title: Large-scale determinants of intestinal schistosomiasis and intermediate host snail distribution across Africa: does climate matter?
abstract: 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 infectious 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 distribution 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 evaluated 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 indicate 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.
authors.affiliation: Center for Macroecology, Evolution and Climate, Department of Biology, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen Ø, Denmark; DBL, Department of Veterinary Disease Biology, University of Copenhagen, Thorvaldsensvej 57, DK-1871 Frederiksberg C, Denmark. Electronic address: asstensgaard@bio.ku.dk.
authors.forename: Anna-Sofie
authors.initials: AS
authors.lastname: Stensgaard
authors.forename: Jürg
authors.initials: J
authors.lastname: Utzinger
authors.forename: Penelope
authors.initials: P
authors.lastname: Vounatsou
authors.forename: Eveline
authors.initials: E
authors.lastname: Hürlimann
authors.forename: Nadine
authors.initials: N
authors.lastname: Schur
authors.forename: Christopher F L
authors.initials: CF
authors.lastname: Saarnak
authors.forename: Christopher
authors.initials: C
authors.lastname: Simoonga
authors.forename: Patricia
authors.initials: P
authors.lastname: Mubita
authors.forename: Narcis B
authors.initials: NB
authors.lastname: Kabatereine
authors.forename: Louis-Albert
authors.initials: LA
authors.lastname: Tchuem Tchuenté
authors.forename: Carsten
authors.initials: C
authors.lastname: Rahbek
authors.forename: Thomas K
authors.initials: TK
authors.lastname: Kristensen
mesh_terms: D000349:Africa / Q000453:epidemiology; D000818:Animals; D001700:Biomphalaria / Q000254:growth & development* / Q000469:parasitology*; D002980:Climate; D006801:Humans; D015233:Models, Statistical; D018570:Risk Assessment; D012550:Schistosoma mansoni / Q000302:isolation & purification*; D012555:Schistosomiasis mansoni / Q000453:epidemiology*; D019371:Topography, Medical