Schistosomiasis mekongi, caused by the blood-living parasite S. mekongi, is a serious health problem in the lower Mekong Basin. We have been conducting a series of surveys on schistosomiasis mekongi in Cambodia since 1997 in collaboration with the National Center for Parasitology, Entomology and Malaria Control (CNM) for the purpose of clarifying its epidemiological status.

 The survey in 2006 was carried out from April to May (the first survey) and in December (the second survey). A seroepidemiological survey was conducted in Stung Treng province (Sdau) and Kratie Province (Kompong Krabei, Kbal Chuor, Sambok, Rokakandal, and Talous) during the first survey. In Sdau, Kbal Chuor, and Talous, we collected blood specimens preferentially from children who showed negative results in ELISA examinations carried out in 2005 to estimate the rate of schistosomiasis incidence. Positive conversion rates were 10.5% (4/38) in Sdau, 43.2% (16/37) in Kbal Chuor, and 3.8% (3/79) in Talous. Positive rates of children who were not examined in 2005, as based on random sampling, were 43.7% (55/126) in Kompong Krabei, 62.9% (44/70) in Kbal Chuor, 32.7% (49/150) in Sambok, 49.2% (32/65) in Rokakandal, 12.5% (87/56) in Talous, and 18% (11/61) in Sdau. These results suggest that an endemic situation still exists in the upstream area of Kratie province.

 Stool examinations were performed in Kbal Chuor (n=6), Rokakandal (n=3), Sdau (n=92), and Chey Oudam (n=4). Schistosome eggs were detected in one specimen from Rokakandal. Rokakandal is a village located near Kratie town. The population of Rokakandal is divided into two groups, Rokakandal I and Rokakandal II. Rokakandal II consists of Cambodians. In contrast, Rokakandal I consists of Vietnamese who live in floating houses, called "floating villages." The status of schistosome infection among floating villages had not been examined for the past 8 years. Thus, we focused on Rokakandal in the second survey.

 Positive rates in ELISA were 29.0% (20/69) in Rokakandal I, 16.7% (15/90) in Rokakandal II, and 11.5% (17/148) in Rokakandal School. Stool examinations were conducted using the Kato-Katz technique and formalin-detergent method. Eggs of S. mekongi were detected in feces from 4 persons (9.3%) in Rokakandal I (n=43). All schistosome egg-positive individuals showed positive ELISA values.

 As a result of the schistosomiasis control program since 1995, disease prevalence has been decreasing dramatically in endemic areas in Cambodia (Sinuon et al., 2007). Since the decreasing prevalence causes a reduction in the worm burden in patients, it is becoming more difficult to detect eggs in feces. As described in this report, our seroepidemiological survey indicates the existence of a risk of contact with schistosomes in villages in Kratie province. The mass drug administration campaign intercepts the transmission of schistosomiasis from humans to snails and has been very effective in reducing the prevalence of schistosomiasis mekongi. In areas where there is still a risk for schistosome infection, more studies on reservoir hosts and intermediate host snails are necessary for further progress in the elimination of the disease.

 Finally, we wish to express our gratitude to the staff of the CNM for joining us during the preceding and present surveys. We are grateful to the technical staff of the Kratie, Stung Treng, and Rattanakiri Provincial Health Offices who were very kind and helpful.

　

　

　

　

　

　

　

　

 The first survey team (from April to May) comprised Mr. Yom Yom, two medical technicians, and a driver from the CNM, Phnom Penh; and Prof. Hajime Matsuda and Dr. Masashi Kirinoki from Dokkyo Medical University School of Medicine, Japan. The team received technical support from local staff of the Provincial Health Departments of Kratie province, Stung Treng province, and Rattanakiri province.

　

 The second survey team (December) comprised Dr. Muth Sinuon, two medical technicians, and two drivers from the CNM, Phnom Penh; and Prof. Hajime Matsuda from Japan. The team received technical support from local staff of the Provincial Health Department of Kratie province.

　

 The epidemiological survey in Cambodia was conducted twice. The first survey was conducted during the period from 23 April to 10 May, and the second survey was from 12 to 23 December 2006. An outline of the schedule is given below.

　

First survey (Prof. H. Matsuda and Dr. M. Kirinoki)

23 April: Depart Japan for Cambodia

24 April: Briefing at the CNM, Phnom Penh

25 April: Travel to Kratie province

26 April: Epidemiological survey in Kompong Krabei

28 April: Epidemiological survey in Kbal Chuor and Sambok

29 April: Epidemiological survey in Talous and Rokakandal

30 April: Travel to Rattanakiri province

1 May: Briefing at the Rattanakiri Provincial Health Department

2 May: Epidemiological survey in Sdau

3 May: Epidemiological survey in Sdau

4 May: Travel to Phnom Penh

5 May: Briefing at the CNM, Phnom Penh

6 May: Depart from Cambodia

7 to 9 May: Cooperative research with Mahidol University (Matsuda)

10 May: Return to Japan (Matsuda)

　

The second survey (Prof. H. Matsuda)

12 Dec: Depart Japan for Cambodia

13 Dec: Briefing at the CNM, Phnom Penh

14 Dec: Travel to Kratie province

15 Dec: Briefing at the Kratie Provincial Health Department

15 to 18 Dec: Epidemiological survey in Rokakandal

19 Dec: Travel to Phnom Penh

20 Dec: Briefing at the CNM, Phnom Penh

21 Dec: Depart Cambedia for Thailand

22 Dec: Cooperative research with Mahidol University

23 Dec: Return to Japan

　

 Schistosomiasis mekongi, caused by the blood-living parasite Schistosoma mekongi, is a serious health problem in the lower Mekong River basin. Until the 1990s, only little was known about epidemiological status of the disease in Cambodia although more than 30 years had passed since the discovery of the disease in 1968 in the town of Kratie, in the northeast of the country. However, no schistosomiasis control program or epidemiological surveys were conducted in Cambodia in the 1970s and 1980s because of social confusion caused by the civil war and revolution. Epidemiological surveys were resumed in the early 1990s. Highly endemic areas were reconfirmed in Kratie province and found along the Mekong River and its tributaries in Stung Treng province. A schistosomiasis mekongi control program in Cambodia has been conducted based on large-scale mass treatment since 1995 by the National Center for Parasitology, Entomology and Malaria Control (CNM), Ministry of Health, Cambodia, with international cooperation.

 We have been conducting a series of surveys on schistosomiasis mekongi in Cambodia since 1997 in collaboration with the CNM to clarify its epidemiological status. Our seroepidemiological surveys have revealed highly endemic areas mainly in the upstream areas of the Mekong River in Kratie province, with decreasing endemicity downstream. The control project covered all the disease-endemic areas and resulted in a dramatic reduction in the prevalence of the infection to fewer than 10% in 2001 in sentinel villages from a baseline prevalence rate of about 70% based on stool examinations (Sinuon et al., Trans Roy Soc Trop Med Hyg, 101, 34-39, 2007). It is now time to consider a new strategy and tactics that would lead to the elimination of schistosomiasis in Cambodia.