Survey of Gymnophalloides seoi Metacercariae in Natural and Cultured Oysters from Several Western Coastal Areas, Korea

Abstract

<i>Gymnophalloides</i> <i>seoi</i> (Digenea: Gymnophallidae) is a human intestinal trematode contracted by eating raw oysters (<i>Crassostrea</i> <i>gigas</i>) in the Republic of Korea (=Korea). It has been known to be highly endemic in Aphae Island, Shinan-gun, Jeollanam-do (Province). However, recent epidemiological status of <i>G</i>. <i>seoi</i> has not been reported since the 1990s. In this study, we investigated the prevalence of <i>G</i>. <i>seoi</i> metacercariae in natural and cultured oysters collected from 3 islands and 2 coastal areas in western parts of Korea. The oysters were examined using the artificial digestion method followed by stereomicroscopy. The overall positive rate of <i>G</i>. <i>seoi</i> metacercariae in natural oysters was 66.0% (99/150), and the oysters collected from Yubu Island showed the highest infection rate (74.0%). However, the metacercarial density per oyster was relatively low (1.5-2.4 per oyster). By contrast, no metacercaria was found in cultured oysters purchased from 2 coastal areas in Chungcheongnam-do. Thus, we could confirm that natural oysters produced from 3 western coastal islands are infected with <i>G</i>. <i>seoi</i> <i>metacercariae</i>, whereas cultured oysters purchased from 2 coastal areas were free from infection.