Dr. Doung Socheat

Director

National Malaria Center

＃372,Blvd,Monivong,

Phnom Penh, Cambodia

　

　A survey of schistosomiasis mekongi in Cambodia was conducted 2-11 May 2001, in which seroepidemiological studies, collecting intermediate host snails and animal reservoir host survey were involved.

　1) Seroepidemiology was conducted at five points along the Mekong River. Sero-positive rates of schoolchildren in Kratie province were 47.3% in Sambok, 37.1% in Achen and 35.2% in Talous, whereas those in Kampong Cham Province were 2.7% in Kor Kor and 8.1% in Rokar Koy.

　2) More than three hundreds of intermediate host snails, Neotricula aperta, were collected in Kanpi and Krakor in Kratie Province. The snails were brought to our laboratory and maintained in the laboratory of Department of Tropical Medicine and Parasitology, Dokkyo University School of Medicine, for the purpose of preparing parasite material for serodiagnosis.

　3) Three-hundred and ten fecal samples of dogs were obtained in Kratie Province and one sample was determined to be positive for the schistosome infection, suggesting that dogs participate in the transmission of Schistosoma mekongi as reservoir hosts in the survey area.

　

　Human schistosomiasis due to S. mekongi is a serious health problem in the lower Mekong Basin. Little is known so far about current epidemiological status of the disease in Cambodia although more than thirty years have passed since the discovery of the disease in 1968 at Kratie town, northeast of the country.

　Our team has been conducting sero-epidemiological and malacological surveys of schistosomiasis mekongi in Cambodia since 1997 in collaboration with the National Malaria Center (CNM) and the field staffs of the Ministry of Health, Cambodia, for the purpose of estimating current epidemiological status of the Mekong schistosomiasis and subsequent effective control operation of the disease.

　

　 Main objectives of the present survey are as follows:

1) to collect Neotricula aperta, the intermediate host snail of S. mekongi, for the purpose of establishing life cycle of the parasite in our laboratory in Japan.

2) to determine the southern limit of endemic transmission of S. mekongi infection in Cambodia in our sero-epidemiological surveys continued since 1 997.

3) to detect natural S. mekongi infection in dogs domesticated in Kratie Province, where the disease is actively transmitted.

　

　 The survey team comprised Dr. Sinuon Muth and three well-trained medical technicians from CNM, Phnom Penh, Professor Hajime Matsuda and Dr. Jun Matsumoto from Dokkyo University, Japan. In addition to these members, several staffs belonging to Provincial Health Department in each study area (Kratie Province and Kampong Cham Province) strongly supported our activities.

　

　 Our survey in Cambodia started on 2 May 2001 and ended on 11 May. The brief schedule of the present survey is as follows:

1 May:	Meeting with Dr. Viroj Kitikoon (Mahidol Univ.) at Bangkok to strengthen our research collaboration
2 MAY:	Briefing at CNM, Phnom Penh with Dr. Sinuon Muth (CNM), Dr. Stefan Hoyer (WHO, Phnom Penh) and staffs of CNM
3 May:	Briefing at Kratie Provincial Health Department with Dr. Cheam Saem (Director of PHD) and staffs of PHD
3-7 May:	Sero-epidemiological, malacological and animal reservoir host surveys in the province of Kratie Province
8 May:	Briefing at Kampong Cham Provincial Health Department with Vice Director and staffs of PHD
8-11 May:	Sero-epidemiological survey in the province of Kampong Cham Province
11 May:	Rebriefing at CNM, Phnom Penh with Dr. S. Muth (CNM), Dr. S. Hoyer (WHO, Phnom Penh)

　

　 In our previous surveys, we had found a large number of Neotricula snailssticking on rocks in shallows of the Mekong River at the districts of Kanpi and Krakor in Kratie Province. On the basis of these observations, we visited the two points again to collect the Neotricula snails for laboratory maintenance. More than three hundreds of the snails were obtained at each point and brought back to our laboratory in Dokkyo University School of Medicine, Japan. The snails are now maintained in water tank and a part of them have been infected with S. mekongi (kind gift from Dr. Viroj Kitikoon, Mahidol University), which will provide us with parasite materials for serodiagnosis in future surveys.

　

　In the present survey, a total of 693 blood samples were donated from schoolchildren: 150 in Sambok, 170 in Achen, 128 in Talous (in the province of Kratie), 110 in Kor Kor, 135 in Rokar Koy (in the province of Kampong Cham).

Sambok and Achen are known to be highly endemic area of the disease demonstrated by stool examination and have a sentinel school. Kor Kor and Rokar Koy are respectively located 6 and 12 km downstream from Ta Meang, where we detected 8 sero-positive subjects out of 100 samples tested, and the southern limit of the disease transmission was not determined in our sero-epidemiological survey conducted last year.

　With these the blood specimens collected, serological test detecting schistosome-specific antibodies were done in our laboratory. Samples with more than 0.20 of optical density (OD) were determined as positive. All of nine negative control samples from Japanese students showed considerably low OD values. The results were summarized in Table. Sero-positive rates in Sambok, Achen and Talous were 47.3% (71/150), 37.1% (63/170) and 35.2% (45/128), respectively. In contrast to these results in Kratie Province, sero-positive rates in Kampong Cham Province were rather low: 2.7% (3/110) in Kor Kor and 8.1% (11/135) in Rokar Koy, but we could not determine the southern limit of endemic transmission of S. mekongi infection in Cambodia.

　

　 In order to detect natural schistosome-infection, we collected 31 O fecal samples of dogs domesticated in Kratie Province. Well-trained medical technicians belonging to Kratie Provincial Health Department examined for the parasite egg by Kato-Katz technique and found one sample to be positive for the schistosome infection. Egg density of the sample was 3456 eggs per gram of stool. The result has confirmed that dogs are animal reservoirs of S. mekongi, and participate in the transmission of the disease in the survey area.

　

　 1) A large number of intermediate host snails were obtained and brought back to our laboratory in Japan. With these snails, we will be able to establish the life cycle of S. mekongi in laboratory setting, which will provide us with the parasite materials to prepare S. mekongi-antigen used in our sero-epidemiological surveys. At present, we have been using S. japonicum-antigen alternatively in serological test as S. mekongi-antigen is not available. However, serum from patients with S. mekongi-infection does not necessarily show strong reaction to S. japonicum-antigen even though he/she is infected with the parasite. Accordingly, we will be able to estimate the disease prevalence more precisely in our sero-epidemiological surveys by using S. mekongi-antigen.

　 2) One of the main objectives in our sero-epidemiological surveys is to determine the southern limit of endemic transmission of schistosomiasis along the Mekong River in Cambodia. In the present survey, we found 3 sero-positive subjects in Kor Kor and 11 in Rokar Koy, Kampong Cham Province, suggesting that there exists the transmission of schistosomiasis mekongi although we could not find intermediate host snails in these survey areas. In order to conduct effective and suitable mass treatment, we have to clarify the disease ecology in our future sero-epidemiological and malacological surveys.

　 3) Natural schistosome-infection in dogs was detected in the province of Kratie by stool examination, suggesting that dogs participate in the transmission of S. mekongi as reservoir hosts in the survey area. Dogs, as well as humans, are to be taken into account in the disease control operations.

　

　 Serological test is much more sensitive in the detection of schistosome-infection than stool examinations, which enable us to discover 'hidden' endemic foci of the disease. In fact, the result of seroepidemiological survey revealed that schistosomiasis is endemic in Talous in Kratie province, which was parasitologically confirmed by stool examination conducted by CNM following the present survey. Accordingly, seroepidemiological survey is indispensable for precise estimation of the disease endemicity in Cambodia and we would like to continue the survey under the collaboration with CNM and Provincial Health Offices.

　

　Health education in relation to schistosomiasis aims help people understand that man plays an important role in the transmission of the disease through indiscriminate defecation and that infection occurs through water contact. We are ready to provide some materials for health education, such as video tapes and illustrations on schistosomiasis, which we found highly effective in health education targeting schoolchildren done in the Philippines for these several years. It is strongly recommended to apply these materials in schistosomiasis control activities in Cambodia.

　

　We are grateful to the Honorable Secretary of State for Health, Dr. Mam Bunheng, for permission to conduct the present survey. We wish to record our deep appreciation of the encouragement received from Dr. Cheam Saem, Director, Kratie Provincial Health Department; Dr. Nguon Sim An, Director, Kampong Cham Provincial Health Department. Special gratitude is expressed to Dr. Duong Socheat, Director, CNM, Dr. Stefan Hoyer, Dr. Viroj Kitikoon, Mahidol University for their valuable advices. Many thanks are due to Dr. Sinuon Muth and other three medical technicians, CNM, for joining us during our field survey. We are grateful to the technical staffs of Kratie and Kampong Cham Provincial Health Department, for their strong help and support. To village leaders and villagers who extended their cooperation and hospitality to us, we wish to express our special gratitude. It should also be emphasized that the present survey would have been impossible without intimate collaboration with teachers and children in primary schools we visited.

　

　

　

Figure.　 Results of serological test detecting Schistosome-specific antibodies (IgG class)