Schistosomiasis in the People's Republic of China: the Era of the Three Gorges Dam

Abstract

SUMMARY The potential impact of the Three Gorges Dam (TGD) on schistosomiasis transmission in China has invoked considerable global concern. The TGD will result in changes in the water level and silt deposition downstream, favoring the reproduction of Oncomelania snails. Combined with blockages of the Yangtze River's tributaries, these changes will increase the schistosomiasis transmission season within the marshlands along the middle and lower reaches of the Yangtze River. The changing schistosome transmission dynamics necessitate a comprehensive strategy to control schistosomiasis. This review discusses aspects of the epidemiology and transmission of Schistosoma japonicum in China and considers the pathology, clinical outcomes, diagnosis, treatment, immunobiology, and genetics of schistosomiasis japonica together with an overview of current progress in vaccine development, all of which will have an impact on future control efforts. The use of synchronous praziquantel (PZQ) chemotherapy for humans and domestic animals is only temporarily effective, as schistosome reinfection occurs rapidly. Drug delivery requires a substantial infrastructure to regularly cover all parts of an area of endemicity. This makes chemotherapy expensive and, as compliance is often low, a less than satisfactory control option. There is increasing disquiet about the possibility that PZQ-resistant schistosomes will develop. Consequently, as mathematical modeling predicts, vaccine strategies represent an essential component in the future control of schistosomiasis in China. With the inclusion of focal mollusciciding, improvements in sanitation, and health education into the control scenario, China's target of reducing the level of schistosome infection to less than 1% by 2015 may be achievable.

Detection of schistosomiasis in an area directly affected by the São Francisco River large-scale water transposition project in the Northeast of Brazil

“…The findings of the present study reinforces the notion that increase in the number of dams on a global scale has allowed the increase in the prevalence of schistosomiasis, as observed in the construction of the Aswan dam in Egypt 31,32 , Three Gorges Dam in China 33,34 , and the Kossou Dam in Cote d'Ivoire 35 . These observations demonstrate the importance of diagnosis in the phases prior to the project operation, in order to allow an early identification and treatment of positive cases, and subsequent prevention and monitoring of the onset of new outbreaks 36 .…”

Modelling the Effects of Mass Drug Administration on the Molecular Epidemiology of Schistosomes

“…Population genetic analyses found close phylogenetic relationships between strains of S. japonicum in human and rodent hosts in hilly parts of Anhui Province, China using microsatellite markers, whilst schistosomes in the humans in the marshland areas were more closely related to those in bovines, which appear to drive reinfection in those areas (Rudge et al, 2009). Bovines were generally assumed to be the primary reservoir of human infection (McManus et al, 2010), but population genetic analyses greatly increased our understanding of these complex interactions in zoonotic parasites. Knowledge of the genetic similarity and transmission potential between hosts was then used to develop a multi-host model of transmission for S. japonicum .…”

Spatio-Temporal Patterns of Schistosomiasis Japonica in Lake and Marshland Areas in China: The Effect of Snail Habitats

“…where γ is the same variogram as in equation (2). For the ST variogram structure, we choose a product-sum covariance model 34 as follows:…”

“…It is estimated that more than 50 million persons in China are at risk; approximately one million persons and several hundred thousand livestock are infected. 2 Major foci of endemicity are found in marsh and lake areas (Poyang Lake and Dongting Lake) along the Yangtze River basin, where elimination of transmission has proven difficult. 3,4 China was one of the first countries in eastern Asia to initiate a national schistosomiasis control program, and achievements in schistosomiasis control have reduced by more than 90% the peak estimates of human prevalence in the mid 1950s, 5 which ranged between 10.5 and 11.8 million.…”