09 October 2008

Mapping the effects of climate change on bluetongue transmission in Europe

Conference in Bangkok (Thailand) and Paris

Helene Guis123, Cyril Caminade4, Andy Morse4, François Roger2, Matthew Baylis1

1 Lucinda (Liverpool University Climate and Infectious Diseases of Animals Group), Liverpool University, UK
2 AGIRs (Animal and Integrated Risk Management Unit), Cirad, France
3 TETIS (Territories, Environment, Remote Sensing and Spatial Information Unit), Cirad, Cemagref, Engref, France
4 Department of Geography, Liverpool University, UK

Bluetongue (BT) is an arboviral disease of ruminants which emerged in Europe in 1998 and has, since then, caused an unprecedented series of epizootics of major economic consequence. Two distinct epidemiological events underlie this emergence: the northward expansion of the Afro-asian midge Culicoides imicola, probably under the influence of climate change; and the involvement of indigenous European Culicoides of the Obsoletus and Pulicaris groups.
In order to assess the effects of climate change in the distribution of BT in Europe, the basic reproduction number R0 of BT was modelled by a unique integration of epidemiological models with state-of-the-art climate models. This approach allows us to map R0 throughout Europe on an annual basis under past, present and future conditions simulated using several different climate models, with outputs in terms of model means and uncertainties
R0 was computed for a population of two hosts as sheep and cattle have different epidemiological roles in the transmission of BT (the latter being less affected by the disease but presenting a long viraemia) and for both the exotic (C. imicola) and indigenous vectors.
Climatic data for recent past (1961-2000) and future (1950-2050) periods was provided by the ENSEMBLES European project at a spatial scale of 25*25 km. For the recent past, improved regional climate simulations were produced by running a subset of four regional climatic models with the most realistic boundary conditions (ERA40 reanalysis) and external forcing. For the future conditions, simulations were carried out by running three regional climate models forced at their boundaries by a general circulation models forced by the IPCC’s (Intergovernmental Panel on Climate Change) Special Report on Emissions Scenario (SRES) A1B (integrated world with a balanced emphasis on all energy sources).
This modelling approach was carried out in three steps to assess the effects of climate change on each of the components of the BT epidemiological cycle: i) viral replication only, ii) viral transmission taking into account host distribution and iii) the combination of the viral, host and vector components. Results show the coherence between past anomalies in R0 and past incursions of Culicoides-borne diseases in Europe and highlight the fact that the vector component is both the most critical and yet the least well-defined one.

Here is the associated presentation:

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