Changing Vector Ecologies: Political Geographic Perspectives
Jonathan D. Mayer, Ph.D.1
Addressing only the changes in vector ecologies that have resulted from globalization is too narrow an approach for understanding the overall changes in disease ecology. If vector ecologies that are relevant to emerging infections are altered, the two relevant causal questions are how and why. Answers to these questions transcend biological factors. The crucial issue is to understand how changing social and human ecologies have interacted with alterations in vector ecologies to produce new patterns of disease. It is only through understanding social, environmental, and biological interactions that one can gain an understanding of static patterns or temporal changes in disease distribution. The Institute of Medicine’s 1992 report on emerging infectious diseases (IOM, 1992) gave implicit credence to this argument, since five of the six factors in emergence (human demographics and behavior, technology and industry, economic development and land use, international travel and commerce, and breakdown in public health) are explicitly social in nature, and the sixth (microbial adaptation and change) is partly the result of social behavior and social change. However, social scientists have been minimally involved in research on emerging disease since 1992, and little social science has been incorporated into epidemiologic, public health, or infectious disease research and policy on emerging infections.
THE NATURE OF GLOBALIZATION
Globalization is a term often used in describing contemporary society, but it is frequently ill defined and misunderstood, and its definition is subject to argument. Indeed, its very conceptualization is “contested” (Buse and Walt, 2002, p. 42). It is frequently taken to mean the process of increasing global interdependency, but this is only part of the process of globalization as understood by contemporary social scientists. In the various descriptions and analyses of the effects of globalization that are found in the health sciences, interdependency, as manifested by increasing international transportation, is seen as the most salient feature that can affect the redistribution and movement of infectious disease. There is a fundamental tension that pervades both the popular and scholarly literature on globalization: globalization as a factor that promotes well-being and economic opportunity versus globalization as an alienating social force that marginalizes those at the periphery of societies.
What, then, is globalization? First, it is important to note that the health sciences could benefit from the explicit understanding of globalization as developed in international relations, political economy, political geography, and other disciplines. As noted in a recent article on the implications of the globalization of cholera for global governance: “an understanding of global health issues at the turn of the twenty-first century could benefit substantially from the voluminous literature on globalization from international relations, including the subfields of social and political theory and international political economy. This is a rich and voluminous literature. It documents what structural changes are occurring toward a global political economy, how power relationships are embedded within this process of change, what varying impacts this may have on individuals and groups…” (Lee and Dodson, 2000, p. 213). Clearly, then, globalization is something that is more profound than merely an increase in international interdependency and international connectivity. Moreover, changes in disease patterns that are the result of globalization are as old as globalization itself: many decades and perhaps centuries old, and the result of long-established historical transformations.
Globalization certainly contains elements of increasing global interdependency, the decline of international boundaries as deterministic social constructs, and the erosion of distance as an inhibitor of human interaction for some but not all segments of societies—though the effects of distance are highly variable, and some societies remain locally constrained. In addition, the term refers not only to increasing movement of goods and people or, as transportation geographers and regional scientists refer to such movement more generally, “spatial interaction,” but also to the movement of capital. What is the movement of capital, and why is it relevant here? The
movement of capital refers to the transferability of money, in its simplest sense, and to the increasing ties that characterize the world’s financial system. The importance of this dimension of globalization is reflected in the fact that the “development of global financial markets” is Soros’ (2002) operational definition of globalization. Thus, when an environmental project is financed in a country by funds from outside that country, it is the result of a global system of finance. This dimension has direct implications for local vector ecologies in the sense that a dam, for example, that is financed from outside the country, and perhaps even planned by a coalition of local and international environmental planners, may then alter the local breeding habitats of potential disease vectors, thereby changing the potential exposure to vectorborne or waterborne diseases.
Yet another dimension of globalization is changes in the locus of power in global decision making. One of the consequences of globalization, many argue, is that some localities are marginalized in their ability to control what happens to local society, and others are made more central and are able to project power over great distances. Society is seen as reflecting this reality in its increasing uniformity, erosion of locally controlled commodities and markets, and general loss of control. It is this dimension that is so politically controversial (e.g., Sassen, 1998) and is responsible for protests at the venues of organizations that are seen as representative of and as advocating increased globalization, such as the 1999 World Trade Organization meeting in Seattle. The process of globalization is nicely summed up by Joseph Stiglitz, former chief economist at The World Bank: “it is the closer integration of the countries and peoples of the world which has been brought about by the enormous reduction of costs of transportation and communication, and the breaking down of artificial barriers to the flows of goods, services, capital, knowledge, and (to a lesser extent) people across borders” (Stiglitz, 2002, p. 9).
THE SOCIAL ECOLOGY OF HUMAN DISEASE
Disease ecology explains infectious disease patterns in terms of the interactions of people and the environment. In the broadest sense, a social approach to disease ecology, even as conceived by May (1958), whose disease ecology was more medical than social, views infectious disease patterns as the result of cultural, social, behavioral, environmental, and biological interactions. In a dynamic sense, alterations in disease ecological relationships through environmental modifications therefore could be expected to alter human–vector relationships. The effects of land clearance projects, dam construction, and other environmental modifications can be seen in a number of examples.
Classic geographic disease ecology has developed incrementally since
World War II. Jacques May was a French surgeon in French Indochina who became intrigued by the interaction of local social and cultural patterns with equally local environmental conditions to produce patterns of contagion for a number of infectious diseases. He eventually gave up his surgical career to become the medical geographer at the American Geographical Society in New York City, where he produced numerous volumes and papers on disease ecology (e.g., May, 1958). As significant as his work was, he did not consider the impact of other regions on local conditions. Interregional patterns of commodity shipments, cultural contact, and cultural change are all aspects of global interdependency that were apparent decades ago. Moreover, May also did not consider the effects of power and politics on local disease conditions. Thus, disease ecology traditionally considered isolated regions in the absence of interaction, temporal change, and political power. The same framework saw fruition in the Soviet Union with the landscape epidemiology of Pavlovsky (1966) and his identification of local “nidi” of disease.
There are a number of examples of how globalization affects local disease ecologies and, by extension, human–vector interactions that are directly relevant to emerging infectious diseases. Most obviously, transportation is a benchmark of globalization because of the parallels between regional interdepedencies and the globalization phenomenon. Transportation moves commodities and people. Vectors may be unintentionally transported on either the transportation vehicle or the commodities that are being moved. An example of the former is the probable movement of anophelines from tropical to temperate areas and the occurrence of many instances of “airport malaria” surrounding major international airports, such as Detroit Metropolitan Airport, JFK Airport, Newark International, Amsterdam’s Schiphol, London’s Heathrow, and many others. An example of the transport of vectors on commodities is the introduction of the Asian tiger mosquito, Aedes albopictus, to the North American continent on rubber tires that were shipped to the port of Houston. Ae. albopictus is one of the vectors of dengue fever.
The movement of people is less subtle in the ways it can alter disease ecologies. Both short-term movement—travel—and longer-term movement—migration—are typical of globalization and have the potential to spread emerging infections. People may be infected with diseases endemic to one region and introduce those diseases to another region. This is almost certainly how HIV was introduced to North America, for example, and how fluoroquinolone-resistant gonococci were introduced from Asia.
A recent example of how movement may have introduced a new disease into a nonendemic area is the introduction of West Nile virus into North America. The most common vector of West Nile virus in the United States, the common household mosquito, Culex pipiens, was already ubiq-
uitous in the New York metropolitan area. The mechanism of introduction is unclear, but it was probably through one of the following means: (1) movement of an infected individual into the New York City area; (2) movement of an infected bird, either via an airplane or other transportation vehicle or, less likely, via avian migration; (3) movement of an infected vector via airplane; or (4) shipment of an infected animal reservoir to the New York area. There may be no way to trace the precise means of introduction, but what is certain is that the disease was not present in North America until 1999 but was present on many other continents. Putatively, one may conclude that the infection came from elsewhere, almost certainly via transportation vehicle. The human–ecosystem relations were suitable in the New York metropolitan area to maintain the infection during the summer of 1999, and then to support its spread during subsequent summers via both human movement and bird migration.
THE POLITICAL ECOLOGY OF DISEASE
One of the useful ways of conceptualizing the impacts of decisions on local disease ecologies uses a combination of political economy and cultural ecology. Together they constitute the political ecology of disease (Mayer, 1996), and this construct has been applied to emerging infectious diseases (Mayer, 2000). These concepts require further explanation.
Political ecology more generally is “the attempt to understand the political sources, conditions, and ramifications of environmental change” (Bryant, 1992, p. 13). Thus, most broadly, the political ecological approach seeks to understand the unintended consequences of environmental decisions, and particularly those consequences that alter human–environment relations.
A dimension of globalization that is greatly emphasized in the social sciences but has received scant attention in the public health literature is the global flows of capital or, as Soros (2002) would have it, the internationalization of financial markets. There are many indirect consequences of this for public health, but the most direct consequence for emerging infections is that the flows of capital have financed projects that have altered human– environment relations at both the local and regional levels. Past examples of this are the construction of the Aswan Dam in Egypt and the Volta River Project in Africa. Unintended consequences of these large-scale water projects were the increased range and incidence of schistosomiasis, onchocerciasis, and malaria upstream of the dams. A more contemporary example is the construction and anticipated completion of the Three Gorges Dam in China. This massive project on the Yangtze River, designed explicitly for powering Chinese industrial growth and furthering China’s position in the global economy, will almost certainly introduce schistosomiasis
(Schistoma. japonicum) into a nonendemic area upstream of the dam (e.g., Sleigh and Jackson, 1998; Xu et al., 1999). The ecological conditions will be conducive to schistosomiasis transmission, and there will be a great deal of human contact with the upstream lake—another case of the desire to be a more active participant in the world economy, and of the movement of global capital altering regional ecological conditions and affecting the transmission of emerging infections.
To generalize about the example of water projects that inevitably alter local vector ecologies, the purpose of these projects is usually to fuel economies through the generation of hydroelectric power. Typically, this has involved financing from outside the local area, providing an example of capital flows that affect disease transmission in more local areas. In the case of projects such as the Three Gorges Dam, financing is almost entirely from domestic sources (though some of that financing comes, indirectly, from business growth due to globalization), but a major purpose of the dam is to provide power to industries that will allow China to participate more fully in the global economy. Typically, there are unintended or unforeseen consequences for disease transmission or introduction in the local area that combine human patterns of interaction and behavior and biological parameters of vector habitat (Hunter et al., 1993). These general principles are not confined to water projects but are equally applicable to land clearance and other economic development projects that alter human–environment relations. For example, the land clearance in Malaysia that was done to permit the construction of rubber plantations, aimed at economic development and the promotion of an export economy, resulted in notable increases in malaria transmission among laborers on the plantation. This was due to the alteration in environmental conditions and vector ecology that made the landscape conducive to anopheline breeding and vastly increased contact by laborers with areas newly populated by anophelines (Meade, 1976).
GLOBAL WARMING AND VECTORBORNE DISEASE
In recent decades, many have noted the movement of vectors and alteration of vector ecologies not involving transportation. Of primary concern in this regard has been the movement of disease vectors, particularly malaria, as a result of global warming (Rogers and Randolph, 2000). Despite rhetoric to the contrary, however, any conclusions about whether global warming is actually causing increases in vectorborne disease prevalence or the movement of vectorborne disease into previously nonendemic areas are quite tentative.
The logic behind claims that global warming is increasing the range of vectorborne disease is quite appealing. Human activities, including industrialization, fossil fuel burning for heat and transportation, and deforesta-
tion cause global warming as a result of the increase of greenhouse gasses and the elimination of carbon sinks (through deforestation). The evidence for this is quite conclusive. It is equally certain that many aspects of vector behavior, including the range of habitability, are driven in part by temperature. Thus, it would appear reasonable to conclude that with global warming, the latitudinal range of tropical and subtropical vectors would move north in the northern hemisphere, south in the southern hemisphere, and higher in mountainous areas. In other words, many of the human activities that take place concomitantly with globalization appear to have the potential to alter the spatial distribution of vectors.
When subject to closer scrutiny, however, the situation is not as clear-cut. Multivariate mathematical and statistical models of transmission dynamics suggest that when variables in addition to temperature are included, the global incidence of malaria could actually decrease with global warming. This is due, in part, to the fact that rainfall would probably also increase, and local anopheline breeding areas would then be washed out. This would tend to override the effects of increased temperature. Moreover, some malarial vectors breed preferentially in warmer temperatures, and others prefer cooler temperatures and cannot even survive in warmer conditions; thus it is difficult to generalize about malaria, which is transmitted by dozens of anopheline species. Moreover, local ecological conditions are far more significant than the generalization of ecological conditions to a larger scale. Mathematical–spatial models are inevitably too coarse and lack sufficient geographic resolution. As Hackett observed in 1937: “Everything about malaria is so molded and altered by local conditions that it becomes a thousand different diseases and epidemiological puzzles. Like chess, it is played with a few pieces, but is capable of an infinite variety of situations” (Hackett, 1937, p. 266).
Adding to the uncertainty of whether global warming has increased vectorborne disease incidence is the fact that empirical studies have been contradictory. Some have correlated recent increases in malaria and dengue incidence with temperature increases, while others have found little or no change in incidence. One intriguing group of analyses used the El Niño Southern Oscillation (ENSO) to simulate, in the short term, longer-term climate changes. These studies then examined the effects of temperature and rainfall fluctuations on vectorborne disease incidence. Again, the results of these studies were contradictory. Moreover, because the weather fluctuations of ENSO are short-term, on the order of several years at the most, and global warming occurs over decades, the use of the ENSO phenomenon does not allow for the social adaptations to climate change that could mitigate its effects. As intriguing as the use of ENSO is as a surrogate for actual climate change, it does not mimic actual long-term changes in climate.
Thus, there is still uncertainty concerning the effects of climate change on vector ecologies and disease incidence. Existing mathematical models are not sophisticated enough to be truly predictive (NRC, 2001), and empirical studies are contradictory because the actual spatial patterns of disease that have occurred with climate change have been geographically variable, even under similar climatic conditions. This is probably because of the extreme sensitivity of local vector ecologies to local physical conditions and to human social and behavioral patterns. Few of the models and empirical studies have considered elements of social structure, demographic or settlement patterns, or human behavior. Rather, they have concentrated too narrowly on the physical and biological variables, and on simplistic deterministic models of vector behavior that are driven by temperature alone.
It is regrettable that there has been so little integration of social scientific concepts into the study of emerging infectious diseases, despite the fact the emergence of new diseases is due largely to social and geographic change. Rather, the vast preponderance of research and policy directed toward disease emergence has been explicitly biological in nature. What is necessary is a synthesis of biological, social, and political concepts to reach an overall understanding of emerging infections. This is particularly true in the context of globalization. One of the consequences of the lack of inclusion of social scientific understanding has been a restrictive definition of globalization in public health—an understanding that has included only the surface phenomena of transportation of people and commodities and of migration. Understanding the relationships between changing vector ecologies and globalization also necessitates an understanding of how political and economic decisions, particularly decisions that alter the landscape, in turn change human–environment relations in local and regional contexts.
Bryant RL. 1992. Political ecology: An emerging research agenda in third world studies. Political Geography 11(1):12–36.
Buse K, Walt G. 2002. Globalisation and multilaterial public-private health parternerships: Issues for health policy. In: Lee K, Bruce K, Fustukian S, eds. Health Policy in a Globalising World. Cambridge, UK: Cambridge University Press. Pp. 41–62.
Hackett LW. 1937. Malaria in Europe: An Ecological Study. Oxford, UK: Oxford University Press.
Hunter JM, Rey L, Chu KY, Adekolu-John EO, Mott KE. 1993. Parasitic Diseases in Water Resources Development: The Need for Intersectoral Negotation. Geneva, Switzerland: WHO.
IOM (Institute of Medicine). 1992. Emerging Infections: Microbial Threats to Health in the United States. Washington, D.C.: National Academy Press.
Lee K, Dodson R. 2000. Globalization and cholera: Implications for global governance. Global Governance 6(2):213–236.
May JM. 1958. The Ecology of Human Disease. New York: M.D. Publications.
Mayer JD. 1996. The political ecology of disease as one new focus for medical geography. Progress in Human Geography 20:441–456.
Mayer JD. 2000. Geography, ecology, and emerging infectious diseases. Social Science and Medicine 50(7–8):937–952.
Meade MS. 1976. Land development and human health in West Malaysia. Annals of the Association of American Geographers 66:428–439.
NRC (National Research Council). 2001. Under the Weather: Climate, Ecosystems, and Infectious Diseases. Washington, D.C.: National Academy Press.
Pavlovsky EN. 1966. The Natural Nidality of Infectious Disease. Urbana, IL: University of Illinois Press.
Rogers and Randolph. 2000. The global spread of malaria in a future, warmer world. Science 289(5485):1763–1766.
Sassen S. 1998. Globalization and Its Discontents. New York: New Press.
Sleigh A, Jackson S. 1998. Public health and public choice: Dammed off at China’s Three Gorges? The Lancet 351(9114):1449–1450.
Soros G. 2002. George Soros on Globalization. New York: Public Affairs.
Stiglitz J. 2002. Globalization and Its Discontents. New York: W.W. Norton.
Xu XJ, Yang XX, Dai YH, Yu GY, Chen LY, Su ZM. 1999. Impact of environmental change and schistosomiasis in the middle reaches of the Yangtze River following the Three Gorges construction project. Southeast Asian Journal of Tropical Medicine and Public Health 30(3):549–555.