Malaria

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.

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.

Host-parasite relations and implications for control

This paper considers the various measures available to control several of the neglected tropical diseases (NTDs). To develop the optimum methods for controlling the parasites that cause these NTDs, knowledge of the life cycles of both the parasites and their vectors are essential. Each NTD requires its own strategy for control based on detailed knowledge of the life cycle, and vector control, chemotherapy, better water supplies and better hygiene are all components that may be appropriate. For some diseases, improved drugs are urgently required, for some the tools are available for elimination, while uniquely guinea worm could be eradicated without any chemotherapeutic drug being used. Several NTDs lend themselves to mass drug administration (MDA) in which human populations are annually offered safe, effective and usually donated drugs with a view to morbidity control and/or elimination. The drugs could and should be used to improve the quality of millions of lives, prevent suffering, stigma, disfigurement and early death. The role of pharmaceutical companies who have donated their drugs for the treatment of millions of disadvantaged people in the developing world is acknowledged. One result of such drug pressure however is that evolutionary change may result, and it is incumbent on scientists during monitoring and evaluation of control programmes to ensure that such changes are recognised. One other unfortunate development is that a paucity of newly trained vector-borne disease experts may constrain future control efforts.

Simulation of the cost-effectiveness of malaria vaccines

Background

A wide range of possible malaria vaccines is being considered and there is a need to identify which vaccines should be prioritized for clinical development. An important element of the information needed for this prioritization is a prediction of the cost-effectiveness of potential vaccines in the transmission settings in which they are likely to be deployed. This analysis needs to consider a range of delivery modalities to ensure that clinical development plans can be aligned with the most appropriate deployment strategies.

Methods

The simulations are based on a previously published individual-based stochastic model for the natural history and epidemiology of Plasmodium falciparum malaria. Three different vaccine types: pre-erythrocytic vaccines (PEV), blood stage vaccines (BSV), mosquito-stage transmission-blocking vaccines (MSTBV), and combinations of these, are considered each delivered via a range of delivery modalities (Expanded Programme of Immunization – EPI-, EPI with booster, and mass vaccination combined with EPI). The cost-effectiveness ratios presented are calculated for four health outcomes, for assumed vaccine prices of US$ 2 or US$ 10 per dose, projected over a 10-year period.

Results

The simulations suggest that PEV will be more cost-effective in low transmission settings, while BSV at higher transmission settings. Combinations of BSV and PEV are more efficient than PEV, especially in moderate to high transmission settings, while compared to BSV they are more cost-effective in moderate to low transmission settings. Combinations of MSTBV and PEV or PEV and BSV improve the effectiveness and the cost-effectiveness compared to PEV and BSV alone only when applied with EPI and mass vaccinations. Adding booster doses to the EPI is unlikely to be a cost-effective alternative to delivering vaccines via the EPI for any vaccine, while mass vaccination improves effectiveness, especially in low transmission settings, and is often a more efficient alternative to the EPI. However, the costs of increasing the coverage of mass vaccination over 50% often exceed the benefits.

Conclusion

The simulations indicate malaria vaccines might be efficient malaria control interventions, and that both transmission setting and vaccine delivery modality are important to their cost-effectiveness. Alternative vaccine delivery modalities to the EPI may be more efficient than the EPI. Mass vaccination is predicted to provide substantial health benefits at low additional costs, although achieving high coverage rates can lead to substantial incremental costs.

Regulatory elements within the prodomain of Falcipain-2, a cysteine protease of the malaria parasite Plasmodium falciparum

Falcipain-2, a papain family cysteine protease of the malaria parasite Plasmodium falciparum, plays a key role in parasite hydrolysis of hemoglobin and is a potential chemotherapeutic target. As with many proteases, falcipain-2 is synthesized as a zymogen, and the prodomain inhibits activity of the mature enzyme. To investigate the mechanism of regulation of falcipain-2 by its prodomain, we expressed constructs encoding different portions of the prodomain and tested their ability to inhibit recombinant mature falcipain-2. We identified a C-terminal segment (Leu¹⁵⁵–Asp²⁴³) of the prodomain, including two motifs (ERFNIN and GNFD) that are conserved in cathepsin L sub-family papain family proteases, as the mediator of prodomain inhibitory activity. Circular dichroism analysis showed that the prodomain including the C-terminal segment, but not constructs lacking this segment, was rich in secondary structure, suggesting that the segment plays a crucial role in protein folding. The falcipain-2 prodomain also efficiently inhibited other papain family proteases, including cathepsin K, cathepsin L, cathepsin B, and cruzain, but it did not inhibit cathepsin C or tested proteases of other classes. A structural model of pro-falcipain-2 was constructed by homology modeling based on crystallographic structures of mature falcipain-2, procathepsin K, procathepsin L, and procaricain, offering insights into the nature of the interaction between the prodomain and mature domain of falcipain-2 as well as into the broad specificity of inhibitory activity of the falcipain-2 prodomain.

Strong gametocytocidal effect of methylene blue-based combination therapy against falciparum malaria: a randomised controlled trial

Background

With the availability of new preventive and curative interventions, global malaria control has been strengthened significantly in recent years. Drugs effective in reducing malaria gametocytaemia might contribute to local elimination and possible long-term eradication. We here report on the effects of methylene blue (MB)-based malaria combination therapy on gametocytaemia during a randomised-controlled trial in Burkina Faso.

Methods

An open-label randomised controlled phase II study in 180 children aged 6–10 years with uncomplicated falciparum malaria was conducted in Nouna, north-western Burkina Faso. Children were randomised to MB–artesunate (AS), MB–amodiaquine (AQ), and AS-AQ (local standard of care). Overall follow-up was for 28 days, follow-up for gametocytaemia was for 14 days.

Findings

The treatment groups were similar in baseline characteristics and there was only one loss to follow-up. Compared to AS-AQ, both MB-containing regimens were associated with significantly reduced gametocyte carrier rates during follow-up days 3, 7, and 14. This effect was seen both in patients with and without P. falciparum gametocytaemia at baseline.

Interpretation

MB reveals pronounced gametocytocidal activity which appears to act against both existing and developing P. falciparum gametocytes. MB-based combination therapy thus has the potential to reduce transmission of P. falciparum malaria in endemic regions, which has important implications for future elimination and eradication strategies.

Trial Registration

ClinicalTrials.gov NCT00354380

Decreasing childhood mortality and increasing proportion of malaria deaths in rural Burkina Faso

BACKGROUND

Malaria is the leading cause of death among children less than five years of age in sub-Saharan Africa (SSA), however, precise estimates on the burden of malaria are lacking. The aim of this study was to describe temporal trends for malaria and all-cause mortality by combining a series of clinical and intervention studies conducted in Burkina Faso.

METHODS

Data from a demographic surveillance system was used to follow-up children under five years who participated in five observational and intervention studies between June 1999 and December 2004 in rural north-western Burkina Faso. Mortality data was analyzed with cause-specific mortality ascertained using the verbal autopsy method. Person-years (PY) of observations were computed and age-standardized mortality rates (MR) for all-causes and malaria (adjusted for missing causes of death) were calculated. Rate ratios to investigate mortality variations over years were calculated using multivariate Poisson regression.

RESULTS

The study followed 6,387 children aged less than five years (mean follow-up: 2.8 years; 16,099 PY). During the study period, 443 deaths were registered with malaria accounting for 49% of all deaths. All-cause and malaria-specific MR were 26.7 (95% CI: 24.2-29.2) and 15.8 (95% CI: 14.217.7) per 1,000 PY. All-cause MR declined over years of follow-up (from 31.2 to 16.3 per 1,000 PY in 1999/2000 to 2004, respectively) but malaria MR remained relatively stable (from 15.8 to 12.1 per 1,000 PY in 1999/2000 to 2004, respectively) resulting in an increasing relative effect of malaria on all-cause mortality. Variations in all-cause and malaria-specific mortality were observed with increasing age and across village town clusters.

CONCLUSION

The findings of this study support the continuously decreasing trend of all-cause mortality in most of SSA, but call for more efforts to comprehensively address malaria with existing control tools such as insecticide-treated bed nets and effective first-line combination therapies.

Efficacy and safety of a fixed dose artesunate-sulphamethoxypyrazine-pyrimethamine compared to artemether-lumefantrine for the treatment of uncomplicated falciparum malaria across Africa: a randomized multi-centre trial

Background

The efficacy of artemisinin-based combination therapy has already been demonstrated in a number of studies all over the world, and some of them can be regarded as comparably effective. Ease of administration of anti-malarial treatments with shorter courses and fewer tablets may be key determinant of compliance.

Methods

Patients with uncomplicated falciparum malaria and over six months of age were recruited in Cameroon, Mali, Rwanda and Sudan. 1,384 patients were randomly assigned to receive artesunate-sulphamethoxypyrazine-pyrimethamine (AS-SMP) three-day (once daily for 3 days) regimen (N = 476) or AS-SMP 24-hour (0 h, 12 h, 24 h) regimen (N = 458) or artemether-lumefantrine (AL), the regular 6 doses regimen (N = 450). The primary objective was to demonstrate non-inferiority (using a margin of -6%) of AS-SMP 24 hours or AS-SMP three days versus AL on the PCR-corrected 28-day cure rate.

Results

The PCR corrected 28-day cure rate on the intention to treat (ITT) analysis population were: 96.0%(457/476) in the AS-SMP three-day group, 93.7%(429/458) in the AS-SMP 24-hour group and 92.0%(414/450) in the AL group. Likewise, the cure rates on the PP analysis population were high: 99.3%(432/437) in the AS-SMP three-day group, 99.5%(416/419) in the AS-SMP 24-hour group and 99.7(391/394)% in the AL group. Most common drug-related adverse events were gastrointestinal symptoms (such as vomiting and diarrhea) which were slightly higher in the AS-SMP 24-hour group.

Conclusion

AS-SMP three days or AS-SMP 24 hours are safe, are as efficacious as AL, and are well tolerated.

Trial registration

NCT00484900 .

Synthesis of novel hybrid molecules from precursors with known antiparasitic activity

Three novel new compounds derived from antiparasitic precursors have been synthesized and tested for their antiamoebic and antigiardial activities. The condensation of 2-(2-methyl-5-1H-nitroimidazolyl)ethylamine (6) with 5-nitro-2-furylacrylic acid (7) gave 3-(5-nitrofuran-2-yl)-N-[2-(5-nitroimidazol-1-yl)ethyl]acrylamide (8). Condensation of 7 with 7-chloro-4-(piperazin-1-yl)quinoline (9) afforded 1-[4-(7-chloroquinolin-4-yl)piperazin-1-yl)-3-(5-nitrofuran-2-yl)propenone as a mixture of two isomers; 10-a (the E-isomer) and 10-b (the Z-isomer). In addition, the reaction of 9 with 1-(2-bromoethyl)-2-methyl-5-nitroimidazole (11) in the presence of K2CO3 and NaI yielded 7-chloro-4-(4-[2-(5-nitroimidazol-1-yl)ethyl]-piprazin-1-yl)quinoline (12). On the basis of preliminary screening data for these new compounds, compound 12 exhibited potent lethal activities against Entamoeba histolytica and Giardia intestinalis; its IC₅₀ ( about 1 µM) was lower, at least by a factor of five, compared to the standard drug, metronidazole. In addition, the IC₅₀ of compound 12 against the tested parasites is 600 times below that against Hep-2 and Vero cells. Compounds 8 and 10-a also exhibited potent or moderate antiamoebic and antigiardial activities with IC_{50 values} of about 5.5 µM, and 140 µM, respectively, against the tested parasites. These two hybrid molecules, 8, 10-a, were also non-cytotoxic at the lethal concentrations against the parasites.

Malaria--a major health problem within an oil palm plantation around Popondetta, Papua New Guinea

BACKGROUND

For companies operating in malaria endemic countries, malaria represents a substantial risk to workers and their dependants, and can lead to significantly reduced worker productivity. This study provides an overview of the malaria epidemiology within an oil palm plantation in Popondetta, south-eastern Papua New Guinea, its implication for the company with its employees and their families and the potential for control.

METHODS

In 2006, we carried out a cross-sectional study within six company villages, which included the determination of parasite rates by conventional microscopy, interviews and haemoglobin measurements. Passive surveillance data were collected from the 13 company aid posts for the years 2005 and 2006.

RESULTS

Malaria prevalence was found to be high: all-age prevalence was 33.5% (95% CI 30.1-37.0) in 723 individuals. Plasmodium falciparum was the dominant species, followed by Plasmodium vivax and Plasmodium malariae. Children between five and nine years of age were most affected (40.3%, 95% CI 0.32-0.49). Haemoglobin levels were found to be low; 11.0 g/dl (95% CI 10.8-11.1) for men and 10.4 g/dl (95% CI 10.3-10.5) for women, respectively. Plasmodium falciparum infections were significantly associated with anaemia (Hb < 10 g/dl). At the aid posts, all malaria cases in 2005 and January-March 2006 were diagnosed by symptoms only, while from April 2006 onwards most cases were tested by rapid diagnostic tests. Between 2005 and 2006, 22,023 malaria cases were diagnosed at the aid posts and malaria accounted for 30-40% of all clinical cases. Of the malaria cases, 13-20% were HOP employees. On average, an employee sick with malaria was absent for 1.8 days, resulting in a total of 9,313 workdays lost between 2005 and 2006. Sleeping outside of the house did not increase the risk of a malaria infection, neither did getting up before 7 am.

CONCLUSION

Malaria was found to be a major health burden in the Higaturu Oil Palm plantation, posing a high risk for company staff and their relatives, including expatriates and other non-immune workers. Reducing the malaria risk is a highly recommended investment for the company.

Multifunctional aspartic peptidase prosegments

The structure-function relationships of aspartic peptidases (APs) (EC 3.4.23.X) have been extensively investigated, yet much remains to be elucidated regarding the various molecular mechanisms of these enzymes. Over the past years, APs have received considerable interest for food applications (e.g. cheese, fermented foods) and as potential targets for pharmaceutical intervention in human diseases including hypertension, cancer, Alzheimer's disease, AIDS (acquired immune deficiency syndrome), and malaria. A deeper understanding of the structure and function of APs, therefore, will have a direct impact on the design of peptidase inhibitors developed to treat such diseases. Most APs are synthesized as zymogens which contain an N-terminal prosegment (PS) domain that is removed at acidic pH by proteolytic cleavage resulting in the active enzyme. While the nature of the AP PS function is not entirely understood, the PS can be important in processes such as the initiation of correct folding, protein stability, blockage of the active site, pH-dependence of activation, and intracellular sorting of the zymogen. This review summarizes the current knowledge of AP PS function (especially within the A1 family), with particular emphasis on protein folding, cellular sorting, and inhibition.

Plasmodium chabaudi: expression of active recombinant chabaupain-1 and localization studies in Anopheles sp

Plasmodium cysteine proteases have been shown to be immunogenic and are being used as malaria potential serodiagnostic markers and vaccine targets. Genes encoding two Plasmodium chabaudi cysteine proteases chabaupain-1 (CP-1) and chabaupain-2 (CP-2) were identified and further expressed in Escherichia coli. Solubilisation of recombinant CP-1 and CP-2 was achieved by decreasing the temperature of induction. Anopheles gambiae tissues infected with Plasmodium were analyzed by Western blotting using the anti-CP-1 antibody showing that CP-1 is only present in the A. gambiae midguts being absent from other infected mosquito biological material. Anti-CP-1 anti-serum recognized a 30 kDa band in P. chabaudi, Plasmodium berghei and Plasmodium yoelii lysates but does not recognize the recombinant CP-2 extracts suggesting high antibody specificity.

Cattle, other domestic animal ownership, and distance between dwelling structures are associated with reduced risk of recurrent Plasmodium falciparum infection in southern Zambia

OBJECTIVES

To examine the associations between household Plasmodium falciparum infection and a number of factors including domestic animal ownership, potential mosquito breeding sites, indoor darkness, density of people, distance between dwelling structures, and insecticide-treated bed net use.

METHODS

Analyses were based on data collected from a household survey conducted in Macha, Zambia. Thirty-four households with recurrent malaria infection in 2005-2008 were selected as case households and compared with 37 control households with no malaria infection randomly selected from the same geographic area. Logistic regression models were used to identify factors associated with household P. falciparum infection.

RESULTS

In multivariate analysis, cattle ownership was associated with reduced risk of P. falciparum infection (adjusted odds ratio = 0.19; 95% CI = 0.05-0.69), as was increased distance between dwelling structures (aOR = 0.26; 95% CI = 0.07-0.98). Ownership of the highest category of cattle, goats, dogs, or cats dramatically reduced the risk of P. falciparum infection (aOR = 0.13; 95% CI = 0.03-0.56).

CONCLUSION

Domestic animal, in particular cattle, ownership and greater distance between dwelling structures were associated with reduced risk of recurrent P. falciparum infection at the household level. These factors should be further investigated as supplemental measures for malaria control in rural African settings.

Mechanical features of Plasmodium falciparum acyl carrier protein in the delivery of substrates

The Acyl Carrier Protein (ACP) is a key element in the biosynthesis of fatty acids being responsible for the acyl group shuttling and delivery within a series of related enzymes. The molecular mechanism of the delivery process is poorly known, and its characterization is essential for in-depth understanding the biosynthetic machinery. A steered molecular dynamics approach has been applied to shed light on the putative delivery pathway, suggesting the small alpha3-helix act as gatekeeper for the transfer process. Preventing the delivery mechanism would be an innovative strategy for the development of pathway-based antimalarial compounds.

Polymeric linear Peptide chimeric vaccine-induced antimalaria immunity is associated with enhanced in vitro antigen loading

Immunization of mice with Plasmodium berghei or Plasmodium yoelii synthetic linear peptide chimeras (LPCs) based on the circumsporozoite protein protects against experimental challenge with viable sporozoites. The immunogenicity of LPCs is significantly enhanced by spontaneous polymerization. To better understand the antigenic properties of polymeric antimalarial peptides, we studied the immune responses elicited in mice immunized with a polymer or a monomer of a linear peptide construct specific for P. yoelii and compared the responses of antigen-presenting cells following incubation with both peptide species. Efficient uptake of the polymeric peptide in vitro resulted in higher expression of the coactivation markers CD80, CD40, and CD70 on dendritic cells and higher proinflammatory cytokine production than with the monomeric peptide. Macropinocytosis seems to be the main route used by polymeric peptides internalized by antigen-presenting cells. Spontaneous polymerization of synthetic antimalarial-peptide constructs to target professional antigen-presenting cells shows promise for simple delivery of subunit malaria vaccines.

Exploiting structural analysis, in silico screening, and serendipity to identify novel inhibitors of drug-resistant falciparum malaria

Plasmodium falciparum thymidylate synthase-dihydrofolate reductase (TS-DHFR) is an essential enzyme in folate biosynthesis and a major malarial drug target. This bifunctional enzyme thus presents different design approaches for developing novel inhibitors against drug-resistant mutants. We performed a high-throughput in silico screen of a database of diverse, drug-like molecules against a non-active-site pocket of TS-DHFR. The top compounds from this virtual screen were evaluated by in vitro enzymatic and cellular culture studies. Three compounds active to 20 microM IC(50)'s in both wildtype and antifolate-resistant P. falciparum parasites were identified; moreover, no inhibition of human DHFR enzyme was observed, indicating that the inhibitory effects appeared to be parasite-specific. Notably, all three compounds had a biguanide scaffold. However, relative free energy of binding calculations suggested that the compounds might preferentially interact with the active site over the screened non-active-site region. To resolve the two possible modes of binding, co-crystallization studies of the compounds complexed with TS-DHFR enzyme were performed. Surprisingly, the structural analysis revealed that these novel, biguanide compounds do indeed bind at the active site of DHFR and additionally revealed the molecular basis by which they overcome drug resistance. To our knowledge, these are the first co-crystal structures of novel, biguanide, non-WR99210 compounds that are active against folate-resistant malaria parasites in cell culture.

Structure and non-essential function of glycerol kinase in Plasmodium falciparum blood stages

Malaria pathology is caused by multiplication of asexual parasites within erythrocytes, whereas mosquito transmission of malaria is mediated by sexual precursor cells (gametocytes). Microarray analysis identified glycerol kinase (GK) as the second most highly upregulated gene in Plasmodium falciparum gametocytes with no expression detectable in asexual blood stage parasites. Phosphorylation of glycerol by GK is the rate-limiting step in glycerol utilization. Deletion of this gene from P. falciparum had no effect on asexual parasite growth, but surprisingly also had no effect on gametocyte development or exflagellation, suggesting that these life cycle stages do not utilize host-derived glycerol as a carbon source. Kinetic studies of purified PfGK showed that the enzyme is not regulated by fructose 1,6 bisphosphate. The high-resolution crystal structure of P. falciparum GK, the first of a eukaryotic GK, reveals two domains embracing a capacious ligand-binding groove. In the complexes of PfGK with glycerol and ADP, we observed closed and open forms of the active site respectively. The 27 degree domain opening is larger than in orthologous systems and exposes an extensive surface with potential for exploitation in selective inhibitor design should the enzyme prove to be essential in vivo either in the human or in the mosquito.

Malaria in Women and Children

After reading this chapter and answering the discussion questions that follow, you should be able to

Explain the global burden of malaria, discuss its clinical manifestations, and appraise its health impact on women and children.

Analyze the mechanisms and consequences of malaria and HIV co-infection and discuss current treatment, control and prevention strategies.

Describe the challenges posed by vector resistance to insecticides, parasite resistance to antimalarials, climate change, wars/conflicts, and HIV/AIDS to malaria control and prevention efforts.

Evaluate social, cultural, and economic limitations of community-based programs for malaria control and prevention.

Efficacy and safety of artemether-lumefantrine dispersible tablets compared with crushed commercial tablets in African infants and children with uncomplicated malaria: a randomised, single-blind, multicentre trial

BACKGROUND

Combination treatments, preferably containing an artemisinin derivative, are recommended to improve efficacy and prevent Plasmodium falciparum drug resistance. Our aim was to show non-inferiority of a new dispersible formulation of artemether-lumefantrine to the conventional crushed tablet in the treatment of young children with uncomplicated malaria.

METHODS

We did a randomised non-inferiority study on children weighing 5-35 kg with uncomplicated P falciparum malaria in Benin, Kenya, Mali, Mozambique, and Tanzania. The primary outcome measure was PCR-corrected 28-day parasitological cure rate. We aimed to show non-inferiority (with a margin of -5%) of dispersible versus crushed tablet. We constructed an asymptotic one-sided 97.5% CI on the difference in cure rates. A computer-generated randomisation list was kept centrally and investigators were unaware of the study medication administered. We used a modified intention-to-treat analysis. This trial is registered with ClinicalTrials.gov, number NCT00386763.

FINDINGS

899 children aged 12 years or younger were randomly assigned to either dispersible (n=447) or crushed tablets (n=452). More than 85% of patients in each treatment group completed the study. 812 children qualified for the modified intention-to-treat analysis (n=403 vs n=409). The PCR-corrected day-28 cure rate was 97.8% (95% CI 96.3-99.2) in the group on dispersible formulation and 98.5% (97.4-99.7) in the group on crushed formulation. The lower bound of the one-sided 97.5% CI was -2.7%. The most common drug-related adverse event was vomiting (n=33 [7%] and n=42 [9%], respectively). No signs of ototoxicity or relevant cardiotoxicity were seen.

INTERPRETATION

A six-dose regimen of artemether-lumefantrine with the new dispersible formulation is as efficacious as the currently used crushed tablet in infants and children, and has a similar safety profile.

Novel therapies for the prevention of malaria

BACKGROUND

Malaria continues to exact a huge toll on the health of residents of endemic countries. Thus, new approaches to prevention and treatment are needed.

OBJECTIVE

To provide an update on novel therapies for the prevention of malaria.

METHODS

Systematic MEDLINE search from 1956 to 2008 using the search term 'malaria' (with the subheadings 'intermittent preventive treatment', 'mass drug administration', 'chemotherapy', 'artemisinin-based combination therapy' and 'home-based management of malaria').

CONCLUSIONS

Chemoprophylaxis is used as a short-term protective measure for non-immune visitors to malaria-endemic countries. However, in malaria-endemic areas, chemoprophylaxis has not been implemented widely because of concerns related to sustainability, cost-effectiveness, appropriate delivery systems and development of drug resistance. Intermittent preventive treatment, a novel approach to malaria control, has the potential to provide some of the benefits of sustained chemoprophylaxis without some of its drawbacks.

Chloroquine-astemizole hybrids with potent in vitro and in vivo antiplasmodial activity

A dual activity, conjugated approach has been taken to form hybrid molecules of two known antimalarial drugs, chloroquine (CQ) and the non-sedating H1 antagonist astemizole. A variety of linkers were investigated to conjugate the two agents into one molecule. Compounds 5-8 possessed improved in vitro activity against a CQ-resistant strain of Plasmodium falciparum, and examples 7 and 8 were active in vivo in mouse models of malaria.

Photodynamic control of human pathogenic parasites in aquatic ecosystems using chlorophyllin and pheophorbid as photodynamic substances

When used at low concentrations and added to the water body, water-soluble chlorophyllin (resulting from chlorophyll after removal of the phytol) and pheophorbid (produced from chlorophyllin by acidification) are able to kill mosquito larvae and other small animals within a few hours under exposure of solar radiation. Under laboratory conditions, the use of chlorophyllin/pheophorbid as photodynamic substances for pest control in water bodies promises to be not only effective and ecologically beneficial but also cheap. The LD50 (50% of mortality in the tested organisms) value in Culex sp. larvae was about 6.88 mg/l, in Chaoborus sp. larvae about 24.18 mg/l, and in Daphnia 0.55 mg/l. The LD50 values determined for pheophorbid were 8.44 mg/l in Culex, 1.05 mg/l in Chaoborus, and 0.45 mg/l in Daphnia, respectively. In some cases, chlorophyllin and pheophorbid were also found to be (less) active in darkness. The results presented in this paper show that chlorophyllin is about a factor of 100 more effective than methylene blue or hematoporphyrine, which were tested earlier for the same purpose. It is also much cheaper and, as a substance found in every green plant, it is 100% biodegradable.

Selection of a trioxaquine as an antimalarial drug candidate

Trioxaquines are antimalarial agents based on hybrid structures with a dual mode of action. One of these molecules, PA1103/SAR116242, is highly active in vitro on several sensitive and resistant strains of Plasmodium falciparum at nanomolar concentrations (e.g., IC(50) value = 10 nM with FcM29, a chloroquine-resistant strain) and also on multidrug-resistant strains obtained from fresh patient isolates in Gabon. This molecule is very efficient by oral route with a complete cure of mice infected with chloroquine-sensitive or chloroquine-resistant strains of Plasmodia at 26-32 mg/kg. This compound is also highly effective in humanized mice infected with P. falciparum. Combined with a good drug profile (preliminary absorption, metabolism, and safety parameters), these data were favorable for the selection of this particular trioxaquine for development as drug candidate among 120 other active hybrid molecules.

Malaria parasite pre-erythrocytic stage infection: gliding and hiding

In malaria, the red blood cell-infectious form of the Plasmodium parasite causes illness and the possible death of infected hosts. The initial infection in the liver caused by the mosquito-borne sporozoite parasite stage, however, causes little pathology and no symptoms. Nevertheless, pre-erythrocytic parasite stages are attracting passionate research efforts not least because they are the most promising targets for malaria vaccine development. Here, we review how the infectious sporozoite makes its way to the liver and subsequently develops within hepatocytes. We discuss the factors, both parasite and host, involved in the interactions that occur during this "silent" phase of infection.

What should vaccine developers ask? Simulation of the effectiveness of malaria vaccines

Background

A number of different malaria vaccine candidates are currently in pre-clinical or clinical development. Even though they vary greatly in their characteristics, it is unlikely that any of them will provide long-lasting sterilizing immunity against the malaria parasite. There is great uncertainty about what the minimal vaccine profile should be before registration is worthwhile; how to allocate resources between different candidates with different profiles; which candidates to consider combining; and what deployment strategies to consider.

Methods and Findings

We use previously published stochastic simulation models, calibrated against extensive epidemiological data, to make quantitative predictions of the population effects of malaria vaccines on malaria transmission, morbidity and mortality. The models are fitted and simulations obtained via volunteer computing. We consider a range of endemic malaria settings with deployment of vaccines via the Expanded program on immunization (EPI), with and without additional booster doses, and also via 5-yearly mass campaigns for a range of coverages. The simulation scenarios account for the dynamic effects of natural and vaccine induced immunity, for treatment of clinical episodes, and for births, ageing and deaths in the cohort. Simulated pre-erythrocytic vaccines have greatest benefits in low endemic settings (<EIR of 10.5) where between 12% and 14% of all deaths are averted when initial efficacy is 50%. In some high transmission scenarios (>EIR of 84) PEV may lead to increased incidence of severe disease in the long term, if efficacy is moderate to low (<70%). Blood stage vaccines (BSV) are most useful in high transmission settings, and are comparable to PEV for low transmission settings. Combinations of PEV and BSV generally perform little better than the best of the contributing components. A minimum half-life of protection of 2–3 years appears to be a precondition for substantial epidemiological effects. Herd immunity effects can be achieved with even moderately effective (>20%) malaria vaccines (either PEV or BSV) when deployed through mass campaigns targeting all age-groups as well as EPI, and especially if combined with highly efficacious transmission-blocking components.

Conclusions

We present for the first time a stochastic simulation approach to compare likely effects on morbidity, mortality and transmission of a range of malaria vaccines and vaccine combinations in realistic epidemiological and health systems settings. The results raise several issues for vaccine clinical development, in particular appropriateness of vaccine types for different transmission settings; the need to assess transmission to the vector and duration of protection; and the importance of deployment additional to the EPI, which again may make the issue of number of doses required more critical. To test the validity and robustness of our conclusions there is a need for further modeling (and, of course, field research) using alternative formulations for both natural and vaccine induced immunity. Evaluation of alternative deployment strategies outside EPI needs to consider the operational implications of different approaches to mass vaccination.

Distribution systems of insecticide-treated bed nets for malaria control in rural Burkina Faso: cluster-randomized controlled trial

BACKGROUND

Insecticide-impregnated bed nets (ITNs) have been shown to be a highly effective tool against malaria in the endemic regions of sub-Saharan Africa (SSA). There are however different opinions about the role of ITN social marketing and ITN free distribution in the roll-out of ITN programmes. The objective of this study was to evaluate the effects of free ITN distribution through antenatal care services in addition to an ITN social marketing programme in an area typical for rural SSA.

METHODS

A cluster-randomised controlled ITN trial took place in the whole Kossi Province in north-western Burkina Faso, an area highly endemic for malaria. Twelve clusters were assigned to long-term ITN (Serena brand) social marketing plus free ITN (Serena brand) distribution to all pregnant women attending governmental antenatal care services (group A), and 13 clusters to ITN social marketing only (group B). The intervention took place during the rainy season of 2006 and thereafter. The trial was evaluated through a representative household survey at baseline and after one year. Serena ITN household ownership was the primary outcome measure.

FINDINGS

A total of 1052 households were visited at baseline in February 2006 and 1050 at follow-up in February 2007. Overall Serena ITN household ownership increased from 16% to 28% over the study period, with a significantly higher increase in group A (13% to 35%) than in group B (18% to 23%) (p<0.001).

INTERPRETATION

The free distribution of ITNs to pregnant women through governmental antenatal care services in addition to ITN social marketing substantially improved ITN household ownership in rural Burkina Faso.

TRIAL REGISTRATION

Controlled-Trials.com ISRCTN07985309.

Enhanced antimalarial activity of novel synthetic aculeatin derivatives

We report the design, synthesis, and in vitro evaluation of novel polyspirocyclic structures, inspired by the antimalarial natural products, the aculeatins. A divergent synthetic strategy was conceived for the practical supply and has allowed the discovery of two novel and more potent analogues active on the Plasmodium falciparum 3D7 strain. Moreover, these compounds proved to be potent against Toxoplasma gondii. A number of features that govern these inhibitions were identified.

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.

Development of pilot scale production process and characterization of a recombinant multiepitope malarial vaccine candidate FALVAC-1A expressed in Escherichia coli

Among the four human malarial species, Plasmodium falciparum causes most of the mortality associated with malaria. Several approaches are being pursued to develop a suitable malaria vaccine since it may be the most effective weapon to fight against malaria. A highly immunogenic, synthetic protein consisting of 21 epitopes from pre-erythrocytic and blood stages of P. falciparum (FALVAC-1A) was constructed and expressed in Escherichia coli. This vaccine candidate was highly immunogenic and induced protective antibodies in rabbits when produced through lab-scale processes in milligram quantities. In order to take this vaccine candidate for further clinical trial, we optimized the process for industrial scale production and purification. Here we describe various methods used in pilot scale production and characterization of FALVAC-1A. A fed-batch cultivation process in a bioreactor at 10-L scale was optimized to express the protein in high yields as inclusion bodies in E. coli cells with the recombinant plasmids. Methods to solubilize, capture and purify the target protein from the inclusion bodies were optimized and the resultant protein was >95% pure based on SDS-PAGE and RP-HPLC. This protein was then refolded and nativity was confirmed by Far-UV CD spectroscopy. Final purified protein was characterized to estimate yield, purity, mass and confirmed to be free of host cell proteins, nucleic acids and bacterial endotoxins. This study confirms that industrial scale clinical grade FALVAC-1A can be produced in a cost-effective manner for clinical trials.

Safety and tolerability of combination antimalarial therapies for uncomplicated falciparum malaria in Ugandan children

Background

Combination antimalarial therapy is recommended for the treatment of uncomplicated falciparum malaria in Africa; however, some concerns about the safety and tolerability of new regimens remain. This study compared the safety and tolerability of three combination antimalarial regimens in a cohort of Ugandan children.

Methods

A longitudinal, single-blind, randomized clinical trial of children was conducted between November 2004 and May 2007 in Kampala, Uganda. Upon diagnosis of the first episode of uncomplicated malaria, participants were randomized to treatment with amodiaquine + sulphadoxine-pyrimethamine (AQ+SP), artesunate + amodiaquine (AS+AQ), or artemether-lumefantrine (AL). Once randomized, participants received the same regimen for all subsequent episodes of uncomplicated malaria. Participants were actively monitored for adverse events for the first 14 days after each treatment, and then passively followed until their next study medication treatment, or withdrawal from study. Outcome measures included the risk of adverse events at 14 and 42 days after treatment.

Results

Of 601 enrolled children, 382 were diagnosed with at least one episode of uncomplicated malaria and were treated with study medications. The median age at treatment was 6.3 years (range 1.1 – 12.3 years). At 14 days of follow-up, AQ+SP treatment was associated with a higher risk of anorexia, weakness, and subjective fever than treatment with AL, and a higher risk of weakness, and subjective fever than treatment with AS+AQ. Treatment with AL was associated with a higher risk of elevated temperature. Repeated episodes of neutropaenia associated with AS+AQ were detected in one participant. Considering only children less than five years, those who received AQ+SP were at higher risk of developing moderate or severe anorexia and weakness than those treated with AL (anorexia: RR 3.82, 95% CI 1.59 – 9.17; weakness: RR 5.40, 95% CI 1.86 – 15.7), or AS+AQ (anorexia: RR 2.10, 95% CI 1.04 – 4.23; weakness: RR 2.26, 95% CI 1.01 – 5.05). Extending the analysis to 42 days of follow-up had little impact on the findings.

Conclusion

This study confirms the safety and tolerability of AS+AQ and AL in Ugandan children, and suggests that AQ+SP is safe, but less well-tolerated, particularly in younger children. As newer antimalarial regimens are deployed, collecting data on their safety and tolerability will be essential.

Trial registration

Current Controlled Trials Identifier ISRCTN37517549

Substandard anti-malarial drugs in Burkina Faso

BACKGROUND

There is concern about an increasing infiltration of markets by substandard and fake medications against life-threatening diseases in developing countries. This is particularly worrying with regard to the increasing resistance development of Plasmodium falciparum against affordable anti-malarial medications, which has led to a change to more expensive drugs in most endemic countries.

METHODS

A representative sample of modern anti-malarial medications from licensed (public and private pharmacies, community health workers) and illicit (market and street vendors, shops) sources has been collected in the Nouna Health District in north-western Burkina Faso in 2006. All drugs were tested for their quality with the standard procedures of the German Pharma Health Fund-Minilab. Detected low standard drugs were re-tested with European Pharmacopoeia 2.9.1 standards for disintegration and ultraviolet-visible spectroscopy at the laboratory of the Heidelberg University for confirmation.

RESULTS

Overall, 86 anti-malarial drug samples were collected, of which 77 samples have been included in the final analysis. The sample consisted of 39/77 (50%) chloroquine, 10/77 (13%) pyrimethamine-sulphadoxine, 9/77 (12%) quinine, 6/77 (8%) amodiaquine, 9/77 (12%) artesunate, and 4/77 (5%) artemether-lumefantrine. 32/77 (42%) drug samples were found to be of poor quality, of which 28 samples failed the visual inspection, nine samples had substandard concentrations of the active ingredient, four samples showed poor disintegration, and one sample contained non of the stated active ingredient. The licensed and the illicit market contributed 5/47 (10.6%) and 27/30 (90.0%) samples of substandard drugs respectively.

CONCLUSION

These findings provide further evidence for the wide-spread existence of substandard anti-malarial medications in Africa and call for strengthening of the regulatory and quality control capacity of affected countries, particularly in view of the now wider available and substantially more costly artemisinin-based combination therapies.

A murine model of falciparum-malaria by in vivo selection of competent strains in non-myelodepleted mice engrafted with human erythrocytes

To counter the global threat caused by Plasmodium falciparum malaria, new drugs and vaccines are urgently needed. However, there are no practical animal models because P. falciparum infects human erythrocytes almost exclusively. Here we describe a reliable falciparum murine model of malaria by generating strains of P. falciparum in vivo that can infect immunodeficient mice engrafted with human erythrocytes. We infected NOD(scid/beta2m-/-) mice engrafted with human erythrocytes with P. falciparum obtained from in vitro cultures. After apparent clearance, we obtained isolates of P. falciparum able to grow in peripheral blood of engrafted NOD(scid/beta2m-/-) mice. Of the isolates obtained, we expanded in vivo and established the isolate Pf3D7(0087/N9) as a reference strain for model development. Pf3D7(0087/N9) caused productive persistent infections in 100% of engrafted mice infected intravenously. The infection caused a relative anemia due to selective elimination of human erythrocytes by a mechanism dependent on parasite density in peripheral blood. Using this model, we implemented and validated a reproducible assay of antimalarial activity useful for drug discovery. Thus, our results demonstrate that P. falciparum contains clones able to grow reproducibly in mice engrafted with human erythrocytes without the use of myeloablative methods.

PbSR is synthesized in macrogametocytes and involved in formation of the malaria crystalloids

Crystalloids are transient organelles that form in developing malaria ookinetes and disappear after ookinete-to-oocyst transition. Their origins and functions remain poorly understood. The Plasmodium berghei scavenger receptor-like protein PbSR is essential for mosquito-to-host transmission of the parasite: PbSR knockout parasites produce normal numbers of oocysts that fail to form sporozoites, pointing to a role for PbSR in the oocyst during sporogony. Here, using fluorescent protein tagging and targeted gene disruption, we show that PbSR is synthesized in macrogametocytes, gets targeted to the crystalloids of developing ookinetes and is involved in crystalloid formation. While oocyst sporulation rates of PbSR knockout parasites are highly reduced in parasite-infected mosquitoes, sporulation rates in vitro are not adversely affected, supporting the view that mosquito factors could be involved in the PbSR loss-of-function phenotype. These findings are the first to identify a parasite protein involved with the crystalloid organelle, and suggest a novel protein-trafficking mechanism to deliver PbSR to the oocysts.

Efficacy of amodiaquine in the treatment of uncomplicated falciparum malaria in young children of rural north-western Burkina Faso

Background

Combination therapy has become a new paradigm in malaria treatment. Amodiaquine is a common partner drug in different malaria combination therapies used or investigated in sub-Saharan Africa, but data on its efficacy as a single drug are scarce.

Methods

The objective of the study was to determine the efficacy of amodiaquine against falciparum malaria in neighbouring rural and urban areas of north-western Burkina Faso. The study was designed as an uncontrolled trial in children aged 6–59 months with uncomplicated falciparum malaria in the Nouna Health District.

Results

During the rainy season 2005, 117 children were enrolled, 62 from the rural and 55 from the urban study area. The crude adequate clinical and parasitological response (ACPR) rate was 103/117 (88%) by day 14 but decreased to 28/117 (24%) by day 28. After PCR correction for reinfections, ACPR rates were 108/117 (92%) and 71/117 (61%) by day 14 and day 28, respectively. There were no significant differences in efficacy between urban and rural areas. The Plasmodium falciparum crt K76T mutation not predict AQ failure, but was selected in parasites re-appearing following treatment. No serious adverse events occurred and only 16 other adverse events were recorded.

Conclusion

Compared to chloroquine, amodiaquine is more effective against uncomplicated falciparum malaria in Burkina Faso. However, a considerable degree of amodiaquine resistance already exists and it is currently unclear how this resistance will develop when amodiaquine in combination with other drugs is used on a large scale.

Trial registration

Current Controlled Trials ISRCTN73824458.

Blood coagulation, inflammation, and malaria

Malaria remains a highly prevalent disease in more than 90 countries and accounts for at least 1 million deaths every year. Plasmodium falciparum infection is often associated with a procoagulant tonus characterized by thrombocytopenia and activation of the coagulation cascade and fibrinolytic system; however, bleeding and hemorrhage are uncommon events, suggesting that a compensated state of blood coagulation activation occurs in malaria. This article (i) reviews the literature related to blood coagulation and malaria in a historic perspective, (ii) describes basic mechanisms of coagulation, anticoagulation, and fibrinolysis, (iii) explains the laboratory changes in acute and compensated disseminated intravascular coagulation (DIC), (iv) discusses the implications of tissue factor (TF) expression in the endothelium of P. falciparum infected patients, and (v) emphasizes the procoagulant role of parasitized red blood cells (RBCs) and activated platelets in the pathogenesis of malaria. This article also presents the Tissue Factor Model (TFM) for malaria pathogenesis, which places TF as the interface between sequestration, endothelial cell (EC) activation, blood coagulation disorder, and inflammation often associated with the disease. The relevance of the coagulation-inflammation cycle for the multiorgan dysfunction and coma is discussed in the context of malaria pathogenesis.

Safety and immunogenicity of a malaria vaccine, Plasmodium falciparum AMA-1/MSP-1 chimeric protein formulated in montanide ISA 720 in healthy adults

Background

The P. falciparum chimeric protein 2.9 (PfCP-2.9) consisting of the sequences of MSP1-19 and AMA-1 (III) is a malaria vaccine candidate that was found to induce inhibitory antibodies in rabbits and monkeys. This was a phase I randomized, single-blind, placebo-controlled, dose-escalation study to evaluate the safety and immunogenicity of the PfCP-2.9 formulated with a novel adjuvant Montanide ISA720. Fifty-two subjects were randomly assigned to 4 dose groups of 10 participants, each receiving the test vaccine of 20, 50, 100, or 200 µg respectively, and 1 placebo group of 12 participants receiving the adjuvant only.

Methods and Findings

The vaccine formulation was shown to be safe and well-tolerated, and none of the participants withdrew. The total incidence of local adverse events (AEs) was 75%, distributed among 58% of the placebo group and 80% of those vaccinated. Among the vaccinated, 65% had events that were mild and 15% experienced moderate AEs. Almost all systemic adverse reactions observed in this study were graded as mild and required no therapy. The participants receiving the test vaccine developed detectable antibody responses which were boosted by the repeated vaccinations. Sixty percent of the vaccinated participants had high ELISA titers (>1∶10,000) of antigen-specific antibodies which could also recognize native parasite proteins in an immunofluorescence assay (IFA).

Conclusion

This study is the first clinical trial for this candidate and builds on previous investigations supporting PfCP-2.9/ISA720 as a promising blood-stage malaria vaccine. Results demonstrate safety, tolerability (particularly at the lower doses tested) and immunogenicity of the formulation. Further clinical development is ongoing to explore optimizing the dose and schedule of the formulation to decrease reactogenicity without compromising immunogenicity.

Trial Registration

Chinese State Food and Drug Administration (SFDA) 2002SL0046; Controlled-Trials.com ISRCTN66850051 [66850051]

HLA-B27 and ankylosing spondylitis geographic distribution as the result of a genetic selection induced by malaria endemic? A review supporting the hypothesis

The geographic distribution of HLA-B27 shows a latitude-related gradient inverse to that of malaria endemic. An apparent exception occurs in New Guinea, a region where malaria is present, but where HLA-B27 frequency shows, however, an orographic gradient antithetic to that of malaria incidence. We therefore suggest that Plasmodium falciparum may have exerted a negative selection on this gene. This might be due to a higher susceptibility to severe forms of malaria, associated with HLA-B27 or other close gene(s). In addition, we suggest here that the same selective pressure that has contributed to reduce the HLA-B27 frequency in some regions has favoured the fixing of newly generated B27 subtypes included in more advantageous HLA haplotypes. In some cases, as for B*2709 in Sardinia and B*2706 in Southeast Asia, these haplotypes may harbour factors that protect from Ankylosing Spondylitis, an autoimmune disease strongly associated with HLA-B27, thus offering a novel, powerful tool to dissect disease pathogenesis, and to identify additional genetic factors of susceptibility.

A magneto-optic route toward the in vivo diagnosis of malaria: preliminary results and preclinical trial data

We report the development of magneto-optic technology for the rapid quantitative diagnosis of malaria that may also be realizable in a noninvasive format. Hemozoin, the waste product of malarial parasitic action on hemoglobin, is produced in a form that under the action of an applied magnetic field gives rise to an induced optical dichroism characteristic of the hemozoin concentration. Here we show that precise measurement of this induced dichroism may be used to determine the level of malarial infection because this correlates, albeit in a complex manner throughout the infection cycle, with the concentration of hemozoin in the blood and tissues of infected patients. Under conservative assumptions for the production of hemozoin as a function of parasitemia, initial results indicate that the technique can match or exceed other current diagnostic techniques. The validity of the approach is confirmed by a small preliminary clinical trial on 13 patients, and measurements on live parasitized cells obtained from in vitro culture verify the possibility of producing in vivo diagnostic instrumentation.

Plasmodium falciparum malaria vaccines in development

The development and implementation of a malaria vaccine would constitute a major breakthrough for global health. Recently, numerous new candidates have entered clinical testing, following strategies that are as diverse as the malaria cycle is complex. While promising results have been obtained, some candidate vaccines have not fulfilled expectations. The challenges are not merely scientific; further progresses will require the development of competent investigator networks, partnerships between academics, industry and funding agencies, and continuous political commitment. In this review, we present the developmental status of all malaria vaccine candidates that are currently in human clinical testing against Plasmodium falciparum, as well as selected malaria vaccine candidates at preclinical development stage, and discuss the main challenges facing the field of malaria vaccine development.

Characterization of VAR2CSA-deficient Plasmodium falciparum-infected erythrocytes selected for adhesion to the BeWo placental cell line

Background

Malaria in pregnancy is characterized by accumulation of infected erythrocytes (IE) in the placenta. The key ligand identified as mediating this process is a Plasmodium falciparum erythrocyte membrane protein 1 family member, termed VAR2CSA. VAR2CSA appears to be the main ligand responsible for adhesion to chondroitin sulphate A (CSA). Whether other PfEMP1 molecules can also mediate placental adhesion, independent of CSA binding, is unclear.

Methods

The parasite line CS2 carrying a disrupted var2csa gene (CS2KO) was selected for adhesion to the BeWo choriocarcinoma cell line, which has been proposed as a model for placental malaria. The selected and control IE were tested for adhesion to placental sections and flow cytometry was used to measure recognition of IE by three serum sets from malaria-exposed men and women.

Results

Wild-type CS2 adhere to BeWo and placental tissue via CSA. CS2KO IE were successfully selected for adhesion to BeWo, and adhered by a CSA-independent mechanism. They bound to immobilized ICAM-1 and CD36. BeWo-selected CS2KO bound at moderate levels to placental sections, but most binding was to placental villi rather than to the syncytiotrophoblast to which IE adherence occurs in vivo. This binding was inhibited by a blocking antibody to CD36 but not to ICAM-1. As expected, sera from malaria-exposed adults recognized CS2 IE in a gender and parity dependent manner. In one serum set, there was a similar but less pronounced pattern of antibody binding to selected CS2KO IE, but this was not seen in two others. One var gene, It4var19, was particularly abundant in the selected line and was detected as full length transcripts in BeWo-selected IE, but not unselected CS2KO.

Conclusion

This study suggests that IE with characteristics similar to the CS2KO have a limited role in the pathogenesis of placental malaria. VAR2CSA appear to be the major ligand for placental adhesion, and could be the basis for a vaccine against pregnancy malaria.

Process and effects of a community intervention on malaria in rural Burkina Faso: randomized controlled trial

BACKGROUND

In the rural areas of sub-Saharan Africa, the majority of young children affected by malaria have no access to formal health services. Home treatment through mothers of febrile children supported by mother groups and local health workers has the potential to reduce malaria morbidity and mortality.

METHODS

A cluster-randomized controlled effectiveness trial was implemented from 2002-2004 in a malaria endemic area of rural Burkina Faso. Six and seven villages were randomly assigned to the intervention and control arms respectively. Febrile children from intervention villages were treated with chloroquine (CQ) by their mothers, supported by local women group leaders. CQ was regularly supplied through a revolving fund from local health centres. The trial was evaluated through two cross-sectional surveys at baseline and after two years of intervention. The primary endpoint of the study was the proportion of moderate to severe anaemia in children aged 6-59 months. For assessment of the development of drug efficacy over time, an in vivo CQ efficacy study was nested into the trial. The study is registered under http://www.controlled-trials.com (ISRCTN 34104704).

RESULTS

The intervention was shown to be feasible under program conditions and a total of 1.076 children and 999 children were evaluated at baseline and follow-up time points respectively. Self-reported CQ treatment of fever episodes at home as well as referrals to health centres increased over the study period. At follow-up, CQ was detected in the blood of high proportions of intervention and control children. Compared to baseline findings, the prevalence of anaemia (29% vs 16%, p < 0.0001) and malaria parameters such as prevalence of P. falciparum parasitaemia, fever and palpable spleens was lower at follow-up but there were no differences between the intervention and control group. CQ efficacy decreased over the study period but this was not associated with the intervention.

DISCUSSION

The decreasing prevalence of malaria morbidity including anaemia over the study period can be explained by an overall increase of malaria prevention and treatment activities in the study area. The lack of effectiveness of the intervention was likely caused by contamination, pre-existing differences in the coverage of malaria treatment in both study groups and an unexpectedly rapid increase of resistance against CQ, the first-line treatment drug at the time of the study.

Coenzyme A biosynthesis: an antimicrobial drug target

Pantothenic acid, a precursor of coenzyme A (CoA), is essential for the growth of pathogenic microorganisms. Since the structure of pantothenic acid was determined, many analogues of this essential metabolite have been prepared. Several have been demonstrated to exert an antimicrobial effect against a range of microorganisms by inhibiting the utilization of pantothenic acid, validating pantothenic acid utilization as a potential novel antimicrobial drug target. This review commences with an overview of the mechanisms by which various microorganisms acquire the pantothenic acid they require for growth, and the universal CoA biosynthesis pathway by which pantothenic acid is converted into CoA. A detailed survey of studies that have investigated the inhibitory activity of analogues of pantothenic acid and other precursors of CoA follows. The potential of inhibitors of both pantothenic acid utilization and biosynthesis as novel antibacterial, antifungal and antimalarial agents is discussed, focusing on inhibitors and substrates of pantothenate kinase, the enzyme catalysing the rate-limiting step of CoA biosynthesis in many organisms. The best strategies are considered for identifying inhibitors of pantothenic acid utilization and biosynthesis that are potent and selective inhibitors of microbial growth and that may be suitable for use as chemotherapeutic agents in humans.

Murine model for assessment of Plasmodium falciparum transmission-blocking vaccine using transgenic Plasmodium berghei parasites expressing the target antigen Pfs25

Currently, there is no animal model for Plasmodium falciparum challenge to evaluate malaria transmission-blocking vaccines based on the well-established Pfs25 target antigen. The biological activity of transmission-blocking antibodies is typically assessed using an assay known as the membrane feeding assay (MFA). It is an in vitro method that involves mixing antibodies with cultured P. falciparum gametocytes and feeding them to mosquitoes through an artificial membrane followed by assessment of infection in the mosquitoes. We genetically modified Plasmodium berghei to express Pfs25 and demonstrated that the transgenic parasites (TrPfs25Pb) are susceptible to anti-Pfs25 antibodies during mosquito-stage development. The asexual growth kinetics and mosquito infectivity of TrPfs25Pb were comparable to those of wild-type parasites, and TrPfs25Pb displayed Pfs25 on the surface of ookinetes. Immune sera from nonhuman primates immunized with a Pfs25-based vaccine when passively transferred to mice blocked transmission of TrPfs25Pb to Anopheles stephensi. Furthermore, mice immunized with Pfs25 DNA vaccine and challenged with TrPfs25Pb displayed reduced malaria transmission compared to mice immunized with wild-type plasmid. These studies describe development of an animal malaria model alternative to the in vitro MFA and show that the model can facilitate P. falciparum transmission-blocking vaccine evaluation based on the target antigen Pfs25. We believe that an animal model to test transmission-blocking vaccines would be superior to the MFA, since there may be additional immune factors that synergize the transmission-blocking activity of antibodies in vivo.

Safety and efficacy of methylene blue combined with artesunate or amodiaquine for uncomplicated falciparum malaria: a randomized controlled trial from Burkina Faso

BACKGROUND

Besides existing artemisinin-based combination therapies, alternative safe, effective and affordable drug combinations against falciparum malaria are needed. Methylene blue (MB) was the first synthetic antimalarial drug ever used, and recent studies have been promising with regard to its revival in malaria therapy. The objective of this study was to assess the safety and efficacy of two MB-based malaria combination therapies, MB-artesunate (AS) and MB-amodiaquine (AQ), compared to the local standard of care, AS-AQ, in Burkina Faso.

METHODS AND FINDINGS

Open-label randomised controlled phase II study in 180 children aged 6-10 years with uncomplicated falciparum malaria in Nouna, north-western Burkina Faso. Follow-up was for 28 days and analysis by intention-to-treat. The treatment groups were similar in baseline characteristics and there was only one loss to follow-up. No drug-related serious adverse events and no deaths occurred. MB-containing regimens were associated with mild vomiting and dysuria. No early treatment failures were observed. Parasite clearance time differed significantly among groups and was the shortest with MB-AS. By day 14, the rates of adequate clinical and parasitological response after PCR-based correction for recrudescence were 87% for MB-AS, 100% for MB-AQ (p = 0.004), and 100% for AS-AQ (p = 0.003). By day 28, the respective figure was lowest for MB-AS (62%), intermediate for the standard treatment AS-AQ (82%; p = 0.015), and highest for MB-AQ (95%; p<0.001; p = 0.03).

CONCLUSIONS

MB-AQ is a promising alternative drug combination against malaria in Africa. Moreover, MB has the potential to further accelerate the rapid parasite clearance of artemisinin-based combination therapies. More than a century after the antimalarial properties of MB had been described, its role in malaria control deserves closer attention.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00354380.

Intermittent preventive therapy for malaria: progress and future directions

PURPOSE OF REVIEW

This review summarizes recent evidence regarding the efficacy of intermittent preventive treatment with focus on infancy (IPTi) and the rationale behind such a control strategy.

RECENT FINDINGS

Pooled safety and efficacy analyses of all six trials of IPTi with sulfadoxine-pyrimethamine conducted between 1999 and 2007 have demonstrated a 30% protective efficacy against clinical malaria, a 24% protective efficacy against all-cause hospital admissions, a 37% protective efficacy against malaria-related hospital admissions, and a 15% protective efficacy against anemia, all in the first year of life. Rebound in malaria following discontinuation of the intervention has not been noted in pooled analyses of the IPTi trials.

SUMMARY

Given the efficacy, excellent safety and tolerability of the intervention and the fact that it is inexpensive and easily deliverable if linked to the Expanded Programme on Immunization, IPTi-sulfadoxine-pyrimethamine appears to add a valuable tool to the malaria-control armamentarium in endemic areas of Africa. Routine monitoring of sulfadoxine-pyrimethamine efficacy will be required to guide future IPTi programme implementation. Variations of IPTi that target older children may be required for areas of Africa with highly seasonal malaria transmission.