of P. falciparum were treated with purified AMPs LR14. The loss in cell viability was assessed by monitoring the incorporation of [(3)H]-hypoxanthine in the nucleic acid of the parasite. The hemolytic activity of AMPs LR14 was monitored at different concentrations and the investigations into the in vivo toxicity of AMPs LR14 were carried out on a mammalian system (Wistar rat). The level of toxicity in the tissues was visualized by histopathological studies conducted on the liver and kidney of the test and control rats. A study was also undertaken to see the production of antibodies in an animal (rabbit) after it was immunized with AMPs LR14.

RESULTS

A loss in cell viability was observed in both test strains of P. falciparum. However, the dose required for inhibition of the chloroquine-resistant strain was ~2 times the dose required for the chloroquine-sensitive strain. At these concentrations, no hemolysis of human erythrocytes was observed. The studies conducted on in vivo toxicity of AMPs LR14 suggest that the lethal dose (LD50) is beyond 1,000 mg/kg body weight, suggesting its safe use against microbes and protozoans. Antibodies were also not detected against these peptides, indicating a non-immunogenic nature.

CONCLUSION

The data indicate that AMPs LR14 are non-toxic, potent anti-plasmodial peptides causing growth inhibition of P. falciparum without causing hemolysis. These results pave the way for the development of bioactive peptides as therapeutics.

Ex vivo anti-malarial drugs sensitivity profile of Plasmodium falciparum field isolates from Burkina Faso five years after the national policy change

BACKGROUND

The recent reports on the decreasing susceptibility of Plasmodium falciparum to artemisinin derivatives along the Thailand and Myanmar border are worrying. Indeed it may spread to India and then Africa, repeating the same pattern observed for chloroquine resistance. Therefore, it is essential to start monitoring P. falciparum sensitivity to artemisinin derivatives and its partner drugs in Africa. Efficacy of AL and ASAQ were tested by carrying out an in vivo drug efficacy test, with an ex vivo study against six anti-malarial drugs nested into it. Results of the latter are reported here.

METHODS

Plasmodium falciparum ex-vivo susceptibility to chloroquine (CQ), quinine (Q), lumefantrine (Lum), monodesethylamodiaquine (MDA), piperaquine (PPQ) and dihydroartemisinin (DHA) was investigated in children (6 months - 15 years) with a parasitaemia of at least ≥4,000/μl. The modified isotopic microtest technique was used. The results of cellular proliferation were analysed using ICEstimator software to determine the 50% inhibitory concentration (IC50) values.

RESULTS

DHA was the most potent among the 6 drugs tested, with IC50 values ranging from 0.8 nM to 0.9 nM (Geometric mean IC50 = 0.8 nM; 95% CI [0.8 - 0.9]). High IC50 values ranged between 0.8 nM to 166.1 nM were reported for lumefantrine (Geometric mean IC50 = 25.1 nM; 95% CI [22.4 - 28.2]). MDA and Q IC50s were significantly higher in CQ-resistant than in CQ-sensitive isolates (P = 0.0001). However, the opposite occurred for Lum and DHA (P < 0.001). No difference was observed for PPQ.

CONCLUSION

Artemisinin derivatives are still very efficacious in Burkina Faso and DHA-PPQ seems a valuable alternative ACT. The high lumefantrine IC50 found in this study is worrying as it may indicate a decreasing efficacy of one of the first-line treatments. This should be further investigated and monitored over time with large in vivo and ex vivo studies that will include also plasma drug measurements.

DRUG TARGET PRIORITIZATION IN PLASMODIUM FALCIPARUM THROUGH METABOLIC NETWORK ANALYSIS, AND INHIBITOR DESIGNING USING VIRTUAL SCREENING AND DOCKING APPROACH

The genome sequence of Plasmodium falciparum reveals that many metabolic pathways are unique as compared to its human host. Metabolic Network Analysis was carried out to find the essential enzymes critical for the survival of the pathogen. In the present study, choke point and load point analysis was used to locate putative targets. The identified targets were further checked to confirm that no alternate pathway or human homolog exists. Among the top 15 enzymes obtained from this analysis, we have selected P. falciparum orotidine-5'-monophosphate decarboxylase (PfODCase) enzyme as it is sequentially and structurally different from that of humans, for searching novel inhibitors. A five-point 3D pharmacophore was generated for the crystal structure of PfODCase complexes with uridine-5'-monophosphate (U5P). The binding site environment shows three H-bond acceptors, one H-bond donor and one negative ionizable feature. This pharmacophore model was used as a 3D query to perform virtual screening experiments against 2,664,779 standard lead compounds obtained from the freely available ZINC database. Top 10 hits obtained from virtual screening were selected for molecular docking experiments against PfODCase in order to verify their results and to have a better insight into their binding modes. Here, docking of U5P with PfODCase is used as a control. We have identified six compounds, among them, few are U5P analogs and others are novel ones with diverse scaffolds. The key residues: Lys42, Asp20, Lys72, Ser127, Ala184, Gln185 and Arg203 at the main binding pocket of PfODCase are responsible for better stability of diverse ligands. These compounds according to their free energy of binding could serve as potent leads for designing novel inhibitors against malarial ODCase enzyme.

Artemisinin resistance in rodent malaria--mutation in the AP2 adaptor μ-chain suggests involvement of endocytosis and membrane protein trafficking

BACKGROUND

The control of malaria, caused by Plasmodium falciparum, is hampered by the relentless evolution of drug resistance. Because artemisinin derivatives are now used in the most effective anti-malarial therapy, resistance to artemisinin would be catastrophic. Indeed, studies suggest that artemisinin resistance has already appeared in natural infections. Understanding the mechanisms of resistance would help to prolong the effective lifetime of these drugs. Genetic markers of resistance are therefore required urgently. Previously, a mutation in a de-ubiquitinating enzyme was shown to confer artemisinin resistance in the rodent malaria parasite Plasmodium chabaudi.

METHODS

Here, for a mutant P. chabaudi malaria parasite and its immediate progenitor, the in vivo artemisinin resistance phenotypes and the mutations arising using Illumina whole-genome re-sequencing were compared.

RESULTS

An increased artemisinin resistance phenotype is accompanied by one non-synonymous substitution. The mutated gene encodes the μ-chain of the AP2 adaptor complex, a component of the endocytic machinery. Homology models indicate that the mutated residue interacts with a cargo recognition sequence. In natural infections of the human malaria parasite P. falciparum, 12 polymorphisms (nine SNPs and three indels) were identified in the orthologous gene.

CONCLUSION

An increased artemisinin-resistant phenotype occurs along with a mutation in a functional element of the AP2 adaptor protein complex. This suggests that endocytosis and trafficking of membrane proteins may be involved, generating new insights into possible mechanisms of resistance. The genotypes of this adaptor protein can be evaluated for its role in artemisinin responses in human infections of P. falciparum.

Efficacy of quinine, artemether-lumefantrine and dihydroartemisinin-piperaquine as rescue treatment for uncomplicated malaria in Ugandan children

Background

The treatment of falciparum malaria poses unique challenges in settings where malaria transmission intensity is high because recurrent infections are common. These could be new infections, recrudescences, or a combination of the two. Though several African countries continue to use quinine as the second line treatment for patients with recurrent infections, there is little information on its efficacy when used for rescue therapy. Moreover, such practice goes against the World Health Organisation (WHO) recommendation to use combination therapy for uncomplicated malaria.

Methods

We conducted a nested, randomized, open label, three-arm clinical trial of rescue therapy in children 6–59 months old with recurrent malaria infection during 28 days post treatment with artemisinin combination treatment (ACT). Patients were randomly assigned to receive either quinine, artemether-lumefantrine (AL) or dihydroartemisinin-piperaquine (DHAPQ), and actively followed up for 28 days.

Findings

Among 220 patients enrolled, 217 (98^.6 %) were assigned an efficacy outcome and 218 (99^.1 %) were assessed for safety. The risk of recurrent infection was significantly higher in patients treated with quinine (70 %, 74/110, HR = 3^.9; 95 % CI: 2^.4–6^.7, p<0^.0001) and AL (60%, 21/35, HR = 3^.3; 95 % CI: 1^.8–6^.3, p<0^.0002), compared to DHAPQ (25%, 18/72). Recrudescence tended to be lower in the DHAPQ (1%, 1/72) than in the quinine (7%, 8/110) or AL (6 %, 2/35) group, though it was not statistically significant. No serious adverse events were reported.

Conclusion

Recurrent infections observed after the administration of an ACT can be successfully treated with an alternative ACT rather than with quinine.

Trial Registration

Current Controlled Trials ISRCTN99046537

Anti-plasmodial action of de novo-designed, cationic, lysine-branched, amphipathic, helical peptides

BACKGROUND

A lack of vaccine and rampant drug resistance demands new anti-malarials.

METHODS

In vitro blood stage anti-plasmodial properties of several de novo-designed, chemically synthesized, cationic, amphipathic, helical, antibiotic peptides were examined against Plasmodium falciparum using SYBR Green assay. Mechanistic details of anti-plasmodial action were examined by optical/fluorescence microscopy and FACS analysis.

RESULTS

Unlike the monomeric decapeptides {(Ac-GXRKXHKXWA-NH2) (X = F,ΔF) (Fm, ΔFm IC50 >100 μM)}, the lysine-branched,dimeric versions showed far greater potency {IC50 (μM) Fd 1.5 , ΔFd 1.39}. The more helical and proteolytically stable ΔFd was studied for mechanistic details. ΔFq, a K-K2 dendrimer of ΔFm and (ΔFm)2 a linear dimer of ΔFm showed IC50 (μM) of 0.25 and 2.4 respectively. The healthy/infected red cell selectivity indices were >35 (ΔFd), >20 (ΔFm)2 and 10 (ΔFq). FITC-ΔFd showed rapid and selective accumulation in parasitized red cells. Overlaying DAPI and FITC florescence suggested that ΔFd binds DNA. Trophozoites and schizonts incubated with ΔFd (2.5 μM) egressed anomalously and Band-3 immunostaining revealed them not to be associated with RBC membrane. Prematurely egressed merozoites from peptide-treated cultures were found to be invasion incompetent.

CONCLUSION

Good selectivity (>35), good resistance index (1.1) and low cytotoxicity indicate the promise of ΔFd against malaria.

Quinine, an old anti-malarial drug in a modern world: role in the treatment of malaria

Quinine remains an important anti-malarial drug almost 400 years after its effectiveness was first documented. However, its continued use is challenged by its poor tolerability, poor compliance with complex dosing regimens, and the availability of more efficacious anti-malarial drugs. This article reviews the historical role of quinine, considers its current usage and provides insight into its appropriate future use in the treatment of malaria. In light of recent research findings intravenous artesunate should be the first-line drug for severe malaria, with quinine as an alternative. The role of rectal quinine as pre-referral treatment for severe malaria has not been fully explored, but it remains a promising intervention. In pregnancy, quinine continues to play a critical role in the management of malaria, especially in the first trimester, and it will remain a mainstay of treatment until safer alternatives become available. For uncomplicated malaria, artemisinin-based combination therapy (ACT) offers a better option than quinine though the difficulty of maintaining a steady supply of ACT in resource-limited settings renders the rapid withdrawal of quinine for uncomplicated malaria cases risky. The best approach would be to identify solutions to ACT stock-outs, maintain quinine in case of ACT stock-outs, and evaluate strategies for improving quinine treatment outcomes by combining it with antibiotics. In HIV and TB infected populations, concerns about potential interactions between quinine and antiretroviral and anti-tuberculosis drugs exist, and these will need further research and pharmacovigilance.

Limited ability of Plasmodium falciparum pfcrt, pfmdr1, and pfnhe1 polymorphisms to predict quinine in vitro sensitivity or clinical effectiveness in Uganda

Quinine is a standard drug for treating severe malaria in Africa, and it is also increasingly used to treat uncomplicated disease. However, failures of quinine therapy are common, and it is unknown if failures in Africa are due to drug resistance. Recent studies have identified associations between in vitro quinine sensitivity and polymorphisms in genes encoding putative transporters, including well-described polymorphisms in pfcrt and pfmdr1 and varied numbers of DNNND or DDNHNDNHNND repeats in microsatellite 4760 (ms4760) of the predicted sodium-hydrogen exchanger, pfnhe1. To better characterize mediators of quinine response, we assessed associations between genetic polymorphisms, in vitro quinine sensitivity, and quinine treatment responses in Kampala, Uganda. Among 172 fresh clinical isolates tested in vitro, decreasing sensitivity to quinine was associated with accumulation of pfmdr1 mutations at codons 86, 184, and 1246. Nearly all parasites had pfcrt 76T, preventing analysis of associations with this mutation. pfnhe1 ms4760 was highly polymorphic. Parasites with 2 copies of either ms4760 repeat showed modest decreases in quinine sensitivity compared to those with 1 or ≥3 repeats, but the differences were not statistically significant. None of the above polymorphisms predicted treatment failure among 66 subjects treated with quinine for uncomplicated malaria. Our data suggest that quinine sensitivity is a complex trait and that known polymorphisms in pfcrt, pfmdr1, and pfnhe1, while associated with quinine sensitivity, are not robust markers for quinine resistance.

Experimental evolution, genetic analysis and genome re-sequencing reveal the mutation conferring artemisinin resistance in an isogenic lineage of malaria parasites

Background

Classical and quantitative linkage analyses of genetic crosses have traditionally been used to map genes of interest, such as those conferring chloroquine or quinine resistance in malaria parasites. Next-generation sequencing technologies now present the possibility of determining genome-wide genetic variation at single base-pair resolution. Here, we combine in vivo experimental evolution, a rapid genetic strategy and whole genome re-sequencing to identify the precise genetic basis of artemisinin resistance in a lineage of the rodent malaria parasite, Plasmodium chabaudi. Such genetic markers will further the investigation of resistance and its control in natural infections of the human malaria, P. falciparum.

Results

A lineage of isogenic in vivo drug-selected mutant P. chabaudi parasites was investigated. By measuring the artemisinin responses of these clones, the appearance of an in vivo artemisinin resistance phenotype within the lineage was defined. The underlying genetic locus was mapped to a region of chromosome 2 by Linkage Group Selection in two different genetic crosses. Whole-genome deep coverage short-read re-sequencing (Illumina^® Solexa) defined the point mutations, insertions, deletions and copy-number variations arising in the lineage. Eight point mutations arise within the mutant lineage, only one of which appears on chromosome 2. This missense mutation arises contemporaneously with artemisinin resistance and maps to a gene encoding a de-ubiquitinating enzyme.

Conclusions

This integrated approach facilitates the rapid identification of mutations conferring selectable phenotypes, without prior knowledge of biological and molecular mechanisms. For malaria, this model can identify candidate genes before resistant parasites are commonly observed in natural human malaria populations.

In vitro activities of quinine and other antimalarials and pfnhe polymorphisms in Plasmodium isolates from Kenya

Resistance to the amino alcohol quinine has been associated with polymorphisms in pfnhe, a sodium hydrogen exchanger. We investigated the role of this gene in quinine resistance in vitro in isolates from Kenya. We analyzed pfnhe whole-gene polymorphisms, using capillary sequencing, and pfcrt at codon 76 (pfcrt-76) and pfmdr1 at codon 86 (pfmdr1-86), using PCR-enzyme restriction methodology, in 29 isolates from Kilifi, Kenya, for association with the in vitro activities of quinine and 2 amino alcohols, mefloquine and halofantrine. In vitro activity was assessed as the drug concentration that inhibits 50% of parasite growth (IC50). The median IC50s of quinine, halofantrine, and mefloquine were 92, 22, and 18 nM, respectively. The presence of 2 DNNND repeats in microsatellite ms4760 of pfnhe was associated with reduced susceptibility to quinine (60 versus 227 nM for 1 and 2 repeats, respectively; P<0.05), while 3 repeats were associated with restoration of susceptibility. The decrease in susceptibility conferred by the 2 DNNND repeats was more pronounced in parasites harboring the pfmdr1-86 mutation. No association was found between susceptibility to quinine and the pfcrt-76 mutation or between susceptibility to mefloquine or halofantrine and the pfnhe gene and the pfcrt-76 and pfmdr1-86 mutations. Using previously published data on the in vitro activities of chloroquine, lumefantrine, piperaquine, and dihydroartemisinin, we investigated the association of their activities with pfnhe polymorphism. With the exception of a modulation of the activity of lumefantrine by a mutation at position 1437, pfnhe did not modulate their activities. Two DNNND repeats combined with the pfmdr1-86 mutation could be used as an indicator of reduced susceptibility to quinine.

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.

Effectiveness of quinine versus artemether-lumefantrine for treating uncomplicated falciparum malaria in Ugandan children: randomised trial

OBJECTIVE

To compare the effectiveness of oral quinine with that of artemether-lumefantrine in treating uncomplicated malaria in children.

DESIGN

Randomised, open label effectiveness study.

SETTING

Outpatient clinic of Uganda's national referral hospital in Kampala.

PARTICIPANTS

175 children aged 6 to 59 months with uncomplicated malaria.

INTERVENTIONS

Participants were randomised to receive oral quinine or artemether-lumefantrine administered by care givers at home.

MAIN OUTCOME MEASURES

Primary outcomes were parasitological cure rates after 28 days of follow-up unadjusted and adjusted by genotyping to distinguish recrudescence from new infections. Secondary outcomes were adherence to study drug, presence of gametocytes, recovery of haemoglobin concentration from baseline at day 28, and safety profiles.

RESULTS

Using survival analysis the cure rate unadjusted by genotyping was 96% for the artemether-lumefantrine group compared with 64% for the quinine group (hazard ratio 10.7, 95% confidence interval 3.3 to 35.5, P=0.001). In the quinine group 69% (18/26) of parasitological failures were due to recrudescence compared with none in the artemether-lumefantrine group. The mean adherence to artemether-lumefantrine was 94.5% compared with 85.4% to quinine (P=0.0008). Having adherence levels of 80% or more was associated with a decreased risk of treatment failure (0.44, 0.19 to 1.02, P=0.06). Adverse events did not differ between the two groups.

CONCLUSIONS

The effectiveness of a seven day course of quinine for the treatment of uncomplicated malaria in Ugandan children was significantly lower than that of artemether-lumefantrine. These findings question the advisability of the recommendation for quinine therapy for uncomplicated malaria in Africa.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00540202.

In silico comparative genome analysis of malaria parasite Plasmodium falciparum and Plasmodium vivax chromosome 4

Malarial parasite has long been a subject of research for a large community of scientists and has yet to be conquered. One of the main obstacles to effectively control this disease is rapidly evolving genetic structure of Plasmodium parasite itself. In this study, we focused on chromosome 4 of the Plasmodium falciparum and Plasmodium vivax species and carried out comparative studies of genes that are responsible for antigenic variation in respective species. Comparative analysis of genes responsible for antigenic variation (var and vir genes in P. falciparum and P. vivax, respectively) showed significant difference in their respective nucleotide sequence lengths as well as amino acid composition. The possible association of exon's length on pathogenecity of respective Plasmodium species was also investigated, and analysis of gene structure showed that on the whole, exon lengths in P. falciparum are larger compared to P. vivax. Analysis of tandem repeats across the genome has shown that the size of repetitive sequences has a direct effect on chromosomes length, which can also be a potential reason for P. falciparum's greater variability and hence pathogenecity than P. vivax.

Failure to detect Plasmodium vivax in West and Central Africa by PCR species typing

Background

Plasmodium vivax is estimated to affect 75 million people annually. It is reportedly absent, however, from west and central Africa due to the high prevalence of the Duffy negative phenotype in the indigenous populations. Despite this, non-African travellers consistently return to their own countries with P. vivax malaria after visiting this region. An attempt was made, therefore, to detect the presence of P. vivax parasites in blood samples collected from the indigenous populations of west and central Africa.

Methods

Parasite species typing (for all four human malaria parasites) was carried out by PCR on 2,588 blood samples collected from individuals from nine African malaria-endemic countries.

Results

Most infections (98.5%) were Plasmodium falciparum, Plasmodium malariae was identified in 8.5% of all infections, and Plasmodium ovale in 3.9%. The prevalence of both parasites varied greatly by country. Only one case of P. vivax was detected from Sao Tome, an island off the west coast of Africa, confirming the scarcity of this parasite in Africa.

Conclusion

The prevalence of P. vivax in local populations in sub-Saharan Africa is very low, despite the frequent identification of this parasite in non-African travellers.

Studies on antimalarial drug susceptibility in Colombia, in relation to Pfmdr1 and Pfcrt

In Colombia, Plasmodium resistance to antimalarials such as chloroquine and antifolates is a serious problem. As a result, the national Colombian health authorities are monitoring the efficacy of alternative drugs and schemes. The study of genetic polymorphisms related with drug resistance is required in the region. In vitro responses to chloroquine, quinine, mefloquine, amodiaquine, desethylamodiaquine, artesunate and dihydroartesunate were carried out by HRP ELISA. SNP analysis in Pfcrt and Pfmdr1 genes was performed by PCR-RFLP in 77 samples from the North West region of Colombia. In vitro resistance to chloroquine was high (74%), followed by mefloquine (30%) and desethylamodiaquine (30%). A positive correlation between the IC(50) of paired drugs was also detected. The allele Pfmdr1 N86 (wild) was present in 100% of the samples and 1246Y (mutant) in 92%. However, their presence did not correlate with in vitro drug resistance. Presence of the mutations K76T and N75E in Pfcrt was confirmed in all samples. Analysis of 4 codons (72, 74, 75 and 76) in pfcrt confirmed the presence of the haplotypes CMET in 91% and SMET in 9% of the samples.

Chloroquine-resistance molecular markers (Pfcrt T76 and Pfmdr-1 Y86) and amodiaquine resistance in Burkina Faso

We investigated the relationship between the two main molecular markers for chloroquine resistance (Pfcrt T76 and Pfmdr-1 Y86) and the clinical efficacy of amodiaquine in Burkina Faso. Before treatment, the prevalence of Pfcrt T76, Pfmdr-1 Y86 or both mutations in the same infection was significantly higher in patients who experienced a recrudescence than in those who successfully responded to the treatment. Therefore, these two molecular markers could be useful in monitoring amodiaquine resistance, particularly in countries where this drug is used in combination with artesunate as first- or second-line treatment.

Artesunate–amodiaquine for the treatment of uncomplicated malaria

Without an effective vaccine for the prevention of malaria, a fundamental component of the strategy for the control of this disease is based on prompt and effective treatment. Due to the high resistance level of Plasmodium falciparum to the most affordable drugs such as chloroquine and sulfadoxine-pyrimethamine, artemisinin-based combination therapies are presently used in many countries or are being developed for registration. One artemisinin combination therapy that is drawing a certain degree of interest is the combination of artesunate (a short half-life drug) plus amodiaquine (a long half-life drug that is presently used in loose combination in many countries). The short half-life drug achieves substantial and rapid parasite killing, while a high concentration of the long half-life drug kills off the remaining malaria parasites. In addition to the effectiveness of 3 days of treatment (rapid clearance of fever and malaria parasites) in western and central Africa, where resistance to amodiaquine is low, the combination of artesunate plus amodiaquine may delay or prevent the emergence of resistance to both drugs. An important step is the recent registration in Morocco (the country where the drug is manufactured) of a fixed combination of artesunate plus amodiaquine by the Drugs for Neglected Diseases initiative with sanofi-aventis as the industrial partner. A prequalification dossier of this fixed combination has been submitted to the WHO. This new co-formulation will almost certainly increase its effectiveness by improving drug compliance.

In vitro assessment of artesunate, artemether and amodiaquine susceptibility and molecular analysis of putative resistance-associated mutations of Plasmodium falciparum from São Tomé and Príncipe

OBJECTIVE

To evaluate the basal in vitro responses of Plasmodium falciparum isolates collected in The Democratic Republic of São Tomé and Príncipe to artemether (ATH), artesunate (ATN) and amodiaquine (AMQ).

METHODS

The prevalence of given single nucleotide polymorphisms in the pfmdr1, pfcrt, pftctp and pfATPase6 genes was assessed by PCR-RFLP or DNA sequencing, and gene copy numbers were estimated by real-time PCR.

RESULTS

Mean IC50s to ATH and ATN were relatively low (1.12 nm and 0.58 nm, respectively). However, 10% of parasites displayed AMQ IC50 values above the accepted resistance threshold of 60 nm and there was a positive association between susceptibility to all three drugs (ATH vs. ATN: R = 0.84; ATH vs. AMQ: R = 0.68; ATN vs. AMQ: R = 0.72). Mutations in the pfcrt and pfmdr1 genes were highly prevalent, while only one synonymous polymorphism was detected in the pfATPase6 gene and no mutations were found in pftctp. All isolates harboured a single copy of the genes studied.

CONCLUSIONS

Artemisinin combination treatment in the São Tomé and Príncipe should be efficacious, although a significant number of AMQ-resistant parasites were detected and the susceptibility to each drug was positively associated with that of the other two. Mutations in the pfcrt and pfmdr1 genes are near fixation, most likely because of high levels of chloroquine resistance, whereas only one protein type of the artemisinin resistance candidate, PfATPase6, was identified.