Spatial comparison of areas at risk for schistosomiasis in the hilly and mountainous regions in the People's Republic of China: evaluation of the long-term effect of the 10-year World Bank Loan Project

The long-term effectiveness of the mainly chemotherapy-based control strategy of the World Bank Loan Project (WBLP) for schistosomiasis control in Chinese hilly and mountainous regions was evaluated with a view to determine the best road forward. Based on the national database of schistosomiasis prevalence for the periods of 1999-2001 and 2007- 2008 in the People's Republic of China, a Bayesian regression model was used for spatial comparison of schistosomiasis risk distribution between two periods taking account of all the potential risk factors simultaneously through two latent components of random effects: spatially correlated heterogeneities (CH) and spatially uncorrelated heterogeneities (UH). Four different types of endemic areas were investigated: those that remained endemic despite control efforts (17 or 37.8%), those that became non-endemic (9 or 20.0%), those that reverted back to endemicity (7 or 15.6%), and those with fluctuating endemicity (12 or 26.7%). The overall prevalence of schistosomiasis was lower in 2007-2008 compared with that in 1999- 2001, but the spatial distribution of risk remained similar. Compared to 1999-2001, the magnitude and range of risk even tended to be greater in 2007-2008. UH showed a fluctuating pattern, while CH increased gradually doubling over the two periods. There was no evidence for long-term effectiveness of the WBLP chemotherapy-based control strategy in this region. Controlling the effect of UH is still the main aspect of current schistosomiasis control strategy for the hilly and mountainous regions, but innovative methods are urgently needed for effectively controlling UH.