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Brian Sharp

Publications and source records attributed to Brian Sharp.

15 recordsLinked to original sources
PubMed2006

El Niño Southern Oscillation (ENSO) and annual malaria incidence in Southern Africa.

We evaluated the association between annual malaria incidence and El Niño Southern Oscillation (ENSO) as measured by the Southern Oscillation Index (SOI) in five countries in Southern Africa from 1988 to 1999. Below normal incidence of malaria synchronised with a negative SOI (El Niño) and above normal incidence with a positive SOI (La Niña), which lead to dry and wet weather conditions, respectively. In most countries there was a positive relationship between SOI and annual malaria incidence, especially where Anopheles arabiensis is a major vector. This mosquito breeds in temporary rain pools and is highly sensitive to fluctuations in weather conditions. South Africa and Swaziland have the most reliable data and showed the strongest associations, but the picture there may also be compounded by the moderating effect of other oscillatory systems in the Indian Ocean. The impact of ENSO also varies over time within countries, depending on existing malaria control efforts and response capacity. There remains a need for quantitative studies that at the same time consider both ENSO-driven climate anomalies and non-ENSO factors influencing epidemic risk potential to assess their relative importance in order to provide an empirical basis for malaria epidemic forecasting models.

Africa, Southern↗
PubMed2006

Developing an evidence-based decision support system for rational insecticide choice in the control of African malaria vectors.

The emergence of Anopheles species resistant to insecticides widely used in vector control has the potential to impact directly on the control of malaria. This may have a particularly dramatic effect in Africa, where pyrethroids impregnated onto bed-nets are the dominant insecticides used for vector control. Because the same insecticides are used for crop pests, the extensive use and misuse of insecticides for agriculture has contributed to the resistance problem in some vectors. The potential for resistance to develop in African vectors has been apparent since the 1950s, but the scale of the problem has been poorly documented. A geographical information system-based decision support system for malaria control has recently been established in Africa and used operationally in Mozambique. The system incorporates climate data and disease transmission rates, but to date it has not incorporated spatial or temporal data on vector abundance or insecticide resistance. As a first step in incorporating this information, available published data on insecticide resistance in Africa has now been collated and incorporated into this decision support system. Data also are incorporated onto the openly available Mapping Malaria Risk in Africa (MARA) Web site (http://www.mara.org.za). New data, from a range of vector population-monitoring initiatives, can now be incorporated into this open access database to allow a spatial understanding of resistance distribution and its potential impact on disease transmission to benefit vector control programs.

Africa↗
PubMed2006

Reduction in infection with Plasmodium falciparum one year after the introduction of malaria control interventions on Bioko Island, Equatorial Guinea.

The Bioko Island Malaria Control Project was initiated in 2003 to substantially reduce malaria on the island of Bioko in Equatorial Guinea. The intervention consisted of generalized indoor residual spraying during the first year of the project. Case management and related measures were introduced during the second year. Two large household and parasitemia surveys of children 2 to < 15 years of age were carried out in 2004 and 2005, respectively, to assess the effect of the intervention after the first year. Patient records were collected retrospectively from one district hospital and analyzed for a comparison of pre-intervention and post-intervention periods. Overall mean prevalence of P. falciparum infection reduced from 46% (95% confidence interval [CI] = 40-51%) at baseline in 2004 to 31% (95% CI = 24-40%) in 2005 (P < 0.001). When the 12-month pre-intervention period was compared with the 12-month post-intervention period, there was a modest but statistically significant reduction in the number of malaria cases among hospital patients.

Adolescent↗
PubMed2005

Reduced variation around drug-resistant dhfr alleles in African Plasmodium falciparum.

We have measured microsatellite diversity at 26 markers around the dhfr gene in pyrimethamine-sensitive and -resistant parasites collected in southeast Africa. Through direct comparison with diversity on sensitive chromosomes we have found significant loss of diversity across a region of 70 kb around the most highly resistant allele which is evidence of a selective sweep attributable to selection through widespread use of pyrimethamine (in combination with sulfadoxine) as treatment for malaria. Retrospective analysis through four years of direct and continuous selection from use of sulfadoxine-pyrimethamine as first-line malaria treatment on a Plasmodium falciparum population in KwaZulu Natal, South Africa, has revealed how recombination significantly narrowed the margins of the selective sweep over time. A deterministic model incorporating selection coefficients measured during the same interval indicates that the transition was toward a state of recombination-selection equilibrium. We compared loss of diversity around the same resistance allele in two populations at either extreme of the range of entomological inoculation rates (EIRs), namely, under one infective bite per year in Mpumalanga, South Africa, and more than one per day in southern Tanzania. EIRs determine effective recombination rates and are expected to profoundly influence the dimensions of the selective sweep. Surprisingly, the dimensions were broadly consistent across both populations. We conclude that despite different recombination rates and contrasting drug selection histories in neighboring countries, the region-wide movement of resistant parasites has played a key role in the establishment of resistance in these populations and the dimensions of the selective sweep are dominated by the influence of high initial starting frequencies.

Africa↗
PubMed2005

Ecological covariates of Ascaris lumbricoides infection in schoolchildren from rural KwaZulu-Natal, South Africa.

OBJECTIVES: To identify environmental factors that could serve to predict Ascaris lumbricoides infection patterns and thus guide control efforts in the absence of epidemiological information; to assess whether A. lumbricoides infection is positively associated with the soil clay content. METHODS: Information on A. lumbricoides infection and re-infection in a cohort of primary schoolchildren and interview data on their socioeconomic background and behaviour were combined with environmental data using a geographical information system (GIS). Multivariate models served to explore the covariation of environmental and infection patterns adjusted for possible confounders. RESULTS: Prevalence maps and spatial statistics revealed considerable spatial clustering of infection in the small study area. Logistic multivariate regression models showed strong positive associations of infection with vegetation density measured as the normalized difference vegetation index (NDVI) at baseline [odds ratio (OR) for a 10% increase: 1.82; 95% confidence interval (95% CI): 1.24-2.68; P=0.002] and after re-infection (OR: 2.22; 95% CI: 1.71-2.87; P<0.001). We also found a strong negative association of re-infection with the sun exposure of the soil surface as estimated from digital elevation models (OR: 0.78; 95% CI: 0.88; P<0.001). The soil clay content was only moderately positively associated with infection and re-infection. Socioeconomic and behavioural variables, although correlated with A. lumbricoides infection, did not appear to confound the above associations in the demographically homogeneous study area. Spatial analysis of the model residuals suggested that as the models accounted for most of the spatial pattern, the model standard errors should not be affected by spatial clustering. CONCLUSION: NDVI seems to have a high potential for the prediction of A. lumbricoides infection as it was strongly associated with infection patterns in the study area. Further advantages are that NDVI information is easy to use, affordable and available with global coverage.

Aluminum Silicates↗
PubMed2005

Ecologic covariates of hookworm infection and reinfection in rural Kwazulu-natal/south Africa: a geographic information system-based study.

Information on hookworm infection and re-infection in a cohort of primary school children and interview data on their socioeconomic background and behavior were combined with environmental data using a geographic information system (GIS). Multivariate models served to explore the covariation of environmental and infection patterns adjusted for possible confounders. Our aim was to identify environmental factors that might serve to predict infection and thus guide control efforts when epidemiologic information is insufficient. Furthermore, we wanted to establish whether soil type has a genuine influence on hookworm infection. Prevalence maps and spatial statistics showed considerable spatial clustering of infection in the small ( approximately 28 x 16 km) study area. The multivariate logistic regression models showed strong positive associations of infection at baseline (baseline prevalence = 83.2%) with settlement density (odds ratio [OR] = 1.24, 95% confidence interval [CI] = 1.10-1.38) and vegetation density (OR = 1.66, 95% CI = 1.25-2.22) and a strong negative association with the clay content of the soil (OR = 0.67, 95% CI = 0.62-0.73). Similar but weaker correlations were found after re-infection. Socioeconomic status and behavior did not seem to confound these associations. Spatial analysis of the model residuals suggested that because the models accounted for most of the spatial pattern, the model standard errors were not affected by spatial clustering. Our study shows that the pattern of hookworm infection is strongly influenced by several environmental factors. The GIS-aided prediction of areas in need of treatment is therefore a promising tool to guide control efforts when epidemiologic information is insufficient.

Child↗
PubMed2004

Intercontinental spread of pyrimethamine-resistant malaria.

Here we present molecular evidence demonstrating that malaria parasites bearing high-level pyrimethamine resistance originally arrived in Africa from southeast Asia. The resistance alleles carried by these migrants are now spreading across Africa at an alarming rate, signaling the end of affordable malaria treatment and presenting sub-Saharan Africa with a public health crisis.

Africa↗
PubMed2004

Historical review of malarial control in southern African with emphasis on the use of indoor residual house-spraying.

Indoor residual house-spraying (IRS) mainly with dichlorodiphenyltrichloroethane (DDT) was the principal method by which malaria was eradicated or greatly reduced in many countries in the world between the 1940s and 1960s. In sub-Saharan Africa early malarial eradication pilot projects also showed that malaria is highly responsive to vector control by IRS but transmission could not be interrupted in the endemic tropical and lowland areas. As a result IRS was not taken to scale in most endemic areas of the continent with the exception of southern Africa and some island countries such as Reunion, Mayotte, Zanzibar, Cape Verde and Sao Tome. In southern Africa large-scale malarial control operations based on IRS with DDT and benzene hexachloride (BHC) were initiated in a number of countries to varying degrees. The objective of this review was to investigate the malarial situation before and after the introduction of indoor residual insecticide spraying in South Africa, Swaziland, Botswana, Namibia, Zimbabwe and Mozambique using historical malarial data and related information collected from National Malaria Control Programmes, national archives and libraries, as well as academic institutions in the respective countries. Immediately after the inception of IRS with insecticides, dramatic reductions in malaria and its vectors were recorded. Countries that developed National Malaria Control Programmes during this phase and had built up human and organizational resources made significant advances towards malarial control. Malaria was reduced from hyper- to meso-endemicity and from meso- to hypo-endemicity and in certain instances to complete eradication. Data are presented on the effectiveness of IRS as a malarial control tool in six southern African countries. Recent trends in and challenges to malarial control in the region are also discussed.

Africa, Southern↗
PubMed2003

Potential effect of climate change on malaria transmission in Africa.

BACKGROUND: Climate change is likely to affect transmission of vector-borne diseases such as malaria. We quantitatively estimated current malaria exposure and assessed the potential effect of projected climate scenarios on malaria transmission. METHODS: We produced a spatiotemporally validated (against 3791 parasite surveys) model of Plasmodium falciparum malaria transmission in Africa. Using different climate scenarios from the Hadley Centre global climate model (HAD CM3) climate experiments, we projected the potential effect of climate change on transmission patterns. FINDINGS: Our model showed sensitivity and specificity of 63% and 96%, respectively (within 1 month temporal accuracy), when compared with the parasite surveys. We estimate that on average there are 3.1 billion person-months of exposure (445 million people exposed) in Africa per year. The projected scenarios would estimate a 5-7% potential increase (mainly altitudinal) in malaria distribution with surprisingly little increase in the latitudinal extents of the disease by 2100. Of the overall potential increase (although transmission will decrease in some countries) of 16-28% in person-months of exposure (assuming a constant population), a large proportion will be seen in areas of existing transmission. INTERPRETATION: The effect of projected climate change indicates that a prolonged transmission season is as important as geographical expansion in correct assessment of the effect of changes in transmission patterns. Our model constitutes a valid baseline against which climate scenarios can be assessed and interventions planned.

Africa↗
PubMed2003

Antifolate antimalarial resistance in southeast Africa: a population-based analysis.

BACKGROUND: Sulfadoxine-pyrimethamine was first introduced for treatment of malaria in Africa during the early 1980s for cases when chloroquine treatment failed, and has since become the first-line treatment in many countries. Resistance to sulfadoxine-pyrimethamine is now increasing, especially in southeast Africa. METHODS: We characterised genetic change in dhfr and dhps genes in the Plasmodium falciparum population of KwaZulu-Natal, South Africa, during 1995-99, a period of rapid deterioration of the effectiveness of sulfadoxine-pyrimethamine. We assessed the evolutionary origin of the resistance by analysing polymorphic microsatellite repeats in the flanking region of the dhfr and dhps genes, which show whether resistance alleles originated through shared or independent ancestral mutation events. We then assessed the current extent of dispersal of dhfr and dhps resistance alleles by doing the same analysis in P falciparum sampled from communities in the Kilimanjaro region of northern Tanzania in 2001. FINDINGS: The large genetic change during 1995-99 in KwaZulu-Natal, South Africa, in both the health facility and the wider community surveys, was at the dhps locus, apparently because resistance at dhfr was established before 1995. The allelic determinants of resistance in this province share a common evolutionary origin with those found in Kilimanjaro, Tanzania, even though the two sites are 4000 km apart. INTERPRETATION: Three resistant dhfr alleles, and one resistant dhps allele, each derived from independent ancestral lineages, have been driven through through southeast Africa. The movement by the dhfr alleles (pyrimethamine resistance) preceded that of the dhps allele (sulfadoxine resistance). Our findings emphasise that gene flow rather than new mutations has been the most common originator of resistance in African countries.

Adult↗
PubMed2002

Rise in malaria incidence rates in South Africa: a small-area spatial analysis of variation in time trends.

Using Bayesian statistical models, the authors investigated spatial and temporal variations in small-area malaria incidence rates for the period mid-1986 to mid-1999 for two districts in northern KwaZulu Natal, South Africa. Maps of spatially smoothed incidence rates at different time points and spatially smoothed time trends in incidence gave a visual impression of the highest increase in incidence occurring where incidence rates previously had been lowest. This was confirmed by conditional autoregressive models, which showed that there was a significant negative association between time trends and smoothed baseline incidence before the steady rise in caseloads began. Growth rates also appeared to be higher in the areas close to the Mozambican border. The main findings of this analysis were that: 1) the spatial distribution of the rise in malaria incidence is uneven and strongly suggests a geographic expansion of high-malaria-risk areas; 2) there is evidence of a stabilization of incidence in areas that had the highest rates before the current escalation of rates began; and 3) areas immediately adjoining the Mozambican border appear to have undergone larger increases in incidence, in contrast to the general pattern of low growth in the more northern, high-baseline-incidence areas, but this was not confirmed by modeling. Smoothing of small-area maps of incidence and growth in incidence (trend) is important for interpretation of the spatial distribution of disease incidence and the spatial distribution of rapid changes in disease incidence.

Bayes Theorem↗
PubMed2002

The use of a GIS-based malaria information system for malaria research and control in South Africa.

The paper aims to outline the innovative development and application of a Geographical Information System based Malaria Information System for malaria research and control in South Africa. This system is a product of collaboration between the Malaria Control Programmes and the Malaria Research Programme of the Medical Research Council of South Africa. The ability of such a system to process data timeously into a usable format is discussed, as well as its relevance to malaria research, appropriate malaria control measures, tourism, and social and economic development.

Communicable Disease Control↗
PubMed2002

Malaria control by residual insecticide spraying in Chingola and Chililabombwe, Copperbelt Province, Zambia.

Malaria is endemic in the whole of Zambia and is the leading cause of morbidity and mortality. Prior to 1980, effective malaria control was achieved in the northern mining towns of Chingola and Chililabombwe by means of annual residual spraying programmes. In the 1970s, incidence rates were as low as 20/1000 p.a., but by 2000 had increased to 68/1000 p.a. in Chingola and to 158/1000 p.a.in Chililabombwe. Konkola Copper Mines (KCM) initiated a malaria control programme in which all dwellings in the two towns and within a 10-km radius were sprayed with either dichlorodiphenyltrichloroethane or a synthetic pyrethroid (Icon by ZENECA or Deltamethrin by Aventis). Houses were sprayed in November and December 2000, at the start of the peak transmission period. There was a statistically significant reduction in malaria incidence recorded at KCM health facilities in the two towns, representing a protective incidence rate ratio of 0.65 (95% CI 0.44, 0.97) when comparing the post-spraying period with the corresponding period of the previous 2 years. This reduction followed a single round of house spraying during a year with higher rainfall than the preceding two and in an area where chloroquine was first-line treatment. This house-spraying programme is an example of private/public sector collaboration in malaria control.

Adult↗