FIRST REPORT OF Marteilia sp. INFECTION IN MANILA CLAM (Ruditapes philippinarum) ON SOUTHERN COAST OF KOREA

Hyun-Sil Kang1*, Naoki Itoh2 and Kwang-Sik Choi1
 
1School of Marine Biomedical Science (BK21 PLUS), Jeju National University, Republic of Korea
2Laboratory of Fish Diseases, Graduate School of Agricultural and Life Science, The University of Tokyo, Japan
hyunsil0818@jejunu.ac.kr

Marteilia, a paramyxean protozoan has been responsible for mass mortalities in oysters, mussels and cockles in Europe and Australia. Recently, Marteilia spp. infection has been reported in Asian waters. In this study, we first report occurrence of Marteilia sp. in Manila clam Ruditapes philippinarum on the south coast of Korea. In histology, the infected clams exhibited plasmodium cells and mature spores of Marteilia sp. in the epithelial cells of intestine and digestive diverticular, with the prevalence of 3.3-13.3%. In TEM, clams from Yeosu showed 3-5 plasmodia and 4 spores of the parasite in the digestive organ, whereas clams from Tongyeong exhibited 4-8 plasmodia and 4 spores with many granules. Marteilia sp. found in clams from Yeosu also exhibited tricellular membranes containing mitochondria and haplosporosome in the spore and striated inclusion and refrigent granule in cytoplasm of the primary cell. In contrast, electron-dense monolayer and many granules were only found in the cytoplasm of Marteilia cells in clams from Tongyeong. Further analysis of 18S rRNA sequence demonstrated that Marteilia sp. from Yeosu has sequence similarity to M. sydneyi and M. refringence as 89.9% and 89.6%, respectively, suggesting that this parasite is a new member in the genus Marteilia. In contrast, amplified 18S rDNA of the parasite in clams from Tongyeong showed 99.8-100% sequence identity to M. granula reported from Japan. Accordingly, we confirmed that R. philippinarum on the south coast of Korea has two different species of Marteilia, although their impacts on the host animals need to be further studied.