First Report on the Prevalence and Subtype Distribution of Blastocystis sp. in Edible Marine Fish and Marine Mammals: A Large Scale-Study Conducted in Atlantic Northeast and on the Coasts of Northern France

International audience; Blastocystis is frequently identified in humans and animal hosts and exhibits a large genetic diversity with the identification of 17 subtypes (STs). Despite its zoonotic potential, its prevalence and ST distribution in edible marine fish and marine mammals remain unknown. A large-scale survey was thus conducted by screening 345 fish caught in Atlantic Northeast and 29 marine mammals stranded on the coasts of northern France for the presence of the parasite using real-time Polymerase Chain Reaction PCR. The prevalence of the parasite was about 3.5% in marine fish. These animals were mostly colonized by poikilotherm-derived isolates not identified in humans and corresponding to potential new STs, indicating that fish are natural hosts of Blastocystis. Marine fishes are also carriers of human STs and represent a likely limited source of zoonotic transmission. 13.8% of the marine mammals tested were colonized and 6 different STs were identified including 3 potential new STs. The risk of zoonotic transmission through marine mammals is insignificant due to the lack of repeated contact with humans. The present survey represents the first data regarding the prevalence and ST distribution of Blastocystis in marine fish and marine mammals and provides new insights into its genetic diversity, host range and transmission.