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Robert W Snow - One of the best experts on this subject based on the ideXlab platform.
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the relationship between facility based malaria test positivity rate and community based Parasite Prevalence
PLOS ONE, 2020Co-Authors: Alice Kamau, Robert W Snow, Grace Mtanje, Christine Mataza, Lucas Malla, Philip BejonAbstract:INTRODUCTION Malaria surveillance is a key pillar in the control of malaria in Africa. The value of using routinely collected data from health facilities to define malaria risk at community levels remains poorly defined. METHODS Four cross-sectional Parasite Prevalence surveys were undertaken among residents at 36 enumeration zones in Kilifi county on the Kenyan coast and temporally and spatially matched to fever surveillance at 6 health facilities serving the same communities over 12 months. The age-structured functional form of the relationship between test positivity rate (TPR) and community-based Parasite Prevalence (PR) was explored through the development of regression models fitted by alternating the linear, exponential and polynomial terms for PR. The predictive ranges of TPR were explored for PR endemicity risk groups of control programmatic value using cut-offs of low (PR <5%) and high (PR ≥ 30%) transmission intensity. RESULTS Among 28,134 febrile patients encountered for malaria diagnostic testing in the health facilities, 12,143 (43.2%: 95% CI: 42.6%, 43.7%) were positive. The overall community PR was 9.9% (95% CI: 9.2%, 10.7%) among 6,479 participants tested for malaria. The polynomial model was the best fitting model for the data that described the algebraic relationship between TPR and PR. In this setting, a TPR of ≥ 49% in all age groups corresponded to an age-standardized PR of ≥ 30%, while a TPR of < 40% corresponded to an age-standardized PR of < 5%. CONCLUSION A non-linear relationship was observed between the relative change in TPR and changes in the PR, which is likely to have important implications for malaria surveillance programs, especially at the extremes of transmission. However, larger, more spatially diverse data series using routinely collected TPR data matched to community-based infection Prevalence data are required to explore the more practical implications of using TPR as a replacement for community PR.
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the impact of urbanization and population density on childhood plasmodium falciparum Parasite Prevalence rates in africa
Malaria Journal, 2017Co-Authors: Caroline W Kabaria, Catherine Linard, Abdisalan M Noor, Robert W Snow, Marius GilbertAbstract:Although malaria has been traditionally regarded as less of a problem in urban areas compared to neighbouring rural areas, the risk of malaria infection continues to exist in densely populated, urban areas of Africa. Despite the recognition that urbanization influences the epidemiology of malaria, there is little consensus on urbanization relevant for malaria Parasite mapping. Previous studies examining the relationship between urbanization and malaria transmission have used products defining urbanization at global/continental scales developed in the early 2000s, that overestimate actual urban extents while the population estimates are over 15 years old and estimated at administrative unit level. This study sought to discriminate an urbanization definition that is most relevant for malaria Parasite mapping using individual level malaria infection data obtained from nationally representative household-based surveys. Boosted regression tree (BRT) modelling was used to determine the effect of urbanization on malaria transmission and if this effect varied with urbanization definition. In addition, the most recent high resolution population distribution data was used to determine whether population density had significant effect on malaria Parasite Prevalence and if so, could population density replace urban classifications in modelling malaria transmission patterns. The risk of malaria infection was shown to decline from rural areas through peri-urban settlements to urban central areas. Population density was found to be an important predictor of malaria risk. The final boosted regression trees (BRT) model with urbanization and population density gave the best model fit (Tukey test p value <0.05) compared to the models with urbanization only. Given the challenges in uniformly classifying urban areas across different countries, population density provides a reliable metric to adjust for the patterns of malaria risk in densely populated urban areas. Future malaria risk models can, therefore, be improved by including both population density and urbanization which have both been shown to have significant impact on malaria risk in this study.
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assembling a global database of malaria Parasite Prevalence for the malaria atlas project
Malaria Journal, 2007Co-Authors: Abdisalan M Noor, Carlos A Guerra, Andrew J Tatem, Simon I Hay, Lorena S Lucioparedes, Priscilla W Gikandi, Robert W SnowAbstract:Background Open access to databases of information generated by the research community can synergize individual efforts and are epitomized by the genome mapping projects. Open source models for outputs of scientific research funded by tax-payers and charities are becoming the norm. This has yet to be extended to malaria epidemiology and control.
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the relationship between the plasmodium falciparum Parasite ratio in childhood and climate estimates of malaria transmission in kenya
Malaria Journal, 2004Co-Authors: Robert W Snow, Judith A Omumbo, Carlos A GuerraAbstract:Background: Plasmodium falciparum morbid and fatal risks are considerably higher in areas supporting Parasite Prevalence ≥25%, when compared with low transmission areas supporting Parasite Prevalence below 25%. Recent descriptions of the health impacts of malaria in Africa are based upon categorical descriptions of a climate-driven fuzzy model of suitability (FCS) for stable transmission developed by the Mapping Malaria Risk in Africa collaboration (MARA). Methods: An electronic and national search was undertaken to identify community-based Parasite Prevalence surveys in Kenya. Data from these surveys were matched using ArcView 3.2 to extract spatially congruent estimates of the FCS values generated by the MARA model. Levels of agreement between three classes used during recent continental burden estimations of Parasite Prevalence (0%, >0 – 0 – <0.75 and ≥0.75) were tested using the kappa (k) statistic and examined as continuous variables to define better levels of agreement. Results: Two hundred and seventeen independent Parasite Prevalence surveys undertaken since 1980 were identified during the search. Overall agreement between the three classes of Parasite Prevalence and FCS was weak although significant (k = 0.367, p < 0.0001). The overall correlation between the FCS and the Parasite ratio when considered as continuous variables was also positive (0.364, p < 0.001). The margins of error were in the stable, endemic (Parasite ratio ≥25%) class with 42% of surveys represented by an FCS <0.75. Reducing the FCS value criterion to ≥0.6 improved the classification of stable, endemic Parasite ratio surveys. Zero values of FCS were not adequate discriminators of zero Parasite Prevalence. Conclusion: Using the MARA model to categorically distinguish populations at differing intensities of malaria transmission in Kenya may under-represent those who are exposed to stable, endemic transmission and over-represent those at no risk. The MARA approach to defining FCS values of suitability for stable transmission represents our only contemporary continental level map of malaria in Africa but there is a need to redefine Africa's population at risk in accordance with both climatic and non-climatic determinants of P. falciparum transmission intensity to provide a more informed approach to estimating the morbid and fatal consequences of infection across the continent.
Niels Piot - One of the best experts on this subject based on the ideXlab platform.
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Bumble bee Parasite Prevalence but not genetic diversity impacted by the invasive plant Impatiens glandulifera
Ecosphere, 2019Co-Authors: Maryse Vanderplanck, Ivan Meeus, Nathalie Roger, Romain Moerman, Guillaume Ghisbain, Maxence Gérard, Dominik Popowski, Sebastian Granica, Denis Fournier, Niels PiotAbstract:While many bee species are experiencing population declines, some host plant generalist bees remain common in Europe, partly because they seem able to shift to new resources. However, foraging on a new alternative plant, such as an invasive species, can modify diet quality and have a potentially detrimental effect on bee health. Herein, we investigated whether the spread of the invasive plant Impatiens glandulifera affects Bombus pascuorum population regarding Parasite Prevalence, genetic structure, and nest density in Belgium. While no difference in bumble bee genetic structure was detected between invaded and uninvaded sites, we show that I. glandulifera occurrence was significantly correlated with a decrease in the Prevalence of Apicystis bombi but not the Prevalence of three other Parasite species (i.e., Crithidia bombi, Nosema bombi, Nosema ceranae, and Nosema sp.). Regarding our investigations, this effect was likely not due to variation in local bumble bee population fitness before I. glandulifera flowering, nor to the relative abundance of other pollinators such as Apis mellifera, but the unique chemical composition (i.e., polyphenol rich) of the pollen of I. glandulifera remained as an interesting hypothesis. Whereas B. pascuorum queens probably colonize all the potential nesting sites in an area, invaded by I. glandulifera or not, the abundance of polyphenol ampelopsin in pollen from I. glandulifera pollen might reduce local Parasite Prevalence. Our field study confirms that bumble bee Parasite Prevalence is potentially related to the particular chemical composition of collected pollen. Plant traits such as secondary metabolite occurrence could play a key role in the health and conservation of bumble bees.
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establishment of wildflower fields in poor quality landscapes enhances micro Parasite Prevalence in wild bumble bees
Oecologia, 2019Co-Authors: Niels Piot, Jeroen Scheper, Theo Linders, David Kleijn, Ivan Meeus, Guy SmaggheAbstract:The current worldwide pollinator decline is caused by the interplay of different drivers. Several strategies have been undertaken to counteract or halt this decline, one of which is the implementation of wildflower fields. These supplementary flowers provide extra food resources and have proven their success in increasing pollinator biodiversity and abundance. Yet such landscape alterations could also alter the host–pathogen dynamics of pollinators, which could affect the populations. In this study, we investigated the influence of sown wildflower fields on the Prevalence of micro-Parasites and viruses in the wild bumble bee Bombus pascuorum, one of the most abundant bumble bee species in Europe and the Netherlands. We found that the effect of sown wildflower fields on micro-Parasite Prevalence is affected by the composition of the surrounding landscape and the size of the flower field. The Prevalence of micro-Parasites increases with increasing size of sown wildflower fields in landscapes with few semi-natural landscape elements. This effect was not observed in landscapes with a high amount of semi-natural landscape elements. We elaborate on two mechanisms which can support these findings: (1) “transmission hot spots” within the altered flower-networks, which could negatively impact hosts experiencing an increased exposure; (2) improved tolerance of the hosts, withstanding higher Parasite populations.
Theo Linders - One of the best experts on this subject based on the ideXlab platform.
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establishment of wildflower fields in poor quality landscapes enhances micro Parasite Prevalence in wild bumble bees
Oecologia, 2019Co-Authors: Niels Piot, Jeroen Scheper, Theo Linders, David Kleijn, Ivan Meeus, Guy SmaggheAbstract:The current worldwide pollinator decline is caused by the interplay of different drivers. Several strategies have been undertaken to counteract or halt this decline, one of which is the implementation of wildflower fields. These supplementary flowers provide extra food resources and have proven their success in increasing pollinator biodiversity and abundance. Yet such landscape alterations could also alter the host–pathogen dynamics of pollinators, which could affect the populations. In this study, we investigated the influence of sown wildflower fields on the Prevalence of micro-Parasites and viruses in the wild bumble bee Bombus pascuorum, one of the most abundant bumble bee species in Europe and the Netherlands. We found that the effect of sown wildflower fields on micro-Parasite Prevalence is affected by the composition of the surrounding landscape and the size of the flower field. The Prevalence of micro-Parasites increases with increasing size of sown wildflower fields in landscapes with few semi-natural landscape elements. This effect was not observed in landscapes with a high amount of semi-natural landscape elements. We elaborate on two mechanisms which can support these findings: (1) “transmission hot spots” within the altered flower-networks, which could negatively impact hosts experiencing an increased exposure; (2) improved tolerance of the hosts, withstanding higher Parasite populations.
Ivan Meeus - One of the best experts on this subject based on the ideXlab platform.
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Bumble bee Parasite Prevalence but not genetic diversity impacted by the invasive plant Impatiens glandulifera
Ecosphere, 2019Co-Authors: Maryse Vanderplanck, Ivan Meeus, Nathalie Roger, Romain Moerman, Guillaume Ghisbain, Maxence Gérard, Dominik Popowski, Sebastian Granica, Denis Fournier, Niels PiotAbstract:While many bee species are experiencing population declines, some host plant generalist bees remain common in Europe, partly because they seem able to shift to new resources. However, foraging on a new alternative plant, such as an invasive species, can modify diet quality and have a potentially detrimental effect on bee health. Herein, we investigated whether the spread of the invasive plant Impatiens glandulifera affects Bombus pascuorum population regarding Parasite Prevalence, genetic structure, and nest density in Belgium. While no difference in bumble bee genetic structure was detected between invaded and uninvaded sites, we show that I. glandulifera occurrence was significantly correlated with a decrease in the Prevalence of Apicystis bombi but not the Prevalence of three other Parasite species (i.e., Crithidia bombi, Nosema bombi, Nosema ceranae, and Nosema sp.). Regarding our investigations, this effect was likely not due to variation in local bumble bee population fitness before I. glandulifera flowering, nor to the relative abundance of other pollinators such as Apis mellifera, but the unique chemical composition (i.e., polyphenol rich) of the pollen of I. glandulifera remained as an interesting hypothesis. Whereas B. pascuorum queens probably colonize all the potential nesting sites in an area, invaded by I. glandulifera or not, the abundance of polyphenol ampelopsin in pollen from I. glandulifera pollen might reduce local Parasite Prevalence. Our field study confirms that bumble bee Parasite Prevalence is potentially related to the particular chemical composition of collected pollen. Plant traits such as secondary metabolite occurrence could play a key role in the health and conservation of bumble bees.
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establishment of wildflower fields in poor quality landscapes enhances micro Parasite Prevalence in wild bumble bees
Oecologia, 2019Co-Authors: Niels Piot, Jeroen Scheper, Theo Linders, David Kleijn, Ivan Meeus, Guy SmaggheAbstract:The current worldwide pollinator decline is caused by the interplay of different drivers. Several strategies have been undertaken to counteract or halt this decline, one of which is the implementation of wildflower fields. These supplementary flowers provide extra food resources and have proven their success in increasing pollinator biodiversity and abundance. Yet such landscape alterations could also alter the host–pathogen dynamics of pollinators, which could affect the populations. In this study, we investigated the influence of sown wildflower fields on the Prevalence of micro-Parasites and viruses in the wild bumble bee Bombus pascuorum, one of the most abundant bumble bee species in Europe and the Netherlands. We found that the effect of sown wildflower fields on micro-Parasite Prevalence is affected by the composition of the surrounding landscape and the size of the flower field. The Prevalence of micro-Parasites increases with increasing size of sown wildflower fields in landscapes with few semi-natural landscape elements. This effect was not observed in landscapes with a high amount of semi-natural landscape elements. We elaborate on two mechanisms which can support these findings: (1) “transmission hot spots” within the altered flower-networks, which could negatively impact hosts experiencing an increased exposure; (2) improved tolerance of the hosts, withstanding higher Parasite populations.
Andrew J Tatem - One of the best experts on this subject based on the ideXlab platform.
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a geostatistical analysis of the association between armed conflicts and plasmodium falciparum malaria in africa 1997 2010
Malaria Journal, 2015Co-Authors: Luigi Sedda, Andrew J TatemAbstract:The absence of conflict in a country has been cited as a crucial factor affecting the operational feasibility of achieving malaria control and elimination, yet mixed evidence exists on the influence that conflicts have had on malaria transmission. Over the past two decades, Africa has seen substantial numbers of armed conflicts of varying length and scale, creating conditions that can disrupt control efforts and impact malaria transmission. However, very few studies have quantitatively assessed the associations between conflicts and malaria transmission, particularly in a consistent way across multiple countries. In this analysis an explicit geostatistical, autoregressive, mixed model is employed to quantitatively assess the association between conflicts and variations in Plasmodium falciparum Parasite Prevalence across a 13-year period in sub-Saharan Africa. Analyses of geolocated, malaria Prevalence survey variations against armed conflict data in general showed a wide, but short-lived impact of conflict events geographically. The number of countries with decreased P. falciparum Parasite Prevalence (17) is larger than the number of countries with increased transmission (12), and notably, some of the countries with the highest transmission pre-conflict were still found with lower transmission post-conflict. For four countries, there were no significant changes in Parasite Prevalence. Finally, distance from conflicts, duration of conflicts, violence of conflict, and number of conflicts were significant components in the model explaining the changes in P. falciparum Parasite rate. The results suggest that the maintenance of intervention coverage and provision of healthcare in conflict situations to protect vulnerable populations can maintain gains in even the most difficult of circumstances, and that conflict does not represent a substantial barrier to elimination goals.
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assembling a global database of malaria Parasite Prevalence for the malaria atlas project
Malaria Journal, 2007Co-Authors: Abdisalan M Noor, Carlos A Guerra, Andrew J Tatem, Simon I Hay, Lorena S Lucioparedes, Priscilla W Gikandi, Robert W SnowAbstract:Background Open access to databases of information generated by the research community can synergize individual efforts and are epitomized by the genome mapping projects. Open source models for outputs of scientific research funded by tax-payers and charities are becoming the norm. This has yet to be extended to malaria epidemiology and control.
