: Le chikungunya dans l'océan Indien

Echogéo est une revue électronique en ligneInternational audienceAmong the large amount of likely hazards in the South West of the Indian Ocean region (hurricanes, torrential rains, tsunamis, infectious diseases ...), some are more devastating and present than others. The Chikungunya epidemic that lasted from 2004 to 2006, as probably the major public health event, has left a strong impact on men, societies, and people's mind. This epidemic hit the states and territories in the region with 25% up to 60% prevalences. In an attempt to characterize the outlines of vulnerability and to determine contextual effects, we conducted an analysis of levels in human, social and health development in the involved countries. Although it has been established emergence factors on a regional scale are nevertheless widely related to social-spatial variables, and given equal hazard, the risk is not proportionally more important than in the known most vulnerable countries. On the scale of La Reunion, a data analysis of the social-spacial and epidemiologic environment with nearly 3000 cases georeferenced during the first phase of the epidemic, allows to assess the main areas at risk on the island.Parmi le grand nombre possible d'aléas dans le sud-ouest de l'océan Indien (cyclones, pluies torrentielles, volcanisme, tsunami, maladies infectieuses ...) certains sont plus dévastateurs et présents que d'autres. L'épidémie de chikungunya, qui s'est déroulée de 2004 à 2006, est sans doute l'événement majeur de santé publique qui a marqué les hommes, les sociétés et les esprits aussi. Cette épidémie a touché les Etats et territoires de la région avec des prévalences de 25 à 60 %. Pour essayer de caractériser les contours de la vulnérabilité et déterminer des effets de contexte nous avons mené une analyse des niveaux de développement humain, social et sanitaire des pays concernés. S'il est établi que les facteurs d'émergence à l'échelle régionale sont très largement liés à des variables socio-spatiales néanmoins, à aléa égal le risque n'est pas proportionnellement plus important dans les pays réputés les plus vulnérables. A l'échelle de La Réunion, une analyse des données de l'environnement socio-spatial et épidémiologique, avec près de 3 000 cas géoréférencés durant la première phase de l'épidémie, permet d'établir les principaux quartiers à risques de l'île

Wolbachia Age-Sex-Specific Density in Aedes albopictus: A Host Evolutionary Response to Cytoplasmic Incompatibility?

Wolbachia bacteria have invaded many arthropod species by inducing Cytoplasmic Incompatibility (CI). These symbionts represent fascinating objects of study for evolutionary biologists, but also powerful potential biocontrol agents. Here, we assess the density dynamics of Wolbachia infections in males and females of the mosquito Aedes albopitcus, an important vector of human pathogens, and interpret the results within an evolutionary framework.Wolbachia densities were measured in natural populations and in age controlled mosquitoes using quantitative PCR. We show that the density dynamics of the wAlbA Wolbachia strain infecting Aedes albopictus drastically differ between males and females, with a very rapid decay of infection in males only.Theory predicts that Wolbachia and its hosts should cooperate to improve the transmission of infection to offspring, because only infected eggs are protected from the effects of CI. However, incompatible matings effectively lower the fertility of infected males, so that selection acting on the host genome should tend to reduce the expression of CI in males, for example, by reducing infection density in males before sexual maturation. The rapid decay of one Wolbachia infection in Aedes albopictus males, but not in females, is consistent with this prediction. We suggest that the commonly observed reduction in CI intensity with male age reflects a similar evolutionary process. Our results also highlight the importance of monitoring infection density dynamics in both males and females to assess the efficiency of Wolbachia-based control strategies

Spatial and temporal distribution patterns of Anopheles arabiensis breeding sites in La Reunion Island - multi-year trend analysis of historical records from 1996-2009

<p>Abstract</p> <p>Background</p> <p>An often confounding facet of the dynamics of malaria vectors is the aquatic larval habitat availability and suitable conditions under which they can thrive. Here, we investigated the impact of environmental factors on the temporal and spatial distribution of larval habitats of <it>Anopheles </it><it>arabiensis </it>in different locations on La Reunion Island.</p> <p>Methods</p> <p>A retrospective examination was made from archival data which provided the complete enumeration of <it>An. arabiensis </it>breeding habitats in three distinct geographic zones - extending North-east, West and South of the island over 14 years, from January 1996 to December 2009. Data on the occurrence and the number of active larval habitats at each of a total of 4376 adjacent ellipsoid grid cells (216,506 square meters each) were used (1) to provide the geographic extent of breeding site availability from year to year and (2) to analyze associations with prevailing environmental factors, habitat types, and locations.</p> <p>Results</p> <p><it>Anopheles arabiensis </it>utilized a spectrum of man-made and natural aquatic habitats, most of which were concentrated primarily in the rock pools located in ravines and river fringes, and also in the large littoral marshes and within the irrigated agricultural zones. The numbers of breeding site per sampling grid differed significantly in different parts of the island. In contrast to an originally more widespread distribution across the island in the 1950s, detailed geographic analyses of the data obtained in the period extending from 1996-2009 showed an intriguing clustered distribution of active breeding sites in three discontinuous geographic zones, in which aquatic habitats availability fluctuates with the season and year. Seasonality in the prevalence of anopheles breeding sites suggests significant responsiveness to climatic factors.</p> <p>Conclusions</p> <p>The observed retreat of <it>An. arabiensis </it>distribution range to lower altitudinal zones (< 400 m) and the upward shift in the most remote littoral areas in the northeast and southwest regions suggest the possible influence of biogeographic factors, changes in land use and control operations. The results of this study would allow for a more rational implementation of control strategies across the island.</p

Evaluation of the Human IgG Antibody Response to Aedes albopictus Saliva as a New Specific Biomarker of Exposure to Vector Bites

Aedes-borne viruses like dengue and chikungunya are a major problem in Reunion Island. Assessing exposure to Aedes bites is crucial to estimating the risk of pathogen transmission. Currently, the exposure of populations to Aedes albopictus bites is mainly evaluated by entomological methods which are indirect and difficult to apply on a large scale. Recent findings suggest that evaluation of human antibody responses against arthropod salivary proteins could be useful in assessing exposure to mosquito bites. The results indicate that 88% of the studied population produce IgG to Ae. albopictus saliva antigens in Reunion Island and show that this biomarker can detect different levels of individual exposure. In addition, little cross-reactivity is observed with Aedes aegypti saliva, suggesting that this could be a specific marker for exposure to Aedes albopictus bites. Taken together, these results suggest that antibody responses to saliva could constitute a powerful immuno-epidemiological tool for evaluating exposure to Aedes albopictus and therefore the risk of arbovirus infection