Implications from assessing environmental effects on spatio-temporal pattern of schistosomiasis in the Yangtze Basin, China.

Schistosomiasis remains a major public health problem in the South China, particularly in lake and marshland regions. Modelling the spatio-temporal pattern of schistosomiasis guides disease prevention and control programs and is a research area of growing interest. However, few attempts have been made to evaluate the changing (nonlinear) effects of environmental determinants on schistosomiasis. In this context, a hierarchical spatiotemporal model was applied to evaluate how environmental determinants affect the changing trend of schistosomiasis in Anhui Province, China, based on annual parasitological and environmental data for the period 1997-2010. Results showed that - compared to changing effect - environmental factors had a constant (linear) effect on schistosomiasis. The disease was also found to fluctuate over time, which was due to the two latest national schistosomiasis control programs. In addition to statistical benefits of this approach, our analysis implied that climate change might not contribute to variation of schistosomiasis; rather, prevention activities affect schistosomiasis when the disease prevalence remains at a low level. Finally, the analytical method proposed in our study provides a template for modelling the spatio-temporal pattern of a disease whose transmission is largely determined by environmental determinants.