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Background  In the past ten years, the Indian Ocean region has been the theatre of severe epidemics of chikungunya and dengue. These outbreaks coincided with a high increase in populations of  Aedes albopictus  that outcompete its sister taxon  Aedes aegypti  in most islands sampled. The objective of this work was to update the entomological survey of the two  Aedes  species in the island of Madagascar which has to face these arboviroses.    Methods  The sampling of  Aedes  mosquitoes was conducted during two years, from October 2007 to October 2009, in fifteen localities from eight regions of contrasting climates. Captured adults were identified immediately whereas immature stages were bred until adult stage for determination. Phylogenetic analysis was performed using two mtDNA genes,  COI  and  ND5  and trees were constructed by the maximum likelihood (ML) method with the gene time reversible (GTR) model. Experimental infections with the chikungunya virus strain 06.21 at a titer of 10 7.5  pfu/mL were performed to evaluate the vector competence of field-collected mosquitoes. Disseminated infection rates were measured fourteen days after infection by immunofluorescence assay performed on head squashes.    Results  The species  Aedes aegypti  was detected in only six sites in native forests and natural reserves. In contrast, the species  Aedes albopictus  was found in 13 out of the 15 sites sampled. Breeding sites were mostly found in man-made environments such as discarded containers, used tires, abandoned buckets, coconuts, and bamboo cuts. Linear regression models showed that the abundance of  Ae. albopictus  was significantly influenced by the sampling region (F = 62.00, p < 2.2 × 10 -16 ) and period (F = 36.22, p = 2.548 × 10 -13 ), that are associated with ecological and climate variations. Phylogenetic analysis of the invasive  Ae. albopictus  distinguished haplotypes from South Asia and South America from those of Madagascar, but the markers used were not discriminant enough to discern Malagasy populations. The experimental oral infection method showed that six  Ae. albopictus  populations exhibited high dissemination infection rates for chikungunya virus ranging from 98 to 100%.    Conclusion  In Madagascar,  Ae. albopictus  has extended its geographical distribution whereas,  Ae. aegypti  has become rare, contrasting with what was previously observed. Changes are predominantly driven by human activities and the rainfall regime that provide suitable breeding sites for the highly anthropophilic mosquito  Ae. albopictus . Moreover, these populations were found to be highly susceptible to chikungunya virus. In the light of this study,  Ae. albopictus  may have been involved in the recent outbreaks of chikungunya and dengue epidemics in Madagascar, and consequently, control measures should be promoted to limit its current expansion.

Biogeography of the two major arbovirus mosquito vectors, Aedes aegypti and Aedes albopictus (Diptera, Culicidae), in Madagascar