Pharmacokinetics of sequential and simultaneous treatment with the combination chloroquine and sulfadoxine-pyrimethamine in acute uncomplicated Plasmodium falciparum malaria in the Philippines

The efficacy and kinetics of the combination chloroquine plus sulfadoxine-pyrimethamine (CQ + SP), given sequentially and simultaneously, were investigated in 32 patients with acute uncomplicated Plasmodium falciparum malaria in Palawan Island, the Philippines. Group 1 with 11 patients received oral CQ 25 mg/kg bw over 3 days followed by a single dose of SP (three tablets 250 mg S + 25 mg P) on Day 4 (CQ0 + SP4). Group 2 with 21 patients received a loading dose of CQ 10 mg/kg plus a single dose of SP three tablets on Day 0, and doses of CQ on Days 1 and 2 (CQ0 + SP0). Patients were followed-up for 28 days until after the clinical and parasitological remission of the disease. Serum samples for CQ, des-ethylchloroquine (DCQ), S and P levels were assayed by high-pressure liquid chromatography with UV and spectrofluorometric detection (HPLC-SF) to determine effective therapeutic concentrations achieved. Parasite and fever clearance times (PCT and FCT) in Group 1 were 48 and 33.5 h, respectively, and 39 and 24 h in Group 2. The parasite elimination half-life (pt1/2) in the CQ + SP0 group was 2.5 h, significantly shorter than the CQ + SP4 group of 5.7 h (P=0.006). Late-treatment failures (R I) were observed in 2/11 patients in Group 1 and in 2/21 patients in Group 2. Serum CQ and DCQ concentrations were effectively adequate. Group 1 pharmacokinetic parameters showed a median maximum concentration (Cmax), area under the curve (AUC) and elimination half-life (t1/2) of 285 ng/ml, 2299 day ng/ml and 5.7 days for CQ, and 89 ng/ml 1845 day ng/ml and 7.3 days for DCQ, respectively. SP was not assayed in Group 1 because of very limited time points. In Group 2, the median Cmax, AUC and t1/2 for CQ and DCQ were at 283 ng/ml 1980 day ng/ml and 5.9 days for CQ and 220 ng/ml, 2680 day ng/ml and 8.5 days for DCQ, respectively. For S and P, the median Cmax, AUC and t1/2 were at 169 microg/ml, 2758 day ng/ml and 10.9 days for sulfadoxine, and 591 ng/ml, 3029 day ng/ml and 2.9 days for pyrimethamine, respectively. Both regimens were well tolerated with a minimum of side-effects, mainly nausea and vomiting. The combination CQ + SP administered simultaneously on Day 0 is more efficacious than when administered sequentially. In the absence of an alternative treatment for acute uncomplicated malaria, this combination is well tolerated, and has an advantage over CQ or SP monotherapy, especially in countries where one drug is still highly effective.     

Sequence heterogeneity of the merozoite surface protein-1 gene (MSP-1) of Plasmodium vivax wild isolates in southeastern Iran

The merozoite surface protein of Plasmodium vivax (PvMSP-1) has been considered as a vaccine candidate, which exhibits antigenic diversity among isolates. We investigated the extent of sequence variation in the polymorphic region 5 of PvMSP-1 in order to characterize the genetic structure and composition of P. vivax in clinical isolates from Iranshahr and Chahbahar districts of Sistan and Baluchistan province, Iran. The PvMSP-1 gene amplification revealed size variation among the isolates, ranging from 430 to 550 bp. Sequences were obtained for 15 Iranian and one Pakistani isolates and 14 different alleles were detected. Results also showed three distinct sequence types of the polymorphic region. Sequence analysis has shown several single nucleotide polymorphisms to occur in this block of PvMSP-1, creating different alleles in the progeny and also microheterogeneity in the region. Thus, this study provides preliminary evidence of sequence heterogeneity in the Iranian P. vivax population.     

Submicroscopic Plasmodium falciparum infections in pregnancy in Ghana

Malarial parasitaemia below the threshold of microscopy but detectable by polymerase chain reaction (PCR) assays is common in endemic regions. This study was conducted to examine prevalence, predictors, and effects of submicroscopic Plasmodium falciparum infections in pregnancy. In a cross-sectional study among 530 pregnant women in Ghana, plasmodial infections were assessed by microscopy and PCR assays. Concentrations of haemoglobin and C-reactive protein (CRP) were measured and antimalarial drugs (chloroquine, pyrimethamine) in urine were demonstrated by ELISA dipsticks. By microscopy, 32% of the women were found to harbour malaria parasites. This rate increased to 63% adding the results of the parasite-specific PCR. P. falciparum was present in all but one infection. With increasing gravidity, infection rates and parasite densities decreased and the proportions of submicroscopic parasitaemia among infected women grew. Correspondingly, anaemia, fever and evidence of inflammation (CRP > 0.6 mg/dl) were more frequent in primigravidae than in multigravidae. Antimalarial drugs were detected in 65% of the women and were associated with a reduced prevalence of P. falciparum infections and a raised proportion of submicroscopic parasitaemia. Both gravidity and antimalarial drug use were independent predictors of submicroscopic P. falciparum infections. These infections caused a slight reduction of Hb levels and considerably increased serum concentrations of CRP. Conventional microscopy underestimates the actual extent of malarial infections in pregnancy in endemic regions. Submicroscopic P. falciparum infections are frequent and may contribute to mild anaemia and inflammation in seemingly aparasitaemic pregnant women.     

Plasmodium falciparum transmission blocking immunity under conditions of low and high endemicity in Cameroon

Transmission blocking immunity (TBI) was studied in relation to age, gametocyte density and transmission intensity. subjects with high gametocytaemias were selected in a hypo-endemic urban district and a hyper-endemic rural area in South Cameroon. TBI was determined in blood from gametocyte carriers in a bioassay (Direct Membrane Feeding Assay), with either autologous plasma (OWN) or control serum (AB). Mosquito infection rates (IR) were compared. infection rates correlated positively with gametocyte and oocyst densities. Three TBI indicators were analysed: the proportion of transmission reducers (IRAB > IROWN, P < 0.01), the mean intensity of TBI (IRAB - IROWN), and the contribution of TBI to total inhibition [(IRAB-IROWN)/(100-IROWN)]. we could not discriminate between areas with regard to either the proportion of transmission reducers (urban 15% and rural 29%) or the mean levels of TBI (urban 10% and rural 9%), or contribution of TBI to total inhibition (urban 10% and rural 13%). there was no relationship between TBI indicators and age, but a trend of increasing values was observed with rising gametocytaemia, which was considered as a confusing factor. a multivariable analysis showed that the probability of being a reducer was 4.6 fold higher in the rural area than in the urban district.     

Cellular and humoral inhibition of Plasmodium falciparum growth in vitro and recovery from acute malaria

Both mononuclear cell cytotoxicity and serum inhibition of Plasmodium falciparum growth in vitro were found to vary according to the stage of infection in Gambian children with clinical malaria. Cytotoxicity was displayed by mononuclear cells and serum from children with acute malaria but this form of parasite killing was more effective in children with low grade P. falciparum infections of at least 10 days duration. Parasite inhibitory antibody was not evident in sera from acutely infected children but was found in sera from children recovering from malaria and reached a peak in convalescent children when P. falciparum growth was inhibited by at least 50%. The humoral response in convalescent children was strain related, being more effective against the most recent infecting parasite strain than against other 'wild' P. falciparum isolates. In contrast, mononuclear cell cytotoxicity was not strain related; when effective, multiplication of all parasite isolates tested was retarded to the same degree. The discussion considers the role of mononuclear cell cytotoxicity in the development of protective immunity and suggests that it may be a 'front line' defense mechanism during each malaria attack.     

Cytokine profile of Plasmodium falciparum-specific T cells in non-immune malaria patients

CD3⁺ T cells are important sources of both pro‐ and anti‐inflammatory cytokines during Plasmodium falciparum malaria. We studied the frequency of interleukin‐2 (IL‐2), gamma interferon (IFN‐γ), tumour necrosis factor‐alpha (TNF‐α) and IL‐10 expressing CD3⁺ cells in 10 non‐immune malaria patients with uncomplicated malaria and in one patient with cerebral malaria after P. falciparum‐specific and non‐specific mitogenic stimulation. Analysis by fluorescence‐activated cell sorting was performed after drug‐induced clearance of parasites to allow previously sequestered T cells to be detected in peripheral blood. CD3⁺ cells of patients responded to P. falciparum infected erythrocytes with significant increases in the percentage of IL‐2, IFN‐γ, and TNF‐α, but also IL‐10, positive cells. CD3⁺ cells from malaria‐naïve donors were also responsive to specific stimulation albeit to a much lesser extent. Mitogenic stimulation of PBMC revealed no significant differences between cells of patients and controls. CD3⁺ cells of the patient with cerebral malaria were hyporesponsive both to the infecting parasite isolate as well as to our laboratory‐adapted P. falciparum isolate, whereas two patients with uncomplicated disease were more responsive to their infecting parasites than to the laboratory‐adapted isolate. The results indicate that the increased responsiveness of in vivo primed compared to malaria‐naïve CD3⁺ cells is Plasmodium‐specific and biased towards production of IFN‐γ and TNF‐α.     

Contribution of the pfmdr1 gene to antimalarial drug-resistance

The emergence of drug-resistance poses a major obstacle to the control of malaria. A homolog of the major multidrug-transporter in mammalian cells was identified, Plasmodium falciparum multidrug resistance protein-1, pfmdr1, also known as the P-glycoprotein homolog 1, Pgh-1. Several studies have demonstrated strong, although incomplete, associations between resistance to the widely used antimalarial drug chloroquine and mutation of the pfmdr1 gene in both laboratory and field isolates. Genetic studies have confirmed a link between mutation of the pfmdr1 gene and chloroquine-resistance. Although not essential for chloroquine-resistance, pfmdr1 plays a role in modulating levels of resistance. At the same time it appears to be a significant component in resistance to the structurally related drug quinine. A strong association has been observed between possession of the wildtype form of pfmdr1, amplification of pfmdr1 and resistance to hydrophobic drugs such as the arylaminoalcohol mefloquine and the endoperoxide artemisinin derivatives in field isolates. This is supported by genetic studies. The arylaminoalcohol and endoperoxide drugs are structurally unrelated drugs and this resistance resembles true multidrug resistance. Polymorphism in pfmdr1 and gene amplification has been observed throughout the world and their usefulness in predicting resistance levels is influenced by the history of drug selection of each population.     

间日疟原虫MSP-1 和 CSP 基因遗传多样性的分析

目的比较间日疟原虫两种主要分子标志(MSP-1 和 CSP)的遗传多样性. 方法分别用MSP-1和CSP基因分型方法鉴定间日疟原虫现场分离株,并进行基因多态性比较和分析. 结果共检测32份海南省现场确诊的间日疟病人血样,MSP-1等位基因型混合感染率为18.75%,平均克隆数1.16;CSP基因型混合感染率为35.29%,平均克隆数为1.47.如果同时考虑两种基因型,混合感染率则为50.00%.空间对应分析发现,热带族与Sal-1型关系密切,PvⅡ型与重组Ⅲ型分布靠近,其他基因型则较分散. 结论同时用MSP-1和CSP两种分子标志检测间日疟原虫,其基因型混合感染率高于用单一标志检测,两种标志检测结果存在一定对应关系.     

云南东南部地区恶性疟原虫对氯喹敏感性纵向观察

目的了解恶性疟原虫对氯喹的敏感性变化趋势,指导合理用药。方法采用WHO推荐的恶性疟原虫对抗疟药敏感性体内临床观察法,进行纵向监测。结果1981～1983年共观察恶性疟病人78例,其中对氯喹敏感(S)2例,抗性(R)76例,包括Ⅰ级抗性(RⅠ)34例、Ⅱ级抗性(RⅡ)12例、Ⅲ级抗性(RⅢ)30例,抗性率为97.44%。2005～2006年共观察32例,其中S19例,S或RⅠ2例,抗性11例(RⅠ8例、RⅡ1例、RⅢ2例),抗性率为36.67%(11/30)。两组病例对氯喹的抗性率和抗性程度差异均有统计学意义(P<0.01)。结论云南省南部地区恶性疟原虫对氯喹的抗性较1983年明显下降,但仍有34.38%(11/32)的抗性病例,且存在着RⅢ抗性病例,提示当前氯喹仍不能用于当地恶性疟现症病人的治疗。     

分子技术在疟疾诊断及其抗药性检测领域的应用

疟疾是目前威胁人类健康最严重的传染性疾病之一.早期诊断和及时有效治疗是缩短其感染期及防治并发症、降低死亡率的重要手段.缺乏快速、准确的诊断方法和疟原虫产生的抗药性是当今世界各地疟疾防治工作面临的主要问题.该文就疟疾诊断及抗药性检测方面的进展,特别是分子生物学技术在这一领域的应用进行综述.