?. Seroepidemiological Surveys
In the preceding survey carried out during our short visit in June l997，a total of 64 blood samples (6 from in-and out-patients of Health Centre in Smbo district; 20 from school chi1dren in Sambo PS; and 38 from school children in Pong Ro PS) were obtained. All the patients and School children in Sambo excepting one girl received chemotherapy with praziquantel in April 1997 (only one case in June 1997), while school children in Pong Ro have so far not received any chemotherapy for schistosomiasis.
ELIZA with those blood specimens were done in the Department of Medical Zoology，Dokkyo University School of Medicine, and the results obtained are summarized in Table 1 and Figure1. In Sambo，ca.30 river km upstream of Kratie，out of 20 specimens from school children examined, 14 (70%) were IgG positive (cut off value = 0.2), being the highest O.D, value 1.155. In addition, as high IgM titre as 0.757 was observed in one case (No. l8). These facts strongly suggests that endemic transmission of schistosomiasis still exists in Sambo, even after mass chemotherapy in April l997.
In Pong Ro, ca. 40 river km downstream of Kratie, 37 (97.3%) out of 38 specimens examined were found to be IgG negative, despite that they have not so far been treated with praziquantel. No IgM positive case eas observed in the 38 specimens. It therefore appears that there is no endemic transmission of the disease in Pong Ro. Either hepatomegaly or splenomegaly was seen in 17 students (44.7%) that may be due to other diseases than schistosomiasis.
In the present survey, a total of 374 blood samples (53 in Kampong Krabei on Koh-Rongiev Island; 60 in Sandan; 60 in KbolChuor; 60 in Sambok; l7 in Roka Kandal''f1oating village''; 4 in peam Te ''floating village''; 60 in Chhlong; and 60 in Hanchey Leu) were donated from school children (Fig. 2). Each child received 20 tablets of vitamin C (Master) and 5 tablets of paracentamol (Para 500) after donation. Balls for soecer or volleyball were presented to schools in Chhlong and Hanchey Leu. The serum speciments will be subjected to immunological analyses such as ELISA and others in the Department of Medical Zoology, Dokkyo University School of Medicine. The res-ults wiIl be informed to you by late April.
In Sambo Hospital, we observed two in-patients of advanced stage, 19- and 27-year old men, with hepatomegaly, splenomegaly, a pronounced collateral circu1ation, and ascites. They were markedly underweight and lacked in their secondary sexual characters.
?. Malacological Surveys
A search for Neotricula aperta was made thoroughly at several sites around Kampe，ca. 15 river km upstream of Kratie. The water level was fairly low, being rather ideal condition for the snail surveys. Large number of several species of snails were observed on stones, rocks, and twigs on the river bed. However, no typical gamma N. aperta was
collected. This is not surprising, since Davis et al. (1976) and Upatham et al. (l980) have reported that in Khong Island, South La-os, neither adult nor young N.aperta can be collected in early March, and by mid or late March young suddenly f1ourish.
