Further snail surveys were done at sites around (l)Don Puay, 25 km upstream of Khong; (2)B. Maphou and Don Phakan, 8 km and 2 km upstream of Champasak respectively; (3) B. Nakhouang and Houayanang-Gnai, 10 km and 15 km upstream of Pakxe respectively.
As a result, large numbers of N. aperta with "tiger-stripes", being much larger and more yellowish in color than the gamma N. tricula in Khong, were widely observed along the Mekong River extending over 120 km upstream of Khong. It is thus of keen interest to examine those snails for their susceptibility to Schistosoma mekongi.
Seroepidemiological surveys
We visited 10 primary schools along the Mekong River forseroepidemiological surveys. A small amount of blood sample was taken from each school child through finger prick and collected onto filter papers for immunodiagnoses. The total number of blood samples obtained was 841; 176 in District Khong, 279 in District Mounlapomak, 278 in District Pathoumphone, and 108 in District Sanasomboune(Table 2). ELISA will be carried out with the blood specimens for schistosome infections in the laboratory.
We have received good co-operation from the local government staff involved. The contributions made by Dr. Rattanaxay Rhetsouvanh and Mr.Boualy Keokhamphavanh ,IMPE, in the present survey deserve due recognition. It should be emphasized that the seroepidemiological surveys would have been impossible without intimate collaboration with teachers and children in the primary schools we visited. We are grateful to Dr. Khamliene Pholsena, Director, IMPE, for his valuable advices. Sincere appreciation is also expressed to you for your kind help and support.
