05-03-2008 - Identifying 'hot spots' for emerging diseases
Identifying 'hot spots' for emerging diseases
A SYSTEMATIC, quantitative analysis of recent global patterns of disease that predict global emerging infectious disease 'hot spots' has recently been published in Nature.
Dr Kate Jones and colleagues from the Zoological Society of London and the US-based Consortium for Conservation Medicine, Columbia University and University of Georgia, collated data on emerging infectious disease 'events' from 1940 to 2004. They identified 335 such events, which were defined as outbreaks of human disease associated with a new species or variant of an infectious agent.
Zoonoses formed the most important category, accounting for 60·3 per cent of the events. Over 71 per cent of these zoonotic events were caused by pathogens with a wildlife origin, and these events had increased significantly over time. They made up to 52 per cent of events in the most recent decade analysed (1990 to 2000). The authors note that this supports the suggestion that zoonotic emerging infectious diseases represent an increasing and very significant threat to global health. They say that it also highlights the importance of understanding the factors that increase contact between wildlife and humans in developing predictive approaches to disease emergence.
They found that the majority of pathogens identified (54·3 per cent) were bacterial or rickettsial. The emergence of drug-resistant bacterial strains, for example, vancomycin-resistant Staphylococcus aureus, represented a typical example of this group.
Their analysis found a significant rise in the number of diseases caused by vectorborne pathogens over time (accounting for 22·8 per cent of diseases over all the years studied, and 28·8 per cent in the last decade). The authors say that this could possibly be linked to climate change, although other explanations could not be ruled out.
The frequency of events rose to a peak in the 1980s and has since fallen (despite increasing reporting effort). The researchers suggest that the peak might reflect the onset of the AIDS pandemic, creating a large and still expanding population that is highly susceptible to concomitant infection.
They found that there was a significant correlation between socioeconomic, environmental and ecological factors in the emergence of disease. Disease events were concentrated at higher latitudes, with the main hot spots in the north-eastern USA, western Europe, Japan and south-eastern Australia. They suggest this result may be due partly to greater reporting effort, but that antibiotic use, high population densities and agricultural practices might also have played a part.
Their analysis also showed that, currently, surveillance and research are concentrated in the richer, developed countries of Europe, North America, Australia and parts of Asia, rather than in developing regions. This contrasted with 'risk maps' that they generated, which suggested that predicted emerging disease hot spots due to zoonotic pathogens from wildlife and vectorborne pathogens were more concentrated in developing countries located at lower latitudes. They call for reallocation of resources for 'smart surveillance' of emerging disease hot spots in lower latitudes such as tropical Africa, Latin America and Asia.
Jones, K. and others (2008) Global trends in emerging infectious diseases. Nature vol 451, pp 990-993