The alveolate protozoan parasite Perkinsus olseni infects a range of marine bivalves inhabiting tidal flats and shallow subtidal zones, causing considerable damage to shellfish industries. Infection by P. olseni is typically assessed using Ray’s fluid thioglycollate medium (RFTM) assay, with gill tissue often employed as a diagnostic proxy for whole-body infection. However, the diagnostic reliability of gill-based assays across diverse ecological settings—particularly under low-infection conditions—remains uncertain. In this study, we investigated tissue-specific distribution and the diagnostic performance of the RFTM assay in detecting P. olseni in Manila clams (Ruditapes philippinarum) collected from 6 tidal flats along Korea’s west and south coast. The assay was applied to 6 different tissues, including gills and visceral mass. Infection prevalence reached 100% at most sites, except at Padori (90%). Whole-body infection intensity ranged from 0.1×104 to 3.7×106 cells per gram of tissue. The visceral mass consistently harbored the largest proportion of parasites (27.8%–49.0%), followed by the mantle (17.4%–30.6%) and gills (19.4%–25.2%). Gill infection levels correlated strongly with whole-body infection intensity (r²=0.6–0.95), supporting their diagnostic value in high-infection areas. However, at Padori—where infection levels were lowest—the efficacy of the gill assay dropped to 56%, resulting in a 44% false negative rate. These results underscore the limitations of relying solely on gill tissue in low-infection environments and highlight the need for a context-dependent diagnostic approach. A dual-tissue strategy incorporating both gill and whole-body samples is recommended to improve diagnostic accuracy in P. olseni surveillance of Manila clam populations.
Citations
Citations to this article as recorded by
First report of mass mortality event caused by Eomarteilia granula in Manila clam Ruditapes philippinarum reared in subtidal and bottom cages on the south coast of Korea Hye-Mi Lee, Hyun-Sil Kang, Nobuhisa Kajino, Hyun-Ki Hong, Young-Ghan Cho, Kwang-Sik Choi Estuarine, Coastal and Shelf Science.2025; 323: 109408. CrossRef
Life cycle stages, including daughter sporocysts, cercariae, and metacercariae, of Parvatrema duboisi (Dollfus, 1923) Bartoli, 1974 (Digenea: Gymnophallidae) have been found in the Manila clam Ruditapes philippinarum from Aphaedo (Island), Shinan-gun, Jeollanam-do, Korea. The daughter sporocysts were elongated sac-like and 307-570 (av. 395) μm long and 101-213 (av. 157) μm wide. Most of the daughter sporocysts contained 15-20 furcocercous cercariae each. The cercariae measured 112-146 (av. 134) μm in total length and 35-46 (av. 40) μm in width, with 69-92 (av. 85) μm long body and 39-54 (av. 49) μm long tail. The metacercariae were 210-250 (av. 231) μm in length and 170-195 (av. 185) μm in width, and characterized by having a large oral sucker, genital pore some distance anterior to the ventral sucker, no ventral pit, and 1 compact or slightly lobed vitellarium, strongly suggesting P. duboisi. The metacercariae were experimentally infected to ICR mice, and adults were recovered at day 7 post-infection. The adult flukes were morphologically similar to the metacercariae except in the presence of up to 20 eggs in the uterus. The daughter sporocysts and metacercariae were molecularly (ITS1-5.8S rDNA-ITS2) analyzed to confirm the species, and the results showed 99.8-99.9% identity with P. duboisi reported from Kyushu, Japan and Gochang, Korea. These results confirmed the presence of various life cycle stages of P. duboisi in the Manila clam, R. philippinarum, playing the role of the first as well as the second intermediate host, on Aphae-do (Island), Shinan-gun, Korea.
Citations
Citations to this article as recorded by
Spatial patterns of trematode-induced pits on bivalve skeletons: Challenges and prospects for research on parasite-host dynamics Alexis Rojas, John Warren Huntley, Monica Caffara, Daniele Scarponi The Holocene.2025; 35(12): 1259. CrossRef
Pearl formation associated with gymnophallid metacercariae in Mytilus galloprovincialis from the Northwestern Adriatic coast: Preliminary observations Erica Marchiori, Francesco Quaglio, Giovanni Franzo, Ginevra Brocca, Sonja Aleksi, Pietrogiovanni Cerchier, Rudi Cassini, Federica Marcer Journal of Invertebrate Pathology.2023; 196: 107854. CrossRef
Molecular phylogeny, distribution, and pathogenicity of a novel thraustochytrid protist in the Manila clam, Ruditapes philippinarum, on the west and south coasts of Korea Biyun Zhao, Seung-Hyeon Kim, Dae-Woong Koh, S.D.N.K. Bathige, Kwang-Sik Choi, Kyung-Il Park Aquaculture.2023; 575: 739779. CrossRef
Biotic and abiotic drivers affect parasite richness, prevalence and abundance inMytilus galloprovincialisalong the Northern Adriatic Sea C. Bommarito, M. Wahl, D.W. Thieltges, C. Pansch, M. Zucchetta, F. Pranovi Parasitology.2022; 149(1): 15. CrossRef
Effects of larval trematode parasitism on the reproductive capacity of Manila clam Ruditapes philippinarum in a sandy-mud tidal flat on the west coast of Korea Young-Ghan Cho, Hye-Mi Lee, Jeong-Hwa Kim, Jong-Seop Shin, Hee-Do Jeung, Kwang-Sik Choi Frontiers in Marine Science.2022;[Epub] CrossRef
Negative Impacts of Perkinsus olseni Infection in Manila Clam Ruditapes philippinarum Observed from Tidal Flats in Anmyeondo Island on the West Coast of Korea During Post-Spawning Period Hye-Mi Lee, Kyung-Il Park, Hyun-Sung Yang, Kwang-Sik Choi Ocean Science Journal.2021; 56(3): 307. CrossRef
Gymnophallid metacercariae found in the Manila clam Ruditapes philippinarum (‘Banjirak’ in Korean) from Gochang-gun, Jeollabuk-do, Korea were morphologically and molecularly confirmed to be Parvatrema duboisi (Dollfus, 1923) Bartoli, 1974. The metacercariae were morphologically characterized by having a large oral sucker, small ventral sucker, genital pore some distance anterior to the ventral sucker, no ventral pit, and 1 compact or slightly lobed vitellarium, which were all compatible with P. duboisi. Some of the metacercariae were experimentally fed to mice, and adult flukes were recovered at day 7 post-infection. The morphology of the adult flukes was basically the same as that of the metacercariae except for the presence of uterine eggs; the uterus was filled with up to 40 eggs. The nucleotide sequences (1,193 bp) from ITS regions (ITS1, 5.8S rDNA, and ITS2) of the metacercariae showed 99.7% identity with P. duboisi and 75.7% identity with Gymnophalloides seoi deposited in GenBank. These results confirmed the presence of P. duboisi metacercariae in the Manila clam R. philippinarum in an estuary region of Gochang-gun, Korea.
Citations
Citations to this article as recorded by
Survey of trematodes in Manila clam Ruditapes philippinarum on the west coast of Korea: A preliminary study Cuong Thanh Le, Hee-Do Jeung, Young-Ghan Cho, Kwang-Sik Choi Journal of Invertebrate Pathology.2024; 206: 108172. CrossRef
Description of a New Species of Bacciger (Digenea: Gymnophalloidea) Infecting the American Gizzard Shad, Dorosoma cepedianum (Lesueur, 1818), and Molecular Characterization of Cercaria rangiae Wardle, 1983, with Molecular Phylogeny of Related Digenea Stephen S. Curran, Micah B. Warren, Stephen A. Bullard Comparative Parasitology.2022;[Epub] CrossRef
Parvatrema duboisi (Digenea: Gymnophallidae) Life Cycle Stages in Manila Clams, Ruditapes philippinarum, from Aphae-do (Island), Shinan-gun, Korea Bong-Kwang Jung, Taehee Chang, Hyejoo Shin, Seungwan Ryoo, Sooji Hong, Jeonggyu Lee, Hyemi Song, Jaeeun Cho, Deok-Gyu Kim, Hojong Jun, Min-Jae Kim, Eun Jeong Won, Eun-Taek Han, Eun-Hee Shin, Jong-Yil Chai The Korean Journal of Parasitology.2021; 59(1): 83. CrossRef
Morphological and molecular characterization of larval digenean trematodes (Parvatrema: Gymnophallidae) and their pathological effects on the clam Leukoma thaca (=Protothaca thaca) (Bivalvia:Veneridae) (Molina, 1782) from northern Chile Diana Montenegro, María Soledad Romero, María Teresa González Parasitology International.2021; 80: 102238. CrossRef
First
Prev
