Rickettsia-like organism infection associated with mass mortalities of blood clam, Tegillarca granosa, in the Yueqing Bay in China |
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Authors: | ZHU Zewen XU Ting HE Zhongyang WU Xinzhong WU Liuji MENG Qingguo and HUANG Jiaqing |
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Institution: | 1.Laboratory of Marine Life Science and Technology, College of Animal Sciences, Zhejiang University, Hangzhou 310029, China2.Fisheries Technical Extension Center of Zhejiang Province, Hangzhou 310012, China |
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Abstract: | A series of mass mortalities of the cultured blood clam, Tegillarca granosa, occurred in the Yueqing Bay of China from 2005 to 2009. An obligate intracellular prokaryote, designated as rickettsia-like
organism (RLO), was frequently found in the moribund or dead blood clam sample during ultrastructural examination. These organisms
were usually round, ellipsoid or occasionally dumbbell-shaped, ranged from approximately 0.28 to 0.71 μm in size and had a
trilaminar cell wall. Two reproductive modes of organisms, transverse binary fission and budding, were observed. The organisms
were able to form eosinophilic inclusions. Most inclusions were found within epithelial and connective tissues of the mantle,
gills and digestive tube. The biological and morphological characteristics indicate that these organisms may belong to the
family Rickettsiaceae. RLOs exhibited significant pathogenicity. Cytopathological examinations revealed extensive necrosis
and destruction in the infected cell. The degree of tissue destruction was positively related to the number of RLO inclusions
in the tissues, and the cytopathological effects were positively related to the number of intracellular RLO. RLOs and their
inclusions were discovered throughout different disease areas and in different time periods. The infection intensity of the
RLOs was positively correlated with the mortality rate of clams. Therefore, RLO infection might be associated with mass mortalities
of cultured blood clams in the Yueqing Bay. |
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Keywords: | blood clam Tegillarca granosa rickettsia-like organism (RLO) inclusions mass mortalities |
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