Disease

Disease. As in all human societies, disease has played a profound but ever‐changing role throughout American history.

The Columbian Encounter and the Early Colonial Era.

When Europeans first reached the New World, they encountered a hitherto unknown indigenous population as well as a novel natural and biological environment. Amerindians probably had migrated from Asia to Alaska across a land bridge produced by a lowering of the oceans during the last Ice Age. Many pathogens responsible for infectious diseases that took a heavy toll in Asia, Europe, and Africa probably did not survive the migration through the harsh climate of Siberia and Alaska. New World peoples were thus isolated from many of the epidemic and endemic diseases that had profoundly shaped population structures elsewhere. The absence of contact with diverse populations also gave them a far more homogeneous genetic inheritance.

These and other factors gave precolumbian America a unique disease environment. Many Old World diseases—malaria, smallpox, bubonic plague, and some of the infectious diseases associated with childhood—were unknown. The greatest risks to the Amerindian population involved accidents, wildlife diseases associated with hunting and food‐gathering, warfare, and sporadic famines and food shortages. The relative absence of domesticated livestock minimized zoonotic (animal‐transmitted) diseases, and low population density and the absence of commercial contacts among tribes reduced the potential dangers of epidemic infectious disease. Nevertheless, life expectancy at birth for Native Americans—as well as Europeans—was generally in the low thirties on the eve of colonization, even though the causes of morbidity and mortality among both varied sharply.

The migration of Europeans to the Americas beginning at the end of the fifteenth century had a catastrophic impact on the indigenous population. The introduction of new diseases into a population often lacking immunological defenses led to extraordinarily high mortality rates. Infants lacked antibodies from their mothers, who had never been exposed to these new diseases. Children and adults often did not receive the kind of care that might have mitigated the impact of disease; neither custom, tradition, nor religion provided any guide. Genetic homogeneity may have also enhanced vulnerability. Whatever the reasons, the Amerindian population suffered a precipitous decline in the period following the first contacts with Europeans. Diseases such as smallpox, measles, whooping cough, chicken pox, and malaria—to cite only a few—exacted a heavy toll. On the eve of colonization the population of the future contiguous United States was between two and twelve million. When the nadir was reached in the early twentieth century, the number of Native Americans had fallen to about 250,000. Disease and the ensuing social demoralization, not military conquest, played the major role in this demographic disaster.

The colonists, meanwhile, faced their own novel health problems. The Atlantic crossing, which could last three or four months, posed its own risks. Within the new environment the settlers faced rigorous conditions. The construction of adequate housing, securing an uncontaminated water supply, and the development of an adequate and varied food supply took time. During the period of adjustment (often aptly described as a process of “seasoning”), many new settlements experienced extraordinarily high mortality and morbidity rates that, if unchecked, threatened their very existences.

The period of seasoning varied from place to place. In New England the process of adjustment was brief; within a short time, mortality rates dropped and inhabitants enjoyed unprecedented levels of health. In seventeenth‐century Andover, Massachusetts, the average age of death among the first generation was nearly seventy‐one, and infant and child mortality was correspondingly low. Nor was Andover unique. Consequently, New England's population grew rapidly in the seventeenth century.

The southern colonies, by contrast, remained dangerous places. The importation of such tropical diseases as malaria and yellow fever into a region with a warm and moist climate proved devastating; mortality rates in the South exceeded those of New England, the Middle Atlantic colonies, and even Great Britain. On average, seventeenth‐century white male New Englanders who survived to the age of twenty outlived their Maryland counterparts by more than two decades. The greater resistance of African Americans to the ravages of imported tropical diseases undoubtedly contributed to the growth of slavery in the South. This pattern of regional variation in mortality and morbidity would persist until well into the twentieth century.

The Era of Infectious Diseases and Epidemics.

The eighteenth century brought changes to the disease ecology of the American colonies. Natural population growth, high rates of immigration, and the geographic mobility that accompanied the growth in trade and commerce enhanced the movement of infectious pathogens. Smallpox and yellow fever epidemics appeared in growing port cities. Since many infectious diseases had not gained a foothold in the American colonies, the population included a disproportionately high number of susceptible persons. The result was the partial replication of the harsh disease environment characteristic of England and Europe. Although the colonial population continued to grow, its curve resembled a saw‐tooth shape on an upward gradient because of the impact of epidemic disease. However hard hit by infectious diseases, colonial America nonetheless had lower mortality rates than those of England and Europe.

Mortality rates among the young from such diseases as measles, mumps, whooping cough, and a variety of respiratory and intestinal disorders rose dramatically during the eighteenth century, particularly in more densely populated towns. Although the spectacular epidemics of yellow fever and smallpox were the most feared, the worst killers were intestinal disorders, including typhoid fever and various forms of dysentery.

Seasonal patterns as well as population density shaped morbidity and mortality patterns. Intestinal diseases were most frequent in warmer months because of stagnant water, contaminated food, and large insect populations that could transmit malaria and yellow fever. Respiratory and pulmonary diseases peaked in cold weather. Because infectious diseases that killed the young were by far the dominant cause of morbidity and mortality, the proportion of aged persons in the population remained low; chronic and degenerative diseases were relatively rare.

The morbidity and mortality patterns in place by the late eighteenth century persisted in one form or another for much of the nineteenth century. Nevertheless, a changing social and physical environment as well as population movements both to and within the United States contributed to a significant modification of the earlier disease environment, especially in urban areas. The immigration of destitute groups such as the Irish into densely populated neighborhoods where squalor and unhygienic conditions prevailed dramatically increased health risks. Infants and young children were particularly susceptible to infectious diseases. Intestinal disorders continued to take the highest toll, but other diseases associated with population density and unsanitary conditions—typhus, typhoid, smallpox, and respiratory disorders—also loomed large. Population growth exceeded the ability of municipal governments to provide a safe water supply or a sanitation system to remove organic waste and to ensure clean streets (which were usually covered with heaps of animal wastes). Housing codes were all but absent; inadequate ventilation and crowding quickly transmitted infectious diseases. Tuberculosis emerged as the leading cause of death. Occupations that posed a threat to health went largely unregulated. Urban areas also continued to experience periodic epidemics related to the quickened pace of trade and commerce. Cholera became an international disease during the nineteenth century as rapid ocean transportation magnified the ability to move pathogens. Southern cities experienced both cholera and yellow fever epidemics. Recent scholarship indicates a decline in the life expectancy of Americans in the nineteenth century. Indeed, only in‐migration from abroad and from rural areas assured urban growth.

Rural areas and small towns, by contrast, often escaped the infectious diseases that plagued urban areas even though health indicators declined during the first half of the nineteenth century. In 1830, for example, urban death rates were between two and three times higher than rural areas; small‐town rates tended to fall midway between. Under certain circumstances, however, the advantage conferred upon rural inhabitants became a liability. During the Civil War, young men recruited from rural areas, lacking the immunity of their urban counterparts who had survived the infectious diseases of infancy and childhood, died in large numbers when they encountered unhygienic conditions and dangerous pathogens in the military camps. Indeed, the overwhelming number of Civil War deaths occurred not from battlefield wounds, but from respiratory and enteric disorders as well as smallpox, measles, malaria, and other diseases.

Although infectious diseases remained the major causes of mortality, their distribution varied by region and class. Malaria, yellow fever, and hookworm, for example, were largely confined to the South. (Malaria had been present in the Northeast and upper Mississippi Valley, but an inhospitable environment contributed to its eventual disappearance.) Social class and race were important factors as well. Lower‐class and minority ethnic and racial groups tended to have higher mortality rates. Nutritional levels and sanitary conditions undoubtedly exacerbated the impact of infectious diseases on these groups. But more prosperous groups did not escape the threat of infectious disease; infant mortality remained high at all levels of the population. Hidden from public view, severe mental illness and other chronic diseases often resulted in dependency.

The Era of Chronic and Infectious Diseases.

Beginning in the second half of the nineteenth century, the United States, as well as England and many European nations, experienced what has become known as the second “epidemiological transition.” The first, which occurred perhaps ten thousand or more years ago, involved the development of agriculture, which created a more stable food supply. The result was a more sedentary population that increased in both size and density. Population growth in turn heightened the potential for epidemic and infectious diseases. During the second epidemiological transition, infectious diseases began a period of sustained decline as a cause of mortality, to be replaced by chronic and degenerative diseases. This unparalleled transformation had a profound impact on virtually all human beings.

Slowly but surely, infectious diseases declined as major elements in mortality in the late nineteenth century. By 1940 most of the infectious diseases associated with childhood—viral diseases such as measles, mumps, whooping cough, and chicken pox, and bacterial diseases that included scarlet and rheumatic fever—were insignificant in mortality rates, while heart disease and cancer loomed much larger. What caused this massive shift in morbidity and mortality? Most scholars agree that medical interventions played virtually no role. Before World War II, the function of medicine was primarily the diagnosis of disease. With the exception of a few surgical procedures and antitoxins, such as the diphtheria antitoxin, physicians had few effective therapies. Antibiotic therapy against bacterial diseases did not become common until after 1945, and the development of vaccines for most viral infectious diseases still lay in the future. Yet in 1945 infectious diseases had ceased to be a major element in shaping mortality patterns.

It is easier to describe the decline of mortality from infectious diseases than to explain it. Many scholars have attributed it to economic growth and a rising standard of living. The difficulty with such global explanations is that they are not based on empirical data that shed light on the precise mechanisms responsible for the mortality decline for specific diseases. Some have pinpointed dietary improvements as the most important factor. Yet the relationship between diet—excluding severe malnutrition, which rarely existed in the United States—and most infectious diseases is tenuous at best. Moreover, economic growth involves more than living standards; it includes rising levels of literacy and education and a variety of other complex social changes. Some of these changes and their interactions—including housing arrangements, population density, water and food purity, personal hygiene, individual behavioral patterns, and public‐health activities—may have had a more direct influence on mortality levels. Although the importance of economic development in the reduction in mortality is generally recognized, no consensus exists on the precise role of specific factors.

In some cases the reduction in mortality followed specific public‐health interventions. Typhoid fever, for example, was generally disseminated by contaminated water. The building of central sewer systems did not seem to have a major impact, but reduced mortality did follow the introduction of water filtration. The reduction in mortality from tuberculosis, on the other hand, presents far greater complexities. Mortality began to fall well before overt efforts were made to contain the disease. Improved diet and a reduction in exposure thanks to better housing and the building of sanitoriums may account for growing resistance to the disease, but the evidence for these explanations remains inconclusive. The fall in infant and child mortality from diarrheal diseases probably followed changes in baby‐feeding practices, improvement in the milk supply, and public‐health authorities' efforts to sensitize parents to more effective means of care and prevention. Whatever the precise reasons, the mortality decline was clearly a function of reduced exposure and greater resistance among the population.

The mortality decline that began in the late nineteenth century also reflected a dramatic increase in survival rates among infants and children. Longevity among the elderly increased as well, but not as spectacularly. As infant and child mortality fell, more Americans survived to adulthood and old age, and the median age and the proportion of elderly in the population increased commensurately.

The change in the age distribution of the population mirrored a shift in the causes of mortality. In the nineteenth century, infectious diseases were the major causes of mortality; death stalked infants and children. In the twentieth century, by contrast, the major causes of death were chronic and degenerative diseases, and death in old age became the norm. Indeed, the longer individuals survived, the more likely they were to die from cancer or cardiovascular, cerebrovascular, or pulmonary diseases. In 1993, heart disease, cancer, strokes, and pulmonary disease accounted for 67 percent of all deaths. Although the etiology of these diseases remains unclear, the presumption is that they involve a complex blend of genetic, environmental, and behavioral factors. To be sure, mortality within each category has not remained constant. Deaths from heart disease peaked in the first half of the twentieth century and declined in the second half. Similarly, the mix of types of cancers has changed even while the overall mortality rate has remained relatively stable. Moreover, mortality within all these categories differs by class, race, ethnicity, and gender. But given the aging of the population and the fact that human beings may have a determinant life span, chronic and degenerative diseases seem likely to remain major elements in mortality.

The decline in mortality from infectious disease and the development of effective antibiotic therapy after 1945 encouraged a belief that such diseases no longer posed a threat. Yet neither past nor present experience justified such optimism. The rapidity of modern transportation and the opening of hitherto uninhabited regions raised the possibility of new viral and bacterial diseases immune to available therapies. The indiscriminate use of antibiotics also led to the emergence of resistant mutant strains that posed major threats to life. Influenza—an old viral disease—periodically reemerged, often in virulent form. The influenza pandemic of 1918–1919 killed more than half a million Americans, and subsequent experience demonstrated that its recurrence remained a distinct possibility. Other viral, bacterial, and rickettsial diseases (such as Rocky Mountain Spotted Fever) have also created a niche for themselves in response to behavioral and environmental changes. The emergence of acquired immunodeficiency syndrome (AIDS), a new disease that became the major cause of mortality among the 25–44‐year‐old age group in the 1990s, demonstrated the importance of changing behavioral patterns, while Lyme disease, a tick‐borne infection first observed in the 1970s, mirrored a novel kind of ecology. Whatever the future brings, disease and death—whatever forms they take—remain inevitable concomitants of life itself.
See also Alzheimer's Disease; Columbian Exchange; Death and Dying; Food and Diet; Hospitals; Indian History and Culture: Migration and Pre‐Columbian Era; Industrial Diseases and Hazards; Life Stages; Poliomyelitis; Poverty; Public Health; Race and Ethnicity; Sickle‐Cell Anemia; Surgery; Urbanization; Venereal Disease.

Bibliography

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Abdel R. Omran , Epidemiologic Transition in the U.S.: The Health Factor in Population Change, Population Bulletin 32 (1977): 3–42.
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Charles Merbs , A New World of Infectious Disease, Yearbook of Physical Anthropology 35 (1992): 3–42.

Gerald N. Grob