Prof Bob W Snow
|Research Area:||Global Health|
|Technology Exchange:||Computational biology|
|Scientific Themes:||Tropical Medicine & Global Health|
|Keywords:||GIS, malaria, public health and mapping|
Bob has worked in Africa since 1984. He is Professor of Tropical Public Health at the Centre for Tropical Medicine, Nuffield Department of Medicine, University of Oxford and Chairman of the Malaria Public Health Department of the KEMRI-Wellcome Trust - University of Oxford Collaborative Programme in Kenya.
Bob's work began with the first African clinical trials of Insecticide-treated bed nets (ITN) between 1985-1987 at the UK's Medical Research Council labs at Farafenni, The Gambia. His interest in the role ITN play in child survival and the need for equitable access has continued for over 25 years, ensuring that a body of science drives national and international policy to guarantee that these interventions reach the most biologically and economically vulnerable communities free of charge across Africa.
Bob's research interests are founded in trying to understand the complex epidemiology of malaria parasite exposure, clinical disease outcomes and optimized, targeted approaches to reducing the malaria burden in Africa. In January 1989, Bob moved to Kilifi, on the Kenyan coast, to establish epidemiological studies in an area surrounding the rural district hospital. Over the last 25 years, this programme has grown into a multidisciplinary internationally recognized centre of research excellence. In 1996, Bob moved to Nairobi to expand the Oxford-Kenyan programme, investigating the epidemiology of severe malaria and malaria mortality across the region, including the establishment of the Pan-African collaboration known as the Mapping Malaria Risk in Africa (MARA/ARMA) collaboration with partners at the MRC in South Africa. MARA served as a prelude to the Malaria Atlas Project (MAP), a global initiative, founded by Bob in 2005. From 2010, this project is co-directed from Kenya with Dr Abdisalan Mohamed Noor, supporting a more effective way of working directly with national, malaria endemic country partners and governments across the African continent and the Arabian Peninsula.
As chairman of various national malaria control programme workshops he continues to promote the value of science in malaria policy development across the region. Working through various international agencies, Bob has been able to maintain a strategic, evidence-based argument for a continued focus on malaria control and disease reduction in Africa and sustain a focus of attention on financing control in poor, high burden countries across the continent. He provided keynote addresses at to the UK's All-Party Parliamentary Group on Malaria and Neglected Tropical Diseases in 2010, the 19th Roll Back Malaria Partnership Board meeting in Lusaka in 2010 and presentations on the need for effective use of evidence to prioritize control and elimination ambitions to ministers of health and various health departments in Kenya, Swaziland, Namibia, Djibouti, Mali, Uganda, Zanzibar, The Gambia, Ethiopia, Nigeria and the Kingdom of Saudi Arabia between 2007-2013. The research from the Malaria Public Health Department has provided the evidence to articulate a science-driven realistic malaria policy to those charged with setting agenda's internationally and nationally and has incrementally improved the use of this research to guide priorities in malaria control.
Bob is committed to developing science capacity and the research-to-policy agenda in Africa. He has supervised 16 post-graduates through their doctoral programmes, seven masters students and has supported five post-doctoral fellows. Bob supports the Kenyan Programme's director, and long time colleague since they worked together in The Gambia, Professor Kevin Marsh, in the evolution and future strategic direction of the wider Kenyan-Oxford programme through to 2020.
Bob has published over 380 articles on malaria with an h-index of over 80 from 22,400 life-time citations. In 2009 he was ranked joint 3rd highest malaria citation author as part of the Wellcome Trust 10 year review and the 5th most cited EU malaria scientist between 1997 and 2007
Bob is a technical advisor to the Kenyan Government. Among other international advisory panels he is a committed advisory board member of the UKs Malaria No More and the Against Malaria Foundation, that was recently voted best charity by the independent auditor, GiveWell. He is supported by the Wellcome Trust (UK) as a Principal Fellow and was made a Fellow of the Academy of Medical Sciences in 2008.
|Prof Simon Brooker||London School of Hygiene and Tropical Medicine||United Kingdom|
|Prof Mike English||Tropical Medicine||University of Oxford||United Kingdom|
|Dr Catherine Goodman||London School of Hygiene and Tropical Medicine||United Kingdom|
|Dr Bruce Larsen||Boston University, Center for International Health||United States|
|Dr Hoda Atta||WHO-EMRO,Malaria Control & Elimination||Egypt|
|Dr Ghasem Zamani||WHO-EMRO, Malaria Control & Elimination||Egypt|
|Dr Yazome Ye||ICF Measure Programme||United States|
|Dr Catherine Linard||L'Université libre de Bruxelles||Belgium|
|Prof Caroline Buckee||Center for Communicable Disease Dynamics, Epidemiology||Harvard School of Public Health||United States|
|Prof Feiko ter Kuile||Liverpool School of Tropical Medicine||United Kingdom|
|Dr Socé Fall||RBM-AFRO||Congo - Brazzaville|
|Prof Umberto D’Alessandro||Medical Research Council||Gambia|
|Richard Kamwi||Ministry of Health & Social Welfare||Namibia|
|Dr Lawrence Kazembe||Department of Statistics||University of Namibia||Namibia|
|Dr Jamal Amran||WHO-EMRO, Malaria Control & Elimination||Somalia|
|Prof Ibrahim El Hassan||University of Jazan||Saudi Arabia|
|Dr Khalid ElMardi||National Vector Borne Disease Programme||Sudan|
|Prof Mukhtar Maowia||Institute of Endemic Diseases||University of Khartoum||Sudan|
|Prof David Hamer||Zambia Center for Applied Health Research & Development||Zambia|
|Dr Alex Rowe||Centers for Disease Control||United States|
|Dr Abdinasir Amin||ICF Measure Programme||United States|
|Dr Clara Burgert||ICF Measure Programme||United States|
|Prof Kevin Marsh||Tropical Medicine||University of Oxford||United Kingdom|
Understanding the historical, temporal changes of malaria risk following control efforts in Africa provides a unique insight into what has been and might be archived towards a long-term ambition of elimination on the continent. Here, we use archived published and unpublished material combined with biological constraints on transmission accompanied by a narrative on malaria control to document the changing incidence of malaria in Africa since earliest reports pre-second World War. One result is a more informed mapped definition of the changing margins of transmission in 1939, 1959, 1979, 1999 and 2009. Hide abstract
BACKGROUND: Health workers' malaria case-management practices often differ from national guidelines. We assessed whether text-message reminders sent to health workers' mobile phones could improve and maintain their adherence to treatment guidelines for outpatient paediatric malaria in Kenya. METHODS: From March 6, 2009, to May 31, 2010, we did a cluster-randomised controlled trial at 107 rural health facilities in 11 districts in coastal and western Kenya. With a computer-generated sequence, health facilities were randomly allocated to either the intervention group, in which all health workers received text messages on their personal mobile phones on malaria case-management for 6 months, or the control group, in which health workers did not receive any text messages. Health workers were not masked to the intervention, although patients were unaware of whether they were in an intervention or control facility. The primary outcome was correct management with artemether-lumefantrine, defined as a dichotomous composite indicator of treatment, dispensing, and counselling tasks concordant with Kenyan national guidelines. The primary analysis was by intention to treat. The trial is registered with Current Controlled Trials, ISRCTN72328636. FINDINGS: 119 health workers received the intervention. Case-management practices were assessed for 2269 children who needed treatment (1157 in the intervention group and 1112 in the control group). Intention-to-treat analysis showed that correct artemether-lumefantrine management improved by 23·7 percentage-points (95% CI 7·6-40·0; p=0·004) immediately after intervention and by 24·5 percentage-points (8·1-41·0; p=0·003) 6 months later. INTERPRETATION: In resource-limited settings, malaria control programmes should consider use of text messaging to improve health workers' case-management practices. FUNDING: The Wellcome Trust. Hide abstract
Background: Insecticide-treated nets and intermittent preventive treatment with sulfadoxine-pyrimethamine are recommended for the control of malaria during pregnancy in endemic areas in Africa, but there has been no analysis of coverage data at a subnational level. We aimed to synthesise data from national surveys about these interventions, accounting for disparities in malaria risk within national borders. Methods: We extracted data for specific strategies for malaria control in pregnant women from national malaria policies from endemic countries in Africa. We identified the most recent national household cluster-sample surveys recording intermittent preventive treatment with sulfadoxine-pyrimethamine and use of insecticide-treated nets. We reconciled data to subnational administrative units to construct a model to estimate the number of pregnant women covered by a recommended intervention in 2007. Findings: 45 (96%) of 47 countries surveyed had a policy for distribution of insecticide-treated nets for pregnant women; estimated coverage in 2007 was 4·7 million (17%) of 27·7 million pregnancies at risk of malaria in 32 countries with data. 39 (83%) of 47 countries surveyed had an intermittent preventive treatment policy; in 2007, an estimated 6·4 million (25%) of 25·6 million pregnant women received at least one dose of treatment and 19·8 million (77%) visited an antenatal clinic (31 countries). Estimated coverage was lowest in areas of high-intensity transmission of malaria. Interpretation: Despite success in a few countries, coverage of insecticide-treated nets and intermittent preventive treatment in pregnant African women is inadequate; increased efforts towards scale-up are needed. Funding: The Malaria in Pregnancy Consortium and Wellcome Trust. © 2011 Elsevier Ltd. Hide abstract
BACKGROUND: Financing for malaria control has increased as part of international commitments to achieve the Millennium Development Goals (MDGs). We aimed to identify the unmet financial needs that would be biologically and economically equitable and would increase the chances of reaching worldwide malaria-control ambitions. METHODS: Populations at risk of stable Plasmodium falciparum or Plasmodium vivax transmission were calculated for 2007 and 2009 for 93 malaria-endemic countries to measure biological need. National per-person gross domestic product (GDP) was used to define economic need. An analysis of external donor assistance for malaria control was done for the period 2002-09 to compute overall and annualised per-person at-risk-funding commitments. Annualised malaria donor assistance was compared with independent predictions of funding needed to reach international targets of 80% coverage of best practices in case-management and effective disease prevention. Countries were ranked in relation to biological, economic, and unmet needs to examine equity and adequacy of support by 2010. FINDINGS: International financing for malaria control has increased by 166% (from $0·73 billion to $1·94 billion) since 2007 and is broadly consistent with biological needs. African countries have become major recipients of external assistance; however, countries where P vivax continues to pose threats to control ambitions are not as well funded. 21 countries have reached adequate assistance to provide a comprehensive suite of interventions by 2009, including 12 countries in Africa. However, this assistance was inadequate for 50 countries representing 61% of the worldwide population at risk of malaria-including ten countries in Africa and five in Asia that coincidentally are some of the poorest countries. Approval of donor funding for malaria control does not correlate with GDP. INTERPRETATION: Funding for malaria control worldwide is 60% lower than the US$4·9 billion needed for comprehensive control in 2010; this includes funding shortfalls for a wide range of countries with different numbers of people at risk and different levels of domestic income. More efficient targeting of financial resources against biological need and national income should create a more equitable investment portfolio that with increased commitments will guarantee sustained financing of control in countries most at risk and least able to support themselves. FUNDING: Wellcome Trust. Hide abstract
Lancet, 376 (9735), pp. 137-139. | Read more2010. Malaria in Africa: progress and prospects in the decade since the Abuja Declaration.
In the past 150 years, roughly half of the countries in the world eliminated malaria. Nowadays, there are 99 endemic countries - 67 are controlling malaria and 32 are pursuing an elimination strategy. This four-part Series presents evidence about the technical, operational, and financial dimensions of malaria elimination. The first paper in this Series reviews definitions of elimination and the state that precedes it: controlled low-endemic malaria. Feasibility assessments are described as a crucial step for a country transitioning from controlled low-endemic malaria to elimination. Characteristics of the 32 malaria-eliminating countries are presented, and contrasted with countries that pursued elimination in the past. Challenges and risks of elimination are presented, including Plasmodium vivax, resistance in the parasite and mosquito populations, and potential resurgence if investment and vigilance decrease. The benefits of elimination are outlined, specifically elimination as a regional and global public good. Priorities for the next decade are described. © 2010 Elsevier Ltd. Hide abstract
BACKGROUND: Efficient allocation of resources to intervene against malaria requires a detailed understanding of the contemporary spatial distribution of malaria risk. It is exactly 40 y since the last global map of malaria endemicity was published. This paper describes the generation of a new world map of Plasmodium falciparum malaria endemicity for the year 2007. METHODS AND FINDINGS: A total of 8,938 P. falciparum parasite rate (PfPR) surveys were identified using a variety of exhaustive search strategies. Of these, 7,953 passed strict data fidelity tests for inclusion into a global database of PfPR data, age-standardized to 2-10 y for endemicity mapping. A model-based geostatistical procedure was used to create a continuous surface of malaria endemicity within previously defined stable spatial limits of P. falciparum transmission. These procedures were implemented within a Bayesian statistical framework so that the uncertainty of these predictions could be evaluated robustly. The uncertainty was expressed as the probability of predicting correctly one of three endemicity classes; previously stratified to be an informative guide for malaria control. Population at risk estimates, adjusted for the transmission modifying effects of urbanization in Africa, were then derived with reference to human population surfaces in 2007. Of the 1.38 billion people at risk of stable P. falciparum malaria, 0.69 billion were found in Central and South East Asia (CSE Asia), 0.66 billion in Africa, Yemen, and Saudi Arabia (Africa+), and 0.04 billion in the Americas. All those exposed to stable risk in the Americas were in the lowest endemicity class (PfPR2-10 < or = 5%). The vast majority (88%) of those living under stable risk in CSE Asia were also in this low endemicity class; a small remainder (11%) were in the intermediate endemicity class (PfPR2-10 > 5 to < 40%); and the remaining fraction (1%) in high endemicity (PfPR2-10 > or = 40%) areas. High endemicity was widespread in the Africa+ region, where 0.35 billion people are at this level of risk. Most of the rest live at intermediate risk (0.20 billion), with a smaller number (0.11 billion) at low stable risk. CONCLUSIONS: High levels of P. falciparum malaria endemicity are common in Africa. Uniformly low endemic levels are found in the Americas. Low endemicity is also widespread in CSE Asia, but pockets of intermediate and very rarely high transmission remain. There are therefore significant opportunities for malaria control in Africa and for malaria elimination elsewhere. This 2007 global P. falciparum malaria endemicity map is the first of a series with which it will be possible to monitor and evaluate the progress of this intervention process. Hide abstract
BACKGROUND: Insecticide-treated bednets (ITNs) provide a means to improve child survival across Africa. Sales figures of these nets and survey coverage data presented nationally mask inequities in populations at biological and economic risk, and do not allow for precision in the estimation of unmet commodity needs. We gathered subnational ITN coverage sample survey data from 40 malaria-endemic countries in Africa between 2000 and 2007. METHODS: We computed the projected ITN coverage among children aged less than 5 years for age-adjusted population data that were stratified according to malaria transmission risks, proximate determinants of poverty, and methods of ITN delivery. FINDINGS: In 2000, only 1.7 million (1.8%) African children living in stable malaria-endemic conditions were protected by an ITN and the number increased to 20.3 million (18.5%) by 2007 leaving 89.6 million children unprotected. Of these, 30 million were living in some of the poorest areas of Africa: 54% were living in only seven countries and 25% in Nigeria alone. Overall, 33 (83%) countries were estimated to have ITN coverage of less than 40% in 2007. On average, we noted a greater increase in ITN coverage in areas where free distribution had operated between survey periods. INTERPRETATION: By mapping the distribution of populations in relation to malaria risk and intervention coverage, we provide a means to track the future requirements for scaling up essential disease-prevention strategies. The present coverage of ITN in Africa remains inadequate and a focused effort to improve distribution in selected areas would have a substantial effect on the continent's malaria burden. Hide abstract
BACKGROUND: To design an effective strategy for the control of malaria requires a map of infection and disease risks to select appropriate suites of interventions. Advances in model based geo-statistics and malaria parasite prevalence data assemblies provide unique opportunities to redefine national Plasmodium falciparum risk distributions. Here we present a new map of malaria risk for Kenya in 2009. METHODS: Plasmodium falciparum parasite rate data were assembled from cross-sectional community based surveys undertaken from 1975 to 2009. Details recorded for each survey included the month and year of the survey, sample size, positivity and the age ranges of sampled population. Data were corrected to a standard age-range of two to less than 10 years (PfPR2-10) and each survey location was geo-positioned using national and on-line digital settlement maps. Ecological and climate covariates were matched to each PfPR2-10 survey location and examined separately and in combination for relationships to PfPR2-10. Significant covariates were then included in a Bayesian geostatistical spatial-temporal framework to predict continuous and categorical maps of mean PfPR2-10 at a 1 x 1 km resolution across Kenya for the year 2009. Model hold-out data were used to test the predictive accuracy of the mapped surfaces and distributions of the posterior uncertainty were mapped. RESULTS: A total of 2,682 estimates of PfPR2-10 from surveys undertaken at 2,095 sites between 1975 and 2009 were selected for inclusion in the geo-statistical modeling. The covariates selected for prediction were urbanization; maximum temperature; precipitation; enhanced vegetation index; and distance to main water bodies. The final Bayesian geo-statistical model had a high predictive accuracy with mean error of -0.15% PfPR2-10; mean absolute error of 0.38% PfPR2-10; and linear correlation between observed and predicted PfPR2-10 of 0.81. The majority of Kenya's 2009 population (35.2 million, 86.3%) reside in areas where predicted PfPR2-10 is less than 5%; conversely in 2009 only 4.3 million people (10.6%) lived in areas where PfPR2-10 was predicted to be > or =40% and were largely located around the shores of Lake Victoria. CONCLUSION: Model based geo-statistical methods can be used to interpolate malaria risks in Kenya with precision and our model shows that the majority of Kenyans live in areas of very low P. falciparum risk. As malaria interventions go to scale effectively tracking epidemiological changes of risk demands a rigorous effort to document infection prevalence in time and space to remodel risks and redefine intervention priorities over the next 10-15 years. Hide abstract
BACKGROUND: The international financing of malaria control has increased significantly in the last ten years in parallel with calls to halve the malaria burden by the year 2015. The allocation of funds to countries should reflect the size of the populations at risk of infection, disease, and death. To examine this relationship, we compare an audit of international commitments with an objective assessment of national need: the population at risk of stable Plasmodium falciparum malaria transmission in 2007. METHODS AND FINDINGS: The national distributions of populations at risk of stable P. falciparum transmission were projected to the year 2007 for each of 87 P. falciparum-endemic countries. Systematic online- and literature-based searches were conducted to audit the international funding commitments made for malaria control by major donors between 2002 and 2007. These figures were used to generate annual malaria funding allocation (in US dollars) per capita population at risk of stable P. falciparum in 2007. Almost US$1 billion are distributed each year to the 1.4 billion people exposed to stable P. falciparum malaria risk. This is less than US$1 per person at risk per year. Forty percent of this total comes from the Global Fund to Fight AIDS, Tuberculosis and Malaria. Substantial regional and national variations in disbursements exist. While the distribution of funds is found to be broadly appropriate, specific high population density countries receive disproportionately less support to scale up malaria control. Additionally, an inadequacy of current financial commitments by the international community was found: under-funding could be from 50% to 450%, depending on which global assessment of the cost required to scale up malaria control is adopted. CONCLUSIONS: Without further increases in funding and appropriate targeting of global malaria control investment it is unlikely that international goals to halve disease burdens by 2015 will be achieved. Moreover, the additional financing requirements to move from malaria control to malaria elimination have not yet been considered by the scientific or international community. Hide abstract
Interest in mapping the global distribution of malaria is motivated by a need to define populations at risk for appropriate resource allocation and to provide a robust framework for evaluating its global economic impact. Comparison of older and more recent malaria maps shows how the disease has been geographically restricted, but it remains entrenched in poor areas of the world with climates suitable for transmission. Here we provide an empirical approach to estimating the number of clinical events caused by Plasmodium falciparum worldwide, by using a combination of epidemiological, geographical and demographic data. We estimate that there were 515 (range 300-660) million episodes of clinical P. falciparum malaria in 2002. These global estimates are up to 50% higher than those reported by the World Health Organization (WHO) and 200% higher for areas outside Africa, reflecting the WHO's reliance upon passive national reporting for these countries. Without an informed understanding of the cartography of malaria risk, the global extent of clinical disease caused by P. falciparum will continue to be underestimated. Hide abstract
The aim of this review was to use geographic information systems in combination with historical maps to quantify the anthropogenic impact on the distribution of malaria in the 20th century. The nature of the cartographic record enabled global and regional patterns in the spatial limits of malaria to be investigated at six intervals between 1900 and 2002. Contemporaneous population surfaces also allowed changes in the numbers of people living in areas of malaria risk to be quantified. These data showed that during the past century, despite human activities reducing by half the land area supporting malaria, demographic changes resulted in a 2 billion increase in the total population exposed to malaria risk. Furthermore, stratifying the present day malaria extent by endemicity class and examining regional differences highlighted that nearly 1 billion people are exposed to hypoendemic and mesoendemic malaria in southeast Asia. We further concluded that some distortion in estimates of the regional distribution of malaria burden could have resulted from different methods used to calculate burden in Africa. Crude estimates of the national prevalence of Plasmodium falciparum infection based on endemicity maps corroborate these assertions. Finally, population projections for 2010 were used to investigate the potential effect of future demographic changes. These indicated that although population growth will not substantially change the regional distribution of people at malaria risk, around 400 million births will occur within the boundary of current distribution of malaria by 2010: the date by which the Roll Back Malaria initiative is challenged to halve the world's malaria burden. Hide abstract
Because of inadequacies in national health information systems, the volumes of drugs required to support an effective policy transition toward artesunate-based combination therapy (ACT) are unknown for most African countries. A series of national surveys and population projections have been used to estimate the age-structured fever burden among 41 malaria endemic countries in Africa. Under present fever-management guidelines, commodity costs and internationally agreed coverage targets, the financial resources to meet the needs of ACT in most African countries are huge. Between US$1.6 billion and US$3.4 billion per annum must be found to give Africa the chance to consider a drug policy based on ACT. Substantial reductions in these costs would be achieved through more effective targeting of resources--only 20% of drugs would be required to manage fevers among the most at-risk pediatric patient populations. Better diagnostics would also be an important consideration for a new ACT policy in Africa. Hide abstract
The public health and economic consequences of Plasmodium falciparum malaria are once again regarded as priorities for global development. There has been much speculation on whether anthropogenic climate change is exacerbating the malaria problem, especially in areas of high altitude where P. falciparum transmission is limited by low temperature. The International Panel on Climate Change has concluded that there is likely to be a net extension in the distribution of malaria and an increase in incidence within this range. We investigated long-term meteorological trends in four high-altitude sites in East Africa, where increases in malaria have been reported in the past two decades. Here we show that temperature, rainfall, vapour pressure and the number of months suitable for P. falciparum transmission have not changed significantly during the past century or during the period of reported malaria resurgence. A high degree of temporal and spatial variation in the climate of East Africa suggests further that claimed associations between local malaria resurgences and regional changes in climate are overly simplistic. Hide abstract
Malaria transmission intensity in Africa varies over several log orders, from less than one infected bite per year to more than one thousand. In this review we examine the consequences in terms of age pattern, clinical spectrum and overall burden of disease and discuss the possible implications for interventions that reduce exposure to infected bites. With very low transmission intensity, all age groups are susceptible to severe malaria. With increasing transmission intensities, older children and adults suffer less severe disease and with high transmission rates the majority of severe cases occur in infants under one year of age. This pattern reflects the increasingly rapid acquisition of immune responses that limit the life-threatening effects of malaria with increasing exposure to the parasite. The clinical spectrum of severe malaria varies with transmission: with high transmission, severe malarial anaemia dominates and cerebral malaria is rare. As one moves towards lower transmission rates, cerebral malaria accounts for an increasingly large proportion of cases. Although the population risk of severe disease falls with age, the risk of death at an individual level may rise with age after an initial fall from very high case fatality rates in children aged under 6 months. Of central interest to malaria control is how the overall amount of disease in childhood varies with transmission. Data from a number of sources suggest that, with low transmission, the amount of malarial disease rises with increasing exposure but that this saturates relatively early. A key issue is whether the same pattern obtains for deaths, both those directly due to malaria and those from all causes. The methodological limitations of ecological comparisons between different areas are discussed before presenting a review of attempts to use this approach in Africa. This suggests that children living in areas of low malarial endemicity have all-cause mortality rates about half of those of children living in areas of moderate to high transmission. Deaths in the first year of life rise linearly with increasing exposure to malaria over a wide range of transmission intensities; by contrast all-cause mortality in children aged 0-4 years appears to saturate at relatively low transmission intensities. These data suggest that interventions that reduce exposure to malaria parasites, such as insecticide-treated bed nets (ITNs), will have the greatest chance of a sustained effect when used in areas where disease burdens are high but the frequency of parasite exposure is low-to-moderate. In conditions of high transmission, initial reductions in mortality may prove difficult to sustain as the reduced level of transmission may still lie on the part of the curve where mortality has saturated. However, at all levels of transmission the overall balance of benefits, including reduced load on families and health services from non-life-threatening malaria, favours the widespread introduction of ITNs in endemic areas of Africa. Hide abstract
During the past few years, there has been a historic series of declarations of renewed commitment to malaria control in Africa. Whether the burden of malaria is increasing in Africa is a moot point. This article attempts to re-construct the evidence for the trends in childhood mortality as a result of Plasmodium falciparum infection over the last century in Africa. Hide abstract
Lancet, 353 (9168), pp. 1965-1967. | Read more1999. Averting a malaria disaster.
Malaria remains the single largest threat to child survival in sub-Saharan Africa and warrants long-term investment for control. Previous malaria distribution maps have been vague and arbitrary. Marlies Craig, Bob Snow and David le Sueur here describe a simple numerical approach to defining distribution of malaria transmission, based upon biological constraints of climate on parasite and vector development. The model compared well with contemporary field data and historical 'expert opinion' maps, excepting small-scale ecological anomalies. The model provides a numerical basis for further refinement and prediction of the impact of climate change on transmission. Together with population, morbidity and mortality data, the model provides a fundamental tool for strategic control of malaria. Hide abstract
Bull World Health Organ, 77 (8), pp. 624-640. Read abstract1999. Estimating mortality, morbidity and disability due to malaria among Africa's non-pregnant population.
The contribution of malaria to morbidity and mortality among people in Africa has been a subject of academic interest, political advocacy, and speculation. National statistics for much of sub-Saharan Africa have proved to be an unreliable source of disease-specific morbidity and mortality data. Credible estimates of disease-specific burdens are required for setting global and national priorities for health in order to rationalize the use of limited resources and lobby for financial support. We have taken an empirical approach to defining the limits of Plasmodium falciparum transmission across the continent and interpolated the distributions of projected populations in 1995. By combining a review of the literature on malaria in Africa and models of acquired functional immunity, we have estimated the age-structured rates of the fatal, morbid and disabling sequelae following exposure to malaria infection under different epidemiological conditions. Hide abstract
BACKGROUND: Malaria remains a major cause of mortality and morbidity in Africa. Many approaches to malaria control involve reducing the chances of infection but little is known of the relations between parasite exposure and the development of effective clinical immunity so the long-term effect of such approaches to control on the pattern and frequency of malaria cannot be predicted. METHODS: We have prospectively recorded paediatric admissions with severe malaria over three to five years from five discrete communities in The Gambia and Kenya. Demographic analysis of the communities exposed to disease risk allowed the estimation of age-specific rates for severe malaria. Within each community the exposure to Plasmodium falciparum infection was determined through repeated parasitological and serological surveys among children and infants. We used acute respiratory-tract infections (ARI) as a comparison. FINDINGS: 3556 malaria admissions were recorded for the five sites. Marked differences were observed in age, clinical spectrum and rates of severe malaria between the five sites. Paradoxically, the risks of severe disease in childhood were lowest among populations with the highest transmission intensities, and the highest disease risks were observed among populations exposed to low-to-moderate intensities of transmission. For severe malaria, for example, admission rates (per 1000 per year) for children up to their 10th birthday were estimated as 3.9, 25.8, 25.9, 16.7, and 18.0 in the five communities; the forces of infection estimated for those communities (new infections per infant per month) were 0.001, 0.034, 0.050, 0.093, and 0.176, respectively. Similar trends were noted for cerebral malaria and for severe malaria anaemia but not for ARI. Mean age of disease decreased with increasing transmission intensity. INTERPRETATION: We propose that a critical determinant of life-time disease risk is the ability to develop clinical immunity early in life during a period when other protective mechanisms may operate. In highly endemic areas measures which reduce parasite transmission, and thus immunity, may lead to a change in both the clinical spectrum of severe disease and the overall burden of severe malaria morbidity. Hide abstract
New tools to prevent malaria morbidity and mortality are needed to improve child survival in sub-Saharan Africa. Insecticide treated bednets (ITBN) have been shown, in one setting (The Gambia, West Africa), to reduce childhood mortality. To assess the impact of ITBN on child survival under different epidemiological and cultural conditions we conducted a community randomized, controlled trial of permethrin treated bednets (0.5 g/m2) among a rural population on the Kenyan Coast. Between 1991 and 1993 continuous community-based demographic surveillance linked to hospital-based in-patient surveillance identified all mortality and severe malaria morbidity events during a 2-year period among a population of over 11000 children under 5 years of age. In July 1993, 28 randomly selected communities were issued ITBN, instructed in their use and the nets re-impregnated every 6 months. The remaining 28 communities served as contemporaneous controls for the following 2 years, during which continuous demographic and hospital surveillance was maintained until the end of July 1995. The introduction of ITBN led to significant reductions in childhood mortality (PE 33%, CI 7-51%) and severe, life-threatening malaria among children aged 1-59 months (PE 44%, CI 19-62). These findings confirm the value of ITBN in improving child survival and provide the first evidence of their specific role in reducing severe morbidity from malaria. Hide abstract
Malaria remains a major public health challenge in sub-Saharan Africa, yet our knowledge of the epidemiology of malaria in terms of patterns of mortality and morbidity is limited. We have examined the presentation of severe, potentially life-threatening malaria to district hospitals in two very different transmission settings: Kilifi, Kenya with low seasonal transmission and Ifakara, Tanzania with high seasonal transmission. The minimum annual rates of severe disease in children below five years in both populations were similar (46 per 1000 children in Kilifi and 51 per 1000 children in Ifakara). However, there were important differences in the age and clinical patterns of severe disease; twice as many patients were under one year of age in Ifakara compared with Kilifi and there was a four fold higher rate of cerebral malaria and three fold lower rate of malaria anaemia among malaria patients at Kilifi compared with Ifakara. Reducing malaria transmission in Ifakara by 95%, for example with insecticide-treated bed nets, would result in a transmission setting comparable to that of Kilifi and although this reduction may yield early successes in reducing severe malaria morbidity and mortality in young, immunologically naive children, place these same children at increased risk at older ages of developing severe and potentially different manifestations of malaria infection hence producing no net cohort gain in survivorship from potentially fatal malaria. Hide abstract
Traditionally malaria epidemiology has focused on factors such as parasite rates and vector dynamics without specific reference to disease. There are limited comprehensive data on malaria as a life-threatening event in African children. We have identified, through hospital surveillance, 581 episodes of severe malaria in residents of a defined area on the Kenya coast over a period of 3 years. This represents an absolute minimum risk of developing severe malaria by the fifth birthday of 1 in 15. The presentation of severe malaria showed marked seasonality, but the timing and magnitude of these fluctuations varied considerably between years. A satellite navigational system was used to define the exact location of the home of each severe malaria case. Space-time clustering of severe malaria was evident in this community. Seasonal peaks in incidence of severe malaria may comprise discrete mini-epidemics. In contrast, parasite rates in the community varied little during the course of the surveillance. The monitoring of disease, as opposed to parasitization, in children may result in more effective targeting of intervention resources. Hide abstract
The verbal autopsy (VA) is an epidemiological tool that is widely used to ascribe causes of death by interviewing bereaved relatives of children who were not under medical supervision at the time of death. This technique was assessed by comparison with a prospective survey of 303 childhood deaths at a district hospital in Kenya where medically confirmed diagnoses were available. Common causes of death were detected by VA with specificities greater than 80%. Sensitivity of the VA technique was greater than 75% for measles, neonatal tetanus, malnutrition, and trauma-related deaths; however, malaria, anaemia, acute respiratory-tract infection, gastroenteritis, and meningitis were detected with sensitivities of less than 50%. There may have been unwarranted optimism in the ability of VAs to detect some of the major causes of death, such as malaria, in African children. VA used in malaria-specific intervention trials should be interpreted with caution and only in the light of known sensitivities and specificities. Hide abstract
The incidence of clinical attacks of malaria was significantly less in Gambian children aged 1-9 years who slept in villages where all the bed nets (mosquito nets) were treated with permethrin than in children who slept in control villages with placebo-treated nets. Significant differences in changes in spleen size and in packed cell volume were also observed between the 2 groups during the course of a rainy season. No side effect was noted. Treatment of bed nets with insecticide is a form of malaria control that is well suited to community participation and can readily be incorporated into primary health care programmes. Insecticide-treated nets may be more effective in areas of seasonal or low intensity transmission than in areas with heavy perennial challenge. Hide abstract