Experimental transmission of Marteilia refringens with special consideration of its life cycle

Ever since its first description the paramyxean parasite Marteilia refringe ns has been recognised as one of the most significant pathogens of bivalve molluscs. The existence of a complex Life cycle has been postulated by many authors. However, the transmission route of M. refringens and its life cyc le remain unresolved. Experimental observations are presented here that may help lead to a satisfactory hypothesis of the M, refringens Life cycle. Tr ials were performed to test the infectivity of purified early and late stag es of M. refringens by different routes of inoculation. Horizontal transmis sion was also tested by cohabitation with carriers in experimental tanks. F ield cohabitation and exposure to natural sources of the parasite helped ex amine the role of the environment in the transmission of M. refringens. Las tly, naturally infected oysters were monitored in experimental tanks, in or der to study infection progression in the oysters through serial samples. T hese experiments provide no evidence to support direct horizontal transmiss ion of M. refringens, but rather suggest that intermediate or alternative h osts, or free-living stages, are essential in the life cycle of the parasit e.