As shown in the results (Table 1& Fig. 1), schistosomiasis mekongi is highly endemic along the branch of the Mekong River (Tonle Kong), especially in Sdau (Stung Treng province; pos. rate=97.1%) and Kbal Chuor (Kratie province; pos. rate=86.8%) along the Mekong River.
As a continuance of our sero-epidemiological surveys to investigate for the southern limit of endemic transmission of Schistosoma mekongi infection in the Mekong River, a total of 190 blood samples; 80 in Kanh Chour, 20 river km downstream of Kratie and 100 samples in Ta Meang, 5 km downstream of Kompong Cham, were also obtained from school children. Seven (7.8%) out of 90 from Kanh Chour and 8 (8.0%) out of 100 serum samples from Ta Meang were found to be IgG positive, suggesting that endemic transmission of schistosomiasis may be exists in this area. Investigation of S. mekongi eggs in their stool will be required. After blood donation, each child received tablets of Vitamin-C, paracetamol and mebendazole together with a notebook and a pencil. Wall clock was also presented to each school.
2. Immunodiagnosis for chronic schistosomiasis mekongi
Immunodiagnosis of the sera from patients suffering from portal hypertension suspected to be due to S. mekongi was carried out in our Department. All the patient sera from Pasteur Institute in Phnom Penh showed positive reaction by ELISA using egg antigen from S. mekongi. Our preliminary results for the immune responses of the patient sera with S. mekongi egg antigen were quite different from those of S. japonicum egg antigen by ELISA (Table 2).
3. Stool examination
Stool examination among schoolchildren in the certain villages using modified formalin-detergent technique was conducted in the present survey. A total of 255 stool samples were collected from 5 villages; Koh Sneng, Sdau, Kbal Chour, Kanh Chour and Ta Meang (Table 3). Only one (0.4%) pupil showed positive for S. mekongi eggs in the stool, however, other intestinal parasites (hookworm, Ascaris etc.) are predominated among school children in this area. This study demonstrated that population-based chemotherapy with praziquantel was an effective strategy to reduce infection and morbidity due to schistosomiasis mekongi in northeastern Cambodia. Intensive yearly chemotherapy with praziquantel and mebendazole must be continued without interruption.
4. Survey for animal reservoir host
Studies on natural infections of S. mekongi in mammals in Southern Laos have indicated that dog is a good reservoir host, and a number of viable eggs are discharged in the feces. No reliable data on the prevalence in mammals in Cambodia have been available. In 1998, we examined fecal samples of various mammalian hosts, but we did not find any positive case in each animal. This year, 28 fecal samples of dogs were collected in Kbal Chuor (Kratie province). These samples were treated by formalin detergent technique and examined for S. mekongi-egg. As a result, one sample was positive and its egg-density was 50 eggs per gram. This is the first case of S. mekongi infection in dogs in Cambodia and shows that dogs play an important role in the transmission of schistosomiasis mekongi in Cambodia.
