Studying relationships between environment and malaria incidence in Camopi (French Guiana) through the objective selection of buffer-based landscape characterisations

<p>Abstract</p> <p>Background</p> <p>Malaria remains a major health problem in French Guiana, with a mean of 3800 cases each year. A previous study in Camopi, an Amerindian village on the Oyapock River, highlighted the major contribution of environmental features to the incidence of malaria attacks. We propose a method for the objective selection of the best multivariate peridomestic landscape characterisation that maximises the chances of identifying relationships between environmental features and malaria incidence, statistically significant and meaningful from an epidemiological point of view.</p> <p>Methods</p> <p>A land-cover map, the hydrological network and the geolocalised inhabited houses were used to characterise the peridomestic landscape in eleven discoid buffers with radii of 50, 100, 200, 300, 400, 500, 600, 700, 800, 900 and 1000 metres. Buffer-based landscape characterisations were first compared in terms of their capacity to discriminate between sites within the geographic space and of their effective multidimensionality in variable space. The Akaike information criterion (AIC) was then used to select the landscape model best explaining the incidences of <it>P. vivax </it>and <it>P. falciparum </it>malaria. Finally, we calculated Pearson correlation coefficients for the relationships between environmental variables and malaria incidence, by species, for the more relevant buffers.</p> <p>Results</p> <p>The optimal buffers for environmental characterisation had radii of 100 m around houses for <it>P. vivax </it>and 400 m around houses for <it>P. falciparum</it>. The incidence of <it>P. falciparum </it>malaria seemed to be more strongly linked to environmental features than that of <it>P. vivax </it>malaria, within these buffers. The incidence of <it>P. falciparum </it>malaria in children was strongly correlated with proportions of bare soil (r = -0.69), land under high vegetation (r = 0.68) and primary forest (r = 0.54), landscape division (r = 0.48) and the number of inhabited houses (r = -0.60). The incidence of <it>P. vivax </it>malaria was associated only with landscape division (r = 0.49).</p> <p>Conclusions</p> <p>The proposed methodology provides a simple and general framework for objective characterisation of the landscape to account for field observations. The use of this method enabled us to identify different optimal observation horizons around houses, depending on the <it>Plasmodium </it>species considered, and to demonstrate significant correlations between environmental features and the incidence of malaria.</p

Environmental, entomological, socioeconomic and behavioural risk factors for malaria attacks in Amerindian children of Camopi, French Guiana

<p>Abstract</p> <p>Background</p> <p>Malaria is a major health issue in French Guiana. Amerindian communities remain the most affected. A previous study in Camopi highlighted the predominant role of environmental factors in the occurrence of malaria. However, all parameters involved in the transmission were not clearly identified. A new survey was conducted in order to clarify the risk factors for the presence of malaria cases in Camopi.</p> <p>Methods</p> <p>An open cohort of children under seven years of age was set up on the basis of biologically confirmed malaria cases for the period 2001-2009. Epidemiological and observational environmental data were collected using two structured questionnaires. Data were analysed with a multiple failures multivariate Cox model. The influence of climate and the river level on malaria incidence was evaluated by time-series analysis. Relationships between <it>Anopheles darlingi </it>human biting rates and malaria incidence rates were estimated using Spearman's rank correlation.</p> <p>Results</p> <p>The global annual incidence over the nine-year period was 238 per 1,000 for <it>Plasmodium falciparum</it>, 514 per 1,000 for <it>Plasmodium visa </it>and 21 per 1,000 for mixed infections. The multivariate survival analysis associated higher malaria incidence with living on the Camopi riverside vs. the Oyapock riverside, far from the centre of the Camopi hamlet, in a home with numerous occupants and going to sleep late. On the contrary, living in a house cleared of all vegetation within 50 m and at high distance of the forest were associated with a lower risk. Meteorological and hydrological characteristics appeared to be correlated with malaria incidence with different lags. <it>Anopheles darlingi </it>human biting rate was also positively correlated to incident malaria in children one month later.</p> <p>Conclusions</p> <p>Malaria incidence in children remains high in young children despite the appearance of immunity in children around three years of age. The closeness environment but also the meteorological parameters play an important role in malaria transmission among children under seven years of age in Camopi.</p

Epidémiologie du paludisme et environnement (étude de deux communautés amérindiennes de l'est et de l'ouest guyanais)

Notre étude s est proposée d analyser l incidence du paludisme et son évolution dans le temps et dans l espace, ainsi que de rechercher les facteurs de risque d accès palustres chez les enfants d un village du Moyen-Oyapock (Camopi), peuplé d Amérindiens wayampi et émerillon, d une part, et d un village du Haut-Maroni (Antecume Pata), peuplé d Amérindiens wayana, d autre part. L approche a été multiple avec, pour chacun des deux sites d étude :- Une analyse de survie (modèle de Cox) à partir des accès palustres confirmés biologiquement dans une cohorte d enfants de moins de sept ans régulièrement suivis, ainsi qu un questionnaire de type Connaissances, Attitudes et Pratiques (CAP), puis les caractéristiques des habitats et la description de leur environnement immédiat.- Une analyse spatiale avec une classification de l occupation du sol à partir d images satellites SPOT 5, l extraction de variables environnementales d intérêt, l étude de leur effet sur la transmission du paludisme et la mise au point d une méthode objective de sélection d un rayon d observation autour des habitations pour la caractérisation de l environnement.- Une étude de séries temporelles (ARIMA) afin de déterminer l effet des évènements climatiques et hydrologiques sur le paludisme, aux niveaux local et plus global (El Niño).Les taux d incidence d accès palustres sur la période 2001-2009 se sont révélés particulièrement élevés chez les jeunes enfants, notamment à Camopi avec une moyenne de 773 par année. Une diminution brutale de l incidence a eue lieu en 2007 sur le Haut-Maroni et ce phénomène est observé à Camopi depuis 2010. Une prémunition se développe assez rapidement au cours de la vie (2-3 ans), surtout contre les reviviscences à Plasmodium vivax. Les facteurs environnementaux se sont avérés être les plus nombreux et les plus fortement liés à l incidence palustre. En effet, le dégagement des alentours du carbet de toute végétation et une certaine distance de celui-ci à la forêt sont des facteurs protecteurs. La composante géographique est également apparue essentielle à Camopi avec une incidence qui variait selon le fleuve d habitation et en fonction de la distance au hameau principal. Les facteurs météorologiques locaux (température et niveau du fleuve) se sont également révélés être liés à l incidence du paludisme à court terme (0-3 mois). Par ailleurs, nos résultats ont permis d émettre un certain nombre d hypothèses quant à la transmission et au(x) vecteur(s) local(ux), et notamment de suggérer la participation d un vecteur autre qu An. darlingi dans la transmission du paludisme à Camopi. Nous avons également prouvé par ce travail que la télédétection et les systèmes d information géographique sont très prometteurs pour la prise en compte de la dimension spatiale et environnementale dans l étude des maladies transmissibles, notamment dans les zones d accès difficile de GuyaneThe aim of our study was to analyze the incidence of malaria in children and its evolution through time and space, as well as to search for risk factors in a village in Mid-Oyapock (Camopi), populated by Amerindians Wayampi and Emerillon, on the one hand, and a village in Upper-Maroni (Antecume Pata), populated by Amerindians Wayana, on the other hand. The approach was multiple with, for both study sites:- A survival analysis (Cox modelling) completed out of biologically confirmed malaria attacks in a cohort of children under seven, as well as a Knowledge, Attitudes, Practices and Behavior (KAPB) questionnaire, and also the characteristics of the houses and the description of their immediate environment.- A spatial analysis with a land cover classification from SPOT 5 satellite images, the extraction of environmental variables, the study of their effect on malaria transmission and the development of an objective method for picking the proper observation horizon around houses in order to characterize the environment.- A time series study (ARIMA) to determine the effect of climatic and hydrological events on malaria at local and global (El Niño) scales.The incidence rates of malaria attacks during the period 2001-2009 were particularly high among young children, especially in Camopi with an average of 773 by year. A sharp decline in incidence occurred in 2007 on the Upper Maroni and this phenomenon has been observed in Camopi since 2010. An acquired immunity develops quite rapidly during the life (2-3 years old), especially against P. vivax relapses. Environmental factors were found to be the most strongly associated with malaria incidence. Indeed, living in a hut cleared from the surrounding vegetation and at a larger distance from the forest are protective factors. The geographic component also appeared essential in Camopi with an incidence which varied with the river of living and with the distance from the main hamlet. The local meteorological factors (temperature and river level) also proved to be linked to malaria incidence in the short term (0-3 months). Moreover, our results have allowed issuing a number of assumptions about the transmission and the local vector(s), in particular to suggest the involvement of another vector than An. darlingi in the malaria transmission in Camopi. We also proved by this work that remote sensing and geographic information systems hold great promise for the inclusion of the spatial and environmental dimensions in the study of transmitted diseases, especially in areas of difficult access in French GuianaCAYENNE-BU (973022101) / SudocSudocFranceF