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In this interesting article Waltner-Toews discusses the notion of ecosystem health and the insights it can provide for confronting the emergence and complexity of infectious diseases. According to him, those who possess the skills required to prevent and treat disease are ill-equipped to promote health. As some authors have pointed out before (Levins et al., 1994) he notes that disease prevention and control programs tend to ignore complexity and may, in fact, create ill-health. In his view, these failures result from our limited ability to predict outcomes and from our incapacity to account for holarchy and to understand non-linear interactions, chaotic attractors, and catastrophic thresholds in complex ecosystems.

Background information is necessary to understand the contributions and possible limitations of the ecosystem health approach proposed in this article. The notion of ecosystem health was first introduced by Rapport (1989) in an international meeting of the Association for Great Lakes Research and was developed later in other publications. In 1994, an international workshop on Agrosystem Health was organized by the University of Guelph with the support of IDRC. The discussions focused then on the contributions of the health paradigms to understand agroecosystems: vigor, resilience, and system organization, as suggested by Constanza (1994), and on the comparative advantages of the ecosystem. health concept over sustainability.

According to some authors (Smit & Smithers, 1994), for practical purposes the concepts were essentially the same, while other authors (Waltner-Toews, 1994) suggested that the health paradigm could provide a more appropriate basis for thought and action in agroecosystems. In this workshop, it was noted that sustainability and ecosystem health are tightly connected but are distinct concepts and that their more exact relationship remained to be determined.

Simultaneously, in the health field, some research groups developed ecosystem approaches to emergence and resurgence of infectious diseases worldwide. In 1991, in the United States, the Harvard New Diseases Group started a transdisciplinary research agenda in this area. Contributions were published later in the Annals of the New York Academy of Sciences (Wilson et al., 1994) and in other publications.

The issues discussed in Waltner-Toews' article can therefore be explored from two distinct epistemological perspectives: the ecologist's viewpoint, the contribution and usefulness of the health paradigm to understand and intervene on complex ecosystems; the public health perspective, the contribution of the ecosystem health notion (or metaphor, as suggested by Gallopín, 1994), to understanding and confronting the complexity of epidemiological profiles and the emergence of diseases.

First, some ecologists view the incorporation of the health paradigm for ecosystem research and monitoring change to maximize ecosystem health as problematic (Gallopín, 1994). The definition of health is crucial here. If health is defined as something that might be kept constant ("people die and ecosystems evolve"), then the notion of ecosystem health would not be appropriate to deal with sustainability in a dynamic and changing world. In contrast, other arguments, as proposed by Waltner-Toews in this article, provide a definition of health that can be broader, incorporating into this approach the notions of balance and harmony on the one hand and capacity to respond to changing environments on the other. From this perspective, the notion of ecosystem health can provide interesting insights.

Second, from the public health perspective the issues concerning the contributions of ecosystem health are even more complex. On the one hand, the ecosystem health notion can provide a crucial and missing ecosystem approach to understand the complexity of epidemiological profiles and the emergence of diseases. On the other, in a world where the economy and societies are being transformed by accelerating globalization and local policy communities are gaining political and economic power, it is important to stress that the conceptual force of the ecosystem health approach will certainly depend on our capacity to incorporate these social and political dimensions into a new theoretical framework.

Ecosystems have become complex social ecosystems (agro-industrial ecosystems and urban ecosystems) increasingly transformed by human activities, interacting and expanding in ways never before imagined. Globalization is increasing local demands for political power and participation, stimulating pressures for social inclusion in sustainable development, particularly in developing countries where social exclusion and poverty are dramatic. Therefore, monitoring change in the structures of ecosystems leading to niches for potential pathogens to emerging diseases, as proposed by Waltner-Toews, requires a new approach. On the one hand, ecological frameworks consider the variability of the physical and biotic environment but tend to homogenize people without taking into account different social systems, classes, or even the commodity as a physically powerful social construct, tending to omit social aspects of survival. On the other, the social sciences correspondingly make use of social differentiation without linking it to patterns of exposure and vulnerability to the biological and physical environment.

Contributions by the social and political sciences to understanding and dealing with the macro-processes permeating ecosystems and health reform strategies should be integrated into a new "social ecosystem health" paradigm (Levins et al., 1994; Possas & Marques, 1994; Levins & Lopez, 1999). Bringing together the socioeconomic and biophysical dimensions of health and trying to understand how social and ecological variables appear to behave in complex systems, as Waltner-Toews has suggested, require more than incorporating these new elements into theory. It is necessary to bridge in a new theoretical framework the conceptual and methodological gaps between paradigms from social sciences and ecology, which have historically been kept apart.

CONSTANZA, R., 1994. Supplementary comments on the concept of ecosystem health. In: Agroecosystem Health: Proceedings of an International Workshop (N. O. Nielsen, ed.), pp. 29-30, Ottawa: University of Guelph/IDRC/CGIAR.

GALOPIN, G. C., 1994 Agrosystem health: A guiding concept for agricultural research?. In: Agroecosystem Health: Proceedings of an International Workshop (N. O. Nielsen, ed.), pp. 51-65, Ottawa: University of Guelph/IDRC/CGIAR.

LEVINS, R.; AWERBUCH, T.; BRINKMAN, U.; ECKARDT, I.; EPSTEIN, P.; MAKHOUL, N.; POSSAS, C. A.; PUCCIA, C.; SPIELMAN, A. & WILSON, M. E., 1994. The emergence of new diseases. American Scientist, 52:60.

LEVINS, R. & LOPEZ, C., 1999. Toward an ecosocial view of health. International Journal of Health Services, 29:261-293.

POSSAS, C. A. & MARQUES, M. B., 1994. Health transitions and complex systems: A challenge to prediction? Annals of the New York Academy of Sciences, 740:285-296.

RAPPORT, D. J., 1989. What constitutes ecosystem health? Perspectives in Biology and Medicine, 33: 120-132.

SMIT, B. & SMITHERS, J., 1994. Sustainable Agriculture and Agroecosystem Health. In: Agroecosystem Health: Proceedings of an International Workshop (N. O. Nielsen, ed.), pp. 31-38, Ottawa: University of Guelph/IDRC/CGIAR.

WALTNER-TOEWS, D., 1994. Ecosystem health: A framework for implementing sustainability in agriculture. In: Agroecosystem Health: Proceedings of an International Workshop (N. O. Nielsen, ed.), pp. 8-20, Ottawa: University of Guelph/IDRC/CGIAR.

WILSON, M.; LEVINS, R. & SPIELMAN, A., 1994. Disease in Evolution. Annals of the New York Academy of Sciences, 740.