Please cite this article in press as: Stensgaard, A.-S., et al., Large-scale determinants of intestinal schistosomiasis and intermediate host snail distribution across Africa: Does climate matter? Acta Trop. (2011), doi:10.1016/j.actatropica.2011.11.010 ARTICLE IN PRESS G Model ACTROP 2764 1–13 Acta Tropica xxx (2011) xxx–xxx Contents lists available at SciVerse ScienceDirect Acta Tropica journa l h o me pa g e: www.elsevier.com/locate/actatropica Large-scale determinants of intestinal schistosomiasis and intermediate host snail distribution across Africa: Does climate matter? 1 2 Anna-Sofie Stensgaard a,b,∗ , Jürg Utzinger c,d , Penelope Vounatsou c,d , Eveline Hürlimann c,d , Q1 Nadine Schur c,d , Christopher F.L. Saarnak b , Christopher Simoonga e , Patricia Mubita f , Narcis B. Kabatereine g , Louis-Albert Tchuem Tchuenté h,i,j , Carsten Rahbek a , Thomas K. Kristensen b 3 4 5 a Center for Macroecology, Evolution and Climate, Department of Biology, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen Ø, Denmark 6 b DBL, Department of Veterinary Disease Biology, University of Copenhagen, Thorvaldsensvej 57, DK-1871 Frederiksberg C, Denmark 7 c Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, P.O. Box, CH-4002 Basel, Switzerland 8 d University of Basel, P.O. Box, CH-4003 Basel, Switzerland 9 e Ministry of Health, P.O. Box 30205, 10101 Lusaka, Zambia 10 f Department of Community Medicine, University of Zambia, P.O. Box 50110, 10101 Lusaka, Zambia 11 g Vector Control Division, Ministry of Health, P.O. Box 1661, Kampala, Uganda 12 h National Programme for the Control of Schistosomiasis and Intestinal Helminthiasis, Ministry of Public Health, Yaoundé, Cameroon 13 i Laboratoire de Biologie Générale, Université de Yaoundé I, Yaoundé, Cameroon 14 j Centre for Schistosomiasis and Parasitology, P.O. Box 7244, Yaoundé, Cameroon 15 16 a r t i c l e i n f o 17 18 Article history: 19 Received 1 March 2011 20 Received in revised form 15 November 2011 21 22 Accepted 18 November 2011 23 Available online xxx 24 Keywords: 25 Schistosomiasis, Schistosoma mansoni, Intermediate host snail, Biomphalaria, Disease ecology, Climate change, Species distribution modelling, Growing degree day, Africa 26 27 28 29 30 a b s t r a c t The geographical ranges of most species, including many infectious disease agents and their vectors and intermediate hosts, are assumed to be constrained by climatic tolerances, mainly temperature. It has been suggested that global warming will cause an expansion of the areas potentially suitable for infec- tious disease transmission. However, the transmission of infectious diseases is governed by a myriad of ecological, economic, evolutionary and social factors. Hence, a deeper understanding of the total disease system (pathogens, vectors and hosts) and its drivers is important for predicting responses to climate change. Here, we combine a growing degree day model for Schistosoma mansoni with species distribu- tion models for the intermediate host snail (Biomphalaria spp.) to investigate large-scale environmental determinants of the distribution of the African S. mansoni-Biomphalaria system and potential impacts of climatic changes. Snail species distribution models included several combinations of climatic and habitat- related predictors; the latter divided into “natural” and “human-impacted” habitat variables to measure anthropogenic influence. The predictive performance of the combined snail–parasite model was eval- uated against a comprehensive compilation of historical S. mansoni parasitological survey records, and then examined for two climate change scenarios of increasing severity for 2080. Future projections indi- cate that while the potential S. mansoni transmission area expands, the snail ranges are more likely to contract and/or move into cooler areas in the south and east. Importantly, we also note that even though climate per se matters, the impact of humans on habitat play a crucial role in determining the distribution of the intermediate host snails in Africa. Thus, a future contraction in the geographical range size of the intermediate host snails caused by climatic changes does not necessarily translate into a decrease or zero-sum change in human schistosomiasis prevalence. © 2011 Elsevier B.V. All rights reserved. 1. Introduction 31 Climate change is currently ongoing (IPCC, 2007), and expected 32 to affect biological systems worldwide (Rosenzweig et al., 2008). 33 ∗ Corresponding author at: Center for Macroecology, Evolution and Climate, Department of Biology, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen Ø, Denmark. Tel.: +45 3532 1262; fax: +45 3532 2321. E-mail address: asstensgaard@bio.ku.dk (A.-S. Stensgaard). Hence a better understanding of how climate – particularly rising 34 temperature – affects the frequency and transmission dynamics 35 of infectious diseases is an important public health issue (Haines 36 et al., 2009; Lafferty, 2009; Chaves and Koenraadt, 2010; Yang et al., 37 2010b). Conventionally, predicted risk profiles of climate-sensitive 38 infectious diseases have emphasised potential increases in disease 39 with climate change, even though recent studies noted range shifts 40 in disease distributions, rather than net expansions (Randolph, 41 2009; Ostfeld, 2009; Lafferty, 2009). Though complex and fraught 42 with uncertainties, understanding how species involved in disease 43 0001-706X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.actatropica.2011.11.010