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Climate and Infectious Diseases: The Past as Prologue

The following review addresses the origins of environmental medicine and its legacy for our current understanding of climate and infectious disease linkages, and reviews some of the important historical milestones in the fields of meteorology and infectious disease epidemiology.

ORIGINS OF ENVIRONMENTAL MEDICINE

Many early civilizations related weather to the appearance of disease and topography to the persistence of disease in a region or population. The most lasting formulation was attributed to Hippocrates (~460 to 377 B.C.), who linked responsibility for disease to observable natural phenomena rather than to deities or demons. The seasonal appearances of particular diseases formed the basis of the Hippocratic treatise on epidemics, and many aphorisms handed down over the centuries similarly attributed various morbid conditions to weather and seasonal change (Hannaway, 1993). Hippocratic medicine focused on predicting the course and outcome of an illness through detailed observations of clinical symptoms and through associations with the way that winds, waters, and seasons appeared to make some diagnoses more likely (Smith, 1979).

Throughout the first millennium, epidemics were explained by changes in the course of the stars and other atmospheric, meteorological, and terrestrial phenomena. Popular ideas of being “under the weather” and the association of some regions with either illness or good health were used to explain the spread of disease among people who otherwise had little in common (Seargent, 1982). However, this tidy synthesis began to break down with the appearance of bubon-



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Page 12 2 Climate and Infectious Diseases: The Past as Prologue The following review addresses the origins of environmental medicine and its legacy for our current understanding of climate and infectious disease linkages, and reviews some of the important historical milestones in the fields of meteorology and infectious disease epidemiology. ORIGINS OF ENVIRONMENTAL MEDICINE Many early civilizations related weather to the appearance of disease and topography to the persistence of disease in a region or population. The most lasting formulation was attributed to Hippocrates (~460 to 377 B.C.), who linked responsibility for disease to observable natural phenomena rather than to deities or demons. The seasonal appearances of particular diseases formed the basis of the Hippocratic treatise on epidemics, and many aphorisms handed down over the centuries similarly attributed various morbid conditions to weather and seasonal change (Hannaway, 1993). Hippocratic medicine focused on predicting the course and outcome of an illness through detailed observations of clinical symptoms and through associations with the way that winds, waters, and seasons appeared to make some diagnoses more likely (Smith, 1979). Throughout the first millennium, epidemics were explained by changes in the course of the stars and other atmospheric, meteorological, and terrestrial phenomena. Popular ideas of being “under the weather” and the association of some regions with either illness or good health were used to explain the spread of disease among people who otherwise had little in common (Seargent, 1982). However, this tidy synthesis began to break down with the appearance of bubon-

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Page 13 ic plague in the 1340s. The first great pandemic was preceded by a rare conjunction of three planets, which provided a convenient explanation for the extraordinary mortality. But subsequent plague epidemics were not so easily linked to meteorological or cosmological phenomena. Moreover, the specific recurrence of identical pathological features—a large swelling in particular locations on the body—linked the new disease with a few designated “contagions,” diseases that were thought to be transmitted through contact (Nutton, 1983; Pelling, 1993). On a more practical level, the extraordinary costs of plague brought a demand for novel strategies in public intervention. In order to predict and manage the local appearance of an epidemic, Italian bureaucrats in the fifteenth century designed mortality registers as a way to anticipate and monitor epidemic disease, leading to the study of temporal and geographical spread of infection. Surveillance and containment practices were invented piecemeal over the next two to three centuries, with greater attention paid to prevention and to populations at greatest risk. Plague victims and their household contacts were segregated during epidemics, which helped reinforce observations that disease was caused by local miasma (an unhealthy environment) or by contagions running rampant in the segregated population. In order to escape containment regulations, people urged physicians to distinguish plague from among the various types of buboes (i.e., swollen glands) and fevers, and this brought a new emphasis on clinical diagnosis (Cipolla, 1981; Slack, 1985; Carmichael, 1991; Pullan, 1992). The theories of Copernicus, Galileo, Descartes, Newton, and other natural philosophers of the sixteenth through the eighteenth centuries displaced the ancient view that events on earth reflect the influence of heavenly bodies with the view that such events are subject to physical laws (Grant, 1994). The explanatory power of these physical laws led philosophers and investigators in the life sciences and medicine to search for a law-like synthesis comparable to Newton's while trying to salvage as much as possible of ancient scientific wisdom. The chosen path for the study of disease was the collection of data, both epidemiological and meteorological. From 1650 until 1850, Western science and medicine sought a comfortable synthesis of the physical and life sciences that would accommodate the vast array of new observations (Glacken, 1967; Barzun, 2000). Weather-related observations intrigued both physicians and “natural philosophers.” Although histories of the development of meteorology, mathematics, and mapping often lack description of the relationship with medicine and health, the interests of many pioneers in these fields were propelled by the desire to use the scientific collection of data to understand geographic patterns of disease (Jordanova, 1979; Riley, 1987). THE EARLY MERGER OF METEOROLOGY AND MEDICINE The quests to understand weather, climate, and disease all posed significant methodological challenges. The Scientific Revolution brought mathematics to

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Page 14 the study of natural phenomena, with the invention of instruments such as barometers, hygrometers, thermometers, microscopes, telescopes, water pumps, rain gauges, and devices to measure wind velocity (Frisinger, 1977). Scientific societies dating to the 1600s, the Italian Accademia del Cimento and the English Royal Society, sponsored efforts to unify and analyze meteorological and medical information. During the eighteenth century, France and Germany began to gather and synthesize local records of death to try to uncover laws of population and disease (Desaive, 1972; Hannaway, 1972). Called “statists,” and their data “statistics,” these early epidemiologists of the eighteenth and early nineteenth centuries expected that their accumulated medical information would inform state policy (Porter, 1986). In the late eighteenth century, environmental medicine reached its apogee. New medical information led to broad social reforms such as the redesign of prisons, the construction of sewer and drainage systems, the early management of water resources, and the firm association of some locales and populations with increased risk of disease and death (Riley, 1987). Physicians of this era enthusiastically measured ambient temperatures, rainfall, seasonal changes in disease patterns, and many features of the natural topography, hoping to uncover an explanatory correlation between weather and disease. France even required a precise collection of meteorological data by physicians three times each day, on forms provided by the Royal Society of Medicine (Desaive, 1972; Hannaway, 1972). In North America the interdependency of medicine and meteorology provides an especially interesting example, because the U.S. national weather bureau emerged unambiguously from the effort to link weather and disease (Cassedy, 1986). Many prominent North Americans, including Thomas Jefferson and Noah Webster, persevered in their observations of climate and disease, and the practice remained routine in U.S. military and naval services until the 1880s (Whitnah, 1965; Fleming, 1990). Continuing interest in distinctive American storms helped inspire record keeping long after European physicians concluded that weather crises could not easily be linked to epidemics (Monmonier, 1999). Because of the severity of the monsoon season in South Asia, British physicians in India also pursued climatic explanations for epidemics far longer than their European counterparts (Fein and Stephens, 1987). Nonetheless, by the 1840s and 1850s the study of climate in Europe and North America became contested professional terrain. Early weather specialists, rather than physicians, began to collect and outline new uses for the data. Systematic collection of meteorological records led to the first American publications of theoretical meteorology (Whitnah, 1965; Kutzbach, 1979; Fleming, 1990). A decade before the Civil War, meteorologists seized the invention of the telegraph and envisioned storm warnings to reduce the losses from floods and cold waves. Aided by a network of telegraph operators and a central collection station at the Smithsonian Institution, scientists pursued the goal of using meteo-

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Page 15 rology for prediction and forecasting, although physicians still collected the weather observations that provided the data for meteorological publications. The military engulfed meteorology, and the first U.S. National Weather Service was created in 1869 as part of the Army's Signal Service. By 1880 meteorology's early origins in medicine were all but invisible, and medical study of epidemics turned away from prediction toward pursuit of disease agents in laboratory-based investigations. METEOROLOGY BECOMES AN INDEPENDENT DISCIPLINE Frederik Nebeker categorized the emerging communities of meteorology from the mid-nineteenth century until the end of World War I into observers, forecasters, and theoreticians (Nebeker, 1995). Of the three traditions, the observers, an empirically-based, observation-driven community of climatologists, maintained the most explicit links to the older tradition of environmental medicine. Historians of meteorology date the breakthrough in modern meteorology to the period during and immediately after World War I, when the demands of war increased interest in weather forecasting. The great pioneer of physics-based meteorology, Vilhelm Bjerknes, founded a school in Norway that was one of the first in theoretical meteorology to accept practical weather forecasting as a necessary application of science to meet societal goals (Friedman, 1989). Bjerknes and other twentieth-century meteorologists created the explicitly war-related terms of “fronts” and “air masses” to describe larger regional atmospheric processes. The prospect of war directed ever greater resources into meteorological research during the twentieth century. The enormous century-long collection of observational meteorological data fueled much of the effort to develop models for making weather predictions. Lewis Frye Richardson, a young mathematician and physicist, devised mathematical equations that would transform atmospheric data from one place and time into a prediction of the weather six hours later. His predictions erred by two orders of magnitude, but his 1922 book, Weather Prediction by Numerical Process, nonetheless represented a breakthrough on the path to theory-based forecasting. Meteorologists responded to Richardson's early attempts to predict weather with demands for more weather stations, more accurate instruments, better training for observers, standardization, and international collaboration (Ashford, 1985). A meteorology program organized by John von Neumann in 1946 revised the dynamic equations of Richardson and applied the new computer technology to weather forecasting models. In 1950 Neumann's group used the ENIAC computer to make the first numerical prediction of weather. The invention of the digital computer lifted the constraint on calculations (Aspray, 1990). With the aid of the computer, however, meteorologists were faced with the problem that very small differences in the initial dataset could yield extremely large differenc-

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Page 16 es in calculated predictions. In response they made refinements to the models and equations as understanding of atmospheric physics advanced. These advances led to unprecedented predictive success and a new mathematics, described by one of its pioneers, meteorologist Edward Lorenz. Lorenz described the theoretical problem of data in a presentation he made before the American Association for the Advancement of Science in 1972 with the memorable title “Predictability: Does the Flap of a Butterfly's Wings in Brazil Set Off a Tornado in Texas?” His application of the mathematics of chaos to weather forecasting demonstrated that prediction in chaotic systems was not impossible, just difficult. Lorenz also offered a corollary: “If the flap of a butterfly's wings can be instrumental in generating a tornado, it can equally well be instrumental in preventing a tornado.” In this model, prediction could also lead to intervention (Lorenz, 1993). MEDICAL ENVIRONMENTALISM WITHOUT METEOROLOGY Epidemiology emerged as a new science-oriented discipline during the 1840s and 1850s. Much of the success of early epidemiologists during the mid-nineteenth century came from studies on specific problems of purifying airs, waters, and places. Others sought to link poverty, hunger, criminality, or occupation to health problems at the population level. Many “miasmatists” or “environmentalists” also blamed disease on the presence of microscopic particles or polluting chemicals (Kunitz, 1987). When analyzing causes for human diseases, scientific medicine of the period from 1850 to 1920 tended to concentrate either on isolation of substances that caused particular diseases (microorganisms, poisons, and toxins) or on the association of disease with place, time, group, season, geographical climate, and more subjective concepts of race and social class. Some epidemiologists even pored over historical compilations of epidemics, famines, floods, and other natural disasters looking for patterns and cycles in much the same fashion as did contemporary meteorologists (Walford, 1879; Hirsch, 1886; Creighton, 1969; Corradi, 1972). The first “revolution” in epidemiology came after 1882 with Robert Koch's elaboration of the germ theory of disease (Winslow, 1980). Younger, statistically knowledgeable epidemiologists accepted the fundamental determinism of germ theory—that a particular microorganism would be found responsible for any given disease. Most Europeans adopted the gospel of urban water purification, followed by the laboratory evidence and logical proof of the germ theory (Evans, 1978). John Snow, a hero of mid-twentieth-century epidemiologists, demonstrated an association between cholera infection and the water delivered by one pump in London in 1854 (Vandenbroucke, 1989). However, Robert Koch did not actually prove the waterborne nature of cholera until 30 years later. Tracing an epidemic back to Calcutta, India, Koch first identified the vibrio or “comma” bacillus (from its shape) in the intestines of cholera victims. Because Koch

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Page 17 could not reproduce infection in an animal model according to his “postulates,” he devised a statistical geographical proof of the transmission of cholera (Coleman, 1987). Table 2-1 presents an outline of twentieth-century epidemiology constructed by Susser and Susser (1996). In this view the post-World War II era witnessed the “second revolution” in epidemiology, a reordered focus on environmental risk factors leading to chronic diseases. “Environmental” by the 1950s included behaviors or habits, along with the old “airs, waters, and places.” Notable studies included the association of tobacco smoking with lung cancer and of particular diets and lifestyles with cardiovascular mortality (Susser, 1985). Susser attributed this revolution primarily to Austin Bradford Hill's assimilation of modern statistical methodology to the study of chronic diseases. Less acknowledgment was made of “popular epidemiology” that focused on the health effects of toxins and industrial pollutants in the environment. Yet this aspect of public health received widespread public attention, especially following the publication of Silent Spring by naturalist Rachel Carson (1962). The firm commitment to statistical methodology and study design has been interpreted as a sign of maturity in the field of epidemiology. With the revisiting of older ideas on the correlations between climate and health, epidemiologists have recently begun to reexamine their disciplinary objectives (Susser, 1986; White, 1991; McMichael, 1994; Susser, 1998). Contemporary epidemiology appreciates the “web of causation” that underlies most public health issues and maintains a strong focus on modeling the complex relationships among multiple risk factors. Yet as noted by Krieger (1994), the field still lacks an “ecosocial” framework that embraces population-level thinking and that truly integrates social and biological understandings of health, disease, and well-being. TWENTIETH-CENTURY TELECONNECTIONS A critical advance in twentieth-century study of climate and weather came from Jacob Bjerknes, who linked the Southern Oscillation (shifts in atmospheric pressure in the eastern South Pacific and Indian oceans) to the periodic El Niño phenomenon (Quinn and Neal, 1992; Glantz, 1996). Recent success in forecasting the 1997/1998 El Niño has fueled the optimistic outlook for predictive meteorology and renewed interest in the history of weather events. Over the last half-century, significant collaborative enterprises between historians and meteorologists have produced a sustained inquiry into regional and global climate variability during the prehistoric and historical past (Wigley et al., 1992). Also, the last 40 or 50 years have witnessed unprecedented interdisciplinary collaboration between such fields as meteorology and oceanography, and widespread public education about weather and climate phenomena. Over this same time period, the epidemiological community has solidified its professional and disciplinary independence from the medical and public health communities and has built the statistical and

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Page 18 TABLE 2-1 Three Eras in the Evolution of Modern Epidemiology Era Approach Paradigm Analytical Approach Preventive Sanitary statistics (first half of nineteenth century) Miasma: poisoning by foul emanations from soil, air, and water Demonstrate clustering of morbidity and mortality Drainage, sewage, sanitation Infectious disease epidemiology (late nineteenth century through first half of twentieth century Germ theory: single agents relate one to one to specific diseases Laboratory isolation and culture from disease sites; experimental transmission and reproduction of lesions Interrupt transmission (vaccines, isolation of the affected through quarantine and fever hospitals, and ultimately antibiotics) Chronic disease epidemiology (later half of twentieth century) Black box: exposure related to outcome without necessity for intervening factors or pathogenesis Risk ratio of exposure to outcome at individual level in populations Control risk factors by modifying lifestyle (diet, exercise, etc.) or environment (pollution, passive smoking, etc.) SOURCE: Susser and Susser, 1996

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Page 19 mathematical sophistication required to begin to address complex issues, such as the potential health impacts of climate change. In broadly simplified terms, the historical objective of modern medicine and public health has been to eliminate illness, starting with the identification of causative agents. Clinical medicine and epidemiology emphasize the identification of disease causes and treatment rather than prediction of future disease outbreaks. In contrast, modem meteorology has focused on prediction, to offset the most deleterious consequences of weather events. Unlike medicine, the primary goal of meteorology is not to “cure” severe weather, that is, to retrain the path of a tornado or hurricane. However, recent debate about possible anthropogenic contributions to long-term climate change has raised the question of whether human interventions to delay or reduce the magnitude of this change should be sought.