First published in Trends in Ecology & Evolution (Tree), Vol 10, No 7, July 1995
Agriculture and medicine have been confronted by disturbing surprises in recent years. Antibiotics gave rise to new pathogens, pesticides increased pest problems, the introduction of high-yielding crops increased human inequality. Infectious diseases, such as tuberculosis, cholera, malaria, dengue and rabies, there were in decline began to expand again, and one after another seemingly new diseases were identified. Legionnaire’s disease, AIDS, Venezuelan hemorrhagic fever, mad cow disease, bean golden mosaic virus, Lassa fever, African swine fever, gemini virus of tomato, Argenting hemorrhagic fever, new fish poisonings, a distemper-like virus of marine mammals, leaf-yellowing syndrome of sugar cane and virulent strains of the familiar E. coli are only a sampling from a growing list of newly recognized infections.
If we step back from the details of the various surprises, we can discern the outlines of a general phenomenon: something is not quite right in the way our species’ current societies are relating to the rest of nature or in the way we attempt to fix what goes wrong. There is a disjunction in science between the exquisite sophistication of the small and the irrationality of the enterprise as a whole.
The only way science has of studying the new is by assuming it is like the old.1 The differences among scientific approaches lie only in which ‘olds’ are chosen as the starting point for studying the new, and which are accepted without question. Do we assume that the state of the system remains the same, or that the short- or long-term trends continue, or that the dynamics that impel those trends persists?
In general, the greater the surprise, the more broadly we have to look to find the science we need and the less we can assume constancy. In the face of the massive surprises and counterproductive outcomes in public health and agriculture, we need as broad a base as possible for an integrated epidemiology.
First, workers in public health, veterinary medicine and plant pathology have to recognize their particular fields as instances of the broader study of parasitism as a universal phenomenon of evolutionary ecology.2 The sorts of problems that need investigation include comparative epidemiology across species of hosts, vectors and pathogens; evolutionary plasticity of pathogenic taxa; the relation between the taxonomic distance between pathogens and clinical similarities; coexistence of pathogens in the same host populations; the patterns of response to natural selection of all the species involved; environmental adaptability of vectors and their natural enemies; population genetics of pathogens in the course of individual infections and outbreaks; and patterns of genetic exchanges across ‘species’ borders. Meanwhile, ecologists should consider parasitism to be at least as interesting as predation and individul mammals as interesting as complex habitats for coexisting microorganisms.
Second, causation must be understood in the broad sense as residing in much larger wholes than are usually considered by the microbiological or clinical paradigms. Thus, an epidemic is 'caused’ by a microorganism of a particular biology, in an environment where it can survive, coming in contact with an exposed and vulnerable population, under conditions that permit successful transmission and infection, allowing enough reproduction within a host to produce disease in the individual and sufficient propagation to initiate enough new cases to affect a population. From this perspective, the current pandemic of cholera can be recognized as being possibly ‘caused’ by plankton blooms increasing the populations of Vibrio cholerae, international shipping transportinng them in coastal ballast water, the dismantling of social services in Latin America, and the reluctance of governments to acknowledge outbreaks that might affect the tourist trade, among other factors. The plankton blooms can be related to eutrophication of coastal waters owing to erosion, agricultural fertilizers and urban sewage as well as the warming of the seas, and the dismantling of social services can be related to budgetary crisis resulting from Third World debt and World Bank insistence on progress through impoverishment.
Third, all the tools of modern biology, including modern biogeography, modern population genetics, modern ecology, modern systematics and bioclimatology, as well as the disciplines that usually appropriate the designation ‘modern,’ have to be brought to bear on the complexity of contemporary epidemiology without the ranking that is usually inversely proportional to the size of the object studied.
Fourth, epidemiological models must become socialized. The parameters that are usually treated as constant, such as contagion rates and recovery rates, must be seen as reflecting class and other social inequities and the limited therapeutic options offered by industries that create knowledge selectively for ease of conversion into commodities. They are also sensitive to shifting behaviors that change with perceptions as to the prevalence of the disease. But how quickly behavior responds depends on long-term beliefs as to whether people can influence what happens to them and whether they can understand the world—beliefs that themselves reflect the realities of the lives of different groups of people. Furthermore, the equations of epidemiology must be able to reflect evolutionary responses of the pathogens to changing patterns of intervention. The ovbious complexity of such models requires a specific effort to develop the mathematical tools appropriate to public health.
Finally, our sciences have to look at themselves reflexively using the tools of history, sociology and philosophy of science, so as to challenge critically the institutional and intellectual boundary conditions that keep our efforts fragmented, reductionist and, in the long run, ineffective.
There are stirrings in these directions—books on evolutionary medicine,3 proposals for a field of ecosystem health,4 calls for inter- or multi- or trans-disciplinary approaches. But there are also strong counter influences. When budgets are cut, theoretical explorations are regarded as luxuries. When research is subsidized, private funders want marketable products and the government wants a search for sure things of a familiar sort that can be justified to legislatures, while program directors see their missions are more narrowly defined. Academics at the vulnerable points of their careers are evaluated by their contributions within department boundaries and their ‘proven success at mobilizing resources.’ The result is excellence in tactics, and lip service, at best to strategies.
Thus we are at a juncture where the practical urgency and intellectual needs for an integrated epidemiology come into conflict with the changing structures and practices of the knowledge industries. The outcome is still in doubt.
References
1. Levins, R. Ecosystem Health (in press)
2. Wilson, M.E., Levins, R. and Spielman, a.. eds (1994) Ann. N.Y. Acad. Sci. 744
3. Lappé, M (1994) Evolutionary Medicine, Sierra Club
4. Rapport, D. Ecosystem Health (in press)
