Epidemiology of Schistosoma japonicum in China: morbidity and strategies for control in the Dongting Lake region

Dongting Lake, covering a very large surface water area of 2691 km(2), is l ocated in Hunan Province in the southern part of the People's Republic of C hina. It is the second-largest freshwater lake in China and plays an import ant role in regulating the amount of water in the Yangtze River, China's lo ngest river. The annual water level of the lake changes by as much as 15 m, rising in summer and falling in winter. Asian schistosomiasis has been end emic in the Dongting Lake region for centuries and it has had a devastating effect on the public health of the local people. After a difficult struggl e for more than four decades, a concerted programme, supported by the World Bank Loan and instigated in 1992, has resulted in remarkable progress in t he control of the disease in many endemic areas of the region. However, the great challenge remains to consolidate and maintain the achievements made to date. The Schistosoma japonicum intermediate host (Oncomelania hupensis hupensis) snail habitats are huge, estimated at 1768 km(2) in 1996; these a re increasing at a rate of 34.7 km(2) annually due to high silt deposition from the Yangtze River itself and from the connecting rivers in Hunan provi nce, and construction of embankments in the Dongting Lake region. It is ant icipated that the construction of the Three Gorges Super Dam, the largest e ngineering project ever undertaken, will substantially extend the range of the snail habitats and increase the number of new schistosomiasis cases. In many areas, human re-infections with S. japonicum after drug (praziquantel ) treatment remain unacceptably high (up to 20% of those treated are re-inf ected annually) due to occupational (mainly fishing) water contact. This pa per reviews the history and the current status of schistosomiasis control i n the lake region, it explores the epidemiological factors which influence the prevalence of the infection and the disease it causes, and it provides insight into future approaches to control which might finally eradicate the infection. (C) 2000 Australian Society for Parasitology Inc. Published by Elsevier Science. All rights reserved.