Simon Hales

Nonstationary Influence of El Niño on the Synchronous Dengue Epidemics in Thailand

Background Several factors, including environmental and climatic factors, influence the transmission of vector-borne diseases. Nevertheless, the identification and relative importance of climatic factors for vector-borne diseases remain controversial. Dengue is the worlds most important viral vector-borne disease, and the controversy about climatic effects also applies in this case. Here we address the role of climate variability in shaping the interannual pattern of dengue epidemics. Methods and Findings We have analysed monthly data for Thailand from 1983 to 1997 using wavelet approaches that can describe nonstationary phenomena and that also allow the quantification of nonstationary associations between time series. We report a strong association between monthly dengue incidence in Thailand and the dynamics of El Niño for the 2–3-y periodic mode. This association is nonstationary, seen only from 1986 to 1992, and appears to have a major influence on the synchrony of dengue epidemics in Thailand. Conclusion The underlying mechanism for the synchronisation of dengue epidemics may resemble that of a pacemaker, in which intrinsic disease dynamics interact with climate variations driven by El Niño to propagate travelling waves of infection. When association with El Niño is strong in the 2–3-y periodic mode, one observes high synchrony of dengue epidemics over Thailand. When this association is absent, the seasonal dynamics become dominant and the synchrony initiated in Bangkok collapses.

Health Aspects of the Millennium Ecosystem Assessment

Biodiversity underpins the resilience of the ecosystems on which humanity depends. Loss of biodiversity is occurring at an unprecedented rate, driven by over-exploitation of productive ecosystems and other factors. This threatens vital ecosystem services, including food production, fresh water, nutrient cycling, waste processing, fuel and fiber, flood and storm protection, and climate stability (Vitousek et al., 1997). The Millennium Ecosystem Assessment (MA) is intended to provide a knowledge base for sustaining ecological systems, while providing for human needs. This ambitious goal has an implicit emphasis on ecological management, while recognizing that social and ecological systems are inextricably linked. The scope of public health policy in relation to ecological sustainability is difficult to define. How, then, does human health feature in the MA? To understand the potential health impacts of ecosystem change, two aspects need to be considered: the current vulnerability of the population under consideration and its future adaptive capacity (Fig. 1). These two are closely related, since vulnerable populations are less able to plan and implement adaptive responses. Vulnerability and adaptive capacity are also tied to the other aspects of well-being (material minimum, freedom and choice, good social relations, and security). The links between ecosystem change and human health—and the limits to human adaptive capacity—are seen most clearly among impoverished communities, which lack the ‘‘buffers’’ that the rich can afford. Poor communities are also the most obviously directly dependent upon productive ecosystems. Material lack is a strong determinant of health as well as other aspects of well-being. Both at the country level and within countries, poorer communities are usually less healthy than richer ones (though with some notable exceptions). At the global level, poorer countries are still battling hazards such as lack of clean water and sanitation, which contribute considerably to their burden of disease. Published online: May 3, 2004 The views expressed in this article are those of the authors and do not necessarily reflect the position of the World Health Organization. Correspondence to: Simon Hales, e-mail: simon.hales@anu.edu.au EcoHealth 1, 124–128, 2004 DOI: 10.1007/s10393-004-0085-7

Precautionary Health Risk Assessment: Case Study of Biological Insecticides

In conventional risk assessment approaches, experts define the scientific questions that can legitimately be asked and the burden of proof is on the potentially exposed community to show that a proposal is unsafe. Here I propose an alternative approach, precautionary health risk assessment, in which the scientific questions to be addressed are defined by community consultation. I illustrate the approach with a case study of exposure to biological insecticides. This illustrates how community consultation can have a critical influence on the outcome of a health risk assessment. Government agencies may be reluctant to involve stakeholders in health risk assessments because this involves a loss of political control of the process. However, precautionary approaches are likely to lead to better health outcomes where decision stakes and scientific uncertainty are both high.