The objective of this proposal is the development of a dynamic model of the influence of anthropogenic changes due to rice farming on the transmission of Schistosoma japonicum in the endemic areas of The Philippines. The model will include several species, their population biology and behavior, including humans, snails and animal reservoir hosts of S. japonicum. We define rice farming, its spatial and temporal variation and its multiple impacts on physical, hydrologic and animal determinants of human S. japonicum infection as anthropogenic environmental change. The model will allow the prediction of the potential effects of anthropogenic environmental changes stemming from variation in rice farming over time and space on the transmission of S. japonicum to humans. Rice farming factors include: variation in rice farming practices, agricultural expansion and intensification; domesticated animal numbers, transmission behaviors and management practices; water use and management practices. Developing generalizable predictive ecological models of schistosomiasis transmission to humans is a fundamental component of the ongoing effort to develop cost-effective and acceptable disease control strategies. There are at present no published models for S.japonicum, which remains endemic in The Philippines and China despite 20 years of treatment of infected humans. After an initial 12-18 month period of determining the equilibrium conditions of transmission in several sites, and use of extant data from the last 40 years on human, snail and animal infection we will develop a dynamic transmission model of S. japonicum. We will then cure all humans in each site and observe the incidence rate and intensity of S. japonicum infection in humans over 18 months. This will permit statistical analyses to determine the relationships of specific transmission factors to the outcome of human infection. It will also allow more accurate construction of an age- structured, population dynamic model of S. japonicum transmission with improved predictabilty and generalizability.
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