Eco-genetics of schistosomiasis in China

In cooperation with Robert C. Spear (University of California, Berkeley), Justin Remais (Emory University, Atlanta), George Davis and Paul Brindley (George Washington University Medical Center, Washington D.C.). Supported by NSF subgrant SA6241-11395

This research focuses on schistosomiasis, a most significant water-borne parasitic disease. The parasite that cycles between man or other mammals and snails affects some 200 million persons and threatens some 600 million in more than 76 countries. The distribution of the disease is extremely sensitive to environmental changes, particularly man-made changes, e.g. construction of dams. The history of large dam construction on increasing the abundance of schistosome infections is well known. One such environmental change of grave concern for public health is the completion of the Three Gorges Dam in China (2009). The super dam, which rises to a height of 180 m on the Yangtze River, will affect Hubei and Sichuan Provinces by creating a reservoir area of 50,700 km² and submerging more than 220 counties. The Three Gorges Area is currently free of schistosomiasis and it is predicted that the dam will bring together the geographically isolated snail hosts Oncomelania hupensis hupensis (below the Three Gorges) and O. h. robertsoni (above the Three Gorges) along with co-evolved Schistosoma japonicum into newly created snail habitat around the reservoir. Moreover, when the Three Gorges Reservoir is filled, the level of water flow in the Yangtze River will be about one meter higher than it is at present. This will yield more permanent snail habitats and snails that are longer lived, with a considerable impact on the huge Poyang and Dongting Lakes and islands of the Yangtze River that are highly endemic for S. japonicum. The construction of the super dam represents a unique opportunity to study pattern and processes of schistosomiasis transmission and disease dynamics before major environmental changes come into effect. This, in turn, could help identifying the ecological and population genetic bases for emerging schistosomiasis and pinpointing potential disease control measures.
The long term objective of the current project is to understand how changes in the environment impact basic ecological factors that drive the evolution of snail-schistosome genetics and different modes of schistosome transmission to man. This objective is based on the overarching hypothesis that there are close co-evolutionary relationships between O. hupensis and S. japonicum. This close relationship, the risk for emerging schistosomiasis in the Three Gorges Area and the fact that the life cycle of S. japonicum can only be maintained in areas with one specific species of snails, makes the intermediate host a crucial target for schistosomiasis research and control. Not only is understanding snail population genetics the most cost effective way to understand S. japonicum genetic divergence and patterns of susceptibility/resistance to infection with schistosomes, it also is a key to predicting emerging schistosomiasis.