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
In order to assess changes in the activity of immunecompetency present in Crassostrea gigas infected with Marteilioides chungmuensis (Protozoa), the total hemocyte counts (THC), hemocyte populations, hemocyte viability, and phagocytosis rate were measured in oysters using flow cytometry. THC were increased significantly in oysters infected with M. chungmuensis relative to the healthy appearing oysters (HAO) (P<0.05). Among the total hemocyte composition, granulocyte levels were significantly increased in infected oysters as compared with HAO (P<0.05). In addition, the hyalinocyte was reduced significantly (P<0.05). The hemocyte viability did not differ between infected oysters and HAO. However, the phagocytosis rate was significantly higher in infected oysters relative to HAO (P<0.05). The measurement of alterations in the activity of immunecompetency in oysters, which was conducted via flow cytometry in this study, might be a useful biomarker of the defense system for evaluating the effects of ovarian parasites of C. gigas.
Citations
Citations to this article as recorded by
Transcriptome-wide identification, functional characterization, and expression analysis of two novel invertebrate-type Toll-like receptors from disk abalone (Haliotis discus discus) Thanthrige Thiunuwan Priyathilaka, S.D.N.K. Bathige, Seongdo Lee, Bo-Hye Nam, Jehee Lee Fish & Shellfish Immunology.2019; 84: 802. CrossRef
The dynamics of total organic matter (tom) on sangkuriang catfish (clarias gariepinus) farming at upt ptpbp2kp and the effectiveness of freshwater bivalve (anodonta woodiana) in reducing the total organic matter with varying density D Arfiati, C D G Putra, A H Tullah, S W A Permanasari, A W Puspitasari IOP Conference Series: Earth and Environmental Science.2019; 236: 012022. CrossRef
The role of copper and zinc accumulation in defense against bacterial pathogen in the fujian oyster (Crassostrea angulata) Bo Shi, Tian Wang, Zhen Zeng, Long Zhou, Weiwei You, Caihuan Ke Fish & Shellfish Immunology.2019; 92: 72. CrossRef
Hybridization improved bacteria resistance in abalone: Evidence from physiological and molecular responses Shuang Liang, Xuan Luo, Weiwei You, Caihuan Ke Fish & Shellfish Immunology.2018; 72: 679. CrossRef
Morphofunctional parameters of hemocytes in the assessment of the physiological status of bivalves A. A. Anisimova Russian Journal of Marine Biology.2013; 39(6): 381. CrossRef
Immunological responses of the mangrove oysters Crassostrea gasar naturally infected by Perkinsus sp. in the Mamanguape Estuary, Paraíba state (Northeastern, Brazil) Fernando Ramos Queiroga, Luis Fernando Marques-Santos, Hélène Hégaret, Philippe Soudant, Natanael Dantas Farias, Aline Daiane Schlindwein, Patricia Mirella da Silva Fish & Shellfish Immunology.2013; 35(2): 319. CrossRef
Relative contribution of reproductive investment, thermal stress and Vibrio infection to summer mortality phenomena in Pacific oysters Carolin C. Wendling, K. Mathias Wegner Aquaculture.2013; 412-413: 88. CrossRef
Characteristic and Functional Analysis of Toll-like Receptors (TLRs) in the lophotrocozoan, Crassostrea gigas, Reveals Ancient Origin of TLR-Mediated Innate Immunity Yang Zhang, Xiaocui He, Feng Yu, Zhiming Xiang, Jun Li, Karen L. Thorpe, Ziniu Yu, Irving Coy Allen PLoS ONE.2013; 8(10): e76464. CrossRef
First
Prev
