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It has been suggested that global warming may alter the frequency and transmission dynamics of vector-borne diseases. To test this claim for schistosomiasis, we conducted a time-series analysis from 1972–2002 for 39 of the 70 counties of Jiangsu province, eastern China, where Schistosoma japonicum is partially endemic. We used a modeling approach to estimate the annual growing degree-days (AGDD), employing a lower temperature threshold of 15.3°C. Our final model included both temporal and spatial components, the former consisting of second order polynomials in time plus a seasonality component, whereas the spatial trend was formed by second order polynomials of the coordinates plus the thin-plate smoothing splines. We found that temperature increased over the past 30 years in all observing stations. There were distinct temporal trends with seasonality and periodicities of 12, 6, and 3 months, whereas only marginal spatial variation was observed. The predicted AGDDs for 2006 and 2003 showed increases for the entire Jiangsu province, with the AGDDs difference between these two time points exhibiting an increase from north to south. Our data suggest that changes in temperature will alter the extent and level of schistosomiasis transmission, which is relevant for the control of S. japonicum in a future warmer China.
Received December 19, 2005. Accepted for publication May 22, 2006.
Acknowledgments: The authors thank the Wuxi Meteorological Center for access to temperature data and the staff from Jiangsu Institute of Parasitic Diseases for their interest and support in the current study.
Financial support: This work received financial support from the UNICEF/UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (TDR), project M8/181/4/Y.88 (ID-A10775) and the Chinese National Science Foundation (Nos. 300070684 and 30590373). The research of A. Gemperli (project no. PBBS2-106801), P. Vounatsou (project no. 3252B0-102136), and J. Utzinger (project no. PP00B-102883) is supported by the Swiss National Science Foundation.
* Address correspondence to Jürg Utzinger, Department of Public Health and Epidemiology, Swiss Tropical Institute, Basel, Switzerland. E-mail: juerg.utzinger{at}unibas.ch
Authors’ addresses: Guo-Jing Yang, Department of Schistosomiasis Control, Jiangsu Institute of Parasitic Diseases, Wuxi 214064, People’s Republic of China. Guo-Jing Yang, Penelope Vounatsou, Marcel Tanner, and Jürg Utzinger, Department of Public Health and Epidemiology, Swiss Tropical Institute, P.O. Box, CH-4002 Basel, Switzerland. Armin Gemperli, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205. Xiao-Nong Zhou, National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Shanghai 200025, People’s Republic of China.
Reprint requests: Jürg Utzinger, Department of Public Health and Epidemiology, Swiss Tropical Institute, P.O. Box, CH-4002 Basel, Switzerland, Telephone: +41-61-284-8129, Fax: +41-61-284-8105, E-mail: juerg.utzinger{at}unibas.ch.
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