A Marteilia-like parasite in blue mussels Mytilus edulis in China

Species of the genus Marteilia (Phylum Paramyxea) are protozoan parasites of marine mollusks. Marteilia spp. have been detected in mollusks from different parts of the world, but the presence of these parasites in China has not been previously reported. Therefore, a survey was conducted to look for the presence of Marteilia spp. in blue mussels Mytilus edulis and Asian green mussels Perna viridis collected along China's coasts. Histological and PCR analyses revealed that 5 of 180 M. edulis (prevalence = 2.8%) were positive for infection with a Marteilia-like organism, whereas the parasite was not detected in any of the 80 P. viridis individuals tested. Total genomic DNA was extracted from the infected tissue sections for PCR amplification. The PCR amplification with Marteilia primers SS1 and SAS1 yielded the expected 641-bp product. Sequencing results showed that the 18S ribosomal RNA gene fragment from the protozoans found in M. edulis from China was 88% similar to that of Marteilia refringens, a species that was reported from M. edulis and European flat oysters Ostrea edulis collected in France. This is the first report of a Marteilia-like organism infecting M. edulis in China.