Publications (14) View all
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Article: Abiotic and biotic factors associated with the presence of Anopheles arabiensis immatures and their abundance in naturally occurring and manmade aquatic habitats.
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ABSTRACT: BACKGROUND: Anopheles arabiensis (Diptera: Culicidae) is a potential malaria vector commonly present at low altitudes in remote areas in Reunion Island. Little attention has been paid to the environmental conditions driving larval development and abundance patterns in potential habitats. Two field surveys were designed to determine whether factors that discriminate between aquatic habitats with and without An. arabiensis larvae also drive larval abundance, comparatively in man-made and naturally occurring habitats. METHODS: In an initial preliminary survey, a representative sample of aquatic habitats that would be amenable to an intensive long-term study were selected and divided into positive and negative sites based on the presence or absence of Anopheles arabiensis larvae. Subsequently, a second survey was prompted to gain a better understanding of biotic and abiotic drivers of larval abundance, comparatively in man-made and naturally occurring habitats in the two studied locations. In both surveys, weekly sampling was performed to record mosquito species composition and larval density within individual habitats, as well as in situ biological characteristics and physico-chemical properties. RESULTS: Whilst virtually any stagnant water body could be a potential breeding ground for An. arabiensis, habitats occupied by their immatures had different structural and biological characteristics when compared to those where larvae were absent. Larval occurrence seemed to be influenced by flow velocity, macrofauna diversity and predation pressure. Interestingly, the relative abundance of larvae in man-made habitats (average: 0.55 larvae per dip, 95%CI [0.3-0.7]) was significantly lower than that recorded in naturally occurring ones (0.74, 95%CI [0.5-0.8]). Such differences may be accounted for in part by varying pressures that could be linked to a specific habitat. CONCLUSIONS: If the larval ecology of An. arabiensis is in general very complex and factors affecting breeding site productivity sometimes not easy to highlight, our results, however, highlight lower populations of An. arabiensis immatures compared to those reported in comparable studies conducted in the African continent. Overall, this low larval abundance, resulting from both abiotic and biotic factors, suggests that vector control measures targeting larval habitats are likely to be successful in Reunion, but these could be better implemented by taking environmental variability into account.Parasites & Vectors 05/2012; 5(1):96. · 2.94 Impact Factor -
Article: Evaluation of the human IgG antibody response to Aedes albopictus saliva as a new specific biomarker of exposure to vector bites.
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ABSTRACT: The spread of Aedes albopictus, a vector for re-emergent arbovirus diseases like chikungunya and dengue, points up the need for better control strategies and new tools to evaluate transmission risk. Human antibody (Ab) responses to mosquito salivary proteins could represent a reliable biomarker for evaluating human-vector contact and the efficacy of control programs. We used ELISA tests to evaluate specific immunoglobulin G (IgG) responses to salivary gland extracts (SGE) in adults exposed to Aedes albopictus in Reunion Island. The percentage of immune responders (88%) and levels of anti-SGE IgG Abs were high in exposed individuals. At an individual level, our results indicate heterogeneity of the exposure to Aedes albopictus bites. In addition, low-level immune cross-reactivity between Aedes albopictus and Aedes aegypti SGEs was observed, mainly in the highest responders. Ab responses to saliva could be used as an immuno-epidemiological tool for evaluating exposure to Aedes albopictus bites. Combined with entomological and epidemiological methods, a "salivary" biomarker of exposure to Aedes albopictus could enhance surveillance of its spread and the risk of arbovirus transmission, and could be used as a direct tool for the evaluation of Aedes albopictus control strategies.PLoS Neglected Tropical Diseases 02/2012; 6(2):e1487. · 4.69 Impact Factor -
Article: Spatial and temporal distribution patterns of Anopheles arabiensis breeding sites in La Reunion Island--multi-year trend analysis of historical records from 1996-2009.
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ABSTRACT: 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 Anopheles arabiensis in different locations on La Reunion Island. A retrospective examination was made from archival data which provided the complete enumeration of An. arabiensis 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. Anopheles arabiensis 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. The observed retreat of An. arabiensis 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.Parasites & Vectors 06/2011; 4:121. · 2.94 Impact Factor -
Article: Insecticide resistance in Culex pipiens quinquefasciatus and Aedes albopictus mosquitoes from La Réunion Island.
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ABSTRACT: Resistance to insecticides was monitored on Culex pipiens quinquefasciatus mosquitoes collected in twelve localities of La Réunion, a geographically isolated island of the Indian Ocean. This mosquito is of medical concern in the region as a known vector for filariasis and a potential vector for West Nile and Rift Valley Fever viruses. Our bioassays indicated the presence of resistance to all tested insecticides, i.e. organochlorides, organophosphates and pyrethroids. A molecular investigation revealed a higher frequency of resistance genes in the coastal areas compared to elevated rural sites, probably reflecting the different nature of insecticide pressures together with the genetic cost of resistance alleles. A simple molecular test was developed to detect Rdl allele, encoding a gamma-aminobutyric acid (GABA) receptor resistant to dieldrin. Unexpectedly high Rdl frequencies were recorded over the whole island, despite this insecticide having been banned for over 15 years. This resistant allele was also detected for the first time in two samples of Aedes albopictus, a species recently involved in severe Chikungunya epidemics on the island. Rdl selection in these two mosquito species discloses current insecticide pressures in urban areas, from unknown origins, that should be taken into account to develop vector control strategies.Insect biochemistry and molecular biology 02/2010; 40(4):317-24. · 3.25 Impact Factor -
Article: Wolbachia age-sex-specific density in Aedes albopictus: a host evolutionary response to cytoplasmic incompatibility?
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ABSTRACT: 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.PLoS ONE 01/2010; 5(3):e9700. · 4.09 Impact Factor
