Malaria Risk In Areas Research Articles

Functional and Immunological Characterization of a Duffy Binding-Like Alpha Domain from Plasmodium falciparum Erythrocyte Membrane Protein 1 That Mediates Rosetting

The Duffy binding-like (DBL) domains are common adhesion modules present in Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) variants, which are responsible for immune evasion and cytoadherence. Knowledge about how immune responses are acquired against polymorphic DBL domains of PfEMP1 can aid in the development of vaccines for malaria. A recombinant DBLalpha domain, encoded by R29 var1, which binds complement receptor 1 to mediate rosetting by the P. falciparum laboratory strain R29, was expressed in Escherichia coli, renatured by oxidative refolding to its native form, and purified to homogeneity. Antibody levels in 704 plasmas obtained from residents of areas of different levels of malaria endemicity in Orissa (India) and Manhiça (Mozambique) were assessed by enzyme-linked immunosorbent assay. The refolded DBLalpha domain was pure, homogeneous, and functional in that it bound human erythrocytes with specificity and was capable of inhibiting rosetting. The proportion of individuals who had measurable anti-DBLalpha immunoglobulin G responses was low in areas of low malaria endemicity in Orissa (6.7%) but high in areas of high endemicity in Orissa (87.5%) and Manhiça (74.5%). Seroprevalence and antibody levels against the recombinant protein increased with the age of inhabitants from areas with high transmission rates (P < 0.001). Half of the children in these areas had seroconverted by the age of 5 years. These findings suggest that in spite of the extreme polymorphism of PfEMP1 DBLalpha domains, the acquisition of specific antibodies is rapid and age related and reflects the reduced risk of malaria in areas with high transmission rates. Further studies are required to elucidate the role of these antibodies in protection from malaria.

Spatial analysis and mapping of malaria risk in Malawi using point-referenced prevalence of infection data

BackgroundCurrent malaria control initiatives aim at reducing malaria burden by half by the year 2010. Effective control requires evidence-based utilisation of resources. Characterizing spatial patterns of risk, through maps, is an important tool to guide control programmes. To this end an analysis was carried out to predict and map malaria risk in Malawi using empirical data with the aim of identifying areas where greatest effort should be focussed.MethodsPoint-referenced prevalence of infection data for children aged 1–10 years were collected from published and grey literature and geo-referenced. The model-based geostatistical methods were applied to analyze and predict malaria risk in areas where data were not observed. Topographical and climatic covariates were added in the model for risk assessment and improved prediction. A Bayesian approach was used for model fitting and prediction.ResultsBivariate models showed a significant association of malaria risk with elevation, annual maximum temperature, rainfall and potential evapotranspiration (PET). However in the prediction model, the spatial distribution of malaria risk was associated with elevation, and marginally with maximum temperature and PET. The resulting map broadly agreed with expert opinion about the variation of risk in the country, and further showed marked variation even at local level. High risk areas were in the low-lying lake shore regions, while low risk was along the highlands in the country.ConclusionThe map provided an initial description of the geographic variation of malaria risk in Malawi, and might help in the choice and design of interventions, which is crucial for reducing the burden of malaria in Malawi.

&lt;i&gt;Plasmodium falciparum&lt;/i&gt; parasite prevalence in East Africa: A Review

Empirical data on malaria endemicity are rarely available for public domain use to guide effective malaria control. This paper describes the work carried in East Africa since 1997 as part of a pan-African collaboration to map the risk of malaria, Mapping Malaria Risk in Africa (MARA) aimed at redressing deficiency. Studies of cross-sectional community estimates of Plasmodium falciparum prevalence among children aged 0-15 years were identified from a variety of sources including electronic searches of published material, manual review of pre-electronic peer reviewed journals and searches of libraries and archives in Kenya, Tanzania and Uganda. Each survey source, infection prevalence, date, longitude and latitude and survey characteristics were recorded. All data were subjected to a number of selection criteria including minimum sample sizes, samples randomly selected, community-based surveys, age ranges of sampled communities within 0-15 years, and surveys that were spatially unique. Of the 2,003 survey data points identified since 1907 in East Africa, only 503 were eligible for inclusion in the analysis dating from 1927 to 2003. The spatial plots of the data demonstrate the paucity of information on malaria prevalence from a number of densely populated areas and highlight the concentration of empirical data in concert with research centres in the sub-region. Models are required to define malaria risk in areas of East Africa where no empirical data are available so that limited resources can be better targeted to those in greatest need.

Intermittent administration of iron and sulfadoxine-pyrimethamine to control anaemia in Kenyan children: a randomised controlled trial

Iron supplementation is recommended for children at high risk of anaemia, but its benefits may not outweigh the associated risk of malaria in areas of seasonal transmission. We investigated the effect on haemoglobin concentrations of intermittent administration of iron supplements and sulfadoxine-pyrimethamine in symptom-free children under intense health surveillance. In a trial of two by two factorial design, 328 anaemic Kenyan children were randomly assigned either iron or placebo and sulfadoxine-pyrimethamine or placebo (82 to each group). Primary outcomes were haemological indicators of iron status and inflammation at the end of the follow-up, and occurrence of malaria attacks. Morbidity surveillance consisted of medical examinations every 4 weeks, continuous passive case detection, and visits twice a week to community health-workers. Analyses were by intention to treat. After 12 weeks, the groups assigned iron plus sulfadoxine-pyrimethamine, iron alone, or sulfadoxine-pyrimethamine alone had higher haemoglobin concentrations than the group assigned placebo (treatment effect adjusted for prognostic factors at baseline: 11.1 g/L [95% CI 7.5 to 14.7]; 10.7 g/L [7.1 to 14.3]; and 3.1 g/L [-0.5 to 6.7]). Administration of iron plus sulfadoxine-pyrimethamine also lowered the proportion with anaemia from 100% at baseline to 36% at 12 weeks, and of iron deficiency from 66% at baseline to 8% at 12 weeks. Survival analysis showed no evidence of substantially increased risk of malaria after iron supplementation. Iron supplementation gives substantial health benefits, which may outweigh possible inherent risks caused by malaria. A larger study than ours is needed to assess benefits and risks of intermittent administration of sulfadoxine-pyrimethamine in reducing the incidence of malaria attacks in areas of seasonal malaria transmission.

WOMEN AND MALARIA—SPECIAL RISK AND APPROPRIATE CONTROL STRATEGY

The factors that make pregnant women particularly vulnerable to morbidity and mortality with falciparum malaria and their relationship to current control strategies are reviewed. Pregnant women, particularly during their first pregnancy, are at greatest risk of severe falciparum malaria in areas of high and continuous malaria transmission and under conditions of unstable malaria in which they do not develop protective immunity. The author recommends chemoprophylaxis with chloroquine for pregnant women living in holoendemic and hyperendemic areas of Africa and Papua, New Guinea. Chloroquine is safe, but drug resistance has increasingly limited its utility, distribution is a formidable problem. In rural areas where poorly developed health care system are better developed and malaria transmission is less intense, the emphasis should be on early diagnosis and treatment. Women are potentially the key to the implementation of malaria control programs, yet recent studies indicate that underprivileged women frequently do not attend malaria clinics and are often missed in projects with passive surveillance. Additional research and community interventions are needed to enable women with malaria to obtain treatment and to involve them in malaria control measures at the village level.