Heterophyid flukes (Trematoda: Heterophyidae) are very small parasites which live in the small intestines of fish-eating birds and mammals. More than 30 species of heterophyid flukes have been known to infect human beings all over the world (Ito, 1964; Yu and Mott, 1994). Out of 10 human-infecting species reported in Korea, six of them, Heterophyes nocens, Heterophyopsis continua, Pygidiopsis summa, Stellantchasmus falcatus, Stictodora fuscata, and Stictodora lari, are contracted through the consumption of the raw flesh of brackish water fishes (Chai and Lee, 2002). Lateolabrax japonicus (perch), Konosirus punctatus (shad), Mugil cephalus (mullet), and Acanthogobius flavimanus (goby) have all been reported as sources of infection (Chun, 1960 & 1963; Seo et al., 1980, 1981, 1984; Chai and Sohn, 1988; Chai et al., 1989; Sohn et al., 1994; Sohn and Moon, 2001). However, the bluespotted mud hopper, Boleopthalmus pectinirostris, and Scartelaos sp. have not been evaluated as intermediate hosts of heterophyid flukes in Korea. Therefore, we collected and surveyed two species of goby, B. pectinirostris and Scartelaos sp., from three coastal areas of Jeollanam-do for heterophyid fluke metacercariae.
Two species of goby, B. pectinirostris and Scartelaos sp. (Fig. 1), were collected in Sooncheon-shi, Gangjin-gun, and Shinan-gun, Jeollanam-do, Korea, between June and September, 1999 (Table 1). All of the collected fish were transferred to our laboratory and examined individually by the pepsin-HCl artificial digestion method for trematode metacercariae.
No metacercariae were detected in 20 B. pectinirostris collected at Sooncheon-shi. H. nocens metacercariae were detected in 24 B. pectinirostris (96.0%) and 14 Scartelaos sp. (63.6%) from Shinan-gun. The detailed infection status of H. nocens metacercariae is provided in Table 2. H. continua metacercariae were found in only one B. pectinirostris (10%) from Gangjin-gun. They were also detected in 11 B. pectinirostris (44.0%) and 21 Scartelaos sp. (95.5%) from Shinan-gun. Data regarding infection status with H. continua metacercariae is shown in Table 3. S. fuscata metacercariae were detected in 18 (72.0%) out of 25 B. pectinirostris from Shinan-gun. The metacercarial density in the fish ranged from 15 to 256 (82.7 in average).
Several investigators in Korea have previously reported on the metacercariae of heterophyid flukes collected from fish acting as intermediate hosts (Chai and Lee, 2002). Chun (1960) first detected H. continua metacercariae from perches and shads. Chun (1963) isolated P. summa metacercariae in mullets. Seo et al. (1980) newly described the metacercariae of H. nocens from mullets. Chai and Sohn (1988) identified S. falcatus metacercariae encysted in mullets. Chai et al. (1989) found Stictodora lari metacercariae in a goby species, A. flavimanus. Sohn et al. (1994) detected S. fuscata metacercariae from gobies. Sohn et al. (2003) also identified Acanthotrema felis metacercariae collected from gobies. Among these metacercariae, those of H. nocens, H. continua, and S. fuscata were found in two goby species, B. pectinirostris and Scartelaos sp., in the present study.
Endemic foci of H. nocens infection are scattered around the southwestern coastal areas and islands, especially in Shinan-gun and Muan-gun, Jeollanam-do, Korea (Chai and Lee, 2002). Some species of brackish water fish, including M. cephalus, A. flavimanus, Tridentiger obscurus, Liza haematocheila, Therapon oxyrhynchus, and Glossogobius giuris brunneus, have been reported as sources of infection in Japan and Korea (Komiya, 1965; Seo et al. 1980, 1981). In the present study we are the first to prove that B. pectinirostris and Scartelaos sp. from Shinan-gun also serve as the second intermediate hosts of H. nocens. They may act as sources of human infection in endemic areas.
Many fish species, such as M. cephalus, L. japonicus, A. flavimanus, K. punctatus, Plecoglossus altivelis, Conger myriaster, Harengula zunasi, Dorosoma thrissa, Coilia sp., Cyprinus carpio, Mugil affinis, Gobius nebulosus, and B. pectinirostris, have been recorded as the second intermediate hosts of H. continua in Japan, Korea, and China (Kanemitsu et al., 1953; Chun 1960; Komiya, 1965; Kobayashi, 1968; Seo et al., 1984; Cho and Kim, 1985; Sohn et al., 1994; Kim et al., 1996; Sohn and Moon, 2001). Among these fish hosts, M. cephalus, L. japonicus, A. flavimanus, K. punctatus, P. altivelis, and C. myriaster have been recorded in Korea. Accordingly, two species of goby, B. pectinirostris and Scartelaos sp., should be added to the list of fish which act as intermediate hosts of H. continua in Korea, although B. pectinirostris has previously been recorded as an intermediate host in China (Kobayashi, 1968).
By the present study, it was first proved that the bluespotted mud hopper, B. pectinirostris, is the second intermediate host of S. fuscata. Up to the present time, two species of brackish water fish, M. cephalus and A. flavimanus, have been recorded as the second intermediate hosts of S. fuscata in Japan and Korea (Onji and Nishio, 1916; Sohn et al., 1994). In the present study, we have confirmed that B. pectinirostris and Scartelaos sp. are newly-identified second intermediate hosts of H. nocens, H. continua, and S. fuscata in Korea.
