Implications of global change and climate variability for vector-borne diseases: generic approaches to impact assessments

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Abstract

Global change is pervasive and occurring at a dramatic rate. It involves changes in land use, vegetation cover, species translocations and even the climate of the planet. The consequences for the biosphere are uncertain. Past research emphasis has been on the science of climate change as the major driver of policy. The present priority in the global-change community is to define the likely nature and extent of those impacts on biodiversity and the functioning of ecosystems. In addition, increasing consideration is now being given to adaptation measures. The way in which that is being initiated is to develop adaptation measures to respond to medium-term climate variability in the form of altered El Nino and similar cycles, and changes in the frequency of extreme events. Given the large number of stakeholders in agriculture, human health and the environment, there is a need for great efficiencies if the scientific community is going to be able to respond in a meaningful way with foreseeable resources. The plethora of problems means that generic approaches are needed. The present situation, with parasitologists each doing their own thing in terms of developing and using software tools, is like the tower of Babel. Parasitologists need common tools and languages to facilitate communication and collaboration. Advances in computing, with object-oriented programming languages and seamless exchange of information between different packages and platforms, are providing some exciting opportunities to overcome these problems.

Introduction

Global change is a term used to encompass all drivers of environmental change. The primary impacts of global-change drivers on some vector-borne diseases in Australia are shown in Table 1. Climate is the most significant driver of vector-borne diseases, with rainfall being the most important element affecting each of the species listed. Irrigation is a dominant contributor to risks from mosquito-borne diseases and accidental imports of vectors pose a major risk to public health in Australia. An effective public-health response will be an important element in mitigating impacts on these human diseases. The potential impacts of global change on public health, agriculture and the environment demand policy responses and the development of adaptation strategies.

Ecosystems contain individual species that respond and disperse separately in a changing environment. Hence we need to address impacts at the species rather than the community level. Most significant environmental changes occur as a result of local land use practices or by a change in the global climate. A species may also experience major changes to its environment if it is moved to a new location, as a result of accidental importation to a new country. Hence, management of global change and invasive species are two sides of a coin as far as pest risk analysis is concerned. In the former the environment changes around the organism, while in the latter case the organism moves to a new environment.

Environmental change is taking place in a climate of uncertain political and economic pressures, increasing demands on resources to support greater consumption, and increasing populations in developing countries. Meanwhile there is widespread questioning of the value of science, judging by the declining level of support for strategic, ‘‘public good’’ science, as opposed to that in pursuit of short-term, profit-driven objectives. In this social and physical environment there is a need to prioritise the use of resources and to extract better value from research funding to address the concerns of policy makers. These are the pressures that have driven researchers to develop generic, cost-effective approaches to impact assessments in agriculture and the environment [1], and hopefully now in the field of public health 2, 3, 4, 5. These approaches need to be based on integrated impact assessments that provide socio-economic measures of costs and benefits. There is also a need to prioritise efforts so that the more urgent issues are considered first. The challenge for parasitologists is to identify likely impacts of each global driver on parasites and vector-borne diseases and then to devise ways in which that knowledge can be put to advantage to improve disease management.

Section snippets

Impact assessment tools

The global scientific community is faced with the huge task of assessing the likely impacts of global-change drivers on vector-borne diseases, in addition to all the other pests, diseases and weeds. The numerous pest species and wide range of stakeholders, combined with the great variation in quality of information and data, make the task more daunting than ever. Information on the ecology of parasite species ranges in detail from anecdotal ‘‘expert opinion’’, through records of species’

CLIMEX—theory

The name ‘‘CLIMEX’’ was derived from the term ‘‘CLIMatic indEX’’ that is intended to capture the two key elements of the program, namely its climatic orientation and its generation of indices rather than either qualitative, text-based estimates or fully quantified population values [10]. CLIMEX is a spatial modelling tool designed to extract maximum information from low density, spatially distributed observational data on the geographical distribution of species or other biological entities. As

Generic modelling

The advent of object-oriented computer programming languages has enabled the fulfilment of a long-held ambition [17]to develop a generic approach to the building of simulation models. A generic modelling toolkit, DYMEX, has been produced by CSIRO and the CRC for Tropical Pest Management [18]. It consists of a ‘‘Builder’’, a ‘‘Simulator’’ and a library of functions that can be incorporated into new models. The products of the system are specific models that describe the population dynamics and

Integrated impact assessments

The primary reason for the production of integrated impact assessments is to supply policy makers with holistic advice in socio-economic terms. Full integration needs treatment of multiple layers of information from the drivers such as climate, to biological systems and onto economic models at the farm, regional or national level. This inevitably requires a mix of tools ranging from climatic matching models, simulation models, geographical information systems and economic spreadsheet models. In

Land use, land cover and microclimates

Deforestation is potentially important in changing both the continuity of the landscape and the local microclimate. Matola et al. [19]reported a change in the microclimate in favour of malaria transmission. They recorded malaria sporozoites in previously disease-free vectors in the Usambara mountains in Tanzania following forest clearing, which increased average temperatures by 5°C. Clearing also exposes water bodies to sunlight that accelerates the breeding of Anopheles gambiae, the primary

Conclusions

Global change is here to stay; it comes in many and changing forms and its effects are pervasive. Local and regional impacts on vector-borne diseases need to be anticipated and adaptation strategies designed. Attention needs to be paid to each of the global-change drivers, and in the case of vector-borne diseases, particularly to issues related to water as it is affected by changes in climate and human management practices such as irrigation. Similarly, there is a need to compare the relative

Acknowledgements

Thanks are due to Dr Rick Bottomley who assisted with the illustrations, Mr Gunter Maywald who provided computing support for the modelling programs and Dr Graeme Hammer who provided the data on the SOI.

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