An update on malaria prevention, diagnosis and treatment for the returning traveller

Novel monoclonal antibodies against Plasmodium falciparum histidine-rich protein 2: development and application in rapid diagnostic tests of malaria in hyperendemic regions of China and Myanmar

BACKGROUND

Malaria presents a considerable threat to public health. Histidine-rich protein 2 (HRP 2) is the major protein released into human blood upon infection by Plasmodium falciparum. In this study, we aimed to evaluate the immunogenicity of HRP 2 exon II and the efficacy of novel monoclonal antibodies (mAbs) against HRP 2 for Point-of-Care Test (POCT).

METHODS

The recombinant protein was expressed in soluble form in E. coli and used to immunize mice for mAb production. Two IgG1 mAbs (1A5 and 1C10) with high affinity, specificity and sensitivity for both native and recombinant HRP 2 were selected after fusion of mouse spleen with myeloma cells. The affinity constant of 1A5 and 1C10 were 7.15 and 4.91 × 10-7 L/mol, respectively. Subsequently, an immunochromatograhic assay was used for screening of clinical samples in endemic regions of China and Myanmar.

RESULTS

The immunochromatographic test retrospectively showed an overall sensitivity of 99.07%, and specificity of 100%. Sensitivity at parasite densities < 200, 200-2000, and > 2000 parasites/μL was 87.5, 98.7, and 100%, respectively.

CONCLUSIONS

These results suggest that HRP 2 exon II contains immunogenic sites similar to those of the native antigen and can be used for the development of mAbs suitable for malaria diagnosis in endemic communities.

Extraction of Artemisinin, an Active Antimalarial Phytopharmaceutical from Dried Leaves of Artemisia annua L., Using Microwaves and a Validated HPTLC-Visible Method for Its Quantitative Determination

A simple, rapid, precise, and accurate high-performance thin-layer chromatographic method coupled with visible densitometric detection of artemisinin is developed and validated. Samples of the dried Artemisia annua leaves were extracted via microwaves using different solvents. This method shows the advantage of shorter extraction time of artemisinin from leaves under the influence of electromagnetic radiations. Results obtained from microwave-assisted extraction (MAE) were compared with hot soxhlet extraction. Chromatographic separation of artemisinin from plant extract was performed over silica gel 60 F254 HPTLC plate using n-hexane : ethyl acetate as mobile phase in the ratio of 75 : 25, v/v. The plate was developed at room temperature 25 ± 2.0°C. Artemisinin separation over thin-layer plate was visualized after postchromatographic derivatization with anisaldehyde-sulphuric acid reagent. HPTLC plate was scanned in a CAMAG’s TLC scanner 3 at 540 nm. Artemisinin responses were found to be linear over a range of 400–2800 ng spot−1 with a correlation coefficient 0.99754. Limits of detection and quantification were 40 and 80 ng spot−1, respectively. The HPTLC method was validated in terms of system suitability, precision, accuracy, sensitivity (LOD and LOQ), and robustness. Additionally, calculation of plate efficiency and flow constant were included as components of validation. Extracts prepared from different parts of the plant (leaves, branches, main stem, and roots) were analyzed for artemisinin content, in which, artemisinin content was found higher in the leaf extract with respect to branches and main stem extracts; however, no artemisinin was detected in root extract. The developed HPTLC-visible method of artemisinin determination will be very useful for pharmaceutical industries, which are involved in monitoring of artemisinin content during different growth stages (in vitro and in vivo) of A. annua for qualitative and quantitative assessment of final produce prior to commercial-scale processing for assessment of cost-benefit ratio.

Natural polyhydroxyalkanoate-gold nanocomposite based biosensor for detection of antimalarial drug artemisinin

The worrisome trend of antimalarial resistance has already highlighted the importance of artemisinin as a potent antimalarial agent. The current investigation aimed at fabricating a biosensor based on natural polymer polyhydroxyalkanoate-gold nanoparticle composite mounting on an indium-tin oxide glass plate for the analysis of artemisinin. The biosensor was fabricated using an adsorbing horse-radish peroxidase enzyme on the electrode surface for which cyclic voltammetry was used to monitor the electro-catalytic reduction of artemisinin under diffusion controlled conditions. Electrochemical interfacial properties and immobilization of enzyme onto a polyhydroxyalkanoate-gold nanoparticle film were evaluated, and confirmed by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The differential pulse voltammetric peak current for artemisinin was increased linearly (concentration range of 0.01-0.08μg mL(-1)) with sensitivity of 0.26μAμg mL(-1). The greater sensitivity of the fabricated biosensor to artemisinin (optimum limits of detection were 0.0035μg mL(-1) and 0.0036μg mL(-1) in bulk and spiked human serum, respectively) could be of much aid in medical diagnosis.

A cluster of Plasmodium vivax malaria in an expedition group to Ethiopia: prophylactic efficacy of atovaquone/proguanil on liver stages of P. vivax

OBJECTIVES

Complete prevention of malaria especially Plasmodium falciparum is the goal of prophylaxis. A survey, designed to ascertain reasons behind the choice of malaria prophylaxis, compliance and side effects, and to gather data on acquired malaria, identified a cluster of Plasmodium vivax infection in a cohort of 33 who travelled to Ethiopia on a scientific expedition.

METHODS

A questionnaire based survey of travellers who took part in a scientific survey and rafting expedition in Ethiopia between October and December 2005 on their return from the expedition and two years later.

RESULTS

31 of 33 subjects completed the survey fully. Evidence was obtained on factors influencing choice of, and adherence to prophylaxis and the incidence and type of malaria related to prophylaxis. Over the two year follow up period 32% of travellers developed P. vivax malaria. Of those taking Mefloquine and Doxycycline 50% and 66% respectively developed malaria, compared to none taking Atovaquone/Proguanil as prophylaxis. Awareness and management of malaria was inadequate in several cases. Failure to use Primaquine led to second relapses.

CONCLUSIONS

Within this cluster, prophylaxis against P. falciparum was successful. Widespread failure of prophylaxis against P. vivax malaria was documented despite the use of recommended regimes of known efficacy against the parasite. Atovaquone/Proguanil had the least side effects and afforded the highest protection. Atovaquone/Proguanil may provide previously unrecognised protection against liver stages of P. vivax.