Perkinsus protozoan infection in short-necked clam tapes (=Ruditapes) philippinarum in Japan

An infection of Perkinsus (Protozoa: Apicomplexa) was found in the short-necked clam in Kumamoto and Hiroshima prefectures, the first record in Japan. Histology revealed a number of trophozoites with a vacuole, forming cyst-like structures, in connective tissues of the gill, heart, mantle, digestive gland and adductor muscle of the infected clam. The protozoan in the gill enlarged by a culture in Ray's fluid thioglycolate medium and was colored by Lugol's iodine solution. The nucleotide sequences of two internal transcribed spacers with 5.8 SrRNA region were PCR-amplified from DNA of prezoosporangia obtained by a culture of the infected clam tissue. These sequences were almost identical to those of Perkinsus atlanticus and P. olseni. These facts suggest that the Perkinsus protozoan which infected short-necked clam in Kumamoto and Hiroshima, Japan is P. atlanticus or closely related species. We designed a PCR method for diagnosis of this Perkinsus protozoan. The PCR diagnostic method indicated high infection rates (64 similar to 94%) of the parasite in short-necked clam in both area.