Conceptual model: bringing land use into public health policy.
The recommendations stemming from the international colloquium are highly relevant to the Millennium Ecosystem Assessment (MEA), a broad multiagency/foundation-sponsored scientific assessment of degraded ecosystem effects on human well-being. A conceptual framework of the MEA already provides an approach to optimize the contribution of ecosystems to human health (MEA 2003
). This framework offers a mechanism to a
) identify options that can better achieve human development and sustainable goals, b
) better understand the trade-offs involved in environment-related decisions, and c
) align response options at all scales, from the local to the global, where they can be most effective. This conceptual framework focuses on human well-being while also recognizing associated intrinsic values. Similar to the MEA, focus is particularly on the linkages between ecosystem services and human health. Workshop participants developed a conceptual model (). Like the MEA, it assumes a dynamic interaction between humans and ecosystems that warrants a multiscale assessment (spatial and temporal).
Figure 1 A systems model of land use change that affects public health. This model shows relationships between drivers of land use change and subsequent levels of environmental change and health consequences. Various levels of investigation and intervention are (more ...)
By using this framework, policy makers may approach development and health at various levels. These levels include specific health risk factors, landscape or habitat change, and institutional (economic and behavioral) levels. For sound health policy, we must shift away from dealing primarily with specific risk factors and look “upstream” to underlying land-use determinants of infectious disease and ultimately the human behavior and established institutions that are detrimental to sustainable population health. The World Health Organization (WHO) has developed a similar DPSEEA (driving forces, pressures, state, exposure, effect, actions) model that in a similar way describes the interlinkage between human health and different driving forces and environmental change (WHO 1997
As such understanding increases, it will become more feasible to plan how to prevent new infectious disease emergence. Yet, because these are rare events, accurate predictions will remain daunting. It is already evident that inserting humans into complex ecosystems can lead to a variety of EIDs, but health outcomes depend on the economic circumstances of the human population. In poor and tropical communities, land use change can lead to major shifts in infectious disease patterns. For these situations, many conventional public health interventions can prevent several infectious diseases at relatively low cost. In rich and temperate-climate communities, the infectious disease shifts tend to be more disease specific, for example, in the case of Lyme disease and habitat fragmentation.
Research on deforestation and infectious disease.
Considering the deforestation that usually accompanies agricultural development, new conservation-oriented agriculture should be pursued. As discussed above, water project development and modern livestock management present major health disease risks. However, often the secondary unintended consequences can also wreak havoc; for example, a leaking dam may present greater risks than the reservoir itself. A distressingly large number of development projects not only have adverse effects on human health but also fail to attain their primary economic purposes in a sustainable manner.
Habitat fragmentation, whether caused by forest destruction, desertification, or land-use conversion, affects human and wildlife health and ecosystem processes. There is already much research undertaken by landscape ecologists on the consequences of habitat fragmentation for wildlife, especially larger animals. It would be important to study the effects of landscape fragmentation on public health hazards. Such research could entail three components. The first component consists of gathering baseline data, including using historical data where possible and beginning monitoring programs where necessary. Key data include identifying and quantifying the relevant pathogen load of wildlife, livestock, and human communities in fragmented landscapes. The goals of this data collection are, first, to identify key infectious diseases, both chronic and emergent or reemergent and, second, to document the consequences of fragmentation on relative abundance of wildlife and subsequent pathogen load. For example, the loss of large predators in fragmented habitats in the northeastern United States has led to a superabundance of rodent vectors for Lyme disease.
The second component of the research program would involve health impact modeling, primarily in three areas: a) estimating changes in the relative abundance of organisms, including infectious disease vectors, pathogens, and hosts; b) projecting potential vector or transmission shifts (e.g., should the Nipah virus shift to pulmonary as well as neurologic expression in humans as in swine); and c) projecting the impact of infectious diseases in a region on different geographic scales.
The results of these analyses, if successful, could support the third component of research: development of decision-support tools. Improved decisions on land-use policy could be made from a better understanding of costs and benefits to health and environmental decision makers. In all probability, however, they will be very location specific. For example, to construct an irrigation scheme in India would likely invite a malaria epidemic, whereas the same activity in sub-Saharan Africa may have little effect on malaria transmission. It is worth mentioning that costs and benefits could depend on the time course over which they are assessed. For example, some land-use changes can lead to short-term increases in transmission followed by longer-term decreases (e.g., irrigation and malaria in Sri Lanka) or vice versa (e.g., deforestation and cutaneous leishmaniasis in Latin America).
Policies to reduce microbial traffic/pathogen pollution.
In today’s interconnected world, it becomes very important to invest in the worldwide control of infectious diseases in developing countries, for example. It is also necessary to control transport to stem the flow from one place to the next.
Improved monitoring of trade is warranted in order to target infectious disease introductions. In the attempt to prevent the invasion of a pathogen (and drug-resistant organisms) into the vulnerable areas subject to land use changes, we need to pay greater attention to controls at the sources. We need to document and map these trades and investigate the vectors, the infectious diseases they harbor, and the populations they threaten. Risk assessment should guide surveillance and the development of test kits, targeting point-of-origin intervention to preempt these processes. Assessments must further include nonmarket costs (usually to the detriment of the environment and long-term sustainable health). We should communicate to both the exporters and consumers the need to make their trades clean, economically viable, and certified “clean and green” by an independent scientific agency at the source and/or destination. Additionally, strategies for screening travelers for pathogens that may be introduced to a region should be improved.
Centers of Excellence in Ecology and Health Research and Training.
One approach to developing the issues to which this article draws attention is the creation of a system of regional- or subregional-based interdisciplinary Centers of Excellence in Ecology and Health Research and Training. Based at regional universities and/or research institutes but with very close links to the surrounding communities, these centers would have the following objectives:
- Providing information based on good science to local communities about the links between environmental change and public health, including the factors that contribute to specific infectious disease outbreaks. The new research agenda must gather information on household and community perspectives about proposals for the use of their land. These perspectives are key to assessing the cost/benefit of a proposed project. Training local professionals in environmental, agricultural, and health science issues, with a particular focus on granting degrees in a new “trans”-discipline linking health and the environment, would be emphasized.
- Acting as centers of integrated analysis of infectious disease emergence, incorporating perspectives and expertise from a variety of natural, social, and health sciences. Research activities would range from taxonomy of pathogens and vectors to identifying best practices for influencing changes in human behavior to reduce ecosystem and health risks.
- Incorporating a “health impact assessment” as an important cross-sectorial decision-making tool in overall development planning (parallel to an environmental impact assessment), along with the need for doing more research.
- Equipping professionals with the ability to recommend policy toward maintaining ecosystem function and promoting sustainable public health for future generations. For example, the link between forest fragmentation and Lyme disease risk could lead to preserving more intact tracts of forest habitat by planning “cluster” housing schemes.
Implementing research and policy programs.
In selecting areas for research and the placement of centers of excellence, it is important to choose geographically representative, highly diverse areas around the world. In addition, research projects should take place in regions or landscapes that have both well characterized and less characterized patterns of infectious disease emergence or transmission for comparison purposes. Local health and environment professionals, who are in the best position to understand local priorities, should make the choices within each region for initial research areas and sites.
Addressing trade-offs among environment, health, and development.
There are some inherent trade-offs when considering land-use change and health. They are ethical values, environmental versus health choices, and disparities in knowledge and economic class. Trade-offs are between short-term benefit and long-term damage. For example, draining swamps may reduce vector-borne disease hazards but also destroy the wetland ecosystem and its inherent services (e.g., water storage, water filtration, biologic productivity, and habitats for fish and wildlife). Research can help decision making by identifying and assessing trade-offs in different land-use-change scenarios. Balancing the diverse needs of people, livestock, wildlife, and the ecosystem will always be a prominent feature.