1. Molecular analysis of Anopheles mosquito receptivity to P. falciparum (Catherine Bourgouin)
To characterize mosquito factors involved into the development of P. falciparum, the human malaria parasite, within the midgut of its african vector Anopheles gambiae, a differential display analysis approach was developed. Several genes expressed in the mosquito midgut and whose expression is regulated by the ingestion of P. falciparum parasites were identified. RT-PCR analysis suggests that some of these genes may be involved in the immune response of the mosquito midgut towards P. falciparum while others may be involved in the development of the parasite. The full length c-DNA corresponding to three genes as good candidates for their implication in P. falciparum development are currently being studied. In addition, a real time PCR analysis of immune response related gene expression, in the midgut of An. gambiae fed on P. falciparum gametocytes, led us to propose that P. falciparum may evade the immune response of its natural vector.
2. Population genetics of Aedes mosquitoes and vector competence for dengue viruses (Anna-Bella Failloux)
Human activities through urban environment changes, mosquito control and intensification of air transportations have been shown to act on mosquito genetic variation and thus, on dengue epidemiology. The present situation of dengue in South-east Asia (Thaïland, Cambodia and Viet Nam) and in Tropical America (French Guiana) leads us to define dengue as a severe public health problem in areas where the domestic form of Ae. aegypti is well established. In West Africa, Ae. aegypti is described as the primitive and selvatic form which is defined as poorly susceptible do dengue viruses. Phylogenetic analyses based on mitochondrial and genomic gene sequences will give us insight about the natural history of species in the Aedes genus. Moreover, Ae. albopictus newly introduced in France has been investigated. To identify more clearly the factors that affect the genetic structure of Ae. albopictus populations, studies have been carried out on populations from isolated areas, such as islands in the Indian Ocean. In La Reunion island, we found that extrinsic factors (climatic, geographic and human density) and intrinsic factors related to mosquito bionomics (host preference) affected the genetic structure and vector competence of Ae. albopictus populations. In addition, the development of molecular markers as microsatellite loci allows a more accurate definition of vector genotype distribution in Ho Chi Minh City necessary to apprehend dengue epidemiology.
3. Eco-epidemiology of Lyme disease (Claudine Pérez-Eid)
Among all tick-borne diseases transmitted to humans, Lyme disease is the most important one with an estimation of more than 10 000 clinical cases per year in France. This polysystemic disease, particularly in Europe, appears in three different clinical presentations depending on the tropism of Borrelia species for a specific organ.
The tick, Ixodes ricinus, can be infected by any of the dozen of Borrelia species of the burgdorferi sensu lato group but among them, only three are pathogenic for humans : B. burgdorferi, B. garinii and B. afzelli. Our team is studying the prevalence of the different Borrelia species in natural populations of ticks. From field collections performed in different geographic areas of France, west (Ille et Vilaine), center (Indre) and north center (Ile de France), we were able to estimate that 54% of the collected ticks were infected with at least one of the three pathogenic species.