Apoptosis modulation in mononuclear cells recovered from individuals exposed to Plasmodium falciparum infection

In endemic areas, asymptomatic infection by the malaria parasite Plasmodium falciparum was found associated with elevated percentages of human host's mononuclear cell spontaneous in-vitro apoptosis. In Dielmo, a village where malaria is holoendemic, apoptosis was age-and parasite-dependent. In-vitro exposure of peripheral blood mononuclear cells (PBMC) to the parasite extract induced a marked increase in the mononuclear cell membrane expression of functional CD95 antigen: a 3-h exposure of the mononuclear cells to anti-CD95 antibodies led to a detectable increase in the mean percentage of apoptotic nuclei found in the cultures carried out in the presence of P. falciparum extracts compared to control cultures. IL-2, IL-4, IL-6 and IL-10 promoted the viability of PBMC in cultures while IL-1alpha or IFN-gamma had no obvious impact and TNFalpha gave conflicting results. IL-2 was the most efficient cytokine at rescuing PBMC from cell death and this effect was associated with a strong increase in T cell activation. In contrast, IL-4 and IL-10 had no such effect on T cell activation, hence they acted as survival factors and not through their mitogenic activity. Taken together, these different observations suggested that the levels of in-vitro apoptosis observed were not only associated with parasite infection, but also potentially modulated by the human host through different pathways.     

Plasmodium falciparum multiplicity correlates with anaemia in symptomatic malaria

In 366 Ghanaian children with symptomatic Plasmodium falciparum malaria, low haemoglobin levels and severe anaemia were associated with a high multiplicity of infection (MOI) and with distinct merozoite surface protein alleles. High MOI not only reflects premunition but may also contribute to anaemia in symptomatic malaria.     

Severe anaemia in Zambian children with Plasmodium falciparum malaria

BACKGROUND: Severe anaemia and cerebral malaria are highly prevalent complications of Plasmodium falciparum malaria among African children. The mechanisms of severe malarial anaemia, and the relative importance of this condition in comparison to cerebral malaria, are not known for many regions of Africa. METHODS We reviewed the records of 6200 children up to 6 years of age admitted to one rural Zambian hospital between 1994 and 1996. Severe malarial anaemia was defined as an haemoglobin concentration < 5.0 g/dl in a patient with asexual forms of P. falciparum in the peripheral blood. Cerebral malaria was defined as impaired consciousness (Blantyre coma score < 5) not attributable to any other cause in a patient with a positive malaria smear. RESULTS Severe malarial anaemia was found in 590 children (9.5% of paediatric admissions) and strictly defined cerebral malaria occurred in 286 children (4.6% of paediatric admissions); 98 of these patients had the combination of both complications. Severe malarial anaemia correlated strongly with the degree of parasitaemia, with malnutrition as indicated by low weight for age, with absence of fever and with presentation late in the malaria season. In comparison, patients with cerebral malaria were more often febrile and presented earlier in the malaria season. The case fatality rate of severe malarial anaemia (0.088) was about half that of cerebral malaria (0.189), but because severe malarial anaemia was more common, these two forms of complicated malaria were implicated in similar numbers of in-hospital paediatric deaths. CONCLUSION Severe anaemia is a more common complication of P. falciparum malaria in hospitalized Zambian children than cerebral malaria and is associated with a similar number of deaths. Malnutrition and changes in immune response patterns due to prolonged exposure to P. falciparum may contribute to the development of this complication.     

Thrombopoietin in Plasmodium falciparum malaria

Thrombopoietin (TPO) is the key growth factor for platelet production and is elevated in states of platelet depletion. As thrombocytopenia is a common finding in malaria, we analysed TPO regulation before, during and after antimalarial treatment. Before treatment, TPO serum levels were significantly higher in patients with severe malaria (n = 35) than in patients with uncomplicated malaria (n = 44; P = 0.024), normalizing within 14-21 d of therapy. The rapid normalization of TPO levels and increase in low peripheral platelet counts after treatment indicate that the biosynthesis of TPO and its regulation in malaria patients are normal.     

Plasma levels of interleukin-18 and interleukin-12 in Plasmodium falciparum malaria

Interleukin (IL)-18 produced primarily by mononuclear phagocytes synergizes with IL-12 for interferon-gamma production from T, B and natural killer cells. It has been also demonstrated that, in Plasmodium falciparum malaria, IL-18 could have an immunoregulatory function. The aim of this study was to detect the plasma levels of IL-12 and IL-18, using an enzyme-linked immunosorbent assay, in 105 African children affected by mild and severe Plasmodium falciparum malaria to correlate the production of these cytokines with the severity of the disease. The levels of IL-18 and IL-12 were higher (25.7 +/- 7.6 pg/ml and 17.1 +/- 7.8 pg/ml, respectively) in children with mild malaria than in children with a severe form of the disease (21.5 +/- 10 pg/ml and 13.2 +/- 5.5 pg/ml, respectively). A positive correlation was observed between IL-18 and IL-12. This finding suggests that the production of these two cytokines (IL-18 and IL 12) may be coregulated and both have an immunoregulatory effect on the immune response in Plasmodium falciparum infection.     

江苏省2010年输人性恶性疟病例分析

目的 通过对江苏省2010年输入性恶性疟病例的个案分析,研究其发病和流行特征,为进一步做好全省输入性恶性疟防控工作提供依据.方法 对江苏省网络直报的恶性疟疫情和流行病学调查资料进行分析.结果 2010年江苏省报告输入性恶性疟病例207例,比2009年(101例)上升104.95％.输入性恶性疟病例主要分布于出国务工人员较集中的苏中和苏北地区,扬州、泰州、南通和淮安4市共报告输入性恶性疟病例为109例,占全部病例的52.66％.207例输入性恶性疟病例均为从非洲或东南亚等疟疾高度流行区的回归人员.207例患者中21例为临床诊断病例,占10.14％,186例为发热患者血片镜检疟原虫阳性,占89.86％;207例患者中初发病例125例,占60.39％,再燃病例82例,占39.61％.结论 江苏省输入性恶性疟日趋增多,应加强重点地区劳务输出归国人员的疟疾防治管理工作.     

Insecticide-treated bednets for the prevention of Plasmodium falciparum malaria in Cambodia: a cluster-randomized trial

OBJECTIVES: To validate and quantify the impact of insecticide-treated bednets (ITN) on malaria morbidity and mortality in Cambodia. METHODS: A paired, cluster-randomized trial of ITN was conducted in Rattanakiri, North East Cambodia. Thirty-four villages with a total population of 10,726 were randomized to receive deltamethrin-impregnated bednets or to control (no net provision). Cross-sectional surveys measured Plasmodium falciparum prevalence at baseline and 10 months after ITN distribution. Village malaria volunteers in control and intervention villages treated dipstick-positive P. falciparum cases with artesunate and mefloquine. The resulting passive surveillance data were used as an estimate of the incidence of clinical P. falciparum infections. RESULTS: There was a protective efficacy of 28% in P. falciparum incidence (adjusted rate ratio 0.72, 95% CI 0.47-1.08) and 9% in P. falciparum prevalence (adjusted prevalence ratio 0.91, 95% CI 0.65-1.28) in ITN relative to control villages; however, neither of these estimates reached statistical significance. Individual-level analysis indicated a greater reduction in P. falciparum prevalence among under 5-year-olds (adjusted OR = 0.63, 95% CI 0.26-1.53) compared to older individuals (interaction P = 0.042). The protective efficacy of 35% (95% CI -28, 67%) with respect to clinical P. falciparum incidence in under 5-year-olds was more pronounced than the corresponding estimates for prevalence but was again not significant. CONCLUSIONS: Lack of statistical significance in the results is likely to be due to a lack of power. The analysis provides further evidence for ITN effectiveness in South East Asia, particularly among individuals under 5 years of age.     

Reversible suppression of bone marrow response to erythropoietin in Plasmodium falciparum malaria

To study the importance of bone marrow inhibition in the pathogenesis of malarial anaemia, haematological and parasitological parameters were followed in patients with acute malaria. Three patient categories were studied, severe malarial anaemia (SA), cerebral malaria (CM) and uncomplicated malaria (UM). Red cell distribution width (RDW) was used as a surrogate marker of release of young erythrocytes and reticulocytes. Initially RDW was low in all patients in spite of markedly increased concentrations of erythropoietin (EPO). 3 d after institution of treatment and coinciding with parasite clearance RDW increased dramatically, reaching the highest levels 1–2 weeks later. Although severe anaemia was corrected by blood transfusion during the first 3 d of treatment, the peak RDW correlated significantly with the initial EPO levels. This suggests that Plasmodium falciparum infection causes a rapidly reversible suppression of the bone marrow response to EPO. Furthermore, the inhibition of bone marrow response was a general finding irrespective of initial haemoglobin levels suggesting that the severity of anaemia depends upon the degree of peripheral erythrocyte destruction in patients with suppressed bone marrow response to EPO.     

Chloroquine resistance of Plasmodium falciparum malaria in Ethiopia and Eritrea

We report on the first 2 years of operation of a new strategy for treatment for P. falciparum malaria patients who were not cured by a standard course of chloroquine. Any such patient who returned to a malaria treatment and detection post within 2 weeks was treated daily under supervision with chloroquine. Patients whose parasitaemia had not decreased below 25% of the initial level by day 3 or cleared completely by day 7 were given sulphadoxine/pyrimethamine (Fansidar). Of 39 824 patients treated initially with chloroquine, 4% returned to the malaria post within 2 weeks of treatment; 87% of these were chloroquine resistant and treated with Fansidar and 28% of the returning patients were RIII resistant. Resistance was associated with geographical area, initial parasite density and age. Earlier studies had shown resistance to be confined to border areas, but we found that it was highest in the centre of the region, notably in the lowlands of the Shewa and Arsi provinces, and lowest in the west. Although imported cases have been held responsible for the development of resistance in border areas, other factors are likely to be important in the middle of the region. The implications of these findings for a treatment policy of P. falciparum malaria in the region are discussed.     

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.     

Cytoadherence of Plasmodium falciparum-infected erythrocytes in the human placenta

In Plasmodium falciparum-parasitized pregnant women, erythrocytes infected by mature stages of the parasite sequester into placental intervillous spaces. The presence of parasites in the placenta causes maternal anaemia and low birth weight of the infant. In-vitro studies suggest placental sequestration may involve the cytoadherence of infected erythrocytes to chondroitin sulphate A (CSA) and/or intercellular adhesion molecule 1 (ICAM-1) expressed by human placental syncytiotrophoblast. We identified P. falciparum receptors expressed on the surface of human syncytiotrophoblast using immunofluorescence of placental biopsies from Cameroon, a malaria-endemic area. In all placentas, a strongly positive staining was observed on the syncytiotrophoblast for CSA, but not for ICAM-1, vascular endothelium cell adhesion molecule-1, E-selectin, nor CD36. The cytoadherence ability of parasites from pregnant women and nonpregnant subjects was assessed on in-vitro cultured syncytiotrophoblast. Parasites from pregnant women bound to the trophoblast via CSA but not ICAM-1. Parasites from nonpregnant hosts either did not bind to the trophoblast culture or bound using ICAM-1. Our data support the idea that placental sequestration may result from cytoadherence to placental trophoblast and that pregnant women are parasitized by parasites that differ from parasites derived from nonpregnant host by their cytoadherence ability.     

Enhanced gametocyte production in Fansidar-treated Plasmodium falciparum malaria patients: implications for malaria transmission control programmes

Gametocytes are the agents in malaria transmissible between the vertebrate host and the mosquito vector, and an increase in their incidence would be expected to have a corresponding impact on the prevalence of malaria, particularly in areas of high transmission. The purpose of this study was to determine whether there is an association between the type of antimalarial drug administered and the production of gametocytes. Two commonly used drugs, Fansidar and chloroquine, were compared in this respect. A total of 94 people (mean age±s.d. 16.94±19.03 years), from a highly endemic malaria area of Zambia, were treated with either Fansidar or chloroquine (Fansidar, n =46, chloroquine, n =48). The percentages of gametocytes generated after treatment were 23.9 for Fansidar and 6.2 for chloroquine. A 2×2 table analysis of the data shows that the P values, both by χ² and Z analysis, were less than 0.02, suggesting a statistically significant difference in the propagation of gametocytes between the two treatment groups. There was no significant difference in the quantitative gametocyte count per 200 white blood cells (Fansidar, 7.5±8.57; chloroquine, 4.5±1.64; P >0.10), probably because of the small size of the 'gametocyte ' sample ( n =14).     

一起冬季内源性恶性疟家庭暴发的调查

本文报道了一起内源性恶性疟冬季家庭暴发疫情,夫妻二人同时发病,经镜检确诊为恶性疟,经静滴蒿甲醚和甘露醇,口服伯氨喹以及对症处理后,患者痊愈,镜检复查未见疟原虫。     

Success in controlling a major outbreak of malaria because of Plasmodium falciparum in Jamaica

In 2006, after 44 years of eradication of malaria, Jamaica had an outbreak of Plasmodium falciparum: 406 confirmed cases between September 2006 and December 2009 with a peak of the epidemic in December 2006. In response to the outbreak, the Ministry of Health launched an emergency response through early detection and prompt treatment of cases, vector control, public education and intersectoral collaboration. Ninety percent (361) of cases were residents of Kingston, and 63.6% were identified through house to house surveillance visits. For 56% of the confirmed cases, treatment with chloroquine was initiated within a week of onset of symptoms. Only one (0.3%) of 358 cases who had a post-treatment smear on day 7 had a persistent asexual parasitaemia, while none of the 149 persons who had a follow-up smear on day 28 was positive. The outbreak highlighted the need for increased institutional capacity for surveillance, confirmation and treatment of malaria as well as effective prevention and control of outbreaks which can occur after elimination. Jamaica appears to have successfully eliminated malaria after its reintroduction.     

Changing scenario of malaria in central India, the replacement of Plasmodium vivax by Plasmodium falciparum (1986-2000)

OBJECTIVES: Since 1986, we have been studying the changing epidemiology of malaria in a forest belt of Mandla, which has the highest number of malaria cases in central India (Madhya Pradesh) to define the epidemiological characteristics of the infection with each Plasmodium species in different seasons of the year. Our long-term objective was to determine the dynamics of Plasmodium vivax vs.P. falciparum infections. METHODS: Five villages underwent fortnightly surveillance of fever cases. Drugs were distributed within 24 h after results of blood smears became available as per Indian National Anti-Malaria Programme. Indoor resting mosquitoes were also collected fortnightly. RESULTS: The only two Plasmodium species encountered were P. vivax and P. falciparum in both children and adults. Relatively more malaria infections were recorded in children (< or =14 years) than adults (>14 years) (chi2=89.94, P<0.00001). However, there were significant falling trends in P. vivax from 1986 to 2000 in both age groups (< or =14 years from 63 to 13, P<0.0001 and >14 years from 84 to 7, P<0.0001). The indoor resting density of Anopheles culicifacies, an efficient vector resistant to both dichlorodiphenyltrichloroethane (DDT) (4%) and hexachlorocyclohexane (HCH) (0.4%), was very high throughout this period in all villages (52.35 +/- 31.8, range 5-200 per man hour). Anopheles fluviatilis was present in small numbers 0.78 +/- 1.24 (range 0-7 per man hour). CONCLUSION: Major contributors of the changing epidemiology of malaria in this area are changing drug sensitivity along with insecticide sensitivity.     

Molecular epidemiology of drug resistance markers of Plasmodium falciparum malaria in Thailand

To determine differences in the distribution of drug resistance mutations in the Plasmodium falciparum chloroquine resistance transporter (pfcrt) and P. falciparum multi-drug resistance 1 (pfmdr1) genes of P. falciparum isolates in Thailand, a study was conducted using polymerase chain reaction-restriction fragment length polymorphism to detect mutations in P. falciparum isolates obtained from three areas with different levels of in vivo mefloquine (MQ) resistance. All isolates carried mutant allele T76 of the pfcrt gene and wild-type allele D1246 of the pfmdr1 gene except for one isolate, which showed the wild-type K76 allele. This isolate was obtained from Chanthaburi Province, an area with high MQ resistance. Relatively low rates of the mutant alleles D1042 and Y86 of the pfmdr1 gene were found among Thai isolates of P. falciparum. However, a statistically significant difference in the distribution was noted. Most of the mutant isolates were found among isolates from areas with moderate or low MQ resistance. Only one isolate with mixed mutant and wild-type N1042 and D1042 and two mutants of Y86 were found among the isolates from areas with high MQ resistance. The findings provide limited support for the hypothesis that mutant alleles of pfmdr1 may be associated with increased sensitivity to MQ.     

多重PCR快速检测恶性疟和间日疟的研究

目的 建立一种简便快速、能同时检测恶性疟和间日疟的核酸检测方法。方法 针对两种疟原虫18S rRNA基因设计2对(3条引物),优化引物浓度与退火温度,建立可扩增出两种疟原虫基因片段的多重PCR。并进行最低检测限确定和临床标本检测,以镜检法为金标准分析灵敏度和特异度等指标。结果 该方法可扩增出431 bp(恶性疟原虫)和341 bp(间日疟原虫)基因片段,最低检测限为10²copies/反应,检测临床标本的结果与镜检法无差别(P＞0.05),敏感度为93.55%,特异度为70.83%,阳性预测值为89.23%,阴性预测值为80.95%。结论 所建立的多重PCR方法可快速检测疟疾感染并鉴别分型,灵敏度高,值得推广。     

A quantitative ultrastructural study of renal pathology in fatal Plasmodium falciparum malaria

OBJECTIVE: To use electron microscopy to examine the role of parasitized red blood cell (PRBC) sequestration in the pathogenesis of acute renal failure in severe falciparum malaria. METHODS: Ultrastructural pathological examination of renal tissues from Southeast Asian adults (n = 63) who died from severe falciparum malaria. Qualitative and quantitative determination of the major pathological features of disease, including PRBC and leukocyte sequestration. Clinico-pathological correlation with the pre-mortem clinical picture and peripheral parasite count. RESULTS: There was a high incidence of malaria-associated renal failure in this population (> 40%) and a correlation between this incidence, severe malarial anaemia and shock. Pathological features included PRBC sequestration in glomerular and tubulo-interstitial vessels, acute tubular damage and mild glomerular hypercellularity resulting from the accumulation of host monocytes within glomerular capillaries. No evidence for an immune complex mediated glomerulonephritis was found. There was a correlation between parasite sequestration in the kidney and pre-mortem renal failure, although overall levels of sequestration were relatively low. Levels of sequestration (Knob+ PRBC) were significantly higher in malaria-associated renal failure than in fatal cases without renal failure (P = 0.005). CONCLUSION: Malaria-associated renal failure is a common and serious complication of severe Plasmodium falciparum malaria in this population, associated with acute tubular injury rather than glomerulonephritis, and linked to localization of host monocytes in the kidney as well as sequestration of PRBCs.     

多糖与恶性疟原虫的分子致病机制

在恶性疟原虫与人体细胞相互作用的过程中,子孢子通过黏附肝内皮细胞受体侵入肝脏,裂殖子通过黏附红细胞表面受体侵入红细胞,感染红细胞利用其表面膜蛋白与人体重要器官的血管内皮细胞表面分子发生黏附,最终导致血流受阻。这些黏附过程均是虫体蛋白与宿主细胞表面带有负电荷的多糖分子相互作用的结果。本文对恶性疟原虫与人体细胞相互作用的分子机制作一综述。