This study was undertaken to elucidate the status of Metagonimus species infection and to demonstrate the first and the second intermediate hosts of the fluke at the several localities along the Gum river, Chungchung-nam Do, Korea from March 1979 to October 1980.

The results are summarized as follows:

1. Total 790 stool specimens of inhabitants from 6 localities along Gum river were examined by the combination of cellophane thick smear technique and formalin-ether concentration technique. The positive rate of intestinal helminths was 80.3%, and the egg positive rate of Metagonimus sp. was 21% from a total of 790 specimens examined. In the age bracket of 20-49, the positive rates of Metagonimus sp. were 31.1-36.5%, and the males (26.8%) were infected three times higher than females (8.9%). By the area of the river, Gumsan which is located upper stream showed the highest positive rate (40.5%) of the fluke, whereas the rates decreased gradually toward upper part of river (Muju) or the descending lower area of the river. The most lower area of river (Gangkyeong and Nonsan), no positive Metagonimus infection case was found.

2. The infection rate of Clonorchis sinensis in 790 was 37.3%, and the status of mixed infection of Metagonimus with C. sinensis was found 127 cases (76%) out of 166 cases with Metagonimus infection.

3. The result of measurement of ova from 166 cases of Metagonimus infection, large ova were found in 41.1%, small size ova in 31.9% and the mixed type in 27.1%, respectively.

4. The adult worms were recovered from the 6 cases after treatment with niclosamide, and the measurements of the worms showed similar morphological characteristics of the Metagonimus yokogawai.

5. Twenty-two species in 5 families of fresh water fish were caught. Out of 22 species of fish, 18 species were found infected with metacercaria of Metagonimus. In order to observe the distribution of metacercariae in the body and the rate of infection of the individual host, a total of 94 Pseudogobio esocinus were examined. Total 84 (89.4%) out of 94 fish were infected with the metacercariae and the rates of distribution of the metacercaria were observed in the following order: on scale; 93.4%, in gill; 3.2%, head part; 2.9%, but a few metacercaria was found in muscle and visceral organs.

6. The development of the metacercariae which were isolated from the scale of Pseudogobio esocinus were experimentally traced in the albino rat host from one day to 30 days after infection. At the 6th day, several eggs were visible in the uterine tubule of the some worms, on the 10th day, worms became 326.0 × 208.0 µm in size, however the bodies of worms grew no more until the 30th day after infection. The oral sucker was larger in size than the ventral sucker during early stage of the worms, but the 7th day after infection, it reversed. The ventral sucker situated on the ventral right side of the body. Right side of testis laid somewhat toward, and uterus and vetellaria extended to the posterior margin of the right testis.

7. Snails(Koreanomelania nodifila var. ovulum) were collected in the river, Buri-Myeon, Gumsan-Gun, and found the natural emerging ophthalmo-pleurophocercus cercaria.

From the above result, the prevalence of Metagonimus species infection showed relatively higher rates from the inhabitants along the middle to upper localities of the river. Even though no sweetfish was caught in the surveyed areas, Gum river basin is the one of the new endemic foci of metagonimiasis in Korea.