Detection of Marteilia refringens infecting the European flat oyster Ostrea edulis and the dwarf oyster Ostrea stentina in southern Portugal and Spain

[Display omitted] •Determine if O. stentina present in southern Iberian Peninsula is infected with M. refringens.•Confirm the presence of M. refringens in Portugal using molecular methods.•We observed M. refringens type O in O. stentina and O. edulis samples and type M in O. stentina. In the present study, Marteilia sp. was detected by histological examination and in situ hybridisation in Ostrea edulis and Ostrea stentina collected in southern Iberian Peninsula. Marteilia refringens DNA was detected by PCR in O. edulis (collected in southern Portugal) and O. stentina (collected in southern Spain and Portugal). Sequencing analysis revealed the presence of M. refringens type O in O. edulis, and type O and M in O. stentina. This is the first confirmed detection of M. refringens in Portugal and the first report on the occurrence of M. refringens infecting O. stentina in Europe.