Search PubMed⌕ Search

Biomedical subjects

R W Snow

Publications and source records attributed to R W Snow.

At least 145 records · Page 8Linked to original sources
PubMedDate not supplied

Sustained protection against mortality and morbidity from malaria in rural Gambian children by chemoprophylaxis given by village health workers.

Mortality and morbidity from malaria were measured in children for a one-year period in a rural area of The Gambia 3-4 years after the introduction of a primary health care programme into some villages in the study area. Among children resident in primary health care villages who received treatment for febrile illnesses from a village health worker resident in their village there was no reduction in overall mortality or in morbidity from malaria compared with levels found in villages without a primary health care worker. However, among children aged 3-59 months who received malaria chemoprophylaxis from a village health worker in addition to treatment there was a 49% reduction in mortality and a 73% reduction in attacks of clinical malaria. The level of protection against malaria achieved by chemoprophylaxis given by village health workers 3-4 years after the chemoprophylaxis programme was started was as high as that obtained shortly after the introduction of the primary health care programme.

Antimalarials↗
PubMedDate not supplied

A comparison of two DNA probes, one specific for Plasmodium falciparum and one with wider reactivity, in the diagnosis of malaria.

The sensitivity and specificity of 2 probes for the detection of malarial infection was studied. 399 blood samples from Gambian children were tested in a deoxyribonucleic acid (DNA) hybridization assay, and the results compared with the microscopical findings from thick blood films. 8 additional pure Plasmodium malariae and 14 pure P. vivax samples were also assayed. One probe, containing a 21 base pair tandem repeat and highly specific for P. falciparum, detected this species in all except 2 of 74 samples with a parasitaemia of 250 per microliter or more; the overall sensitivity of the probe was 76%. The other probe, a 6 kilobase pair organelle DNA, is conserved in all Plasmodium species so far tested. Its sensitivity for P. falciparum was lower than the 21 base pair repeat, but it detected P. vivax and P. malariae at low levels of parasitaemia, and thus could be useful in field studies.

Animals↗
PubMedDate not supplied

The relationship between anthropometric measurements and measurements of iron status and susceptibility to malaria in Gambian children.

Anthropometric measurements were made and serum iron and ferritin levels determined in a group of Gambian children at the beginning of the rainy season and these findings were related to the malaria experience of the children during the following malaria transmission season. Susceptibility to malaria was not correlated with prior weight-for-age, height-for-age, weight-for-height or serum albumin, or with serum iron, serum iron binding capacity nor serum ferritin. Thus, our findings do not provide any support for the view that poor nutritional status, as assessed by anthropometric measurements, or iron deficiency protect against malaria infection. Children who developed a clinical attack of malaria accompanied by a high level of parasitaemia tended to have a higher mean weight-for-age at the beginning of the rainy season than did children who had a clinical attack accompanied by a low level of parasitaemia, but the difference between groups was not statistically significant. However, they had a significantly higher mean serum ferritin level (P less than 0.01).

Anthropometry↗
PubMedDate not supplied

Malaria chemoprophylaxis, birth weight and child survival.

Study of the effects of malaria chemoprophylaxis given during pregnancy on birthweight and investigation of the influence of birthweight on child survival suggest that, in a rural area of The Gambia, chemoprophylaxis given during pregnancy might reduce infant mortality by about one-fifth in the children of primigravidae but by less than 5% in the children of multigravidae. In malaria endemic areas, primigravidae should be protected against malaria not only for their own sake but also for that of their infants.

Antimalarials↗
PubMedDate not supplied

The role of shops in the treatment and prevention of childhood malaria on the coast of Kenya.

A community survey of 388 mothers in a rural and peri-urban population surrounding a district hospital on the coast of Kenya revealed that the preferred choice of treatment for childhood febrile illnesses was with proprietary drugs bought over the counter at shops and kiosks (72% of interviews). 67% of the mothers who reported using shops claimed they would buy chloroquine-based drugs. Preventative measures such as mosquito nets were uncommon (6.2%), but the use of commercial pyrethrum mosquito coils was reported more frequently (46.4%). Separate investigations of treatment given to 394 children before presentation at hospital with severe and mild malaria was consistent with the reports in the community of high usage of shop-bought anti-malarials and anti-pyretics. The involvement of the private sector in peripheral health care delivery for malaria is discussed.

Adult↗
PubMedDate not supplied

Measurement of serum haptoglobin as an indicator of the efficacy of malaria intervention trials.

Serum haptoglobin levels were measured by an enzyme-linked immunosorbent assay in Gambian children who participated in 3 malaria intervention trials with untreated or impregnated bed nets. In one study, in which a significant effect on clinical malaria was observed, the mean serum haptoglobin level was significantly higher in the intervention than in the control group. In the other 2 studies, in which no significant protection was observed, mean haptoglobin levels were similar in intervention and control groups. Measurement of serum haptoglobin may provide a useful indirect measure of the effectiveness of malaria control programmes.

Bedding and Linens↗
PubMedDate not supplied

Periodicity and space-time clustering of severe childhood malaria on the coast of Kenya.

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.

Age Factors↗
PubMedDate not supplied

Mortality and morbidity from malaria after stopping malaria chemoprophylaxis.

Gambian children who had received malaria chemoprophylaxis for a variable period of time during their first 5 years of life were followed to determine whether they experienced a rebound in mortality or in morbidity from malaria during the period after chemoprophylaxis was stopped. The risk of dying between the ages of 5 years, when chemoprophylaxis was stopped, and 10 years was no higher among children who had received chemoprophylaxis with Maloprim (pyrimethamine plus dapsone) for some period during their first 5 years of life than among children who had received placebo (21 vs. 24 deaths) and the beneficial effect of chemoprophylaxis on mortality observed during the first 5 years of life was sustained. The incidence of clinical attacks of malaria during the year after medication was stopped was significantly higher among children who had previously received Maloprim for several years than among children who had previously received placebo. However, at the end of this year, there was no significant difference in spleen rate, parasite rate or packed cell volume between the 2 groups of children. Thus, stopping chemoprophylaxis after a period of several years increased the risk of clinical malaria but did not result in a rebound in mortality in Gambian children. However, the number of deaths recorded was small, so a modest effect on mortality cannot be excluded.

Animals↗
PubMedDate not supplied

Evidence for a mass community effect of insecticide-treated bednets on the incidence of malaria on the Kenyan coast.

The use of insecticide-treated bednets (ITBNs) has been shown to be effective in reducing mortality and morbidity from malaria. However, there is mixed evidence as to whether or not community-wide use of ITBNs engenders a 'mass effect', such that those not sleeping under bednets are offered protection from widespread ITBN use in the area in which they live. We have analysed data collected in Kilifi, Kenya, from a cohort of children followed from birth to investigate how the degree of net usage in the locality of a child affects the risk of developing malaria. This effect was explored using a Cox proportional hazards model. For those not using ITBNs, we found that an increasing level of ITBN usage within the area surrounding each child was associated with a decreasing risk of developing malaria, thus providing evidence in support of a mass community effect. The size and significance of this effect were found to decrease as non-overlapping areas of increasing distance away from a child's home were considered. The effect was significant for areas at distances of up to 1.5 km away from each child.

Bedding and Linens↗
PubMedDate not supplied

Annual Plasmodium falciparum entomological inoculation rates (EIR) across Africa: literature survey, Internet access and review.

This paper presents the results of an extensive search of the formal and informal literature on annual Plasmodium falciparum entomological inoculation rates (EIR) across Africa from 1980 onwards. It first describes how the annual EIR data were collated, summarized, geo-referenced and staged for public access on the internet. Problems of data standardization, reporting accuracy and the subsequent publishing of information on the internet follow. The review was conducted primarily to investigate the spatial heterogeneity of malaria exposure in Africa and supports the idea of highly heterogeneous risk at the continental, regional and country levels. The implications for malaria control of the significant spatial (and seasonal) variation in exposure to infected mosquito bites are discussed.

Africa↗
PubMedDate not supplied

Changing patterns of clinical malaria since 1965 among a tea estate population located in the Kenyan highlands.

The changing epidemiology of clinical malaria since 1965 among hospitalized patients was studied at a group of tea estates in the western highlands of Kenya. These data indicate recent dramatic increases in the numbers of malaria admissions (6.5 to 32.5% of all admissions), case fatality (1.3 to 6%) and patients originating from low-risk, highland areas (34 to 59%). Climate change, environmental management, population migration, and breakdown in health service provision seem unlikely explanations for this changing disease pattern. The coincident arrival of chloroquine resistance during the late 1980s in the subregion suggests that drug resistance is a key factor in the current pattern and burden of malaria among this highland population.

Altitude↗
PubMedDate not supplied

Malaria in pregnancy as an indirect cause of infant mortality in sub-Saharan Africa.

Although randomized controlled trials of interventions to reduce malaria in pregnancy have demonstrated an increase in the birthweight of the newborn in primigravidae, the subsequent impact on infant mortality in all-parities has not been assessed. The aim of this paper was to model the possible impact of placental malarial infection on infant mortality through reduced birthweight. An extensive literature search was undertaken to define a series of parameters describing the associations between placental infection, birthweight and premature mortality in sub-Saharan Africa. It was shown that a baby is twice as likely to be born of low birthweight if the mother has an infected placenta at the time of delivery (all-parities: 23% vs 11%, primigravidae only: 32% vs 16%), and that the probability of premature mortality of African newborns in the first year of life is 3 times higher in babies of low birthweight than in those of normal birthweight (16% vs 4.6%). Assuming 25% of pregnant women in malaria-endemic areas of Africa harbour placental malarial infection, it is suggested that 5.7% of infant deaths in malarious areas could be an indirect cause of malaria in pregnancy. This would imply that, in 1997, malaria in pregnancy could have been responsible for around 3700 infant deaths under the diverse epidemiological conditions in Kenya. Placental infection with Plasmodium falciparum appears to have a more significant role in infant survival in Africa than has been previously assumed. This may explain the high reduction in infant mortality rates from interventions aimed at reducing transmission, over and above that expected from a decline in direct malaria-specific mortality alone.

Africa South of the Sahara↗
PubMedDate not supplied

Epileptic seizures and malaria in Kenyan children.

Between October 1990 and November 1991 data were collected on the frequency, causes, and nature of epileptic seizures in children admitted to the paediatric ward at Kilifi District Hospital, Kenya, from a defined study area. During this period, 1324 children were studied, of whom 15.8% had seizures as part of their illness. Malaria was by far the commonest cause of seizures, accounting for 69.0%; no other single condition caused more than 4.4%. The proportion of respiratory infections complicated by seizures was 4.0% compared to 31.3% for malaria. Only 25% of malaria-related epileptic seizures were associated with cerebral malaria; the remainder were associated with otherwise uncomplicated malaria and, in this group, 84% had complex seizures, with 47% being partial and over 70% repetitive. There was no relationship with fever, with 54% of observed seizures occurring at rectal temperatures below 38 degrees C. The minimum community incidence of complex seizures in association with non-cerebral malaria was 5.8 per 1000 per year. Complex epileptic seizures in association with otherwise uncomplicated malaria are common and may be a significant cause of longer term morbidity in malaria endemic areas.

Age Factors↗
PubMedDate not supplied

Malaria is an important cause of anaemia in primigravidae: evidence from a district hospital in coastal Kenya.

A study was undertaken in order to determine the prevalence and aetiology of anaemia in pregnancy in coastal Kenya, so as to establish locally important causes and enable the development of appropriate intervention strategies. 275 women attending the antenatal clinic at Kilifi district hospital, Kenya, were recruited in November 1993. The prevalence of anaemia (haemoglobin [Hb] < 11 g/dL) was 75.6%, and the prevalence of severe anaemia (Hb < 7g/dL) was 9.8% among all parities; 15.3% of 73 primigravidae were severely anaemic, compared with 7.9% of 202 multigravidae (P = 0.07). In primigravidae, malaria infection (Plasmodium falciparum) was strongly associated with moderate and severe anaemia (chi 2 test for trend, P = 0.003). Severe anaemia was more than twice as common in women with peripheral parasitaemia as in those who were aparasitaemic, and parasitaemia was associated with a 2.2g/dL decrease in mean haemoglobin level (P < 0.001). In multigravidae, iron deficiency and hookworm infection were the dominant risk factors for anaemia. Folate deficiency and human immunodeficiency virus infection were not strongly associated with anaemia. It is suggested that an intervention that can effectively reduce malaria infection in primigravidae could have a major impact on the health of these women and their infants.

Anemia↗
PubMedDate not supplied

Models to predict the intensity of Plasmodium falciparum transmission: applications to the burden of disease in Kenya.

There is an increasing need to provide spatial distribution maps of the clinical burden of Plasmodium falciparum malaria in Africa. Recent evidence suggests that risk groups and the clinical spectrum of severe malaria are related to the intensity of P. falciparum transmission. Climate operates to affect the vectorial capacity of P. falciparum transmission and this is particularly important in the Horn of Africa and parts of East Africa. We have used a fuzzy logic climate suitability model to define areas of Kenya unsuitable for stable transmission. Kenya's unstable transmission areas can be divided into areas where transmission potential is limited by low rainfall or low temperature and, combined, encompass over 8 million people. Among areas of stable transmission we have used empirical data on P. falciparum infection rates among 124 childhood populations in Kenya to develop a climate-based statistical model of transmission intensity. This model correctly identified 75% (95% confidence interval CI 70-85) of 3 endemicity classes (low, < 20%; high, > or = 70%; and intermediate parasite prevalences). The model was applied to meteorological and remote sensed data using a geographical information system to provide estimates of endemicity for all of the 1080 populated fourth level administrative regions in Kenya. National census data for 1989 on the childhood populations within each administrative region were projected to provide 1997 estimates. Endemicity-specific estimates of morbidity and mortality were derived from published and unpublished sources and applied to their corresponding exposed-to-risk childhood populations. This combined transmission, population and disease-risk model suggested that every day in Kenya approximately 72 and 400 children below the age of 5 years either die or develop clinical malaria warranting in-patient care, respectively. Despite several limitations, such an approach goes beyond 'best guesses' to provide informed estimates of the geographical burden of malaria and its fatal consequences in Kenya.

Child, Preschool↗
PubMedDate not supplied

Predicting malaria seasons in Kenya using multitemporal meteorological satellite sensor data.

This article describes research that predicts the seasonality of malaria in Kenya using remotely sensed images from satellite sensors. The predictions were made using relationships established between long-term data on paediatric severe malaria admissions and simultaneously collected data from the Advanced Very High Resolution Radiometer (AVHRR) on the National Oceanic and Atmospheric Administrations (NOAA) polar-orbiting meteorological satellites and the High Resolution Radiometer (HRR) on the European Organization for the Exploitation of Meteorological Satellites' (EUMETSAT) geostationary Meteosat satellites. The remotely sensed data were processed to provide surrogate information on land surface temperature, reflectance in the middle infra-red, rainfall, and the normalized difference vegetation index (NDVI). These variables were then subjected to temporal Fourier processing and the fitted Fourier data were compared with the mean percentage of total annual malaria admissions recorded in each month. The NDVI in the preceding month correlated most significantly and consistently with malaria presentations across the 3 sites (mean adjusted r2 = 0.71, range 0.61-0.79). Regression analyses showed that an NDVI threshold of 0.35-0.40 was required for more than 5% of the annual malaria cases to be presented in a given month. These thresholds were then extrapolated spatially with the temporal Fourier-processed NDVI data to define the number of months, in which malaria admissions could be expected across Kenya in an average year, at an 8 x 8 km resolution. The resulting maps were compared with the only existing map (Butler's) of malaria transmission periods for Kenya, compiled from expert opinion. Conclusions are drawn on the appropriateness of remote sensing techniques for compiling national strategies for malaria intervention.

Data Collection↗
PubMedDate not supplied

Environmental and entomological risk factors for the development of clinical malaria among children on the Kenyan coast.

Several malariometric studies have examined the impact on human-vector contact of house construction, demographics, bed net and insect repellent use. However, few studies have documented the significance of these proximate determinants on the risks of clinical disease. We undertook a matched case-control study of the risks of both mild clinical malaria and severe life-threatening malaria according to a range of putative factors which would influence the frequency of child-vector encounters in Kilifi district on the Kenyan coast. Among 394 severe disease cases, 380 age-matched mild disease cases, and their respective location and age-matched community controls, we were unable to demonstrate any statistically significant effect upon disease outcome of house construction, presence of domestic animals, or bed net use. Higher population density within a 250 m radius of the homes conferred significant protection from the risks of developing severe malaria compared to community controls. The risks of developing severe malaria compared to the community controls and the transition from mild to severe disease were statistically significantly lower in those who reported use of mosquito coils, local repellents or aerosol insecticides. We concluded that it is likely that the impact of household features on disease outcome is dependent upon both the density of infecting mosquitoes and acquired immunity within a given locality.

Case-Control Studies↗