Contribution à l’étude de la transmission de Bonamia ostreae, parasite protozoaire de l’huître plate européenne, Ostrea edulis

Ostrea edulis is a native European oyster species. Since the late 1960s, it has been struck by two epizootic diseases, which are still reducing production to extremely low volumes : marteiliosis and bonamiosis, respectively caused by the protozoan parasites Marteilia refringens and Bonamia ostreae. Nevertheless, oyster farmers have recently shown a renewed interest in this native species, recently described as a keystone species in the coastal ecosystem. As bonamiosis still have a considerable impact on production, research projects focus on host / parasite / environment interactions and its parasitic cycle. The bibliographic analysis of the available data allowed us to propose a conceptual transmission model of B. ostreae and to identify key parameters that we have chosen to study experimentally : survival and excretion of the parasite outside its host. Our results have shown the value of our approach of filtration and realtime PCR analysis to detect and quantify the parasite from a sea water sample. The study of its survival revealed that the DNA of B. ostreae remain detectable in seawater for 2 days. The study of the excretion of the parasite revealed an individual and temporal variation in the excretion rate, as well as a correlation between the excretion rate and the level of infection (low, moderate, high) or the status (living or dead) of the host. Our results also allowed us to improve our conceptual model, and to propose new experimental protocols to improve our understanding of the transmission of the disease.