Roles of tumour necrosis factor in the illness and pathology of malaria

Evidence is accumulating that the illness and pathology observed in malaria are not caused directly by parasite products, but by normal components of the immune response, mainly monokines such as tumor necrosis factor (TNF), produced in excess. These mediators are released from the host's monocytes and macrophages, apparently in response to stimulation by parasite products. Recombinant TNF, if injected into a range of animal species or into tumour patients, is demonstrably toxic, giving rise to changes typical of acute malaria, and several groups have detected circulating TNF in serum from patients acutely ill with malaria. The short serum clearance time of TNF and TNF tolerance have to be considered when interpreting such data. Current studies indicate that some malarial antigens, in the absence of lipopolysaccharide, can trigger release of TNF. This and other monokines could contribute to cerebral malaria in at least 2 ways: by increasing thrombospondin secretion, and hence favouring local sequestration of knob-bearing parasitized red cells, and, as has been demonstrated in clinical trials in tumour patients, by causing neurological symptoms directly. In addition, it seems that TNF does not act alone, but as part of an interdependent synergizing network of polypeptide mediators. These evidently act together to induce secretion of other cell products, such as platelet-activating factor, prostaglandins, reactive oxygen species and procoagulant activity, that actually cause illness, biochemical change and tissue damage. Understanding these processes should lead to a range of new therapeutic interventions.     

Serum tumor necrosis factor associated with malaria in patients in the Solomon Islands

There is now significant evidence that tumor necrosis factor (TNF) is involved in the pathogenesis of malaria. We have tested sera from patients presenting with a febrile illness admitted to hospital in Honiara, Solomon Islands, for the presence of TNF, interferon-gamma, and interleukin-1 (IL-1). This study differs from previous reports as the subjects were mainly adults from a semi-immune population living in an endemic area. The results from 2 different commercially-available assays for TNF were compared, and one was found to be superior to the other. Serum TNF concentrations correlated with malarial parasite density and the patients' temperatures, but not with interferon or IL-1. The results are discussed in the context of the immunopathology of this disease.     

Analysis of the genetic factors controlling malarial infection in man

Genetic factors have clearly been shown to play a role in controlling malarial infection in animal models. There is now also increasing evidence for the genetic control of malaria in man. We carried out a segregation analysis based on blood parasite load phenotype for a population of the town of Bobo-Dioulasso (Burkina-Faso). This analysis demonstrated a strong genetic effect. Our results were not consistent with the segregation of a major gene and thus suggest that parasite load is under the control of minor genes. The genetic effect was stronger in children than in adults. We carried out a regression analysis in children and found that there was an association between the phenotype for blood parasite load and the q31-33 region of chromosome 5. We identified a gene in this region, Pfil1 (Plasmodium falciparum infection levels 1), which accounted for almost 50% of the variance in blood parasite load and which played a fundamental role in the control of infection. The 5q31-33 region contains several genes encoding cytokines that regulate T lymphocytes. The identification of genes controlling malarial infection opens up new possibilities for preventive and treatment strategies. It should be possible in the near future to identify individuals at risk of malaria, who would derive the greatest benefit from preventive and therapeutic measures. Finally, a deeper understanding of these genes controlling protective immune responses could be of value for the development of vaccines.     

Detection and measurement of species-specific malarial antibodies by immunofluorescence tests.

Species-specific serodiagnosis of malaria could be made by means of the standardized indirect fluorescent antibody test, either by determination of the usual end-point titres or by fluorescent intensity measurements on antigens. The malarial antibody levels could also be measured by the fluorescent intensity measurements at a single serum dilution. Thus the fluorescent intensity measurements could effectively replace the end point titre determination, with the advantages of standardization and saving in technician time.     

Life-threatening severe malarial anaemia

Despite our improved understanding of the pathophysiology of severe malaria, major changes in clinical management have not been forthcoming. However, in the case of life-threatening severe malarial anaemia, preliminary evidence suggests that changes in current clinical practice rather than the introduction of novel interventions may improve child survival. This review argues that further research into the clinical physiology of this syndrome is required and could provide compelling evidence for changes in practice particularly with regard to blood transfusion. We focus on the syndrome of severe, symptomatic malarial anaemia associated with a metabolic acidosis which has a high fatality rate. However, it should be remembered that a far greater number of children without signs of life-threatening disease nonetheless experience significant morbidity from severe anaemia. Many of these less-severely ill children may also require blood transfusion. However, the mode and rationale for transfusion in this less-severely ill group is specifically not addressed. Indeed, the arguments presented should not be extrapolated to suggest a uniform approach to transfusion is warranted, the role of blood in the less-critically ill child with severe malaria anaemia being a further area that requires urgent research.     

A simple and rapid method of staining malarial parasites in thick blood smears

A method is described by which malarial parasites may be stained in thick blood smears in one second. Tests of this method in several hundreds of cases of acute malaria have shown that the great speed in malarial diagnosis which its use makes possible is consistent with fair accuracy.     

Erythrocyte miRNA regulators and malarial pathophysiology

Pathophysiology of Plasmodium falciparum and Plasmodium vivax in malaria vis a vis host and the parasite genome interactions has been deciphered recently to present the biology of cerebral malaria, severe anaemia and placental malaria. Small non-coding RNAs have exhibited their potential to be considered as indicators and regulators of diseases. The malarial pathologies and their associated mechanisms mediated by miRNAs and their role in haematopoiesis and red cell-related disorders are elucidated. Evidence of miRNA carrying exosome-like vesicles released during infection, delivering signals to endothelial cells enhancing gene expression, resulting in parasite sequestration and complications leading to pathologies of cerebral malaria are important breakthroughs. Pregnancy malaria showed Plasmodium surface antigen promoted erythrocyte sequestration in the placental intervillous space, provoking disease development and assorted complications. Syncytiotrophoblast-derived microparticles during pregnancy and fetus development may predict pathophysiological progression on account of their altered miRNA cargoes in malaria.     

The dependence of cell-mediated immune activation in malaria on age and endemicity

In vitro, neopterin, a pyrazino-[2, 3-d]-pyrimidine compound, is produced by human monocytes-macrophages following induction by either supernatants from activated T lymphocytes or by recombinant gamma interferon. In vivo, its determination in urine or serum provides a sensitive and specific test for the activation grade of cell-mediated immune reactions. Urinary neopterin levels were measured in 128 Tanzanian individuals (age 6 months to 54 years) with parasitologically proven malaria. Levels in a subgroup of 117 previously untreated patients were compared with those previously reported from 19 untreated malarial patients from Bangkok, Thailand (age 7 to 62 years). The influence of concomitant variables such as age, fever, parasitaemia, duration of symptoms and local endemicity of malaria upon neopterin excretion levels was analysed. In the Thai patients, levels were considerably higher than in Tanzanian subjects of similar age. Among the Tanzanian patients, an overwhelming influence of age was detected, children showing extremely high neopterin excretion levels. The other variables did not influence neopterin levels significantly. Our findings are in accord with recent data on the prevalence and mean titres of antibodies to the circumsporozoite protein of Plasmodium falciparum, which indicate that in endemic areas acquired humoral immunity develops slowly with increasing age, while prevalence and severity of disease decline.     

Iron delocalisation in the pathogenesis of malarial anaemia

There is consensus that the pathophysiology of malaria-associated anaemia is multifactorial, but the precise mechanisms behind many of the haematological changes during malaria remain unclear. In this review, we attempt to build a composite picture of the pathophysiology of malarial anaemia using evidence from experimental, human and animal studies. We propose that cytokine- and hepcidin-mediated iron delocalisation, a principal mechanism in the anaemia of inflammation, plays an important role in the aetiology of malarial anaemia, and can explain some of the clinical and laboratory findings. These mechanisms interact with other aetiological determinants, such as dietary iron and micronutrient supply, helminth load, other infections and genetic variation, in determining the severity and associated features of anaemia. We suggest that iron delocalisation as a mechanism for malarial anaemia could be exploited for the development of alternative therapeutic strategies for post-malaria anaemia.     

Anaemia in pregnant Ghanaian women: importance of malaria, iron deficiency, and haemoglobinopathies

In sub-Saharan Africa, anaemia in pregnancy results from multiple causes including malaria, iron deficiency and haemoglobinopathies. In a cross-sectional study among 530 pregnant women in Ghana in November-December 1998, red blood cell indices were analysed with respect to malaria, serum concentrations of ferritin and C-reactive protein (CRP), and the haemoglobin and alpha-globin genotypes. Anaemia (haemoglobin [Hb] < 11 g/dL) was found in 54% of the women; 63% harboured malaria parasites at predominantly low numbers. Ferritin levels were considerably influenced by malaria and inflammatory processes (CRP > 0.6 mg/dL). Depending on the definition applied, the prevalence of iron deficiency ranged between 5% and 46%. The HbAS trait was observed in 14%, HbAC and elevated HbF in 7% each, and sickle cell disease in 1%. Heterozygous beta-thalassaemia was present in 1% of the women and alpha(+)-thalassaemia in 33% (29% heterozygous, 4% homozygous). Women with HbAS had higher malaria parasite densities than those with HbAA. In individuals with highly elevated HbF (> 10%), parasitaemia occurred in 27% only. Low gravidity, second trimester of pregnancy, malaria, raised CRP levels, and homozygous alpha(+)-thalassaemia were independent risk factors for anaemia in multivariate analysis. alpha(+)-Thalassaemia, however, was associated with a lesser degree of malarial anaemia when compared to non-thalassaemic women. Iron deficiency appears not to be a major health problem in this population. Haemoglobinopathies are common but, except for homozygous alpha(+)-thalassaemia, do not substantially contribute to anaemia in pregnancy. alpha(+)-Thalassaemia ameliorates malarial anaemia in pregnant women.     

Relationship between malarial parasitaemia and symptoms of the disease: A review of the literature

The relationship between parasitaemia and the clinical manifestations of malaria is a highly complex subject, considered by the WHO Expert Committee on Malaria which met in September 1958 to warrant further investigation since it has an important bearing on the organization of eradication programmes. As a first step, the author has reviewed the existing literature on such aspects of malaria epidemiology as the prevalence of gametocytes at various stages of a malarial infection, the limit of infectiousness of the human host, the period of survival of the malaria parasite in man, and the development of immunity through repeated infection. From this study of the works published during the past 60 years, he concludes that much more information as to the role of asymptomatic parasitaemia in the transmission of malaria is required and suggests that it will best be obtained through a critical analysis of the data recorded during the eradication campaigns now under way in many countries.     

驻利比里亚维和医疗队无药物预防下防疟措施效果评价

目的 观察利比里亚任务区维和官兵在无药物预防下的防疟效果,为执行维和任务官兵的防疟措施提供参考.方法 开展防疟知识教育、整治环境、降低蚊虫密度、双层纱帘倒开、长效药物驱蚊蚊帐、分时防护的综合措施,防止蚊虫叮咬,预防疾病传播.结果 维和官兵通过1年以上随访,维和期间3人检出疟原虫,均为男性,感染率为6.97%,疑似1人.维和官兵回国后6月、1年疟原虫检测均为阴性.结论 在未使用药物预防的条件下,采取综合防护的措施,能够达到预防疟疾感染的目的 .     

驻利比里亚维和医疗队无药物预防下防疟措施效果评价

目的 观察利比里亚任务区维和官兵在无药物预防下的防疟效果,为执行维和任务官兵的防疟措施提供参考.方法 开展防疟知识教育、整治环境、降低蚊虫密度、双层纱帘倒开、长效药物驱蚊蚊帐、分时防护的综合措施,防止蚊虫叮咬,预防疾病传播.结果 维和官兵通过1年以上随访,维和期间3人检出疟原虫,均为男性,感染率为6.97%,疑似1人.维和官兵回国后6月、1年疟原虫检测均为阴性.结论 在未使用药物预防的条件下,采取综合防护的措施,能够达到预防疟疾感染的目的 .     

The impact of malarial infection and diet on the anaemia status of rural pregnant Malawian women

OBJECTIVE: To investigate haematological and biochemical iron indices in relation to malaria, gravida, and dietary iron status in rural pregnant Malawian women. DESIGN: In this self-selected sample, haemoglobin, haematocrit, red cell indices, serum ferritin, serum iron, serum transferrin, and serum transferrin receptor (TfR) were measured. Infection was assessed by a malaria slide, serum C-reactive protein, and white blood cell count. Dietary iron variables were measured by three 24-h interactive recalls. SETTING AND SUBJECTS: 152 rural pregnant women recruited at 24 weeks gestation while attending a rural antenatal clinic in Southern Malawi; 36% were primagravid; 43% were gravida 2-4; 26% were gravida >5. RESULTS: Of the women, 69% (n=105) were anaemic (haemoglobin <110 g/l); 37% (n=39) had anaemia and malarial parasitaemia on the test day; 17% (n=26) with malaria were also classified with iron deficiency (ID) anaemia (based on serum ferritin < or = 50 microg/l and Hb <110 g/l) while an additional seven with malaria were classified with ID without anaemia. In malarial-free subjects, 32% were classified with IDA (serum ferritin <12 microg/l and Hb <110 g/l) and 17% with ID (serum ferritin <12 microg/l; Hb > or = 110 g/l). Serum TfR concentrations were elevated in anaemic women (P<0.01). In non-malarial parasitaemic subjects, serum TfR correlated negatively with haemoglobin (r=-0.313; P<0.001) but not serum ferritin. Of the women, 49% were at risk for inadequate iron intakes. Most dietary iron was non-haem; plant foods provided 89%; flesh foods (mainly fish) only 9%. Malarial parasitaemia and intakes of available iron impacted significantly on iron status. CONCLUSION: Anaemia prevalence from all causes was high (that is, 69%); three factors were implicated: malaria, and deficiencies of iron and possibly folate, induced partly by an inadequate dietary supply and/or secondary to malarial parasitaemia. Sponsorship: International Development Research Centre (IDRC) of Canada. Opportunities for Micronutrient Interventions (OMNI) Project. Natural Sciences and Engineering Research Council of Canada.     

Ahaptoglobinaemia in Melanesia: DNA and malarial antibody studies

To assess the relative contributions of genetic and acquired factors, particularly malaria, to the high frequencies of ahaptoglobinaemia found in Melanesia we have performed DNA and malarial antibody studies in a population from Vanuatu. No gene deletion or rearrangement was found on gene mapping in any ahaptoglobinaemic individual and the frequencies of the Hp1 and Hp2 alleles in the ahaptoglobinaemic group were similar to controls. However, antibodies to Plasmodium falciparum were significantly elevated in the ahaptoglobinaemics. These data suggest that malaria rather than genetic factors is the major cause of ahaptoglobinaemia in Melanesia.     

Transgenic Plasmodium that expresses HIV-1 Gag elicits immunity and protects mice against vaccinia virus-gag and malarial parasites

Malaria and human immunodeficiency virus type 1 (HIV-1) infection overlap in many regions of the world. Our goal was to determine the feasibility of developing transgenic Plasmodium berghei that expresses HIV-1 Gag, PbGAG, as a conceptual bivalent vaccine against both HIV-1 infection and malaria. Immunization of mice with PbGAG induced specific responses to the HIV-1 Gag. Importantly, mice vaccinated with PbGAG were significantly protected from challenge with vaccinia virus-gag (VV-gag) with an average 30-fold reduction in titer (P<0.05). In addition, mice immunized with PbGAG developed Plasmodium-specific immune responses and the immunized animals were protected from challenges with blood-stage P. berghei NK65 and Plasmodium yoelii 17XL. We demonstrated a novel vaccination strategy that uses a live transgenic protozoan parasite-based bivalent vaccine to immunize mice and confer significant levels of protection against VV-gag and malarial parasite challenges. These observations have important implications for the development of a new form of bivalent vaccine against both HIV-1 and malaria.     

山东省的疟疾防治与监测

目的　总结疟疾防治工作中的经验。方法　从建国初期始 ,详细阐述了不同年代和不同发病时期所采取的相应防制措施 ,从而有效地降低了疟疾发病 ,控制其暴发流行 ,直至达到基本消灭 ,嗣后进入监测阶段。结果　基本消灭疟疾后继续采取卓有成效的监测措施 ,使疟疾疫情始终保持稳定 ,巩固了疟防成果。结论　疟疾防制工作只要领导重视 ,措施得力 ,即能降低其发病 ,疟防成果即可得到巩固和加强     

Prognostic risk factors and post mortem findings in cerebral malaria in children.

We have examined the possible risk factors for poor prognosis in cerebral malaria in 61 Nigerian children in an area of high malaria transmission. The level of coma, decerebrate rigidity, hypoglycaemia, and high urea levels were indicators of poor prognosis. Pyrexia, vomiting, and anaemia did not influence prognosis. Post-mortem findings suggest gross cerebral oedema and raised intracranial pressure in 4 of 7 cases with petechial haemorrhages and small focal necrosis (Durck's granuloma).     

The metabolic effects of quinine in children with severe and complicated Plasmodium falciparum malaria in Dar es Salaam.

Quinine is widely used for the treatment of severe and complicated malaria, although resistant strains of Plasmodium falciparum may occur. The drug has been incriminated as a cause of hypoglycaemia in some malaria patients. To determine if quinine has untoward metabolic effects during treatment of severe and complicated malaria we have studied the effects of quinine on blood glucose and intermediary metabolites, serum insulin, C-peptide, plasma glucagon and non-esterified fatty acids in 97 children with severe malaria in Dar es Salaam. All patients responded clinically. No patient developed hypoglycaemia while on quinine therapy given as 10 mg/kg in 10 ml/kg of 5% dextrose infused over 4 h every 8 h. Endogenous insulin secretion, as reflected by C-peptide levels, increased after 4 h but insulin levels did not change significantly. Blood lactate, 3-hydroxybutyrate, plasma non-esterified fatty acids and plasma glucagon all fell appropriately during treatment. We conclude that quinine, when administered at the recommended dose and rate, does not disrupt blood glucose homeostasis, and is still the drug of choice for severe and complicated malaria in children.     

Precipitating antibody response to malarial S-antigens

The gel diffusion test has been used to detect antibodies to malarial S-antigens. Sera were obtained from entire Gambian village communities, from young children with acute P. falciparum malaria, from children convalescent from such infections and from immune adults. In community studies, small selections of S-antigens detected antibody frequently in sera from older persons but rarely in sera from young children. Larger panels of antigens detected antibodies in sera from half of 50 malarious children while homologous antibody responses were observed in 22% of 267 children followed at intervals during convalescence from malaria. In these latter cases, antibody tended to appear more swiftly when antigen was lost rapidly from the circulation, and observations made on individual responses indicated that antibody production was influenced by factors other than the intrinsic properties of the antigens. In adult sera antibodies usually occurred in association with IgG.