Sarah E. Randolph1, David J. Rogers2
1Oxford Tick Research Group and 2TALA Research Group, Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK.
Nature reviews. Microbiology. April 2010, doi:10.1038/nrmicro2336
The impact of human activities on the principles and processes governing the arrival, establishment and spread of exotic pathogens is illustrated by vector-borne diseases such as malaria, dengue, chikungunya, West Nile, bluetongue and Crimean-Congo haemorrhagic fever. Competent vectors, which are commonly already present in the areas, provide opportunities for infection by exotic pathogens that are introduced by travel and trade. At the same time, the correct combination of environmental conditions (both abiotic and biotic) makes many far-flung parts of the world latently and predictably, but differentially, permissive to persistent transmission cycles. Socioeconomic factors and nutritional status determine human exposure to disease and resistance to infection, respectively, so that disease incidence can vary independently of biological cycles.
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VBORNET comment: 2010-05-28
Largely based on the experience gained with the other partners of the EDEN project, Emerging Diseases in a changing European Environment, Sarah Randolph and David Rogers review the factors underpinning the arrival, establishment and spread of exotic diseases. Here exotic has to be taken in its most strict sense which is ‘introduced from another country, not native to the place where found’, and therefore not systematically assimilated to ‘tropical’. As recently pointed out recently in a special report in New Scientist (NS2760, 35-45), there is a major difference between climate change skeptics and deniers. Each scientist has the duty to remain skeptical of any evidence provided. In this paper the authors systematically evaluate claims one by one carefully considering evidence and also clearly pointing out when evidence is still missing or point of views are conflicting and not avoiding complexity. As a result, the paper is one of the better recent reviews of ongoing global changes taken as a whole and their impact on the emergence of vector borne diseases.
A point of discussion which may remain is the content of box three addressing the issue of risk mapping to identify areas prone to invasion. The example chosen by the authors is the spatial modeling of Culicoides imicola in the Mediterranean basin and temperate Europe based on 87 sampling points in Portugal. In doing so two important aspects are underestimated: (a) the eco-climatic conditions prevailing in Portugal may not be representative for the entire area for which modeling outputs have been provided, and (b) C. imicola as an invasive species may not have reached its full spread range in Portugal at the time of the sampling. Therefore predictions made with this type of modeling approach based on presence/ absence records at a given point in time, and in a very limited area, though interesting from a scientific point of view (see discussion Tatem et al. 2003) may be very misleading for decision makers. Whilst the proposed modeling approach certainly is valid to model the potential distribution of resident species provided the samples taken are representative of the entire modeled area, other methods need to be adopted to predict future spread in other areas.
Finally whilst in their conclusions the authors correctly stress the fact that risk mapping can be an important prerequisite for planning active surveillance, it may have been helpful to also briefly address the issue of responsiveness. Recent experiences with invasive mosquito species in Europe (see VBORNET NL2, special issue on mosquitoes) have shown that in many cases countries are not legally prepared to eliminate invasive mosquitoes in a natural environment. Knowledge in itself may therefore not be enough to solve a problem!