1 Medical Research Unit, Albert Schweitzer Hospital, Lambaréné, B. P. 118, Gabon; 2 Department of Parasitology, Institute of Tropical Medicine, University of Tübingen, Wilhelmstrasse 27, D-72074 Tübingen, Germany; 3 John F. Kennedy School of Government, Harvard University, Cambridge, MA 02138, USA
Received 10 January 2002; returned 16 May 2002; revised 29 May 2002; accepted 12 August 2002
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Abstract |
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Keywords: Plasmodium malariae, artesunate, chemotherapy, malaria, Gabon
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Introduction |
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Materials and methods |
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At baseline, children were screened for plasmodial infections. Giemsa-stained thick blood films were prepared by the Lambaréné method as described previously,10 and asexual parasitaemia was assessed per microlitre. Briefly, 10 µL of peripheral blood was evenly spread in an area of 18 mm by 10 mm on a clean slide. Slides were subsequently dried and stained with Giemsa (20%, pH 7.2, 20 min). Parasites were counted in at least 100 high-powered fields (HPFs; 1000x magnification), and the number of parasites per microlitre was calculated by multiplying the mean number of parasites per HPF by 600. This factor was previously determined for the study microscope and depends on the magnification and the size of the HPF of a particular microscope.10 The factor was calculated according to the following formula: area of blood on slide/(area of HPF at 1000x magnification x volume of blood on slide). Thin blood smears were dried, fixed with methanol, stained for 30 min with Giemsa (20%, pH 7.2) and then examined microscopically for at least 30 min (1000x). Standard morphological characteristics were used to distinguish parasite species. Specifically, diagnosis of P. malariae infections was made if at least one of the following criteria was fulfilled: (i) identification of P. malariae schizonts on the thick blood film and (ii) identification of characteristic P. malariae stages (late trophozoites with band forms, schizonts or gametocytes) on the thin blood smear. All blood smears were read by two independent and experienced microscopists. PCR analysis to confirm the species specificity of microscopic diagnosis was not carried out. Haemoglobin was measured on days 0 and 56 with a portable photometric analyser (DHT Hb 523; Developing Health Technologies, UK). Reagent strips (Roche, Germany) were used for the semi-quantitative assessment of proteinuria. The treatment regimens were allocated sequentially according to the randomization code of the trial evaluating artesunate and praziquantel for the treatment of asymptomatic S. haematobium infections. The details of the randomization procedures have been decribed previously.8
One hundred and eight eligible children with asymptomatic S. haematobium infections were included in the study in Nombakélé. On study day 0, 40 children received artesunate (Sanofi, France) 4 mg/kg/day for 3 days and praziquantel placebo (Medochemie, Cyprus), 35 received artesunate placebo (Sanofi) and praziquantel (Medochemie), 23 received artesunate (identical dose) combined with praziquantel and 10 received placebo. For our analysis, we pooled all children who received artesunate in one group (n = 63) and the remaining children in the comparator group (n = 45). To the best of our knowledge, praziquantel has never been demonstrated to be effective against plasmodia, including negative results from analyses of our own unpublished data, and thus, for the purpose of this study on the efficacy of artesunate in asymptomatic P. malariae infections, the comparator group was considered as the placebo group for artesunate. Efficacy was assessed on days 7 and 56 by means of methodology identical to that used for screening. Proportional data were compared using Fishers exact test, and exact binomial confidence intervals were calculated (Stata v7; Stata Corporation, College Station, TX, USA).
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Results |
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For all parasitaemic children at baseline, the results comparing efficacy of artesunate treatment against placebo are given in Table 2. In the artesunate group, all children had cleared P. malariae infections by day 7, and six of 35 children had reappearance of parasites of P. malariae on day 56 (a cure rate of 83%) compared with ongoing infections in all children in the placebo group on days 7 and 56 (P < 0.0001 for the comparisons on days 7 and 56; Table 2). There was no difference in the cure rate between children who received artesunate and praziquantel or artesunate and placebo (19 of 23, 83%, versus 10 of 12, 83%; P = 0.96). Artesunate cleared P. falciparum parasitaemia in all children except one by day 7 (98%), but the cure rate fell to 38% on day 56 (Table 2). Both treatment regimens cleared P. ovale infections (two infections in the artesunate group and one in the placebo group).
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Discussion |
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The reported cure rate has not been corrected for by PCR, which would have enabled us to distinguish recrudescent from new infections. Assuming the possibility of reinfections occurring during the 56 day follow-up period, our results are therefore likely to underestimate the exact cure rate. Nonetheless, a parasitological cure rate of 83% compares favourably with findings for P. falciparum where 3-day regimens of artesunate are associated with high recrudescence rates by day 28 in Thailand.11 No studies evaluating the efficacy of the 3-day regimen in Africa have been published so far. We hypothesize that the difference is primarily due to parasite species-related drug sensitivities. In addition, the different levels of initial parasitaemiaP. malariae infections do not produce the high parasite load seen with P. falciparumand differences in the level of host immune responses may also play an important role. Additional studies are now needed to confirm the efficacy of a short course of artesunate alone, or preferably in combination, for curing clinical episodes of P. malariae infections in non-immune and semi-immune populations.
The importance of P. malariae for the development of complications of falciparum malaria (e.g. severe anaemia) remains so far unknown. However, morbidity from P. malariae infections contributes to the excessive but preventable disease burden in sub-Saharan African countries. Co-infections of P. malariae with P. falciparum are common, and the diagnostic repertoire to differentiate between the species is limited. Treatment decisions in sub-Saharan Africa are overwhelmingly based on clinical criteria, and light microscopy plays a negligible role. An ideal anti-malarial will thus be cheap and well tolerated as well as highly effective not only against P. falciparum but also against P. malariae and P. ovale. Pending the confirmation of our results in symptomatic P. malariae infections, our study adds support to the use of a 3-day course of artesunate in combination with other anti-malarials in future malaria control programmes.
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Acknowledgements |
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Footnotes |
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References |
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