Nam and Sohn: Infection status with trematode metacercariae in pond smelts, Hypomesus olidus
Abstract
Many Koreans usually eat raw pond smelts, Hypomesus olidus, in the winter. This study was performed to evaluate the infection status with trematode metacercariae in pond smelts from January 1998 through February 1999. Among 1,305 fish collected, 459 were purchased from wholesale dealers in Chinchon-gun, Chungchongbuk-do, and the rest of them were caught with a casting net in Soyangho (Lake), Taehoman (Bay) and Paekkokchosuchi (Pond). Seven species of trematode metacercariae including two unidentified ones were detected from 1,305 pond smelts. The number of detected trematode metacercariae according to the species are as follow: Clonorchis sinensis 8, Holostephanus nipponicus 7, Cyathocotyle orientalis 24, Diplostomum sp. 14, and Metorchis orientalis 7. From the above results, it was confirmed that H. olidus plays a role as the second intermediate host of some kinds of trematode including C. sinensis in Korea. Our report shows possible clonorchiasis caused by eating raw pond smelts.
Key words: Hypomesus olidus, Clonorchis sinensis, Holostephanus nipponicus, Cyathocotyle orientalis, Diplostomum sp., Metorchis orientalis
Recently, pond smelts, Hypomesus olidus, have become one of the most popular freshwater fish eaten in raw, especially during the winter in Korea. Pond smelts are believed to have no parasites because they live in clean and cold water. However, in Japan, they have been reported as the second intermediate hosts of Clonorchis sinensis and Exorchis oviformis ( Morishita et al., 1965). There have been no known reported cases of trematode infection caused by pond smelts in Korea. Therefore, the present study was aimed to investigate the infection status of trematode metacercariae in pond smelts in Korea. Fish collections and examinations were carried out ten times from January 1998 through February 1999. Among 1,305 H. olidus collected, 459 were purchased from wholesale dealers in Chinchon-gun, Chungchongbuk-do, and the rest of them were caught with a casting net in Soyangho (Lake), Taehoman (Bay), and Paekkokchosuchi (Pond) ( Fig. 1). All of the pond smelts were cleanly washed with tap water, ground into small pieces, and digested with pepsin-HCl solution in a 36℃ incubator. Digested samples were washed with 0.85% saline and examined under a stereo-microscope to collect trematode metacercariae. Seven species of trematode metacercariae, including two unidentified ones were detected from 1,305 pond smelts. The number of detected metacercariae according to the species are as follow: C. sinensis 8, Holostephanus nipponicus 7, Cyathocotyle orientalis 24, Diplostomum sp. 14, and Metorchis orientalis 7 ( Table 1). The prevalence of helminthiasis has remarkably decreased in Korea. Especially, infection by soil-transmitted helminths such as Ascaris lumbricoides, Trichuris trichiura, and hookworms is no longer a threat to public health. However, clonorchiasis is still highly prevalent in many endemic areas and is regarded as the most important parasitic disease in Korea ( Ministry of Health and Welfare and Korea Association of Health, 1997). Until now, many types of freshwater fishes have been reported as the second intermediate hosts of C. sinensis in Korea ( Kim et al., 1979; Kang et al., 1985; Rim, 1986; Joo, 1988; Sohn and Choi, 1997). However, the role of H. olidus as a intermediate host for parasites has not been reported yet in Korea. In the present study, it was confirmed that the pond smelt indeed plays a role as the second intermediate host for certain types of trematode including C. sinensis. Thus, it is recommended to avoid eating raw pond smelts to prevent possible clonorchiasis.
Notes
This study was supported by a grant from Soonchunhyang University research fund (1998).
REFERENCES
1. Joo CY. Changing patterns of infection with digenetic larval trematodes from fresh-water fish in river Taewha, Kyongnam province. Korean J Parasitol 1988;26:263-274.  2. Kang SY, Kim SI, Cho SY. Seasonal variations of metacercarial density of Clonorchis sinensis in fish intermediate host, Pseudorasbora parva. Korean J Parasitol 1985;23:87-94. 3. Kim YK, Kang SY, Lee SH. Study on the frequency distribution of the metacercarial density of Clonorchis sinensis in fish host, Pseudorasbora parva. Korean J Parasitol 1979;17:127-131. 4. Ministry of Health and Welfare, Korea Association of Health. Prevalence of intestinal parasitic infections in Korea - The sixth report -. 1997, (in Korean).
5. Morishita K, Komiya Y, Matsubayashi H. Progress of medical parasitology in Japan Volume II. 1965, Tokyo, Japan. Meguro parasitological museum. pp 88-167.
6. Rim HJ. The current pathobiology and chemotherapy of clonorchiasis. Korean J Parasitol 1986;24(Suppl):41-45. 7. Sohn WM, Choi YS. Infection status with trematode metacercariae in the fresh-water fish from Chunamchosuchi (pond), Uichang-gun, Kyongsangnam-do, Korea. Korean J Parasitol 1997;35:165-170. PMID: 9335181. 
Fig. 1
The pond smelts, Hypomesus olidus. 
Table 1.
The infection status of trematode metacercariae in 1,305 Hypomesus olidus examined
|
Year |
Month & date |
No. of fish examined |
Source of fish examined |
No. of metacercariae detected |
|
1998 |
Jan. 12 |
28 |
Wholesale dealer |
Csa) 2, Hnb) 5, Coc) 19 |
|
Feb. 1 |
21 |
Paekkokchosuchi |
— |
|
Feb. 1 |
131 |
Wholesale dealer |
Cs 1, Mod) 6, Dip.sp.e) 6 |
|
Mar. 3 |
120 |
Wholesale dealer |
Hn 2 |
|
Mar. 6 |
180 |
Wholesale dealer |
Dip.sp. 3 |
|
Dec. 18 |
62 |
Taehoman |
Cs 3, Mo 1, Co 5 |
|
Dec. 21 |
249 |
Soyangho |
— |
|
|
1999 |
Jan. 13 |
156 |
Soyangho |
unidentified sp.I 83 |
|
Feb. 3 |
156 |
Soyangho |
Cs 2, Dip.sp. 5 |
|
|
|
|
unidentified sp.I 55 |
|
|
|
|
unidentified sp.II 1 |
|
Feb. 11 |
202 |
Soyangho |
unidentified sp.I 20 |
|
|
Total |
10 times |
1,305 |
|
|
|
|
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