Search

Increasing evidence indicates that dams impact riverine ecosystems and human diseases. Poyang Lake, one of the largest schistosomiasis endemic environments in China, will change due to the construction of the Yangtze River Three Gorges Dam. We assess changes in Oncomelania hupensis hupensis, the snail host for Schistosoma japonicum, in response to changing water levels and weather from 1998 to 2002. In the 5 years following the major flooding of Poyang Lake in 1998, seasonal water levels have gradually decreased, concomitant with decreases in mean and variance of fall snail densities. Nonlinear relationships suggest that the highest spring density is associated with current, 2-, and 3-month prior temperatures of 18°, 9.1°, and 5.8°C, while the highest fall density is associated with 2- and 3-month prior water levels of 17 and 18 m, respectively. This suggests that lower, more stable water levels downstream of the dam may result in a reduction in mean fall densities and their variance. However, additional data are needed to determine whether snail populations that are typically destroyed by seasonal floods may live longer in more stable environments created by the dam. [ABSTRACT FROM AUTHOR]

Abstract: Human helminthiases are common in China, especially in rural areas where sanitation conditions are poor. Co- and multiple infections with helminths are strikingly frequent. A cross-sectional parasitological and questionnaire survey was carried out in a population of 3205 individuals belonging to 498 families from five villages in the Poyang Lake region, Jiangxi Province, China, to assess their helminth infection status and to collect information on risk factors for infection. The prevalences for Ascaris lumbricoides, Schistosoma japonicum and Trichuris trichiura were 30.9%, 15.7% and 47%, respectively. Hookworm infection prevalence was low (0.7%). A significant association was observed between A. lumbricoides and T. trichiura infection, and also between S. japonicum and T. trichiura infection. Variance components analysis was undertaken to investigate the aggregation of S. japonicum and the soil-transmitted helminths, A. lumbricoides and T. trichiura. While A. lumbricoides was found to aggregate only at a household level, T. trichiura was shown to cluster predominantly in families. Both genetic and household effects were found to be important in determining the risk of infection with S. japonicum. Variance components analysis for A. lumbricoides/T. trichiura co-infections indicated a significant domestic environmental effect, attributable for 32.7% of the co-infection risk. Aggregation of S. japonicum/T. trichiura co-infection was also observed at a household level. The risk of infection with multiple helminth species, although mainly environmentally influenced, was also shown to have significant involvement of genetic and household components. The results of this study indicate that a shared household is a major contributing risk factor for helminth co-infections and emphasises the need for increased standards of sanitation and hygiene to prevent parasite transmission. Further, the results suggest that susceptibility to one helminth infection is not completely independent of another, and that there exist common genetic factors underlying infection with multiple helminth species. [Copyright &y& Elsevier]