Malaria: current status of control, diagnosis, treatment, and a proposed agenda for research and development

Development of a highly sensitive genus-specific quantitative reverse transcriptase real-time PCR assay for detection and quantitation of plasmodium by amplifying RNA and DNA of the 18S rRNA genes

A highly sensitive genus-specific quantitative reverse transcriptase real-time PCR (qRT-PCR) assay for detection of Plasmodium has been developed. The assay amplifies total nucleic acids (RNA and DNA) of the 18S rRNA genes with a limit of detection of 0.002 parasite/μl using cultured synchronized ring stage 3D7 parasites. Parasite densities as low as 0.000362 parasite/μl were detected when analyzing clinical samples. Analysis of clinical samples showed that detection of 18S rRNA genes from total nucleic acids increased the analytical sensitivity of the assay by more than 1 log unit compared to DNA only. When clinical samples with no parasites present by microscopy were analyzed by qRT-PCR, 90% (117 of 130) were positive for the presence of Plasmodium nucleic acids. Quantification of clinical samples by qRT-PCR using total nucleic acid versus DNA was compared to microscopy. There was a significantly greater correlation of parasite density to microscopy when DNA alone was used than with total nucleic acid. We conclude that analysis of total nucleic acids by qRT-PCR is a suitable assay for detection of low parasite levels in patients with early-stage malaria and/or submicroscopic infections and could greatly benefit malaria diagnosis, intervention trials, and malaria control and elimination efforts.

Best practices for an insecticide-treated bed net distribution programme in sub-Saharan eastern Africa

Insecticide-treated bed nets are the preeminent malaria control means; though there is no consensus as to a best practice for large-scale insecticide-treated bed net distribution. In order to determine the paramount distribution method, this review assessed literature on recent insecticide treated bed net distribution programmes throughout sub-Saharan Eastern Africa. Inclusion criteria were that the study had taken place in sub-Saharan Eastern Africa, targeted malaria prevention and control, and occurred between 1996 and 2007. Forty-two studies were identified and reviewed. The results indicate that distribution frameworks varied greatly; and consequently so did outcomes of insecticide-treated bed net use. Studies revealed consistent inequities between urban and rural populations; which were most effectively alleviated through a free insecticide-treated bed net delivery and distribution framework. However, cost sharing through subsidies was shown to increase programme sustainability, which may lead to more long-term coverage. Thus, distribution should employ a catch up/keep up programme strategy. The catch-up programme rapidly scales up coverage, while the keep-up programme maintains coverage levels. Future directions for malaria should include progress toward distribution of long-lasting insecticide-treated nets.

The substrate binding preferences of Plasmodium thymidylate kinase

Plasmodium falciparum thymidylate kinase (PfTMK) is a potential chemotherapeutic target as it can tolerate a range of substrates, which distinguishes it from other thymidylate kinases. An important step in drug development is to determine the interaction of ligands competing for their target sites in a proposed drug target. The estimated binding affinity of thymidylate (TMP) with PfTMK/deoxyguanylate complex was as low as 0.9×10(4) M(-1) with a very low exothermic signal of -3.9 kcal mol(-1). Furthermore, titration of PfTMK/TMP with deoxyguanylate (dGMP) showed a very small heat signal corresponding to nonspecific background heat. Titration of PfTMK with a 1:1 mixture of TMP and dGMP showed a binding affinity corresponding to the average of the binding affinity for individual reactions. Thus, dGMP was unable to displace TMP from its binding site, while TMP was able to partially displace dGMP from the its binding site accompanied by a weak exothermic signal and lowered affinity. Based on these results, we propose that pyrimidine based inhibitors will compete with TMP and may be able to more efficiently displace dGMP from binding sites compared with purine based compounds. In addition, the synthesis of purine based compounds as inhibitors of PfTMK will be highly selective for the parasitic enzyme, however, they need to be potent enough to displace TMP from its binding site.

Prevention and treatment of malaria in pregnancy

Malaria in pregnancy is a substantial public health issue in many tropical countries. However, its prevention and treatment have been hindered because of fears of adverse drug effects in pregnant women recruited to intervention studies. This article details the pharmacological agents and management strategies currently or potentially available for use in pregnant women with or at risk of malaria. There are deficiencies in pharmacokinetic, tolerability, safety and efficacy data for even well-established drugs and combinations. This can have serious implications for the design of rational dose regimens. Approaches such as intermittent preventive treatment are increasingly employed in endemic areas with proven benefits, but the emergence of parasite drug resistance means that new strategies and drug regimens should be continually evaluated.

An automated, polymer-assisted strategy for the preparation of urea and thiourea derivatives of 15-membered azalides as potential antimalarial chemotherapeutics

A series of 15-membered azalide urea and thiourea derivatives has been synthesized and evaluated for their in vitro antimalarial activity against chloroquine-sensitive (D6), chloroquine/pyremethamine resistant (W2) and multidrug resistant (TM91C235) strains of Plasmodium falciparum. We have developed an effective automated synthetic strategy for the rapid synthesis of urea/thiourea libraries of a macrolide scaffold. Compounds have been synthesized using a solution phase strategy with overall yields of 50-80%. Most of the synthesized compounds had inhibitory effects. The top 10 compounds were 30-65 times more potent than azithromycin, an azalide with antimalarial activity, against all three strains.

Environmental, pharmacological and genetic influences on the spread of drug-resistant malaria

Plasmodium falciparum malaria is subject to artificial selection from antimalarial drugs that select for drug-resistant parasites. We describe and apply a flexible new approach to investigate how epistasis, inbreeding, selection heterogeneity and multiple simultaneous drug deployments interact to influence the spread of drug-resistant malaria. This framework recognizes that different human 'environments' within which treatment may occur (such as semi- and non-immune humans taking full or partial drug courses) influence the genetic interactions between parasite loci involved in resistance. Our model provides an explanation for how the rate of spread varies according to different malaria transmission intensities, why resistance might stabilize at intermediate frequencies and also identifies several factors that influence the decline of resistance after a drug is removed. Results suggest that studies based on clinical outcomes might overestimate the spread of resistant parasites, especially in high-transmission areas. We show that when transmission decreases, prevalence might decrease without a corresponding change in frequency of resistance and that this relationship is heavily influenced by the extent of linkage disequilibrium between loci. This has important consequences on the interpretation of data from areas where control is being successful and suggests that reducing transmission might have less impact on the spread of resistance than previously expected.

Specific inhibition of the aspartate aminotransferase of Plasmodium falciparum

Aspartate aminotransferases (AspATs; EC 2.6.1.1) catalyze the conversion of aspartate and α-ketoglutarate into oxaloacetate and glutamate and are key enzymes in the nitrogen metabolism of all organisms. Recent findings suggest that the plasmodial enzyme [Plasmodium falciparum aspartate aminotransferase (PfAspAT)] may also play a pivotal role in energy metabolism and in the de novo biosynthesis of pyrimidines. However, while PfAspAT is a potential drug target, the high homology between the active sites of currently available AspAT structures hinders the development of specific inhibitors of these enzymes. In this article, we report the X-ray structure of the PfAspAT homodimer at a resolution of 2.8 Å. While the overall fold is similar to the currently available structures of other AspATs, the structure presented shows a significant divergence in the conformation of the N-terminal residues. Deletion of these divergent PfAspAT N-terminal residues results in a loss of activity for the recombinant protein, and addition of a peptide containing these 13 N-terminal residues results in inhibition both in vitro and in a lysate isolated from cultured parasites, while the activity of human cytosolic AspAT is unaffected. The finding that the divergent N-terminal amino acids of PfAspAT play a role in catalytic activity indicates that specific inhibition of the enzyme may provide a lead for the development of novel compounds in the treatment of malaria. We also report on the localization of PfAspAT to the parasite cytosol and discuss the implications of the role of PfAspAT in the supply of malate to the parasite mitochondria.

Computational approaches for drug repositioning and combination therapy design

Heterogeneous high-throughput biological data become readily available for various diseases. The amount of data points generated by such experiments does not allow manual integration of the information to design the most optimal therapy for a disease. We describe a novel computational workflow for designing therapy using Ariadne Genomics Pathway Studio software. We use publically available microarray experiments for glioblastoma and automatically constructed ResNet and ChemEffect databases to exemplify how to find potentially effective chemicals for glioblastoma--the disease yet without effective treatment. Our first approach involved construction of signaling pathway affected in glioblastoma using scientific literature and data available in ResNet database. Compounds known to affect multiple proteins in this pathway were found in ChemEffect database. Another approach involved analysis of differential expression in glioblastoma patients using Sub-Network Enrichment Analysis (SNEA). SNEA identified angiogenesis-related protein Cyr61 as the major positive regulator upstream of genes differentially expressed in glioblastoma. Using our findings, we then identified breast cancer drug Fulvestrant as a major inhibitor of glioblastoma pathway as well as Cyr61. This suggested Fulvestrant as a potential treatment against glioblastoma. We further show how to increase efficacy of glioblastoma treatment by finding optimal combinations of Fulvestrant with other drugs.

Pyrophosphate interactions at the transition states of Plasmodium falciparum and human orotate phosphoribosyltransferases

Orotate phosphoribosyltransferases from Plasmodium falciparum and human sources (PfOPRT and HsOPRT) use orotidine as a slow substrate in the pyrophosphorolysis reaction. With orotidine, intrinsic kinetic isotope effects (KIEs) can be measured for pyrophosphorolysis, providing the first use of pyrophosphate (PPi) in solving an enzymatic transition state. Transition-state structures of PfOPRT and HsOPRT were solved through quantum chemical matching of computed and experimental intrinsic KIEs and can be compared to transition states solved with pyrophosphate analogues as slow substrates. PfOPRT and HsOPRT are characterized by late transition states with fully dissociated orotate, well-developed ribocations, and weakly bonded PPi nucleophiles. The leaving orotates are 2.8 A distant from the anomeric carbons at the transition states. Weak participation of the PPi nucleophiles gives C1'-O(PPi) bond distances of approximately 2.3 A. These transition states are characterized by C2'-endo ribosyl pucker, based on the beta-secondary [2'-(3)H] KIEs. The geometry at the 5'-region is similar for both enzymes, with C3'-C4'-C5'-O5' dihedral angles near -170 degrees . These novel phosphoribosyltransferase transition states are similar to but occur earlier in the reaction coordinate than those previously determined with orotidine 5'-monophosphate and phosphonoacetic acid as substrates. The similarity between the transition states with different substrate analogues supports similar transition state structures imposed by PfOPRT and HsOPRT even with distinct reactants. We propose that the transition state similarity with different nucleophiles is determined, in part, by the geometric constraints imposed by the catalytic sites.

Increasing use of artemisinin-based combination therapy for treatment of malaria infection in Nigerian hospitals

OBJECTIVES

This study aimed at describing the pattern of outpatient antimalarial drug prescribing in a secondary and a tertiary hospital, and to assess adherence to the National Antimalarial Treatment Guideline (ATG).

METHODS

An audit of antimalarial prescription files from the two health facilities for a period of six months in 2008 was conducted. Semi structured questionnaires were used to collect information from the doctors and pharmacists on their awareness and knowledge of the National Antimalarial Treatment Guideline.

RESULTS

Artemisinin-based combination therapies (ACTs) were the most prescribed antimalarials. Overall, 81.4% of the total prescriptions contained ACTs, out of which 56.8% were artemetherlumefantrine. However, adherence to the drugs indicated by national guideline within the DU90% was 38.5% for the tertiary and 66.7 % for the secondary hospital. The standard practice of prescribing with generic name was still not adhered to as evidenced in the understudied hospitals. The percentage of health care providers that were aware of the ATG was 88.2% for doctors and 85.1% for pharmacists. However, 13.3% and 52.2% of doctors and pharmacists respectively could not properly list the drugs specified in the guideline. Amodiaquine was the most commonly preferred option for managing children aged 0 - 3 months with malaria infection against the indicated oral quinine.

CONCLUSION

This study showed an increased use of artemisinin-based combination therapy for the treatment of uncomplicated malaria compared previous reports in Nigeria. This study also highlights the need for periodic in-service quality assurance among health professionals with monitoring of adherence to and assessment of knowledge of clinical guidelines to ensure the practice of evidence based medicine.

The impact of human reservoir of malaria at a community-level on individual malaria occurrence in a low malaria transmission setting along the Thai-Myanmar border

Background

The probability of contracting malaria in a given individual is determined not only by the individual's characteristics, but also the ecological factors that characterize the level of human-vector contact in the population. Examination of the relationship between "individual" and "supra-individual" variables over time is important for understanding the local malaria epidemiology. This is essential for planning effective intervention strategies specifically for each location.

Methods

A retrospective cohort study was conducted, which followed a community-cohort of about 3,500 residents in seven hamlets along the Thai-Myanmar border between 1999 and 2006. Potential malaria determinants measured at different levels (temporal variables, individual variables, and hamlet variables) were incorporated into multilevel models to estimate their effects on an individual's risk of malaria attack.

Results

The monthly minimum temperature was significantly associated with the seasonal variation of malaria risk. An individual risk of malaria attack decreased by about 50% during the period that active surveillance was conducted; an additional 15% and 25% reduction of Plasmodium falciparum and Plasmodium vivax incidence, respectively, was observed after the use of artesunate-mefloquine combination therapy (ACT) for treatment of P. falciparum. Male children (age < 16 years old) were at highest risk of both P. falciparum and P. vivax attack. An increase in the hamlet's incidence of P. falciparum and P. vivax by 1 per 100 persons in a previous month resulted in 1.14 and 1.34 times increase in the risk of P. falciparum and P. vivax, respectively, among individuals in a particular hamlet.

Conclusion

In a small area with low malaria transmission intensity, the variation in mosquito abundance is relatively similar across the residential areas; incidence of malaria between hamlets, which reflects the community level of human infectious reservoirs, is an important predictor for the malaria risk among individuals within these hamlets. Therefore, local malaria control strategies should focus on interventions that aim to reduce the gametocyte carriage in the population, such as early detection and treatment programmes and the use of ACT for P. falciparum.

Descriptive study on the efficacy of artemether-lumefantrine in the treatment of uncomplicated Plasmodium falciparum malaria in Sudan

PURPOSE

The aim of this study was to investigate the efficacy of artemether-lumefantrine in treating uncomplicated Plasmodium falciparum malaria in four sentinel areas in Sudan with different malaria transmission (Damazin, Sinnar, and Kosti in the north, and Juba in the south).

METHODS

World Health Organization protocol for assessing antimalarial drug efficacy in treating uncomplicated P. falciparum malaria was employed. A total of 2,139 patients were screened, and 771 had P. falciparum monoinfection. Only 291 met the enrollment criteria and gave written consent to be recruited in the study. Patients were treated with artemether-lumefantrine tablets in a six-dose regimen calculated according to body weight. Tablets were given at 0, 8, 24, 36, 48, and 60 h. Patients were followed up for 28 days.

RESULTS

A total of 291 patients were recruited to the study, of whom ten [3.4; 95% confidence interval (CI):1.8-6.4%] patients showed early treatment failure (ETF) or late clinical failure (LCF) and were excluded from further follow-up. Of the remaining 281 patients, 276 (98.2%; 95% CI: 95.7-99.3%) completed the 28-day follow-up. Of these, 274 (99.3%; 95% CI: 97.1-99.9%) had adequate clinical and parasitological response (ACPR), and two (0.7%; 95% CI: 0.13-2.9%) showed late parasitological failure (LPF) at days 21 and 28. The overall mean +/- standard deviation (SD) of parasitemia and fever clearance times were 36.4 (23.7) h and 34.6 (19.2) h, respectively. Mild and reversible adverse effects were reported by 11 patients (3.8%; CI: 2.0- 7.0%) and were relieved without the need for termination of drug therapy or supportive treatment.

CONCLUSIONS

Our findings showed that artemether-lumefantrine was an effective and safe drug for treating uncomplicated P. falciparum malaria in northern and southern Sudan.

Anti-malarial market and policy surveys in sub-Saharan Africa

At a recent meeting (Sept 18, 2009) in which reasons for the limited access to artemisinin-based combination therapy (ACT) in sub-Saharan Africa were discussed, policy and market surveys on anti-malarial drug availability and accessibility in Burundi and Sierra Leone were presented in a highly interactive brainstorming session among key stakeholders across private, public, and not-for-profit sectors. The surveys, the conduct of which directly involved the national malaria control programme managers of the two countries, provides the groundwork for evidence-based policy implementation. The results of the surveys could be extrapolated to other countries with similar socio-demographic and malaria profiles. The meeting resulted in recommendations on key actions to be taken at the global, national, and community level for better ACT accessibility. At the global level, both public and private sectors have actions to take to strengthen policies that lead to the replacement of loose blister packs with fixed-dose ACT products, develop strategies to ban inappropriate anti-malarials and regulate those bans, and facilitate technology and knowledge transfer to scale up production of fixed-dose ACT products, which should be readily available and affordable to those patients who are in the greatest need of these medicines. At the national level, policies that regulate the anti-malarial medicines market should be enacted and enforced. The public sector, including funding donors, should participate in ensuring that the private sector is engaged in the ACT implementation process. Research similar to the surveys discussed is important for other countries to develop and evaluate the right incentives at a local level. At the community level, community outreach and education about appropriate preventive and treatment measures must continue and be strengthened, with service delivery systems developed within both public and private sectors, among other measures, to decrease access to ineffective and inappropriate anti-malarial medicines. What was clear during the meeting is that continuing commitment, strengthened interaction and transparency among various stakeholders, with focus on communities, national governments, and evidence-based policy and action are the only way to sustainably address the control of malaria, a disease which continues to have a significant health and socio-economic impact worldwide, particularly in sub-Saharan Africa. Details on the methodology employed in carrying out the studies discussed at this meeting, as well as more detailed results, data analysis and discussion of the studies are soon to be published.

Anti-malarial market and policy surveys in sub-Saharan Africa

At a recent meeting (Sept 18, 2009) in which reasons for the limited access to artemisinin-based combination therapy (ACT) in sub-Saharan Africa were discussed, policy and market surveys on anti-malarial drug availability and accessibility in Burundi and Sierra Leone were presented in a highly interactive brainstorming session among key stakeholders across private, public, and not-for-profit sectors. The surveys, the conduct of which directly involved the national malaria control programme managers of the two countries, provides the groundwork for evidence-based policy implementation. The results of the surveys could be extrapolated to other countries with similar socio-demographic and malaria profiles. The meeting resulted in recommendations on key actions to be taken at the global, national, and community level for better ACT accessibility. At the global level, both public and private sectors have actions to take to strengthen policies that lead to the replacement of loose blister packs with fixed-dose ACT products, develop strategies to ban inappropriate anti-malarials and regulate those bans, and facilitate technology and knowledge transfer to scale up production of fixed-dose ACT products, which should be readily available and affordable to those patients who are in the greatest need of these medicines. At the national level, policies that regulate the anti-malarial medicines market should be enacted and enforced. The public sector, including funding donors, should participate in ensuring that the private sector is engaged in the ACT implementation process. Research similar to the surveys discussed is important for other countries to develop and evaluate the right incentives at a local level. At the community level, community outreach and education about appropriate preventive and treatment measures must continue and be strengthened, with service delivery systems developed within both public and private sectors, among other measures, to decrease access to ineffective and inappropriate anti-malarial medicines. What was clear during the meeting is that continuing commitment, strengthened interaction and transparency among various stakeholders, with focus on communities, national governments, and evidence-based policy and action are the only way to sustainably address the control of malaria, a disease which continues to have a significant health and socio-economic impact worldwide, particularly in sub-Saharan Africa. Details on the methodology employed in carrying out the studies discussed at this meeting, as well as more detailed results, data analysis and discussion of the studies are soon to be published.

Purification, crystallization and preliminary X-ray analysis of the aspartate aminotransferase of Plasmodium falciparum

Aspartate aminotransferases (EC 2.6.1.1) catalyse the conversion of aspartate and alpha-ketoglutarate to oxaloacetate and glutamate in a reversible manner. Thus, the aspartate aminotransferase of Plasmodium falciparum (PfAspAT) plays a central role in the transamination of amino acids. Recent findings suggest that PfAspAT may also play a pivotal role in energy metabolism and the de novo biosynthesis of pyrimidines. While therapeutics based upon the inhibition of other proteins in these pathways are already used in the treatment of malaria, the advent of multidrug-resistant strains has limited their efficacy. The presence of PfAspAT in these pathways may offer additional opportunities for the development of novel therapeutics. In order to gain a deeper understanding of the function and role of PfAspAT, it has been expressed and purified to homogeneity. The successful crystallization of PfAspAT, the collection of a 2.8 A diffraction data set and initial attempts to solve the structure using molecular replacement are reported.

Plant-derived antimalarial agents: new leads and efficient phythomedicines. Part I. Alkaloids

Malaria remains one of the most serious world health problem and the major cause of mortality and morbidity in the endemic regions. Brazil is among the 30 high-burden countries and most of the cases occur in the Legal Amazonian Region. New chemotherapeutical agents are needed for the treatment of malaria. Many plant species are used in traditional medicines of malarious countries and a relatively few number of these have been investigated for evaluation of their antimalarial effect. Still lower is the number of those that have had the active natural compounds isolated and the toxicity determined. This area is, then, of great research interest. discovery project of antimalarial natural products from plants traditionally used to treat malaria must include in vitro and in vivo assays as well as bioguided isolation of active compounds. The final products would be antimalarial chemical entities, potential new drugs or templates for new drugs development, and/or standardized antimalarial extracts which are required for pre-clinical and clinical studies when the aim is the development of effective and safe phythomedicines. This review discusses these two approaches, presents briefly the screening methodologies for evaluation of antimalarial activity and focuses the activity of alkaloids belonging to different structural classes as well as its importance as new antimalarial drugs or leads and chemical markers for phytomedicines.

Bioinformatics, enzymologic properties, and comprehensive tracking of Plasmodium falciparum nucleoside diphosphate kinase

The gene encoding for nucleoside diphosphate kinase from Plasmodium falciparum was obtained by polymerase chain reaction (PCR) and expressed in Escherichia coli. Tracking kinases is strenuous work due to many functional and technical deficits. Tracking of Plasmodium falciparum nucleoside diphosphate kinase (PfNDK) was carried out by conventional enzyme assays combined by isothermal titration calorimetry (ITC). ITC proved an efficient tracking method with rapid, accurate, and confident target confirmation. In addition, it provides substrate affinity and full thermodynamic profile in one experiment. Magnesium ions were found to be essential for nucleoside diphosphate (NDP) kinase activity; however, the absence of Mg(2+) did not completely interfere with the binding of nucleotides. The substrate recognition was found to depend on enthalpic forces with little entropic contributions. However, in the absence of magnesium ions the nucleotides actively bind to the enzyme driven by hydrophobic forces. The enzyme showed specific activity that was within the average of known enzymes; however, it was at least two-fold higher than that of the human enzyme.

Synthesis and antiprotozoal activity of cationic 1,4-diphenyl-1H-1,2,3-triazoles

Novel dicationic triazoles 1-60 were synthesized by the Pinner method from the corresponding dinitriles, prepared via the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The type and the placement of cationic moieties as well as the nature of aromatic substituents influenced in vitro antiprotozoal activities of compounds 1-60 against Trypanosoma brucei rhodesiense, Plasmodium falciparum, and Leishmania donovani and their cytotoxicity for mammalian cells. Eight congeners displayed antitrypanosomal IC(50) values below 10 nM. Thirty-nine dications were more potent against P. falciparum than pentamidine (IC(50) = 58 nM), and eight analogues were more active than artemisinin (IC(50) = 6 nM). Diimidazoline 60 exhibited antiplasmodial IC(50) value of 0.6 nM. Seven congeners administered at 4 x 5 mg/kg by the intraperitoneal route cured at least three out of four animals in the acute mouse model of African trypanosomiasis. At 4 x 1 mg/kg, diamidine 46 displayed better antitrypanosomal efficacy than melarsoprol, curing all infected mice.

Malaria management: past, present, and future

The prospect of malaria eradication has been raised recently by the Bill and Melinda Gates Foundation with support from the international community. There are significant lessons to be learned from the major successes and failures of the eradication campaign of the 1960s, but cessation of transmission in the malaria heartlands of Africa will depend on a vaccine and better drugs and insecticides. Insect control is an essential part of reducing transmission. To date, two operational scale interventions, indoor residual spraying and deployment of long-lasting insecticide-treated nets (LLINs), are effective at reducing transmission. Our ability to monitor and evaluate these interventions needs to be improved so that scarce resources can be sensibly deployed, and new interventions that reduce transmission in a cost-effective and efficient manner need to be developed. New interventions could include using transgenic mosquitoes, larviciding in urban areas, or utilizing cost-effective consumer products. Alongside this innovative development agenda, the potential negative impact of insecticide resistance, particularly on LLINs, for which only pyrethroids are available, needs to be monitored.

Quantitation of artemether in pharmaceutical raw material and injections by high performance liquid chromatography

The quantitation of artemether in both pharmaceutical raw material and injections was carried out by high performance liquid chromatography (HPLC) with ultraviolet detection. A Zorbax C18 column (150 x 4.6 mm; 5 μm), at 30 °C, and a mobile phase composed of acetonitrile and water (70:30), at a flow rate of 1ml/min, were used. The detection wavelength was 216 nm and the injection volume was 20 μL. The method proved to be linear (r²=0.9999), precise (RSD < 20% for intra-day and inter-day precision), accurate and selective regarding possible impurities and excipients of the samples. The detection and quantitation limits were 8 μg/mL and 25 μg/mL, respectively. The artemether content obtained in the raw material analysis was 99.26% and in the injections, 102.08%. The optimized and validated method may be successfully employed to perform routine quality control analyses.

Safety and immunogenicity of the malaria vaccine candidate MSP3 long synthetic peptide in 12-24 months-old Burkinabe children

Background

A Phase Ia trial in European volunteers of the candidate vaccine merozoite surface protein 3 (MSP3), a Plasmodium falciparum blood stage membrane, showed that it induces biologically active antibodies able to achieve parasite killing in vitro, while a phase Ib trial in semi-immune adult volunteers in Burkina Faso confirmed that the vaccine was safe.

The aim of this study was to assess the safety and immunogenicity of this vaccine candidate in children aged 12–24 months living in malaria endemic area of Burkina Faso.

Methods

The study was a double-blind, randomized, controlled, dose escalation phase Ib trial, designed to assess the safety, reactogenicity and immunogenicity of three doses of either 15 or 30 µg of MSP3-LSP adsorbed on aluminum hydroxide in 45 children 12 to 24 months of age randomized into three equal groups. Each group received 3 vaccine doses (on days 0, 28 and 56) of either 15 µg of MSP3-LSP, 30 µg of MSP3-LSP or of the Engerix B hepatitis B vaccine. Children were visited at home daily for the 6 days following each vaccination to solicit symptoms which might be related to vaccination. Serious adverse events occurring during the study period (1 year) were recorded. Antibody responses to MSP3-LSP were measured on days 0, 28, 56 and 84.

Results

All 45 enrolled children received three MSP3 vaccine doses. No serious adverse events were reported. Most of the adverse events reported were mild to moderate in severity. The only reported local symptoms with grade 3 severity were swelling and induration, with an apparently dose related response. All grade 3 adverse events resolved without any sequelae. Both MSP3 doses regimens were able to elicit high levels of anti-MSP3 specific IgG1 and IgG3 antibodies in the volunteers with very little or no increase in IgG2, IgG4 and IgM classes: i.e. vaccination induced predominantly the isotypes involved in the monocyte-dependent mechanism of P. falciparum parasite-killing.

Conclusion

Our results support the promise of MSP3-LSP as a malaria vaccine candidate, both in terms of tolerability and of immunogenicity. Further assessment of the efficacy of this vaccine is recommended.

Trial Registration

ClinicalTrials.gov NCT00452088

Optimally timing primaquine treatment to reduce Plasmodium falciparum transmission in low endemicity Thai-Myanmar border populations

BACKGROUND

Effective malaria control has successfully reduced the malaria burden in many countries, but to eliminate malaria, these countries will need to further improve their control efforts. Here, a malaria control programme was critically evaluated in a very low-endemicity Thai-Myanmar border population, where early detection and prompt treatment have substantially reduced, though not ended, Plasmodium falciparum transmission, in part due to carriage of late-maturing gametocytes that remain post-treatment. To counter this effect, the WHO recommends the use of a single oral dose of primaquine along with an effective blood schizonticide. However, while the effectiveness of primaquine as a gametocidal agent is widely documented, the mismatch between primaquine's short half-life, the long-delay for gametocyte maturation and the proper timing of primaquine administration have not been studied.

METHODS

Mathematical models were constructed to simulate 8-year surveillance data, between 1999 and 2006, of seven villages along the Thai-Myanmar border. A simple model was developed to consider primaquine pharmacokinetics and pharmacodynamics, gametocyte carriage, and infectivity.

RESULTS

In these populations, transmission intensity is very low, so the P. falciparum parasite rate is strongly linked to imported malaria and to the fraction of cases not treated. Given a 3.6-day half-life of gametocyte, the estimated duration of infectiousness would be reduced by 10 days for every 10-fold reduction in initial gametocyte densities. Infectiousness from mature gametocytes would last two to four weeks and sustain some transmission, depending on the initial parasite densities, but the residual mature gametocytes could be eliminated by primaquine. Because of the short half-life of primaquine (approximately eight hours), it was immediately obvious that with early administration (within three days after an acute attack), primaquine would not be present when mature gametocytes emerged eight days after the appearance of asexual blood-stage parasites. A model of optimal timing suggests that primaquine follow-up approximately eight days after a clinical episode could further reduce the duration of infectiousness from two to four weeks down to a few days. The prospects of malaria elimination would be substantially improved by changing the timing of primaquine administration and combining this with effective detection and management of imported malaria cases. The value of using primaquine to reduce residual gametocyte densities and to reduce malaria transmission was considered in the context of a malaria transmission model; the added benefit of the primaquine follow-up treatment would be relatively large only if a high fraction of patients (>95%) are initially treated with schizonticidal agents.

CONCLUSION

Mathematical models have previously identified the long duration of P. falciparum asexual blood-stage infections as a critical point in maintaining malaria transmission, but infectiousness can persist for two to four weeks because of residual populations of mature gametocytes. Simulations from new models suggest that, in areas where a large fraction of malaria cases are treated, curing the asexual parasitaemia in a primary infection, and curing mature gametocyte infections with an eight-day follow-up treatment with primaquine have approximately the same proportional effects on reducing the infectious period. Changing the timing of primaquine administration would, in all likelihood, interrupt transmission in this area with very good health systems and with very low endemicity.

Impact of delayed introduction of sulfadoxine-pyrimethamine and arthemeter-lumefantrine on malaria epidemiology in KwaZulu-Natal, South Africa

OBJECTIVE

To investigate how delayed introduction of sulfadoxine-pyrimethamine (Fansidar) and arthemeter-lumefantrine (Coartem) as first-line drugs for malaria in KwaZulu-Natal contributed to the reported epidemics of 1985-1988 and 1997-2001.

METHODS

Ecological study assessing the association between malaria incidence and the emergence and degree of resistance to chloroquine from 1982 to 1988 and to sulfadoxine-pyrimethamine from 1991 to 2001, when each was the first-line malaria treatment.

RESULTS

The relative risk for malaria infection after the level of drug resistance reached 10% was 4.5 (95% CI: 4.0-5.2) in the chloroquine period and 5.9 (95% CI: 5.7-6.1) in the sulfadoxine-pyrimethamine period. In the chloroquine period, the relative risk of death from malaria was tenfold (95% CI: 1.3-78.1) and the case fatality doubled after drug resistance had reached 10%. The risk of death during the sulfadoxine-pyrimethamine period was 10.8 (95% CI: 5.9-19.2) and case fatality 1.8 times higher after drug resistance had reached 10%, than before.

CONCLUSION

Malaria epidemics in KwaZulu-Natal, South Africa have been exacerbated by failing drug regimens. The establishment of sentinel sites for monitoring drug failure and the prompt adoption of guidelines based on World Health Organization standards in drug resistance should improve malaria control.

A comparative, randomized clinical trial of artemisinin/naphtoquine twice daily one day versus artemether/lumefantrine six doses regimen in children and adults with uncomplicated falciparum malaria in Côte d'Ivoire

Background

Drug resistance in Plasmodium falciparum poses a major threat to malaria control. Combination anti-malarial therapy, including artemisinins, has been advocated to improve efficacy and limit the spread of resistance. The fixed combination of oral artemether-lumefantrine (AL) is highly effective and well-tolerated. Artemisinin/naphtoquine (AN) is a fixed-dose ACT that has recently become available in Africa.

The objectives of the study were to compare the efficacy and safety of AN and AL for the treatment of uncomplicated falciparum malaria in a high transmission-intensity site in Ivory Coast.

Methods

We enrolled 122 participants aged 6 months or more with uncomplicated falciparum malaria. Participants were randomized to receive either artemisinin/naphtoquine or artemether/lumefantrine with variable dose according to their weight. Primary endpoints were the risks of treatment failure within 28 days, either unadjusted or adjusted by genotyping to distinguish recrudescence from new infection.

Results

Among 125 participants enrolled, 123 (98.4%) completed follow-up. Clinical evaluation of the 123 participants showed that cumulative PCR-uncorrected cure rate on day 28 was 100% for artemisinin/naphtoquine and 98.4% for artemether/lumefantrine. Both artemisinin-based combinations effected rapid fever and parasite clearance.

Interpretation

These data suggest that Arco^® could prove to be suitable for use as combination antimalarial therapy. Meanwhile, pharmacokinetic studies and further efficacy assessment should be conducted before its widespread use can be supported.

Development of a Polymerase Chain Reaction (PCR) method based on amplification of mitochondrial DNA to detect Plasmodium falciparum and Plasmodium vivax

In this study we standardized a new technical approach in which the target mitochondrial DNA sequence (mtDNA) is amplified using a simple but sensitive PCR method as a tool to detect Plasmodium falciparum and Plasmodium vivax. Specific primers were designed to hybridize with cytochrome c oxidase genes of P. falciparum (cox III) and P. vivax (cox I). Amplification products were obtained for all positive samples, presenting homology only for species-specific mtDNA. Sensitivity and specificity were 100%. The applicability of the method was tested in a cross-sectional study, in which 88 blood samples from individuals naturally exposed to malaria in the Brazilian Amazon region were analyzed. Based on the results, the sensitivity and specificity were 100% and 88.3%, respectively. This simple and sensitive PCR method can be useful in specific situations and in different settings of malaria management, in endemic as well as non-endemic areas (travelers), and in clinical or epidemiological studies, with applications in malaria control programs.

Does Insecticide Treated Mosquito Nets (ITNs) prevent clinical malaria in children aged between 6 and 59 months under program setting?

Inconsistent use of the mosquito nets and other social and technical factors were shown to influence efficacy of mosquito nets at field trials. But to date, experience with local factors influencing effectiveness of ITN programs remain very limited. The objective of this study was to assess the effectiveness of ITNs for preventing clinical malaria in under-five children of Omo Nada Woreda, Jimma Zone South West Ethiopia. Matched case-control study was conducted in the catchments population of Asendabo and Nada health centers, Omo Nada Woreda, South West Ethiopia on a sample of 273 under-five children. Each case of fever and parasitemia in a child was paired with two controls. Cases and controls were compared with regard to ITN ownership and other factors assessed by a pre-coded, pre-tested structured questionnaire. Data was analyzed using EPI-INFO version 3.3.2 software. To control the effect of confounding variables, conditional logistic regression model was used. Sleeping under the mosquito net the night (OR = 8.28 95% CI: 0.96, 71.1) and the week (OR = 2.41 95% CI: 0.41, 14.0) before the survey date were strongly, but not significantly associated with clinical malaria. Mosquito net possession and appropriate utilization of mosquito net were not associated with clinical malaria. In the comparison of cases with all the controls rolling out of mosquito net & corrugated iron roof were found to be independent predictors of clinical malaria. Knowledge about the sign and symptoms of malaria and its modes of transmission were also independent predictors of clinical malaria in comparison of cases with health center and community controls, respectively. With the presence of many programmatic deficiencies like poor ITN distribution and re-treatment services, ITNs were not significantly associated with clinical malaria in under-five children when used during low-transmission period. Further research using a large sample size is required. In line with ITN scale up, information Education Communication (IEC) about the preventive practices against malaria, causes of malaria, treatment and sign and symptoms of malaria should be given to the community.

Sequence diversity and evolutionary dynamics of the dimorphic antigen merozoite surface protein-6 and other Msp genes of Plasmodium falciparum

Immune evasion by Plasmodium falciparum is favored by extensive allelic diversity of surface antigens. Some of them, most notably the vaccine-candidate merozoite surface protein (MSP)-1, exhibit a poorly understood pattern of allelic dimorphism, in which all observed alleles group into two highly diverged allelic families with few or no inter-family recombinants. Here we describe contrasting levels and patterns of sequence diversity in genes encoding three MSP-1-associated surface antigens of P. falciparum, ranging from an ancient allelic dimorphism in the Msp-6 gene to a near lack of allelic divergence in Msp-9 to a more classical multi-allele polymorphism in Msp-7. Other members of the Msp-7 gene family exhibit very little polymorphism in non-repetitive regions. A comparison of P. falciparum Msp-6 sequences to an orthologous sequence from P. reichenowi provided evidence for distinct evolutionary histories of the 5' and 3' segments of the dimorphic region in PfMsp-6, consistent with one dimorphic lineage having arisen from recombination between now-extinct ancestral alleles. In addition, we uncovered two surprising patterns of evolution in repetitive sequence. First, in Msp-6, large deletions are associated with (nearly) identical sequence motifs at their borders. Second, a comparison of PfMsp-9 with the P. reichenowi ortholog indicated retention of a significant inter-unit diversity within an 18-base pair repeat within the coding region of P. falciparum, but homogenization in P. reichenowi.

Structure-activity study of pentamidine analogues as antiprotozoal agents

Diamidine 1 (pentamidine) and 65 analogues (2-66) have been tested for in vitro antiprotozoal activities against Trypanosoma brucei rhodesiense, Plasmodium falciparum, and Leishmania donovani, and for cytotoxicity against mammalian cells. Dications 32, 64, and 66 exhibited antitrypanosomal potencies equal or greater than melarsoprol (IC(50) = 4 nM). Nine congeners (2-4, 12, 27, 30, and 64-66) were more active against P. falciparum than artemisinin (IC(50) = 6 nM). Eight compounds (12, 32, 33, 44, 59, 62, 64, and 66) exhibited equal or better antileishmanial activities than 1 (IC(50) = 1.8 microM). Several congeners were more active than 1 in vivo, curing at least 2/4 infected animals in the acute mouse model of trypanosomiasis. The diimidazoline 66 was the most promising compound in the series, showing excellent in vitro activities and high selectivities against T. b. rhodesiense, P. falciparum, and L. donovani combined with high antitrypanosomal efficacy in vivo.

Loop-mediated isothermal amplification (LAMP): a rapid, accurate, and cost-effective diagnostic method for infectious diseases

Loop-mediated isothermal amplification (LAMP) is an established nucleic acid amplification method offering rapid, accurate, and cost-effective diagnosis of infectious diseases. This technology has been developed into commercially available detection kits for a variety of pathogens including bacteria and viruses. The current focus on LAMP methodology is as a diagnostic system to be employed in resource-limited laboratories in developing countries, where many fatal tropical diseases are endemic. The combination of LAMP and novel microfluidic technologies such as Lab-on-a-chip may facilitate the realization of genetic point-of-care testing systems to be used by both developed and developing countries in the near future. This review will describe the historical, current, and future developments of such technologies.

Cost-effectiveness analysis of the available strategies for diagnosing malaria in outpatient clinics in Zambia

BACKGROUND

Malaria in Zambia accounts for about 4 million clinical cases and 8 000 deaths annually. Artemether-lumefantrine (ACT), a relatively expensive drug, is being used as first line treatment of uncomplicated malaria. However, diagnostic capacity in Zambia is low, leading to potentially avoidable wastage of drugs due to unnecessary anti malarial treatment.

METHODS

A cost-effectiveness evaluation of the three current alternatives to malaria diagnosis (clinical, microscopy and Rapid Diagnostic Tests- RDT) was conducted in 12 facilities from 4 districts in Zambia. The analysis was conducted along an observational study, thus reflecting practice in health facilities under routine conditions. Average and incremental cost effectiveness ratios were estimated from the providers' perspective. Effectiveness was measured in relation to malaria cases correctly diagnosed by each strategy.

RESULTS

Average cost-effectiveness ratios show that RDTs were more efficient (US$ 6.5) than either microscopy (US$ 11.9) or clinical diagnosis (US$ 17.1) for malaria case correctly diagnosed. In relation to clinical diagnoses the incremental cost per case correctly diagnosed and treated was US$ 2.6 and US$ 9.6 for RDT and microscopy respectively. RDTs would be much cheaper to scale up than microscopy. The findings were robust to changes in assumptions and various parameters.

CONCLUSION

RDTs were the most cost effective method at correctly diagnosing malaria in primary health facilities in Zambia when compared to clinical and microscopy strategies. However, the treatment prescription practices of the health workers can impact on the potential that a diagnostic test has to lead to savings on antimalarials. The results of this study will serve to inform policy makers on which alternatives will be most efficient in reducing malaria misdiagnosis by taking into account both the costs and effects of each strategy.

Transition states of Plasmodium falciparum and human orotate phosphoribosyltransferases

Orotate phosphoribosyltransferases (OPRT) catalyze the formation of orotidine 5'-monophosphate (OMP) from alpha-D-phosphoribosylpyrophosphate (PRPP) and orotate, an essential step in the de novo biosynthesis of pyrimidines. Pyrimidine de novo biosynthesis is required in Plasmodium falciparum , and thus OPRT of the parasite (PfOPRT) is a target for antimalarial drugs. De novo biosynthesis of pyrimidines is also a feature of rapidly proliferating cancer cells. Human OPRT (HsOPRT) is therefore a target for neoplastic and autoimmune diseases. One approach to the inhibition of OPRTs is through analogues that mimic the transition states of PfOPRT and HsOPRT. The transition state structures of these OPRTs were analyzed by kinetic isotope effects (KIEs), substrate specificity, and computational chemistry. With phosphonoacetic acid (PA), an analogue of pyrophosphate, the intrinsic KIEs of [1'-(14)C], [1, 3-(15)N(2)], [3-(15)N], [1'-(3)H], [2'-(3)H], [4'-(3)H], and [5'-(3)H(2)] are 1.034, 1.028, 0.997, 1.261, 1.116, 0.974, and 1.013 for PfOPRT and 1.035, 1.025, 0.993, 1.199, 1.129, 0.962, and 1.019 for HsOPRT, respectively. Transition state structures of PfOPRT and HsOPRT were determined computationally by matching the calculated and intrinsic KIEs. The enzymes form late associative D(N)*A(N)(double dagger) transition states with complete orotate loss and partially associative nucleophile. The C1'-O(PA) distances are approximately 2.1 A at these transition states. The modest [1'-(14)C] KIEs and large [1'-(3)H] KIEs are characteristic of D(N)*A(N)(double dagger) transition states. The large [2'-(3)H] KIEs indicate a ribosyl 2'-C-endo conformation at the transition states. p-Nitrophenyl beta-D-ribose 5'-phosphate is a poor substrate of PfOPRT and HsOPRT but is a nanomolar inhibitor, supporting a reaction coordinate with strong leaving group activation.

Poisoning pyridoxal 5-phosphate-dependent enzymes: a new strategy to target the malaria parasite Plasmodium falciparum

The human malaria parasite Plasmodium falciparum is able to synthesize de novo pyridoxal 5-phosphate (PLP), a crucial cofactor, during erythrocytic schizogony. However, the parasite possesses additionally a pyridoxine/pyridoxal kinase (PdxK) to activate B6 vitamers salvaged from the host. We describe a strategy whereby synthetic pyridoxyl-amino acid adducts are channelled into the parasite. Trapped upon phosphorylation by the plasmodial PdxK, these compounds block PLP-dependent enzymes and thus impair the growth of P. falciparum. The novel compound PT3, a cyclic pyridoxyl-tryptophan methyl ester, inhibited the proliferation of Plasmodium very efficiently (IC(50)-value of 14 microM) without harming human cells. The non-cyclic pyridoxyl-tryptophan methyl ester PT5 and the pyridoxyl-histidine methyl ester PHME were at least one order of magnitude less effective or completely ineffective in the case of the latter. Modeling in silico indicates that the phosphorylated forms of PT3 and PT5 fit well into the PLP-binding site of plasmodial ornithine decarboxylase (PfODC), the key enzyme of polyamine synthesis, consistent with the ability to abolish ODC activity in vitro. Furthermore, the antiplasmodial effect of PT3 is directly linked to the capability of Plasmodium to trap this pyridoxyl analog, as shown by an increased sensitivity of parasites overexpressing PfPdxK in their cytosol, as visualized by GFP fluorescence.

Inhibition of Plasmodium falciparum proliferation in vitro by double-stranded RNA directed against malaria histone deacetylase

Acetylation and deacetylation of histones play important roles in transcription regulation, cell cycle progression and development events. The steady state status of histone acetylation is controlled by a dynamic equilibrium between competing histone acetylase and deacetylase (HDAC). We have used long PfHDAC-1 double-stranded (ds)RNA to interfere with its cognate mRNA expression and determined the effect on malaria parasite growth and development. Chloroquine- and pyrimethamine-resistant Plasmodium falciparum K1 strain was exposed to 1-25 microg of dsRNA/ml of culture for 48 h and growth was determined by [3H]-hypoxanthine incorporation and microscopic examination. Parasite culture treated with 10 microg/ml pfHDAC-1 dsRNA exhibited 47% growth inhibition when compared with either untreated control or culture treated with an unrelated dsRNA. PfHDAC-1 dsRNA specifically blocked maturation of trophozoite to schizont stages and decreased PfHDAC-1 transcript 44% in treated trophozoites. These results indicate the potential of HDAC-1 as a target for development of novel antimalarials.

Sensitive periods for developmental toxicity of orally administered artesunate in the rat

BACKGROUND

Artesunate has been reported to cause embryolethality and malformations when administered orally to rats during organogenesis. The purpose of this study was to determine the most sensitive period(s) for the induction of these effects in order to provide clues about possible mechanisms and to identify a short treatment regimen for further studies.

METHODS

Pregnant rats were orally administered artesunate (10, 17 or 30 mg/kg/day) on single or multiple days of gestation. Cesarean sections and fetal evaluations were conducted on Day 21 postcoitum (pc).

RESULTS

Embryolethality, cardiovascular malformations and a syndrome of skeletal defects were observed after single doses on days 10 to 14 pc, while no developmental effects were observed before (day 9 pc) or after (days 16 or 17 pc) that period. The most sensitive day for embryo lethality was day 11 pc, where lethality occurred with a very steep dose response (postimplantation loss was approximately 15% at 10 mg/kg and 100% at 17 mg/kg/day). The most sensitive day for the induction of malformations was day 10 pc. Malformations tended to occur in partially resorbed litters and included cardiovascular defects and bent and misshapen long bones and scapulae.

CONCLUSIONS

The sensitive window for developmental toxicity of artesunate in the rat was identified as days 10 to 14 pc. Single oral doses produced embryolethality and similar cardiovascular and skeletal malformations as previously reported in longer term dosing experiments. These single dose treatment regimens could be useful to further investigate the mechanistic basis for artesunate-induced developmental toxicity.

Artesunate: developmental toxicity and toxicokinetics in monkeys

BACKGROUND

The developmental toxicity, toxicokinetics, and hematological effects of the antimalarial drug, artesunate, were previously studied in rats and rabbits and have now been studied in cynomolgus monkeys.

METHODS

Groups of up to 15 pregnant females were dosed on Gestation Days (GD) 20-50 or for 3-7-day intervals.

RESULTS

At 30 mg/kg/day, 6 embryos died between GD30 and GD40. Histologic examination of 3 live embryos (GD26-GD36) revealed a marked reduction in embryonic erythroblasts and cardiomyopathy. At 12 mg/kg/day, 6 embryos died between GD30 and GD45. Four surviving fetuses examined on GD100 had no malformations, but long bone lengths were slightly decreased. At the developmental no-adverse-effect-level (4 mg/kg/day), maternal plasma AUC was 3.68 ng.h/mL for artesunate and 6.93 ng.h/ml for its active metabolite, dihydroartemisinin (DHA). No developmental toxicity occurred with administration of 12 mg/kg/day for 3 or 7 days, GD29-31 or GD27-33 (maternal plasma AUC of 9.84 ng.h/mL artesunate and 16.4 ng.h/mL DHA). Exposures at embryotoxic doses were substantially lower than human therapeutic exposures. However, differences in monkey and human Vss for artesunate (0.5 L/kg vs. 0.18 L/kg) confound relying solely on AUC for assessing human risk. Decreases in reticulocyte count occur at therapeutic doses in humans. Changes to reticulocyte counts at embryotoxic doses in monkeys (> or =12 mg/kg/day) were variable and generally minor.

CONCLUSIONS

Artesunate was embryolethal at > or =12 mg/kg/day when dosed for at least 12 days at the beginning of organogenesis, but not when dosed for 3 or 7 days, indicating that developmental toxicity of artesunate is dependent upon duration of dosing in cynomologus monkeys.

Mutational, inhibitory and microcalorimetric analyses of Plasmodium falciparum TMP kinase. Implications for drug discovery

Plasmodium falciparum thymidylate kinase (PfTMK) can tolerate a range of substrates, which distinguishes it from other thymidylate kinases. The enzyme not only phosphorylates TMP and dUMP but can also tolerate bulkier purines, namely, dGMP, GMP, and dIMP. In order to probe the flexibility of PfTMK in accommodating ligands of various sizes, we developed 6 mutant enzymes and subjected these to thermodynamic, inhibitory and catalytic evaluation. Kinase activity was markedly affected by introducing a larger lysine residue instead of A111. The lack of the hydroxyl group after inducing mutation of Y107F affected enzyme activity, and had a more severe impact on dGMP kinase activity. PfTMK can be inhibited by both purine and pyrimidine nucleosides, raising the possibility of developing highly selective drugs. Thermodynamic analysis revealed that enthalpic forces govern both purine and pyrimidine nucleoside monophosphate binding, and the binding affinity of both substrates was highly comparable. The heat produced due to dGMP binding is lower than that attributable to TMP. This indicates that additional interactions occur with TMP, which may be lost with larger dGMP. Targeting PfTMK not only affects thymidine nucleotide synthesis but may also affect purine nucleotides, and thus the enzyme represents an attractive antimicrobial target.

UDP-Gal: N-acetylglucosamine beta 1-4 galactosyltransferase expressing live attenuated parasites as vaccine for visceral leishmaniasis

As compared to cutaneous leishmaniasis, vaccination against visceral leishmaniasis (VL) has received limited attention. In this study, we demonstrate for the first time that an UDP-Galactose: N-acetylglucosamine beta 1-4 galactosyltransferase (GenBank Accession No. EF159943) expressing attenuated LD clonal population (A-LD) is able to confer protection against the experimental challenge with the virulent LD AG83 parasite. A-LD was also effective in established leishmania infection. The vaccinated animals showed both cell mediated (in vitro T-cell proliferation, and DTH response) and humoral responses (Th1 type). These results demonstrate the potential of the attenuated clones as an immunotherapeutic and immunoprophylactic agent against visceral leishmaniasis.

Drugs for treating uncomplicated malaria in pregnant women

BACKGROUND

Women are more vulnerable to malaria during pregnancy, and malaria infection may have adverse consequences for the fetus. Identifying safe and effective treatments is important.

OBJECTIVES

To compare the effects of drug regimens for treating uncomplicated falciparum malaria in pregnant women.

SEARCH STRATEGY

We searched the Cochrane Infectious Diseases Group Specialized Register (February 2008), CENTRAL (The Cochrane Library 2008, Issue 1), MEDLINE (1966 to February 2008), EMBASE (1974 to February 2008), LILACS (February 2008), mRCT (February 2008), reference lists, and conference abstracts. We also contacted researchers in the field, organizations, and pharmaceutical companies.

SELECTION CRITERIA

Randomized and quasi-randomized controlled trials of antimalarial drugs for treating uncomplicated malaria in pregnant women.

DATA COLLECTION AND ANALYSIS

Two authors assessed trial eligibility and risk of bias, and extracted data. We performed a quantitative analysis only where we could combine the data. We combined dichotomous data using the risk ratio (RR) and presented each result with a 95% confidence interval (CI).

MAIN RESULTS

Ten trials (1805 participants) met the inclusion criteria. Two were quasi-randomized, seven did not describe allocation concealment, and all adjusted treatment failure to exclude new infections. One trial reported fewer treatment failures at day 63 with artesunate plus mefloquine compared with quinine (RR 0.09, 95% CI 0.02 to 0.38; 106 participants). One trial reported fewer treatment failures at day 63 with artesunate plus atovaquone-proguanil compared with quinine (RR 0.14, 95% CI 0.03 to 0.57; 80 participants). One trial reported fewer treatment failures at day 28 when amodiaquine was compared with chloroquine (RR 0.20, 95% CI 0.08 to 0.46; 420 participants) and when amodiaquine plus sulfadoxine-pyrimethamine was compared with chloroquine (RR 0.02, 95% CI 0.00 to 0.26; 418 participants). Compared with sulfadoxine-pyrimethamine given alone, one trial reported fewer treatment failures at delivery (or day 40) with artesunate plus sulfadoxine-pyrimethamine (RR 0.15, 95% CI 0.04 to 0.59; 79 participants) and azithromycin plus sulfadoxine-pyrimethamine (RR 0.27, 95% CI 0.10 to 0.76; 82 participants).

AUTHORS' CONCLUSIONS

Data are scant. Some combination treatments appear to be effective at treating malaria in pregnancy; however, safety data are limited.

Should countries implementing an artemisinin-based combination malaria treatment policy also introduce rapid diagnostic tests?

Background

Within the context of increasing antimalarial costs and or decreasing malaria transmission, the importance of limiting antimalarial treatment to only those confirmed as having malaria parasites becomes paramount. This motivates for this assessment of the cost-effectiveness of routine use of rapid diagnostic tests (RDTs) as an integral part of deploying artemisinin-based combination therapies (ACTs).

Methods

The costs and cost-effectiveness of using RDTs to limit the use of ACTs to those who actually have Plasmodium falciparum parasitaemia in two districts in southern Mozambique were assessed. To evaluate the potential impact of introducing definitive diagnosis using RDTs (costing $0.95), five scenarios were considered, assuming that the use of definitive diagnosis would find that between 25% and 75% of the clinically diagnosed malaria patients are confirmed to be parasitaemic. The base analysis compared two ACTs, artesunate plus sulfadoxine/pyrimethamine (AS+SP) costing $1.77 per adult treatment and artemether-lumefantrine (AL) costing $2.40 per adult treatment, as well as the option of restricting RDT use to only those older than six years. Sensitivity analyses considered lower cost ACTs and RDTs and different population age distributions.

Results

Compared to treating patients on the basis of clinical diagnosis, the use of RDTs in all clinically diagnosed malaria cases results in cost savings only when 29% and 52% or less of all suspected malaria cases test positive for malaria and are treated with AS+SP and AL, respectively. These cut-off points increase to 41.5% (for AS+SP) and to 74% (for AL) when the use of RDTs is restricted to only those older than six years of age. When 25% of clinically diagnosed patients are RDT positive and treated using AL, there are cost savings per malaria positive patient treated of up to $2.12. When more than 29% of clinically diagnosed cases are malaria test positive, the incremental cost per malaria positive patient treated is less than US$ 1. When relatively less expensive ACTs are introduced (e.g. current WHO preferential price for AL of $1.44 per adult treatment), the RDT price to the healthcare provider should be $0.65 or lower for RDTs to be cost saving in populations with between 30 and 52% of clinically diagnosed malaria cases being malaria test positive.

Conclusion

While the use of RDTs in all suspected cases has been shown to be cost-saving when parasite prevalence among clinically diagnosed malaria cases is low to moderate, findings show that targeting RDTs at the group older than six years and treating children less than six years on the basis of clinical diagnosis is even more cost-saving. In semi-immune populations, young children carry the highest risk of severe malaria and many healthcare providers would find it harder to deny antimalarials to those who test negative in this age group.

The relevance of molecular markers in the analysis of malaria parasite populations

Malaria is one of the main human public health problems in the tropical world and is possibly becoming an emerging disease too in regions where it has been controlled. It has been an excellent model in the area of molecular studies, with scientific validation of techniques, application of data mainly in studies of parasite diversity and information on a number of different aspects associated with infection and disease. The transfer of the gathered knowledge and experience in malaria to other infections is of great use and we briefly review a number of molecular markers, methodologies and techniques mostly used for Plasmodium detection, as well as identification or characterization of parasite populations. Selection of appropriate techniques depends on the questions raised and the studies' objectives--the antigen-coding genes, microsatellite loci and drug-resistance associated markers being the three most analysed classes of markers. The need of validation and standardization of laboratory protocols is addressed and discussed as it may determine the comparison of data between different studies and laboratories, with relevance in field-collected samples or studies.

Quantification of artemisinin in Artemisia annua extracts by 1H-NMR

Artemisinin is a polycyclic sesquiterpene lactone that is highly effective against multidrug-resistant strains of Plasmodium falciparum, the etiological agent of the most severe form of malaria. Determination of artemisinin in the source plant, Artemisia annua, is a challenging problem since the compound is present in very low concentrations, is thermolabile and unstable, and lacks chromophoric or fluorophoric groups. The ain of this study was to develop a simple protocol for the quantification of artemisinin in a plant extract using an (1)H-NMR method. Samples were prepared by extraction of leaf material with acetone, treatment with activated charcoal to remove chlorophylls and removal of solvent. (1)H-NMR spectra were measured on samples dissolved in deuterochloroform with tert-butanol as internal standard. Quantification was carried out using the using the delta 5.864 signal of artemisinin and the delta 1.276 signal of tert-butanol. The method was optimised and fully validated against a reference standard of artemisinin. The results were compared with those obtained from the same samples quantified using an HPLC-refractive index (RI) method. The (1)H-NMR method gave a linear response for artemisinin within the range 9.85-97.99 mm (r(2) = 0.9968). Using the described method, yields of artemisinin in the range 0.77-1.06% were obtained from leaves of the A. annua hybrid CPQBA x POP, and these values were in agreement with those obtained using an HPLC-RI.

The persistent problem of malaria: addressing the fundamental causes of a global killer

Despite decades of global eradication and control efforts and explosive global economic development, malaria is the most important vector-borne disease of our day, killing more people today than 40 years ago and affecting millions worldwide, particularly poor residents of tropical regions. Global eradication efforts from the 1950s through the 1980s largely failed, leaving vector and parasite resistance in their wake. The persistence of malaria and the magnitude of its effects call for an action paradigm that links the traditional proximal arenas of intervention with malaria's fundamental causes by addressing the environmental, economic, and political dimensions of risk. We explore the more distal determinants of malaria burden that create underlying vulnerabilities, evaluating malaria risk as a function of socioeconomic context, environmental conditions, global inequality, systems of health care provision, and research. We recommend that future action to combat malaria be directed by a broad-spectrum approach that meaningfully addresses both the proximal and fundamental causes of this disease.