Potential Impact of Climate Change on Schistosomiasis Transmission in China Xiao-Nong Zhou,* Guo-Jing Yang, Kun Yang, Xian-Hong Wang, Qing-Biao Hong, Le-Ping Sun, John B. Malone, Thomas K. Kristensen, N. Robert Bergquist, and Jürg Utzinger National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Shanghai, People’s Republic of China; Department of Schistosomiasis Control, Jiangsu Institute of Parasitic Diseases, Wuxi, People’s Republic of China; School for Environmental Research, Charles Darwin University, Darwin, Australia; Department of Pathobiological Sciences, School of Veterinary Medicine, Skip Bertman Drive, Louisiana State University, Baton Rouge, Louisiana; DBL – Institute for Health Research and Development, University of Copenhagen, Charlottenlund, Denmark; Ingerod 407, Brastad, Sweden; Department of Public Health and Epidemiology, Swiss Tropical Institute, Basel, Switzerland Abstract. Appraisal of the present and future impact of climate change and climate variability on the transmission of infectious diseases is a complex but pressing public health issue. We developed a biology-driven model to assess the potential impact of rising temperature on the transmission of schistosomiasis in China. We found a temperature threshold of 15.4°C for development of Schistosoma japonicum within the intermediate host snail (i.e., Oncomelania hupensis), and a temperature of 5.8°C at which half the snail sample investigated was in hibernation. Historical data suggest that the occurrence of O. hupensis is restricted to areas where the mean January temperature is above 0°C. The combination of these temperature thresholds, together with our own predicted temperature increases in China of 0.9°C in 2030 and 1.6°C in 2050 facilitated predictive risk mapping. We forecast an expansion of schistosomiasis transmission into currently non-endemic areas in the north, with an additional risk area of 783,883 km 2 by 2050, translating to 8.1% of the surface area of China. Our results call for rigorous monitoring and surveillance of schistosomiasis in a future warmer China. INTRODUCTION Growing evidence points to emissions of greenhouse gases related to human activities as a key factor of climate change, which in turn affects human health and well-being. 1–5 On average, the Earth’s climate has warmed by about 0.6°C over the past 100 years with temperature increases especially pro- nounced since the mid-1970s, particularly over land in the northern hemisphere at high altitudes and during the winter months. 6 Based on the outcome for the average climate for the period 1961–1990, the World Health Organization (WHO) currently estimates that > 150,000 deaths and a bur- den of 5.5 million disability-adjusted life years (DALYs) can be attributed to climate change and climate variability each year. 4 An ensemble of recent climate simulations predicts an increase in the mean global temperature from 1990–2100 of 2.4–5.4°C. 7 Climate warming will be accompanied by pertur- bations in the global hydrologic cycle, 8 precipitation, and pro- nounced changes in water availability. 9 Collectively, pre- dicted risk profiles of climate-sensitive diseases tend to worsen for most parts of the world, and hence require adap- tation and mitigation strategies. 3,4 Reviews are available about how climate change and cli- mate variability are likely to affect health, drawing on em- pirical studies that document past and present risks, and pre- dictive models that conjecture future risks. 1–5 However, most of the published work focuses on directly acting temperature effects (e.g., excess mortality and morbidity due to heat waves, floods, and droughts), effects on the risk of disasters and malnutrition, and changes in the transmission of infec- tious diseases. 1–5 With regard to a changing climate and in- fectious diseases, most studies have centered on malaria. 10–15 Time-series analysis and predictions suggest that the popula- tion at risk of malaria in Africa will slightly increase due to rising temperatures, primarily through expansion of the dis- ease into higher altitudes, and lengthened malaria transmis- sion seasons. 4 The potential impact of climate change on the global distribution of dengue has also been modeled. Under the scenario of contributing factors other than temperature remaining unchanged, the models predict that a large propor- tion of the human population would be at risk. 16 Only a few attempts have been made to predict changes in the spatial distribution of schistosomiasis transmission due to global warming; results have been conflicting. 17,18 Although an early model of global warming predicted that the area conducive for schistosomiasis transmission would expand, 17 later models forecasted a decrease in the epidemic potential of schistosomiasis. 18 Although the nature and extent of cli- mate change on the transmission of schistosomiasis remain poorly understood, 19 there is consensus that the most sensi- tive areas are around the borders of the current transmission. 2 Clearly, new research is warranted to develop regional cli- mate change models and to assess the biologic significance of model outcomes. 4,15 Despite huge efforts in implementing and sustaining the national schistosomiasis control program in China, recent data suggest that the disease is re-emerging. 20–22 Regional climate change in the face of profound demographic, ecologic, and socioeconomic transformations has been advanced as a contributing factor. 20,21,23 Here, we present the results from a biology-based model developed with an emphasis on the ef- fects of rising temperature on the future transmission of schis- tosomiasis in China. MATERIALS AND METHODS Digital map and temperature data. A digital map of China (scale: 1:1,000,000) was obtained from the Chinese State Bu- reau of Surveying and Mapping (Beijing, China). Average daily temperatures from 1951–2000 at 193 observing stations across China were made available from the Chinese National Satellite Meteorological Center (Beijing, China). * Address correspondence to Xiao-Nong Zhou, National Institute of Parasitic Diseases, Chinese Center for Disease Control and Preven- tion, 207 Rui Jin Er Road, Shanghai 200025, People’s Republic of China. E-mail: ipdzhouxn@sh163.net Am. J. Trop. Med. Hyg., 78(2), 2008, pp. 188–194 Copyright © 2008 by The American Society of Tropical Medicine and Hygiene 188