Modeling Transmission of Environmentally-Mediated Schistosomiasis - from Understanding to Control
Song Liang (College of Public Health, The Ohio State University)
(May 15, 2007 3:30 PM - 4:30 PM)
Schistosomiasis remains a major public health problem in many developing countries and represents a class of infectious diseases with strong environmental links. Environmental effects on the transmission of schistosomiasis are well recognized, but the role of specific factors like climate and agricultural practices in modulating transmission is seldom characterized quantitatively. To understand the effects of these factors in the transmission and to explore how the understanding could help to inform better control strategies, a mathematical model was developed for the site-specific characterization of schistosomiasis transmission in irrigated agricultural environments in western China. The model incorporated impact of microclimatic condition on infective stages, the ecology of intermediate snail host, and spatial and temporal heterogeneities associated with human exposure. The model was then calibrated using field data from intervention studies in three villages and simulated to predict the effects of alternative control options. Both the results of these interventions and earlier epidemiological findings confirm the central role of environmental factors, particularly those relating to snail habitat, site and timing of exposure and agricultural and sanitation practices. Moreover, the findings indicate the inadequacy of current chemotherapy-mollusciciding strategies alone to achieve sustainable interruption of transmission in some endemic areas. More generally, the analysis suggests a village-specific index of transmission potential and how this potential is modulated by time-varying factors, including climatological variables, seasonal water-contact patterns, and irrigation practices, which altogether provide a framework for evaluating the likelihood of sustained schistosomiasis transmission and suggest an approach to quantifying the role of environmental factors for other environmentally-mediated infectious diseases.