We conducted ultrasonographic (US) examinations in seven Cambodian villages where schistosomiasis mekongi is endemic. These villages were Sdau and Koh-Sneng in Stung Treng province, and Achen, Sambor, Kahh-Chor, Chhlong and Kampong Krabei in Kratie province (Table 2). The 421 inhabitants (96 in Stoung Treng, 325 in Kratie) had an age range of 6-64 years. A Fukuda Denshi (UF-4000) ultrasonograph with a Sony (VP-890) printer was used in the study. We also measured serum ammonia levels in 236 adult villagers in Achen. Sambor, and Kampong Krabei using a portable analyzer (F-kit, ammonia).

　

　

In this study, we did not find the typical "network" or "fish scale" pattern which characterizes advanced cases of schistosomiasis japonica, among the villagers inhabiting the schistosomiasis mekongi endemic area. In S. mekongi infections, most of the US images were similar to those of S. mansoni infections. So based on the classification of US images of S. mansoni infections (Workshop report of ultrasound in schistosomiasis, edited by TDR, WHO 1998), we classified US images obtained in the schistosomiasis mekongi endemic area (Table 3). However, in some cases we found US images resembling irregular fatty liver and an atypical "network" pattern, which have not been reported in S. mansoni infections.

　

　

When we compared US images in Kratie and Stung Treng provinces, we found many images indicative of advanced disease in Kratie province in 2000, including more advanced periportal fibrosis and more severe splenomegaly (Table 4). Sdau in Stung Treng province was a highly endemic area as estimated by seroimmunology, but morbidity estimated by US was low.

In Kratie province, many splenomegaly cases were detected by US. Kratie province is endemic for schistosomiasis mekongi and malaria, and these diseases cause splenomegaly. Endemicity of malaria was evaluated by the ratio of children aged 2 to 9 years with splenomegaly. In Kratie province, we found splenomegaly with collateral vessels among the adult villagers. Therefore in Kratie, splenomegaly appears to be due mainly to schistosomiasis mekongi.

　

　

We measured the serum levels of ammonia using a portable analyzer in 144 villagers with collateral vessels and 92 villagers without (Table 5). In those infected with S. japonicum and possessing splenomegaly and collateral vessels, because of portal vein to vena cava shunt, there was consciousness disturbance due to high serum levels of ammonia. However, in S. mekongi infections in Cambodia, there was no difference of serum ammonia levels between patients with and without collateral vessels.

In this study, most of the US findings in the schistosomiasis mekongi endemic area were similar to those due to S. mansoni infection. However, a US image resembling irregular fatty liver which was found in Kratie province has not been reported in other kinds of schistosome infections. To understand the pathophysiologic changes due to schistosomiasis mekongi, an investigation of the pathological basis of US images is expected. Since the introduction of a mass treatment programme in 1995, US findings have drastically changed in the schistosomiasis endemic area of Cambodia. In Sdau, Stung Treng province, endemicity estimated by seroimmunology was different from morbidity detected by US. In order to monitor the changes of endemicity and morbidity after the mass treatment programme, we need to investigate further the relationship between the results of seroimmunodiagnosis and US examinations.

In the schistosomiasis endemic area of Cambodia, we did not find high serum levels of ammonia. If patients with high ammonia levels undergo splenectomy, they sometimes develop hepatic coma. Therefore in Japan, a very high level of serum ammonia is a contraindication for splenectomy, However in Cambodia, we found no high serum ammonia levels among individuals infected with S. mekongi and showing collateral vessels. Accordingly, splenectomy may be recommended for patients with severe splenomegaly and collateral vessels.

　

　

We are grateful to Dr. Mam Bunheng, the Honorable Secretary of State for Health, Cambodia. for permission to conduct the present survey. We wish to record our deep appreciation of the encouragement received from the Directors of the Provincial Health Departments of Stung Treng, Kratie and Kampong Cham provinces. Special gratitude is expressed to Dr. Duong Socheat, Director, CNM, and Dr. Viroj Kitikoon, Mahidol University, for their valuable advice. Many thanks are extended to Dr. Suon Siela and three other medical technicians, CNM, for joining us during our field survey. We are grateful to the staff of Stung Treng, Kratie and Kampong Cham Provincial Health Departments, for their valuable help and support, and to village leaders and villagers who extended their cooperation and hospitality to us. It should also be emphasized that the present survey would have been impossible without intimate collaboration with teachers and children in the primary schools we visited.