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

La déforestation dans la région de Saint-Georges de l’Oyapock (Guyane française)

Pratiquée en Guyane française sur de petites superficies généralement inférieures à 1 ha, l’agriculture itinérante sur brûlis, désignée localement par le vocable abattis, laisse des empreintes relativement discrètes, voire imperceptibles à moyenne ou petite échelle. Pourtant, ce mode de défrichement agricole est souvent perçu, à tort ou à raison, comme l’une des principales causes de la déforestation tropicale. Pour évaluer son emprise spatiale et suivre les mutations récentes dans l’occupation du sol à l’échelle locale, nous nous sommes intéressés à la région de Saint-Georges de l’Oyapock. L’étude a été réalisée à partir de trois séries de photographies aériennes aux échelles comprises entre 1/10 000 et 1/50 000, prises en 1958, 1987 et 1997. Après géoréférencement et réalisation des mosaïques, les différentes composantes de l’occupation du sol ont été identifiées par photo-interprétation, actualisée par les observations et les relevés effectués sur le terrain en 1998. Une base d’informations spatialisée intégrée dans un SIG a été mise en place pour une exploitation informatique des données. À partir de cette base d’informations, nous avons dressé des cartes d’occupation du sol aux différentes dates et obtenu des statistiques sur l’emprise spatiale des abattis et son évolution au cours du temps. Les résultats mettent en évidence le rôle des routes et pistes dans la colonisation agricole de la forêt amazonienne et permettent de mieux apprécier l’impact de l’agriculture itinérante sur brûlis sur la dynamique de la forêt à l’échelle locale. On relève qu’en 1998, 58% des abattis sont situés à une distance de 200 m de part et d’autre d’une route ou d’une piste. Cette proportion passe à 83% pour une distance de 500 m. Tout autour de Saint - Georges, 53% des abattis en cours d’exploitation sont situés dans un rayon de 2 km. Ils représentent 28% dans un rayon de 1 km. Sur une surface totale cartographiée de 3 231 ha, les défrichements agricoles (abattis et autres surfaces pastorales) occupent 16% des superficies en 1998, contre 11% en 1958. Les défrichements récents se font essentiellement au profit des pâturages qui ont ainsi grignoté 12% de forêt. Toutefois, sur les 708 ha de surfaces non forestières en 1958, 273 ha sont à nouveau recouvertes de forêt en 1998, soit une recolonisation forestière de 8% de l’espace cartographié. Entre 1958 et 1998, le taux de déforestation locale a été de 0,26% par an. L’exploitation des données aériennes intégrées dans un SIG constitue un précieux outil de suivi de la dynamique de la déforestation à l’échelle locale, dans une région sous peuplée et enclavée. La méthode utilisée est reproductible et adaptable à d’autres sites de même nature.The Deforestation of the Region of St. Georges de l’Oyapock, French Guiana. The shifting cultivation, known locally as abattis, is generally practiced on small areas, less than one heetare. It leaves relatively discrete traces, if any at all at average or small scales. However, this method of land clearing is often regarded, rightly or wrongly, as one of the principal causes of tropical deforestation. To evaluate its surface extent and study the recent changes in the spatial use occurring at a local scale, we have studied the example of St.-Georges de l’Oyapock. The study was based on three series of aerial photographies with scales ranging between 1/10 000 and 1/50 000, taken respectively in 1958, 1987 and 1997. After geometric corrections, mosaics of aerial photographies were set up and various land cover and land use types were derived from them by computer-aided photomapping, supplemented by field surveys and ground readings taken in 1998. A spatialised information data base integrated in a GIS was constituted for computer-assisted analysis. With this data base, we drew up land cover maps at different dates, and obtained statistics showing surface extent and spatial distribution of land cover and land use, and their variations in time. The results highlight the role of roads and trails in the agricultural colonization of the Amazonian forest and make it possible to appreciate better the impact of traditional shifting farming on the dynamics of the forest at a local scale. We noted that in 1998, 58% of the shifting patterns are located within a radius of 200 m on both sides of a road or trail, this proportion increases by 83 % for a distance of 500 m. Around the settlement of St. Georges, 53 % of agricultural parcels still under cultivation are located in a range of 2 kilometers.  They represent 28 % in a range of 1 kilometer. Of the total surface area of 3,231 hectares mapped, the agricultural clearings (small clearing and other pasture lands) occupy 16 % of the surfaces in 1998, against 11 % in 1958. The recent forest conversion pointed out is first of all due to pastures, which thus nibbled 12 % of forest cover. However, of the 708 hectares of non-forest surfaces in 1958, 273 hectares are re-covered again by forest in 1998, therefore suggesting a forest recolonization of 8 % of the mapped area. Between 1958 and 1998, the rate of local deforestation was 0,26 % per year. The use of aerial data integrated in a GIS constitutes an invaluable tool for the follow-up studies of deforestation dynamics at a local scale, in an area that is underpopulated and landlocked. The method used is reproducible and can be adapted to other sites of comparable nature

Ecological niche partitioning between Anopheles gambiae molecular forms in Cameroon: the ecological side of speciation

<p>Abstract</p> <p>Background</p> <p>Speciation among members of the <it>Anopheles gambiae </it>complex is thought to be promoted by disruptive selection and ecological divergence acting on sets of adaptation genes protected from recombination by polymorphic paracentric chromosomal inversions. However, shared chromosomal polymorphisms between the M and S molecular forms of <it>An. gambiae </it>and insufficient information about their relationship with ecological divergence challenge this view. We used Geographic Information Systems, Ecological Niche Factor Analysis, and Bayesian multilocus genetic clustering to explore the nature and extent of ecological and chromosomal differentiation of M and S across all the biogeographic domains of Cameroon in Central Africa, in order to understand the role of chromosomal arrangements in ecological specialisation within and among molecular forms.</p> <p>Results</p> <p>Species distribution modelling with presence-only data revealed differences in the ecological niche of both molecular forms and the sibling species, <it>An. arabiensis</it>. The fundamental environmental envelope of the two molecular forms, however, overlapped to a large extent in the rainforest, where they occurred in sympatry. The S form had the greatest niche breadth of all three taxa, whereas <it>An. arabiensis </it>and the M form had the smallest niche overlap. Correspondence analysis of M and S karyotypes confirmed that molecular forms shared similar combinations of chromosomal inversion arrangements in response to the eco-climatic gradient defining the main biogeographic domains occurring across Cameroon. Savanna karyotypes of M and S, however, segregated along the smaller-scale environmental gradient defined by the second ordination axis. Population structure analysis identified three chromosomal clusters, each containing a mixture of M and S specimens. In both M and S, alternative karyotypes were segregating in contrasted environments, in agreement with a strong ecological adaptive value of chromosomal inversions.</p> <p>Conclusion</p> <p>Our data suggest that inversions on the second chromosome of <it>An. gambiae </it>are not causal to the evolution of reproductive isolation between the M and S forms. Rather, they are involved in ecological specialization to a similar extent in both genetic backgrounds, and most probably predated lineage splitting between molecular forms. However, because chromosome-2 inversions promote ecological divergence, resulting in spatial and/or temporal isolation between ecotypes, they might favour mutations in other ecologically significant genes to accumulate in unlinked chromosomal regions. When such mutations occur in portions of the genome where recombination is suppressed, such as the pericentromeric regions known as speciation islands in <it>An. gambiae</it>, they would contribute further to the development of reproductive isolation.</p

Living at the edge: biogeographic patterns of habitat segregation conform to speciation by niche expansion in Anopheles gambiae

<p>Abstract</p> <p>Background</p> <p>Ongoing lineage splitting within the African malaria mosquito <it>Anopheles gambiae </it>is compatible with ecological speciation, the evolution of reproductive isolation by divergent natural selection acting on two populations exploiting alternative resources. Divergence between two molecular forms (M and S) identified by fixed differences in rDNA, and characterized by marked, although incomplete, reproductive isolation is occurring in West and Central Africa. To elucidate the role that ecology and geography play in speciation, we carried out a countrywide analysis of <it>An. gambiae </it>M and S habitat requirements, and that of their chromosomal variants, across Burkina Faso.</p> <p>Results</p> <p>Maps of relative abundance by geostatistical interpolators produced a distinct pattern of distribution: the M-form dominated in the northernmost arid zones, the S-form in the more humid southern regions. Maps of habitat suitability, quantified by Ecological Niche Factor Analysis based on 15 eco-geographical variables revealed less contrast among forms. M was peculiar as it occurred proportionally more in habitat of marginal quality. Measures of ecological niche breadth and overlap confirmed the mismatch between the fundamental and realized patterns of habitat occupation: forms segregated more than expected from the extent of divergence of their environmental envelope – a signature of niche expansion. Classification of chromosomal arm 2R karyotypes by multilocus genetic clustering identified two clusters loosely corresponding to molecular forms, with 'mismatches' representing admixed individuals due to shared ancestral polymorphism and/or residual hybridization. In multivariate ordination space, these karyotypes plotted in habitat of more marginal quality compared to non-admixed, 'typical', karyotypes. The distribution of 'typical' karyotypes along the main eco-climatic gradient followed a consistent pattern within and between forms, indicating an adaptive role of inversions at this geographical scale.</p> <p>Conclusion</p> <p>Ecological segregation between M and S is consistent with niche expansion into marginal habitats by chromosomal inversion variants during early lineage divergence; presumably, this process is promoted by inter-karyotype competition in the higher-quality core habitat. We propose that the appearance of favourable allelic combinations in other regions of suppressed recombination (e.g. pericentromeric portions defining speciation islands in <it>An. gambiae</it>) fosters development of reproductive isolation to protect linkage between separate chromosomal regions.</p

Combiner analyse spatiale et épidémiologie pour l'aide à la décision dans la lutte contre la tuberculose en Guyane française

Le travail de thèse vise à comprendre les processus et les dynamiques spatiales de la tuberculose en Guyane, en particulier sur l'Ile de Cayenne, et ce par l'identification des facteurs de risque liés à l'émergence et/ou à la persistance de la maladie sur plusieurs années (1996-2003). La caractérisation des agrégats spaciaux de cas de tuberculose est combinée à une analyse phylogéographique des souches de Mycobacterium tuberculosis isolées en Guyane afin de caractériser les grappes génétiques de cas, et de déterminer les circuits de transmission de la maladie. Un système d'Information Géographique permet ensuite de cartographier les populations à risque de tuberculose sur l'Ile de Cayenne. Cette carte est produite en couplant la cartographie des cas de tuberculose à un indice de vulnérabilité de la population, basé sur l'analyse qualitative de l'environnement urbain. Cette étude révèle certains patrons de transmission de la tuberculose sur l'Ile de Cayenne, apportant à la fois des réponses pour les politiques de santé en Guyane et de nouvelles perspectives de recherche.This thesis work aims to understand the processes and spatial dynamics of human tuberculosis in the Ile-de-Cayenne, French Guiana. This is done by the identification of factors related to the diffusion and the persistence of the disease over several years (1996-2003). The spatial cluster analysis of tuberculosis cases is combined to a phylogeographic analysis of Mycobacterium tuberculosis strains isolated in French Guiana. This analysis dealt with the description of genetic and spatial clusters, as well as the routes of transmission responsible for the maintenance of the disease. A Geographic Information system is then used to map tuberculosis risk among populations of the Ile-de-Cayenne. This map is established by coupling the distribution of tuberculosis cases with a vulnerability index of populations, derived from a qualitative analysis of urban landscape. This study reveals some transmission patterns of tuberculosis in the Ile-de-Cayenne, providing support for the development of health policies in French Guiana, and offers perspectives on issues for future research.ORLEANS-BU Lettres (452342103) / SudocSudocFranceF