This thesis has been conducted in the context of the reemergence of schistosomiasis caused by Schistosoma mansoni (flatworm trematode) in Dhofar (Oman). The work focuses on the host-parasite interactions and their implications on schistosome transmission. The first part is devoted to a spatiotemporal study of the population genetics iof Biomphalaria pfeifferi (freshwater gastropod snail). Nine microsatellite markers were used for characterization of 18 populations of B. pfeifferi. The results showed that intrapopulations genetic variability was very low. However, the population were highly differentiated. Temporal differentiation was also recorded in same populations. A second part concerns to the study of the life-history traits and host-parasite relationships. It was conducted using eight host-parasite combinations that differ either by the parasite population (human versus murine), by the waterbody category (natural versus man-made) or by the morph of the snail (pigmented versus albino). The following life-history traits were analyzed: growth, fecundity and survival of B. pfeifferi and rate of infection, prepatent period and cercarial production of S. mansoni. The results show that both the origin of S. mansoni and the pigmentation of B. pfeifferi play a major role in transmission of schistosomiasis in Dhofar. The results are discussed in terms of host-parasite compatibility
