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Korean J Parasitol > Volume 33(1):1995 > Article

Original Article
Korean J Parasitol. 1995 Mar;33(1):1-7. English.
Published online Mar 20, 1995.  http://dx.doi.org/10.3347/kjp.1995.33.1.1
Copyright © 1995 by The Korean Society for Parasitology
Oysters, Crasostrea gigas, as the second intermediate host of Gymnophalloides seoi (Gymnophallidae)
Soon-Hyung Lee,*Min-Ho Choi,Min Seo and Jong-Yil Chai
1Department of Parasitology and Institute of Endemic Diseases, Seoul National University College of Medicine, Seoul 110-799, Korea.
Received February 09, 1995; Accepted February 27, 1995.


Gymnophalloides seoi has drawn medical attentions since the discovery of the first human case and a highly endemic area on a southwestern coastal island of Shinangun, Korea. Marine bivalves especially oysters were strongly suspected as the source of infection. In this study the oysters, Crassostrea gigas, naturally produced from the endemic area were examined whether they contain gymnophallid metacercariae. All of 50 oysters examined were infected with the metacercariae of a gymnophallid,with the metacercarial density per oyster of 610 on average (2-4, 792 in range). Later they were identified as G. seoi by obtaining adult worms from experimental mice. The metacercariae were unencysted, and firmly attached on the mantle surface of the oysters with their oral sucker. In sectioned specimens they were equipped with the ventral pit, a peculiar organ of the genus Gymnophalloides, and non-muscular genital pore which was connected dorsally to the seminal vesicle. The seminal vesicle was in a great majority mono-sac. By this study, it has been confirmed that the oyster is a 2nd intermediate host of G. seoi as well as the major source of human infection with this fluke.


Figs. 1-4
Fig. 1. The oysters, Crassostrea gigas, collected from Aphae Island. Fig. 2. Grouped metacercariae of G. Seoi (arrows) on the mantle surface of the oyster. Scale bar: 1.5 cm. Fig. 3. Magnification of Fig. 2, showing numerous unencysted metacercariae of G. seoi (arrows) on the surface of the oyster. Scale bar: 2mm. Fig. 4. A metacercaria of G. seoi showing the oral sucker, ventral sucker (VS), ventral pit (VP), and excretory bladder (EB). Scal bar = 100 µm

Figs. 5-8
Fig. 5. Section of an oyster infected with G. seoi metacercariae. Some of them are sucking the extrapallial --------of the oyster with their oral sucker. × 100. Fig. 6. Magnification of a metacercaria in Fig. 5, --------- the oral sucker (OS) sucking the epithelium and tissue of the oyster, ventral sucker (VS), ventral-------(VP), excretory bladder, and cecum ©. × 400. Fig. 7. A group of G. seoi metacercariae attached on ------ mantle surface of an oyster as observed by scanning electron microscopy. Scale bar = 179 µm Fig. 8. --------adult worm of G. seoi recovered from the small intestine of an experimentally infected mouse. VS: ------- sucker, VP: ventral pit, T: testes, EB: excretory bladder. Scale bar = 100 µm


Table 1
Metacercarial density of Gymnophalloides seoi in oysters, Crassostrea gigas, collected from Aphae-myon, Shinan-gun

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