Abstract
This article explores four key questions about statistical models developed to describe the recent past and future of vector-borne diseases, with special emphasis on dengue: (1) How many variables should be used to make predictions about the future of vector-borne diseases?(2) Is the spatial resolution of a climate dataset an important determinant of model accuracy?(3) Does inclusion of the future distributions of vectors affect predictions of the futures of the diseases they transmit?(4) Which are the key predictor variables involved in determining the distributions of vector-borne diseases in the present and future?Examples are given of dengue models using one, five or 10 meteorological variables and at spatial resolutions of from one-sixth to two degrees. Model accuracy is improved with a greater number of descriptor variables, but is surprisingly unaffected by the spatial resolution of the data. Dengue models with a reduced set of climate variables derived from the HadCM3 global circulation model predictions for the 1980s are improved when risk maps for dengue's two main vectors (Aedes aegypti and Aedes albopictus) are also included as predictor variables; disease and vector models are projected into the future using the global circulation model predictions for the 2020s, 2040s and 2080s. The Garthwaite–Koch corr-max transformation is presented as a novel way of showing the relative contribution of each of the input predictor variables to the map predictions.
Highlights
When, in 1930, Wolgang Pauli first hypothesized the existence of a new particle he wrote apologetically to his fellow physicists:I have done something very bad today by proposing a particle that cannot be detected; it is something no theorist should ever do.Pauli described his idea as ‘a desperate remedy’ to account in full for the observed loss of energy during radioactive beta decay
Relative humidity was chosen as the single predictor because this is related to vapour pressure, the single variable used by Hales et al [18] in their models of dengue, in which 7 they claimed an over-riding importance of vapour pressure
Dengue occurs in areas of higher rather than lower humidity, but areas of high humidity occur at high latitudes which are predicted, incorrectly, to be suitable for dengue
Summary
In 1930, Wolgang Pauli first hypothesized the existence of a new particle (later to be called the neutrino by Enrico Fermi) he wrote apologetically to his fellow physicists:. All dengue or vector species’ models were run using only the 3 meteorological or the A1F1 or B1 scenario GCM output data Both altitude and other variables such as human population density are thought to be important in determining dengue’s distribution at the present time [20]. In contrast to biological or process-based models, which are generally predicting the species’ ‘fundamental niche’ (i.e. its distribution constrained only by its physiological tolerance of temperature, humidity, etc.), statistical models are more nearly predicting the species’ ‘realized niche’, the fundamental niche modified by all non-climatic variables, including competitors, predators, parasites and, in the case of vector-borne diseases, various human activities which either directly (e.g. insecticides) or indirectly (e.g. the provision of safe, piped water supplies; or changing agricultural practices [52]) affect the vectors’ or disease’s distribution. This seems to be a more preferable starting point for such studies than any based on either fundamental niche predictions (which need to incorporate all the factors limiting this to the realized niche) or on making other assumptions about how development in each climatic regime will change as those regimes shift geographically
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Schedule a callMore From: Philosophical transactions of the Royal Society of London. Series B, Biological sciences
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